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Spatiotemporal patterns and variations of winter extreme precipitation over terrestrial northern hemisphere in the past century (1901–2017)
Journal Pre-proof Spatiotemporal patterns and variations of winter extreme precipitation over terrestrial northern hemisphere in the past century (1901–2017) Tao Pan, Lijuan Zhang, Hongwen Zhang, Chong Ren, Yongsheng Li PII:
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DOI:
https://doi.org/10.1016/j.pce.2019.102828
Reference:
JPCE 102828
To appear in:
Physics and Chemistry of the Earth
Received Date: 7 November 2019 Revised Date:
16 December 2019
Accepted Date: 18 December 2019
Please cite this article as: Pan, T., Zhang, L., Zhang, H., Ren, C., Li, Y., Spatiotemporal patterns and variations of winter extreme precipitation over terrestrial northern hemisphere in the past century (1901– 2017), Physics and Chemistry of the Earth (2020), doi: https://doi.org/10.1016/j.pce.2019.102828. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
CRediT Author Statement
Tao Pan: Conceptualization, Methodology, Software, Formal analysis, Writing - Original Draft Lijuan Zhang: Conceptualization, Methodology, Writing Review & Editing Hongwen Zhang: Methodology, Software, Formal analysis Chong Ren: Resources, Formal analysis Yongsheng Li: Formal analysis
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Spatiotemporal patterns and variations of winter extreme precipitation over
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terrestrial Northern Hemisphere in the past century (1901–2017)
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Tao Pana, Lijuan Zhang a*, Hongwen Zhang b, Chong Rena, c, Yongsheng Lid
4
a
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Service in Cold Regions, Harbin Normal University, Harbin 150025, Heilongjiang, China
6
b
7
of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, Gansu, China
8
c
Heilongjiang Vocational Institute of Ecological Engineering, Harbin 150025, Heilongjiang, China
9
d
Climate Center of Heilongjiang Province, Harbin 150030, Heilongjiang, China
Heilongjiang Province Key Laboratory of Geographical Environment Monitoring and Spatial Information
Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Northwest Institute
10 11
Abstract
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In this study, the spatiotemporal distributions and variation characteristics of winter extreme
13
precipitation in the Northern Hemisphere over the past century (1901–2017) were analyzed using
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trend analysis and spatial analysis. These analyses utilized the monthly average dataset of surface
15
climatic factors (CRU TS4.03), and years with extreme precipitation was defined based on the
16
standard deviation method. The following results were obtained. (1) In the past century, the
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frequency of years with more winter extreme precipitation (denoted as more-extreme years) in
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the Northern Hemisphere was higher than that of years with less winter extreme precipitation
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(denoted as less-extreme years), with return periods of 10 years and 14 years, respectively. The
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frequency of more-extreme years increased significantly(P<0.05), and the less-extreme years
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were minimal changes (P>0.05) (2) The frequencies of more-extreme years and less-extreme
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years were higher in middle and high latitudes than in low latitudes. Significant increases in the
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frequencies of more-extreme years were observed in middle and high latitudes, while an
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significant increase in the frequency of less-extreme years was observed in low latitudes. The
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frequency of more-extreme years in high latitudes increased the most rapidly. (3) In the past
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century, the frequencies of more-extreme years and less-extreme years over terrestrial Northern
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Hemisphere ranged from 5–15%. The frequency of more-extreme years tended to increase over
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approximately 2/3 of the Northern Hemisphere, and increased significantly over approximately
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1/5 of the Northern Hemisphere. In contrast, the frequency of less-extreme years tended to Received: Accepted: Author: Tao Pan (1990)-, PhD Candidate, E-mail address: [email protected] Corresponding author: Lijuan Zhang (1965-), PhD and Professor, E-mail address: [email protected]
1
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increase over 1/2 of the Northern Hemisphere, and increased significantly over 1/10 of the
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Northern Hemisphere. (4) Spatially, at high latitudes, the proportions of grid points with
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more-extreme years and less-extreme years were the largest, and the increase in the variation of
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winter extreme precipitation was the greatest. In low latitude areas, the number of grid points
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with significant decreases of more-extreme years was smaller than the number with significant
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increases of less-extreme years, indicating that low latitudes were mainly dominated by an
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increase in the frequency of less-extreme years.
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Keywords: Northern Hemisphere, frequency of winter extreme precipitation, spatiotemporal
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patterns and variations, century
40 41
1 INTRODUCTION
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According to the Fifth Assessment Report of the Intergovernmental Panel on Climate
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Change (IPCC, 2013), the global annual average surface temperature has increased by 0.85°C in
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the past century. There is no doubt that climate warming exists. Compared with the climate
45
average, extreme climate events are more sensitive to climate change (Katz and Brown, 1992).
46
Therefore, in the context of climate warming, extreme weather, extreme climate event changes,
47
and their impacts have become hot research topics (Kong et al., 2017; Wang et al., 2017).
48
Research has revealed that with climate warming, the amount, frequency, and intensity of
49
extreme precipitation have all exhibited increasing trends, regardless of whether these results
50
have been based on observation value analysis or on model simulation methods (Donat et al.,
51
2016; Min et al., 2011; Wiel et al., 2017; Yang et al., 2019). Until now, however, there have been
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few studies on the effects of climate warming on winter extreme precipitation. Thus far, the
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following main conclusions have been drawn: freezing precipitation in the area above 40°N will
54
increase (Jeong et al., 2019); large-scale climate anomalies are exerting a significant impact on
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the trend of winter daily maximum precipitation in Canada, and the change of winter extreme
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precipitation is higher than that of the other three seasons (Tan et al., 2017); in the next 50 years,
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the intensity of winter extreme precipitation events in the western region of the United States
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will continue to increase significantly (Dominguez et al., 2012); under the influence of climate
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change, the frequency of winter extreme precipitation events in 1901–2012 exhibited an
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increasing trend in the northern part of Eurasia (Chen and Zhang, 2016); and from 1951 to 2003,
2
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winter extreme precipitation exhibited significant increases in the southern and central United
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States, northern Russia, and Canada, but showed minimal changes in other regions globally
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(Alexander et al., 2006). In this study, the spatiotemporal variation characteristics of winter
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extreme precipitation over terrestrial Northern Hemisphere in the past century (1901–2017) were
65
analyzed based on the monthly average dataset of surface climatic factors (CRU-TS4.03). This
66
study could provide a basis for exploring the impact of climate warming on the variation of
67
global extreme precipitation.
68 69
2 MATERIALS AND METHODS
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2.1 Data sources
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The Climate Research Unit (CRU) of the University of East Anglia in the UK has integrated
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several well-known databases and rebuilt a relatively comprehensive, high-resolution, and
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continuous dataset of surface meteorological factors. This dataset covers the global terrain,
74
including measurements from deserts and plateaus. At present, it has been updated to version
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CRU-TS4.03. This dataset covers the period January 1901 to December 2018, and its horizontal
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grid resolution is 0.5° × 0.5°. This dataset is widely used to analyze changes in global surface
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and upper air meteorological factors (Jones and Moberg, 2003; Wen et al., 2006). In this study,
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the monthly precipitation data of the 1000 hPa grid points in this dataset were selected, for the
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time period December 1901 to February 2018. The winter period (December of the current year
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to February of the following year) was analyzed. The data were downloaded from
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https://crudata.uea.ac.uk/cru/data after registration. The land area of the Northern Hemisphere
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was defined according to the number of grid points on land north of the equator, totaling 49,627
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grid points.
84
2.2 Methods
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(1) Determination of the years with extreme precipitation
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At present, there is no unified and mature standard for defining the extreme precipitation
87
threshold. The most common methods are the percentile method (Zolina et al., 2004) and the
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standard deviation method (Qian et al., 2007). In this study, the standard deviation method was
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used to determine the threshold value of extreme precipitation:
90 91
̄±
(1)
where ̄ is the mean value of the annual winter precipitation, 3
is the standard deviation, and
92 93
is a mathematical coefficient. In the analytical process, different researchers select different
values for specific data
94
distributions. The most commonly used values are 2.576, 1.960, and 1.645, which represent
95
events with probabilities < 0.01, < 0.05, and < 0.10, respectively. A preliminary analysis of the
96
CRU data showed that when the
97
years was too small to be representative. Thus, the value of
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years having annual winter precipitation with probabilities < 0.20 were selected as extreme
99
precipitation years. In the actual calculation process, each grid point was the calculation unit. If
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the winter precipitation in a given year of a grid point was higher than the threshold value, that
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year was denoted a more-extreme year; otherwise, if the winter precipitation of this grid point in
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that year was lower than the threshold value, that year was denoted a less-extreme year.
value was set to 1.645, the number of extreme precipitation was selected to be 1.282, and the
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The time period of this study was 1901–2017, thus including only 7 years in 2010s. If the
104
number of winter extreme precipitation years in each decade was analyzed, the number of years
105
in each decade would not be equal, and therefore could not be compared. For this reason, the
106
frequency method (number of extreme winter precipitation years per decade) was used to
107
compare the variations in extreme precipitation among decades. For the actual calculation, before
108
the 2010s, the frequency was the number of winter extreme precipitation years/10, while after the
109
2010s, the frequency was calculated as the number of winter extreme precipitation years/7.
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(2) Trend analysis
111 112
A linear regression equation of winter extreme precipitation ( ) and the corresponding time ( ) was established using the linear tendency estimation method (Mao et al., 2011): =
113
+
= 1,2, ⋯ ,
(2)
114
Here,
is the linear regression coefficient, indicating the variation rate of winter extreme
115
precipitation. The positive and negative values of
indicates the direction of the data series
116
change with time. The larger the absolute value of
, the greater the variation trend of winter
117
extreme precipitation, and the larger the variation range.
118
(3) Mann-Kendall test
119
The Mann Kendall (MK) test is a kind of nonparametric statistical test method (Mann, 1945;
120
Kendall, 1975). Its advantage is that it does not need the sample to follow a certain distribution,
121
and it is not affected by a few outliers. It is more suitable for type variables and sequence
122
variables, and the calculation is more convenient. 4
123
For time series X with n sample sizes, a rank series is constructed: =∑
124 125
=
127
(& = 1,2, … , )
(4)
"# $"% else
time greater than that at the time j. Under the assumption of random independence of time series, a statistic is defined: '( =
130
)*+ ,-(*+ ).
,
5, … , 6
( = 1,2, … , )
/012(*+ )
Where, '( =0，3( )，4
131
133
1 0
Sk is a rank sequence composed of the accumulated number of values at the time i than at
129
132
(3)
where
126
128
( = 2,3,4, … , )
(5)
( ) are the mean and variance of the Sk respectively. When
are independent of each other and has the same continuous distribution, they can be
calculated by the following formula:
134
3( ) =
135
4
6(67 )
( )=
(6)
8
6(6, )(5679)
(7)
:5
136
'( is the standard normal distribution. At a given significance levelα, look up the normal
137
distribution table. If '( | > '= , it indicates that there is an obvious trend change in the sequence.
138
According to the time series X in reverse order(
139
and the variables
6 , 6,
,…,
), the above process was repeated,
'> =−'( , = , − 1, … ,1, '> =0 were constructed.
140
The advantage of the Mann Kendall test is that it is not only simple to calculate, but also
141
can determine the time of mutation initiation and point out the mutation region. Therefore, it is a
142
common method to analyze mutation.
143 144
3 RESULTS AND ANALYSIS
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3.1 Decadal Variation Characteristics of Winter Extreme Precipitation Over Terrestrial
146
Northern Hemisphere in the Past Century
147
In the past century, the frequencies of more-extreme years and less-extreme years in the
148
Northern Hemisphere were 9.64% and 7.33%, i.e., these extreme years had return periods of
149
approximately 10 years and 14 years, respectively (Figure 1a). The frequency of more-extreme 5
150
years was higher than that of less-extreme years. In the past century, the frequency of winter
151
extreme precipitation has changed with time. A significant increase was observed in the
152
frequency of more-extreme years, at a rate of 0.87%/10a (P < 0.01); the frequency of the
153
less-extreme years were minimal changes，at a rate of 0.10%10a (P > 0.05). In the past century,
154
the anomaly map of the frequency of winter extreme precipitation (Figure 1b) shows that there
155
were clear stages in the distribution of winter extreme precipitation. Specifically, the frequency
156
of the more-extreme years changed after the 1950s, exhibiting a negative anomaly before the
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1950s and a positive anomaly after the 1950s. These results show that after the middle of the
158
20th century, the frequency of more-extreme years over terrestrial Northern Hemisphere has
159
increased significantly. Meanwhile, the frequency of less-extreme years was relatively low
160
before the 1920s and after the 2000s, and relatively high between the 1920s and the 2000s.
Frequency%
(a1). more-extreme years
(a2). less-extreme years
19
10.2
17 15 13 11
9.2 8.2 7.2 6.2
9 7 5
y = 0.8718x + 3.9762 R² = 0.666
5.2
y = 0.1002x + 6.6815 R² = 0.0518
4.2
3
3.2
161 8
(b1). more-extreme years
6
Frequency%
4 2
y = 0.8718x - 5.6669 R² = 0.666
2
(b2). less-extreme years y = 0.1002x - 0.6511 R² = 0.0518
1 0
-2
-1
-6
163 164 165
3
0
-4
162
4
-2 -3 -4
Fig. 1. (a) Decadal changes and (b) anomaly variations in the frequency of winter extreme precipitation in the Northern Hemisphere in 1901–2017.
166
The Northern Hemisphere was divided into low latitude, middle latitude, and high latitude
167
regions, with boundaries of 0–30°N, 30–60°N, and 60–90°N, respectively. Table 1 shows that
168
extreme precipitation exhibited varying characteristics with latitude. In the past century, the
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frequencies of more-extreme years as well as those of less-extreme years were higher in middle
170
and high latitudes than in low latitudes, indicating that the interannual variations of extreme
171
precipitation in middle and high latitudes were higher than in low latitudes. In the past century, 6
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the frequency of more-extreme years in high latitudes exhibited significantly increased (P < 0.01),
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and the increasing rate of the frequency of more-extreme years in high latitudes was higher than
174
that in middle latitudes. The frequency in low latitudes were minimal changes (P > 0.05).
175
However, the frequency of less-extreme years were minimal changes in middle and high
176
latitudes (P > 0.05), and increased significantly in low latitudes (P < 0.01). Overall, these results
177
reveal that the number of more-extreme years in middle and high latitudes increased significantly,
178
while the number of less-extreme years in low latitudes increased significantly. The increasing
179
rate of the frequency of more-extreme years in high latitudes was higher than that of
180
less-extreme years in low latitudes.
181
It can be seen from the anomaly distribution (Figure 2) that after the 1950s the
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more-extreme years displayed positive anomalies at all latitudes, indicating that after the 1950s
183
the frequency of more-extreme years over terrestrial Northern Hemisphere was high. The
184
variation of less-extreme years differed with latitude. In the middle and high latitudes changes
185
occurred after the 1970s and 1980s, while in low latitudes changes occurred after the 1950s. The
186
frequency of less-extreme years in the middle and high latitudes was low after the 1970s and
187
1980s, respectively, while in the low latitudes it was high after the 1950s. The above result shows
188
that, relatively speaking, since the middle of the 20th century the number of more-extreme years
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in the Northern Hemisphere has increased, while the number of less-extreme years has decreased
190
in middle and high latitudes, and increased in low latitudes.
191 192 193 194
Table 1 Frequency and decadal variation trend of winter extreme precipitation at high, middle, and low latitudes in the Northern Hemisphere (** indicates P < 0.01). Total Years with more winter Years with less winter frequency
extreme precipitation
extreme precipitation
Frequency
Variation trend
Frequency
Variation trend
(%)
(%/10a)
(%)
(%/10a)
High latitudes
18.26
9.70
1.50**
8.56
−0.11
Middle latitudes
18.91
10.52
0.80**
8.39
0.09
Low latitudes
12.02
8.04
0.23
3.98
0.37**
7
195 (a1).High latitudes
14
Frequency%
9
196
3 1
4 -1 -1 -3 -6
-5
-11
-7
5
(b1).High latitudes
Frequency%
(b2).Middle latitudes
2
2
0
0
-1
-1
-2
-2
-3
-3
-3
-4
-4
-4
-2
(b3).Low latitudes
y = 0.3699x - 2.4046 R² = 0.5322
1
0 -1
y = 0.231x - 1.5016 R² = 0.1693
3 y = 0.0911x - 0.592 R² = 0.0288
2 1
1
(a3).Low latitudes
5 4 3 2 1 0 -1 -2 -3 -4
4
3 y = -0.1078x + 0.7009 R² = 0.0276
3
198 199 200 201
y = 0.7969x - 5.1797 R² = 0.6744
4
4
197
(a2).Middle latitudes
5
y = 1.5049x - 9.7816 R² = 0.6747
Fig. 2. Decadal anomaly variations in the frequency of winter extreme precipitation at different latitudes in the Northern Hemisphere in 1901–2017.(a1、a2、a3)more-extreme years and (b1、 b2、b3)less-extreme years.
202
The results of MK test show that there are mutation points of more-extreme years in the
203
northern hemisphere land and in high, middle and low latitudes (Figure 3). The mutation point of
204
more-extreme years in northern hemisphere is the 1930s, while the mutation point of
205
more-extreme years in high, middle and low latitudes is 1930s, 1940s and 1910s respectively.
206
The mutation point of less-extreme years only appears in low latitudes, which is the 1940s. The
207
more-extreme years increased significantly after the 1950s, and the less-extreme years increased
208
significantly in low latitudes after the 1950s, and their changes all occurred after the mutation
209
point. (a1).Northern Hemisphere
(a4).Low latitudes 4
(a2).High latitudes 4
2
3
3
3
1
2
2
2
1
1
1
0
0
0
-1
-1
-1
0 -1 -2
210
(a3).Middle latitudes
3
-3
4
-2 UF
UB
-3
-2
UF
UB
-3
8
-2 UF
UB
-3
UF
UB
(b2).High latitudes 4
(b1).Northern Hemisphere 3
3
2
(b2).Middle latitudes 4
(b3).Low latitudes 4
3
3
2
2
1
1
2 1
1 0
0 -1 -2 -3
-1
0
0
-2
-1
-1
-3 -4
-2
-2
-3
211 212 213 214 215
Fig. 3. The results of the Mann-Kendall test in the frequency of winter extreme precipitation at different latitudes in the Northern Hemisphere in 1901–2017. (a1、a2、a3、a4)more-extreme years and(b1、b2、b3、b4)less-extreme years.
216
3.2 Spatial distribution Pattern and Variation Characteristics of Winter Extreme
217
Precipitation Over Terrestrial Northern Hemisphere
218
3.2.1 Spatial pattern distributions and variations of more-extreme years
UF
UB
UF
UB
-3
UF
UB
UF
UB
219
In the past century, the spatial distribution of the frequency of more-extreme years in the
220
Northern Hemisphere is shown in Figure 4. It can be seen that the frequency of more-extreme
221
years in the Northern Hemisphere ranged 0–38.33%, and the spatial distribution was not uniform.
222
The data were tallied in 5% increments. As shown in Figure 5, the frequency of more-extreme
223
years in most regions was distributed in the range of 5–10% and 10–15%, with 10–15% being
224
the most common. The regions with frequencies of more-extreme years > 15% were mainly
225
distributed in northeastern and eastern Canada, the western United States, northeastern Mali,
226
southern Egypt, central Russia, northern Kazakhstan, and northern India.
227 228 229 230
Fig. 4. Spatial distribution of the frequency of more-extreme years in the Northern Hemisphere in 1901–2017(unit: %).
9
231 232 233 234 235
Fig. 5. Number of grid points for the frequency of winter extreme precipitation in the Northern Hemisphere in 1901–2017.
236
Northern Hemisphere. As shown in this figure, the grid points that exhibited an increasing trend
237
in the frequency of more-extreme years accounted for 71.68% of the Northern Hemisphere’s land
238
area, while those displaying a decreasing trend accounted for 21.50%, and those that were
239
unchanged accounted for 6.82%. It can be seen that in the past century the grid points of nearly
240
2/3 of the land areas in the Northern Hemisphere had an increasing trend in the frequency of
241
more-extreme years. Among them, 20.54% exhibited a significant increasing trend (Figure 7),
242
with an average linear trend value of 2.57%/10a, while 1.37% showed a significant decreasing
243
trend, with an average linear trend value of −2.03%/10a. The overall proportions of grid points
244
showing significant increases in high, middle, and low latitudes were 34.31%, 19.09%, and
245
6.31%, respectively. It can be seen that the proportion of the area with significant increases was
246
the largest in high latitudes. The proportions of grid points with significant decreases in high,
247
middle, and low latitudes were 0.02%, 1.88%, and 2.14%, respectively, revealing that the
248
proportion of the area with significant decreases was the largest in the low latitudes. The areas
249
with significant increases in the frequency of more-extreme years were primarily located in
250
western Alaska, northeastern Canada, the vicinity of Greenland, most of Iceland, and
251
northwestern and central Eurasia. The areas with significant decreases in the frequency of
252
more-extreme years were mainly in the northern part of the Indian peninsula, central Kazakhstan,
Figure 6 shows the linear trend distribution of the frequency of more-extreme years in the
10
253
and southern Africa.
254
255 256 257 258
259 260 261 262 263 264
Fig. 6. Linear trend distribution of the frequency of more-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a).
Fig. 7. Linear trend distribution of the frequency of more-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a). Color areas indicates P < 0.05.
3.2.2 Spatial pattern distribution and variations of less-extreme years
265
Figure 8 illustrates the spatial distribution of the frequency of less-extreme years in the
266
Northern Hemisphere from 1901 to 2017. It can be seen that the frequency of less-extreme years
267
in the Northern Hemisphere over the past century ranged 0–20.83%, and the spatial distribution
268
was not uniform. The frequency was mainly between 5–10%, accounting for 57.12% of the grid
269
points, while the frequencies of 0–5% and 10–15% accounted for 22.57% and 10.86% of all grid
270
points, respectively (Figure 5). The regions in which the frequency of less-extreme years was >
271
15% were mainly distributed in eastern and northeastern Canada, western Norway, western
272
Romania, and northern and central Russia.
11
273
274 275 276 277 278
Fig. 8. Spatial distribution of the frequency of less-extreme years in the Northern Hemisphere in 1901–2017 (unit: %).
279
Hemisphere in the past century is shown in Figure 9. As seen in this figure, the grid points
280
exhibiting an increasing trend in the frequency of less-extreme years accounted for 47.45% of
281
the Northern Hemisphere’s land area, those exhibiting a decreasing trend accounted for 38.68%,
282
and those that were unchanged accounted for 13.87%. Among them, 8.43% of the grid points
283
showed a significant increasing trend (Figure 10), with a trend value of 2.15%/10a, while 5.47%
284
showed a significant decreasing trend, with a trend value of −2.47%/10a. The proportions of grid
285
points with significant increases in high, middle, and low latitudes were 10.26%, 7.56%, and
286
7.71%, respectively, while the proportions of grid points with significant decreases in high,
287
middle, and low latitudes were 11.81%, 3.84%, and 0.58%, respectively. It can thus be seen that
288
the high latitude region had the largest area of increase as well as the largest area of decrease in
289
the frequency of less-extreme years. Therefore, high latitudes experienced the most significant
290
changes in less-extreme years. In the middle and low latitudes, the overall area with a significant
291
increase in the frequency of less-extreme years was larger than the overall area with a significant
292
decrease. The areas with a significant increase were mainly located in northeastern North
293
America, central and eastern Eurasia, Central Asia, northern China, and southern Mongolia; the
294
areas with a significant decrease were mainly distributed in western Greenland, as well as
295
northwestern, north central, and northeastern Eurasia.
The linear variation trend of the frequency of less-extreme years over terrestrial Northern
12
296 297 298
299 300 301 302 303
Fig. 9. Linear trend distribution of the frequency of less-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a).
Fig. 10. Linear trend distribution of the frequency of less-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a). Color areas indicates P < 0.05. Based on the above analysis, we can see that the frequencies of more-extreme years and
304
less-extreme years in the Northern Hemisphere ranged from 5% to 15%, and the spatial
305
distribution was not uniform. The grid points that had an increasing trend of more-extreme years
306
and less-extreme years both accounted for a large proportion, and the number of grid points with
307
a significant increase was larger than the number with a significant decrease. The proportion of
308
grid points with a significant increase in the frequency of more-extreme years was the largest in
309
the high latitude region, and the proportion of grid points with a significant decrease in the
310
frequency of less-extreme years was the largest also in the high latitude region, indicating that
311
the high latitudes of the Northern Hemisphere experienced the largest variation in extreme
312
precipitation.
313 314 315 13
316
4 DISCUSSION AND CONCLUSIONS
317
4.1 Discussion
318
(1) In theory, an increase in temperature will lead to an increase in water vapor content and
319
precipitation (Wentz et al., 2007). Observational data have also confirmed the theoretical
320
inference of increasing air moisture content due to increasing temperature (Trenberth et al.,
321
2005). Global warming is an important reason for the increase in extreme heavy precipitation
322
(Goswami et al., 2006). Therefore, under the influence of global warming, the effect of
323
temperature change on the variation of spatiotemporal patterns of extreme precipitation is
324
non-negligible. This study utilized CRU data to analyze the distribution and variation of the
325
frequency of the years with winter extreme precipitation over terrestrial Northern Hemisphere in
326
the past century. This analysis could provide a new basis for the study of extreme precipitation
327
change under the background of climate warming, and in particular, it enriches the study of
328
winter extreme precipitation change as influenced by climate warming.
329
(2) The Fifth Assessment Report of the IPCC pointed out that extreme precipitation changed
330
significantly in the 20th century, during which time it increased significantly in the middle and
331
high latitudes (Stocker et al., 2013). In addition to the significant increase in the frequency of
332
more-extreme years in the middle and high latitudes, it was further discovered in the current
333
study that the frequency of less-extreme years in low latitudes also significantly increased. Chen
334
and Zhang (2016) reported that the frequency of winter extreme heavy precipitation events
335
increased significantly during 1901–2012 in the northern coastal areas across the entire Eurasian
336
continent. In the present study, it was shown that the frequency of more-extreme years increased
337
significantly in 1/5 of the land area of the Northern Hemisphere over the past century, covering a
338
relatively large region including the entire northern coastal areas of the Eurasian continent.
339
López-Moreno et al. (2011) used a regional climate model to simulate the frequency and
340
intensity of heavy snow events at an altitude of 1000 m under the condition of future temperature
341
rise, and found a significant decrease. Moreover, a study by Kenneth et al. (2009) revealed that
342
the frequency of extreme snow years in the United States has decreased due to climate warming.
343
These conclusions differ from those drawn in the present study, which deduced that the
344
frequency of more-extreme years increased at high latitudes of the Northern Hemisphere over the
345
past century.
346
(3) It is concluded in this study that over the past century the frequency of more-extreme
14
347
years in the Northern Hemisphere increased significantly (P < 0.05). The frequency of
348
less-extreme years were minimal changes (P > 0.05). Since 1901, wintertime land temperatures
349
in the Northern Hemisphere exhibited an extremely significant increasing trend (Figure 11), with
350
an increase rate of 0.15°C/10a (P < 0.01). Winter temperatures in the high, middle, and low
351
latitude areas have all displayed significant increasing trends, among which the rate of increase
352
was highest in the high latitude area, averaging approximately 0.19°C/10a (P < 0.01), followed
353
by that in the middle latitudes (0.16°C/10a; P < 0.01) and low latitudes (0.07°C/10a; P < 0.01).
354
The rate of temperature increase in the high latitudes was the greatest, while that in the low
355
latitudes was the smallest. The results show that the areas with a higher increase in temperature
356
exhibited a greater increase in the frequency of more-extreme years, while the areas with a lower
357
rate of temperature increase displayed a greater increase in the frequency of less-extreme years.
358
The spatial distribution of the tendency rate of winter average temperature in the past century
359
(Figure 12) reveals that winter temperatures in the terrestrial Northern Hemisphere generally
360
increased significantly, with greater increases in the middle and high latitude areas than in the
361
low latitude areas. This further proved that the temperature change was related to the variation of
362
extreme precipitation, although the temperature change was not highly consistent with the
363
change in extreme precipitation spatially.
364 -4 (a).Northern Hemisphere
Temperature\℃
-5 -6
-23
y = 0.015x - 8.0008 R² = 0.4698
-25
366 367 368
-6 y = 0.0191x - 28.171 R² = 0.3329
-7
(d).Low latitudes
21
-27
y = 0.0069x + 19.291 R² = 0.3291
20
-8
-10 1901
22
y = 0.0166x - 9.527 R² = 0.342
-8
-10
-29
-9
365
(c).Middle latitudes
(b).High latitudes
1930
1959
1988
2017
-31 1901
1930
1959
1988
2017
-12 1901
19
1930
1959
1988
2017
18 1901
1930
1959
1988
2017
Fig. 11. Interannual change in winter temperatures over terrestrial Northern Hemisphere in 1901–2017.
15
369 370 371 372 373
Fig. 12. Linear trend distribution of winter temperatures over terrestrial Northern Hemisphere in 1901–2017 (unit: °C/10a).Shading indicates P < 0.05.
374
Northern Hemisphere, as well as the mutation points of the average winter temperature in high,
375
middle and low latitudes (Figure 13). The results show that there is no intersection between UF
376
and UB in the 0.05 probability range, so the annual average temperature of land in the northern
377
hemisphere in winter has no mutation in 1901-2017, and the winter average temperature in high,
378
middle and low latitudes has no mutation in 1901-2017. Therefore, it can be concluded that the
379
change of extreme precipitation on time scale does not exactly match the change of temperature.
Furthermore, the MK test is used to analyze the winter temperature in the terrestrial
380 (a3).Middle latitudes 9
9
7
7
7
7
5
5
5
5
3
3
3
3
1
1
1
(a1).Northern Hemisphere
-11901
381
1930
-3
9
1959
1988
UF
(a2).High latitudes
2017
UB
(b1).Northern Hemisphere
7 5
-11901
1930
-3
1959
1988
UF
2017
UB
-11901
1 1930
-3
1959
1988
UF
2017
UB
-11901
(b2).High latitudes
(b3).Middle latitudes
9
9
9
7
7
7
5
5
3
3
3
1
1
1
-3
1930
1959
UF
1988
2017
UB
-11901 -3
1930
1959
UF
1988
2017
UB
-11901 -3
1959
1988
UF
2017
UB
(b4).Low latitudes
5
1901
1930
-3
3
-1
382 383 384 385 386
(a4).Low latitudes
9
9
1 1930
1959
UF
1988
2017
UB
-11901 -3
1930
1959
UF
1988
2017
UB
Fig. 13. The results of the Mann-Kendall test in winter temperatures(a) and annual average temperatures(b) in the Northern Hemisphere in 1901–2017. Meanwhile, we analyzed the winter temperature anomaly and annual average temperature
387
anomaly in the northern hemisphere in the past century (Figure 14), and found that the
388
temperature changes occurred in the late 1980s, which was not consistent with the turning point 16
389
of the extreme precipitation frequency anomaly. It is further explained that the distribution and
390
change of extreme precipitation are related to temperature, but not completely affected by
391
temperature, but also by atmospheric circulation and other factors.
392 4
(a1).Northern Hemisphere
3
Temperature\℃
393
Temperature\℃
1901
1930
1959
1988
2017
-1
1930
1959
1988
2017
-1
-2 -3
-3
-3
-4
-4
-4
(b1).Northern Hemisphere 2
1930
1959
1988
1959
1988
2
(b3).Middle latitudes
1959
1988
1930
1959
1988
2017
1
y = 0.0127x - 0.7465 R² = 0.612
(b4).Low latitudes 1
1901
2017
1930
1959
1988
y = 0.0072x - 0.4259 R² = 0.5254
0.5
0 1930
1901
2017
-2
y = 0.0138x - 0.8127 R² = 0.4313
1901
2017
1930
-1
0 1901
-2
1901
(b2).High latitudes
1
0 -1
0
0 1901
-2
y = 0.0116x - 0.6862 R² = 0.5964
y = 0.0069x - 0.4057 R² = 0.3291
1
1
-2
1
y = 0.0166x - 0.9823 R² = 0.342
2
0
0
2
394 395 396 397 398
3
1
1
(a4).Low latitudes
2
(a3).Middle latitudes
4
y = 0.0191x - 1.1292 R² = 0.3329
2
y = 0.015x - 0.8824 R² = 0.4698
2
-1
(a2).High latitudes
4
3
2017
0 1901
-1
-1
-0.5
-2
-2
-1
1930
1959
1988
2017
Fig. 14. Interannual anomaly variations in winter temperatures(a) and annual average temperatures(b) over terrestrial Northern Hemisphere in 1901–2017. (4) The results of this analysis reveal that the frequencies of more-extreme years and
399
less-extreme years in the Northern Hemisphere over the past century in the high and middle
400
latitudes were higher than those in the low latitudes. Since 1901, winter precipitation over
401
terrestrial Northern Hemisphere have shown a significant increasing trend (Figure 15), increasing
402
at a rate of 0.16 mm /10a (P < 0.01). Moreover, winter precipitation in the high and middle
403
latitudes has shown an extremely significant increasing trend, increasing at rates of 0.37 mm/10a
404
(P < 0.01) and 0.14 mm/10a (P < 0.01), respectively. Meanwhile, winter precipitation in low
405
latitudes has decreased at a rate of -0.04 mm/10 a (P > 0.05). It can be seen that the greatest rate
406
of winter precipitation increase occurred at high latitudes, and the smallest occurred at low
407
latitudes. This reveals that the number of more-extreme years increased in the regions with
408
significant increases in winter precipitation over the past century, while the number of
409
less-extreme years increased in the regions with minimal changes in winter precipitation (Figure
410
16).
411
17
(b).High latitudes
Precipitation/mm
(a).Northern Hemisphere
412 413 414 415
y = 0.0164x + 28.25 R² = 0.2203
32 30
27 25
45
y = 0.0371x + 20.039 R² = 0.4613
40
23
37
1959
1988
2017
17 1901
y = -0.0042x + 29.724 R² = 0.005
32
35 27 30
19 1930
(d).Low latitudes
y = 0.0137x + 33.115 R² = 0.0593
21
28 26 1901
(c).Middle latitudes
1930
1959
1988
2017
25 1901
1930
1959
1988
2017
22 1901
1930
1959
1988
2017
Fig. 15. Interannual variation in winter precipitation over terrestrial Northern Hemisphere in 1901–2017.
416 417 418 419
Fig. 16. Linear trend distribution of winter precipitation over terrestrial Northern Hemisphere in 1901–2017 (unit: mm/10a)Shading indicates P < 0.05.
420
4.2 Conclusions
421
(1) During 1901–2017, the frequency of more-extreme years over terrestrial Northern
422
Hemisphere was higher than that of less-extreme years, with specific values of 9.64% and 7.33%,
423
respectively, corresponding to return periods of approximately 10 years and 14 years. The
424
frequency of more-extreme years was higher than that of less-extreme years, and the frequency
425
of more-extreme years had a significant increasing trend, with a trend value of 0.87%/10a. The
426
frequency of less-extreme years also exhibited an increasing decadal trend, albeit not significant.
427
(2) During 1901–2017, the frequencies of more-extreme years and less-extreme years over
428
terrestrial Northern Hemisphere in the middle and high latitudes were higher than those at low
429
latitudes. The frequency of more-extreme years in the middle and high latitudes exhibited a
430
significant increasing trend, with the maximum increase rate of 1.50%/10a appearing at high
431
latitudes. However, the frequency of less-extreme years showed no significant change in the
432
middle and high latitudes, while the frequency at low latitudes displayed a significant increasing
433
trend, with a rate of 0.37%/10a. The frequencies of both the more-extreme years and
434
less-extreme years increased at all latitudes after the 1950s. 18
435
(3) During 1901–2017, the frequencies of more-extreme years and less-extreme years over
436
terrestrial Northern Hemisphere ranged 5–15%. In the Northern Hemisphere, an increasing trend
437
in the frequency of more-extreme years was observed at 71.68% of the grid points, and a
438
significant increasing trend was observed at 20.54% of the grid points, with an average linear
439
trend value of 2.57%/10a. An increasing trend in the frequency of less-extreme years was
440
observed at 47.45% of the grid points, and a significant increasing trend was observed at 8.43%
441
of the grid points, with an average linear trend value of 2.15%/10a. Over the past century, the
442
Northern Hemisphere was mainly characterized by an increase in winter extreme precipitation.
443 444
Acknowledgments: This research is funded by the National Natural Science Foundation of
445
China (Grant No. 41771067).
446 447
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Kendall, M.G., 1975: Rank correlation methods. Charles Griffin, London.
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Kong, F., Shi, P., Fang, J., Lu, L., Fang, J., Gou, J., 2017. Advances and prospects of
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Mann, H.B., 1945: Nonparametric tests against trend. Econometrica 13, 245–259.
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Mao, S.-S., Cheng, Y.-M., Pu, X., 2011. Probability theory and mathematical statistics. Higher
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Education Press, Beijing. Min, S.-K., Zhang, X., Zwiers, F.W., Hegerl, G.C., 2011. Human contribution to more-intense precipitation extremes. Nature 470, 378. Qian, W., Lin, X., Zhu, Y., Xu, Y., Fu, J., 2007. Climatic regime shift and decadal anomalous events in China. Climatic Change 84, 167-189.
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Tan, X., Gan, T.Y., Shao, D., 2017. Effects of persistence and large-scale climate anomalies on
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Trenberth, K.E., Fasullo, J., Smith, L., 2005. Trends and variability in column-integrated atmospheric water vapor. Climate dynamics 24, 741-758. Wang, A., Su, B., Wang, Y., Huang, J., Wen, S., Jiang, T., 2017. Variation of the extreme low
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Zolina, O., Kapala, A., Simmer, C., Gulev, S.K., 2004. Analysis of extreme precipitation over
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21
Highlights: We analyze characteristics of winter extreme precipitation in the northern hemisphere. The frequency of years with extreme winters in high latitudes exhibited a significant increase. The frequency of less extreme winters in low latitudes exhibited a significant increase.
Conflict of Interest Statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript.
S1474-7065(19)30220-7
DOI:
https://doi.org/10.1016/j.pce.2019.102828
Reference:
JPCE 102828
To appear in:
Physics and Chemistry of the Earth
Received Date: 7 November 2019 Revised Date:
16 December 2019
Accepted Date: 18 December 2019
Please cite this article as: Pan, T., Zhang, L., Zhang, H., Ren, C., Li, Y., Spatiotemporal patterns and variations of winter extreme precipitation over terrestrial northern hemisphere in the past century (1901– 2017), Physics and Chemistry of the Earth (2020), doi: https://doi.org/10.1016/j.pce.2019.102828. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.
CRediT Author Statement
Tao Pan: Conceptualization, Methodology, Software, Formal analysis, Writing - Original Draft Lijuan Zhang: Conceptualization, Methodology, Writing Review & Editing Hongwen Zhang: Methodology, Software, Formal analysis Chong Ren: Resources, Formal analysis Yongsheng Li: Formal analysis
1
Spatiotemporal patterns and variations of winter extreme precipitation over
2
terrestrial Northern Hemisphere in the past century (1901–2017)
3
Tao Pana, Lijuan Zhang a*, Hongwen Zhang b, Chong Rena, c, Yongsheng Lid
4
a
5
Service in Cold Regions, Harbin Normal University, Harbin 150025, Heilongjiang, China
6
b
7
of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, Gansu, China
8
c
Heilongjiang Vocational Institute of Ecological Engineering, Harbin 150025, Heilongjiang, China
9
d
Climate Center of Heilongjiang Province, Harbin 150030, Heilongjiang, China
Heilongjiang Province Key Laboratory of Geographical Environment Monitoring and Spatial Information
Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Northwest Institute
10 11
Abstract
12
In this study, the spatiotemporal distributions and variation characteristics of winter extreme
13
precipitation in the Northern Hemisphere over the past century (1901–2017) were analyzed using
14
trend analysis and spatial analysis. These analyses utilized the monthly average dataset of surface
15
climatic factors (CRU TS4.03), and years with extreme precipitation was defined based on the
16
standard deviation method. The following results were obtained. (1) In the past century, the
17
frequency of years with more winter extreme precipitation (denoted as more-extreme years) in
18
the Northern Hemisphere was higher than that of years with less winter extreme precipitation
19
(denoted as less-extreme years), with return periods of 10 years and 14 years, respectively. The
20
frequency of more-extreme years increased significantly(P<0.05), and the less-extreme years
21
were minimal changes (P>0.05) (2) The frequencies of more-extreme years and less-extreme
22
years were higher in middle and high latitudes than in low latitudes. Significant increases in the
23
frequencies of more-extreme years were observed in middle and high latitudes, while an
24
significant increase in the frequency of less-extreme years was observed in low latitudes. The
25
frequency of more-extreme years in high latitudes increased the most rapidly. (3) In the past
26
century, the frequencies of more-extreme years and less-extreme years over terrestrial Northern
27
Hemisphere ranged from 5–15%. The frequency of more-extreme years tended to increase over
28
approximately 2/3 of the Northern Hemisphere, and increased significantly over approximately
29
1/5 of the Northern Hemisphere. In contrast, the frequency of less-extreme years tended to Received: Accepted: Author: Tao Pan (1990)-, PhD Candidate, E-mail address: [email protected] Corresponding author: Lijuan Zhang (1965-), PhD and Professor, E-mail address: [email protected]
1
30
increase over 1/2 of the Northern Hemisphere, and increased significantly over 1/10 of the
31
Northern Hemisphere. (4) Spatially, at high latitudes, the proportions of grid points with
32
more-extreme years and less-extreme years were the largest, and the increase in the variation of
33
winter extreme precipitation was the greatest. In low latitude areas, the number of grid points
34
with significant decreases of more-extreme years was smaller than the number with significant
35
increases of less-extreme years, indicating that low latitudes were mainly dominated by an
36
increase in the frequency of less-extreme years.
37 38
Keywords: Northern Hemisphere, frequency of winter extreme precipitation, spatiotemporal
39
patterns and variations, century
40 41
1 INTRODUCTION
42
According to the Fifth Assessment Report of the Intergovernmental Panel on Climate
43
Change (IPCC, 2013), the global annual average surface temperature has increased by 0.85°C in
44
the past century. There is no doubt that climate warming exists. Compared with the climate
45
average, extreme climate events are more sensitive to climate change (Katz and Brown, 1992).
46
Therefore, in the context of climate warming, extreme weather, extreme climate event changes,
47
and their impacts have become hot research topics (Kong et al., 2017; Wang et al., 2017).
48
Research has revealed that with climate warming, the amount, frequency, and intensity of
49
extreme precipitation have all exhibited increasing trends, regardless of whether these results
50
have been based on observation value analysis or on model simulation methods (Donat et al.,
51
2016; Min et al., 2011; Wiel et al., 2017; Yang et al., 2019). Until now, however, there have been
52
few studies on the effects of climate warming on winter extreme precipitation. Thus far, the
53
following main conclusions have been drawn: freezing precipitation in the area above 40°N will
54
increase (Jeong et al., 2019); large-scale climate anomalies are exerting a significant impact on
55
the trend of winter daily maximum precipitation in Canada, and the change of winter extreme
56
precipitation is higher than that of the other three seasons (Tan et al., 2017); in the next 50 years,
57
the intensity of winter extreme precipitation events in the western region of the United States
58
will continue to increase significantly (Dominguez et al., 2012); under the influence of climate
59
change, the frequency of winter extreme precipitation events in 1901–2012 exhibited an
60
increasing trend in the northern part of Eurasia (Chen and Zhang, 2016); and from 1951 to 2003,
2
61
winter extreme precipitation exhibited significant increases in the southern and central United
62
States, northern Russia, and Canada, but showed minimal changes in other regions globally
63
(Alexander et al., 2006). In this study, the spatiotemporal variation characteristics of winter
64
extreme precipitation over terrestrial Northern Hemisphere in the past century (1901–2017) were
65
analyzed based on the monthly average dataset of surface climatic factors (CRU-TS4.03). This
66
study could provide a basis for exploring the impact of climate warming on the variation of
67
global extreme precipitation.
68 69
2 MATERIALS AND METHODS
70
2.1 Data sources
71
The Climate Research Unit (CRU) of the University of East Anglia in the UK has integrated
72
several well-known databases and rebuilt a relatively comprehensive, high-resolution, and
73
continuous dataset of surface meteorological factors. This dataset covers the global terrain,
74
including measurements from deserts and plateaus. At present, it has been updated to version
75
CRU-TS4.03. This dataset covers the period January 1901 to December 2018, and its horizontal
76
grid resolution is 0.5° × 0.5°. This dataset is widely used to analyze changes in global surface
77
and upper air meteorological factors (Jones and Moberg, 2003; Wen et al., 2006). In this study,
78
the monthly precipitation data of the 1000 hPa grid points in this dataset were selected, for the
79
time period December 1901 to February 2018. The winter period (December of the current year
80
to February of the following year) was analyzed. The data were downloaded from
81
https://crudata.uea.ac.uk/cru/data after registration. The land area of the Northern Hemisphere
82
was defined according to the number of grid points on land north of the equator, totaling 49,627
83
grid points.
84
2.2 Methods
85
(1) Determination of the years with extreme precipitation
86
At present, there is no unified and mature standard for defining the extreme precipitation
87
threshold. The most common methods are the percentile method (Zolina et al., 2004) and the
88
standard deviation method (Qian et al., 2007). In this study, the standard deviation method was
89
used to determine the threshold value of extreme precipitation:
90 91
̄±
(1)
where ̄ is the mean value of the annual winter precipitation, 3
is the standard deviation, and
92 93
is a mathematical coefficient. In the analytical process, different researchers select different
values for specific data
94
distributions. The most commonly used values are 2.576, 1.960, and 1.645, which represent
95
events with probabilities < 0.01, < 0.05, and < 0.10, respectively. A preliminary analysis of the
96
CRU data showed that when the
97
years was too small to be representative. Thus, the value of
98
years having annual winter precipitation with probabilities < 0.20 were selected as extreme
99
precipitation years. In the actual calculation process, each grid point was the calculation unit. If
100
the winter precipitation in a given year of a grid point was higher than the threshold value, that
101
year was denoted a more-extreme year; otherwise, if the winter precipitation of this grid point in
102
that year was lower than the threshold value, that year was denoted a less-extreme year.
value was set to 1.645, the number of extreme precipitation was selected to be 1.282, and the
103
The time period of this study was 1901–2017, thus including only 7 years in 2010s. If the
104
number of winter extreme precipitation years in each decade was analyzed, the number of years
105
in each decade would not be equal, and therefore could not be compared. For this reason, the
106
frequency method (number of extreme winter precipitation years per decade) was used to
107
compare the variations in extreme precipitation among decades. For the actual calculation, before
108
the 2010s, the frequency was the number of winter extreme precipitation years/10, while after the
109
2010s, the frequency was calculated as the number of winter extreme precipitation years/7.
110
(2) Trend analysis
111 112
A linear regression equation of winter extreme precipitation ( ) and the corresponding time ( ) was established using the linear tendency estimation method (Mao et al., 2011): =
113
+
= 1,2, ⋯ ,
(2)
114
Here,
is the linear regression coefficient, indicating the variation rate of winter extreme
115
precipitation. The positive and negative values of
indicates the direction of the data series
116
change with time. The larger the absolute value of
, the greater the variation trend of winter
117
extreme precipitation, and the larger the variation range.
118
(3) Mann-Kendall test
119
The Mann Kendall (MK) test is a kind of nonparametric statistical test method (Mann, 1945;
120
Kendall, 1975). Its advantage is that it does not need the sample to follow a certain distribution,
121
and it is not affected by a few outliers. It is more suitable for type variables and sequence
122
variables, and the calculation is more convenient. 4
123
For time series X with n sample sizes, a rank series is constructed: =∑
124 125
=
127
(& = 1,2, … , )
(4)
"# $"% else
time greater than that at the time j. Under the assumption of random independence of time series, a statistic is defined: '( =
130
)*+ ,-(*+ ).
,
5, … , 6
( = 1,2, … , )
/012(*+ )
Where, '( =0，3( )，4
131
133
1 0
Sk is a rank sequence composed of the accumulated number of values at the time i than at
129
132
(3)
where
126
128
( = 2,3,4, … , )
(5)
( ) are the mean and variance of the Sk respectively. When
are independent of each other and has the same continuous distribution, they can be
calculated by the following formula:
134
3( ) =
135
4
6(67 )
( )=
(6)
8
6(6, )(5679)
(7)
:5
136
'( is the standard normal distribution. At a given significance levelα, look up the normal
137
distribution table. If '( | > '= , it indicates that there is an obvious trend change in the sequence.
138
According to the time series X in reverse order(
139
and the variables
6 , 6,
,…,
), the above process was repeated,
'> =−'( , = , − 1, … ,1, '> =0 were constructed.
140
The advantage of the Mann Kendall test is that it is not only simple to calculate, but also
141
can determine the time of mutation initiation and point out the mutation region. Therefore, it is a
142
common method to analyze mutation.
143 144
3 RESULTS AND ANALYSIS
145
3.1 Decadal Variation Characteristics of Winter Extreme Precipitation Over Terrestrial
146
Northern Hemisphere in the Past Century
147
In the past century, the frequencies of more-extreme years and less-extreme years in the
148
Northern Hemisphere were 9.64% and 7.33%, i.e., these extreme years had return periods of
149
approximately 10 years and 14 years, respectively (Figure 1a). The frequency of more-extreme 5
150
years was higher than that of less-extreme years. In the past century, the frequency of winter
151
extreme precipitation has changed with time. A significant increase was observed in the
152
frequency of more-extreme years, at a rate of 0.87%/10a (P < 0.01); the frequency of the
153
less-extreme years were minimal changes，at a rate of 0.10%10a (P > 0.05). In the past century,
154
the anomaly map of the frequency of winter extreme precipitation (Figure 1b) shows that there
155
were clear stages in the distribution of winter extreme precipitation. Specifically, the frequency
156
of the more-extreme years changed after the 1950s, exhibiting a negative anomaly before the
157
1950s and a positive anomaly after the 1950s. These results show that after the middle of the
158
20th century, the frequency of more-extreme years over terrestrial Northern Hemisphere has
159
increased significantly. Meanwhile, the frequency of less-extreme years was relatively low
160
before the 1920s and after the 2000s, and relatively high between the 1920s and the 2000s.
Frequency%
(a1). more-extreme years
(a2). less-extreme years
19
10.2
17 15 13 11
9.2 8.2 7.2 6.2
9 7 5
y = 0.8718x + 3.9762 R² = 0.666
5.2
y = 0.1002x + 6.6815 R² = 0.0518
4.2
3
3.2
161 8
(b1). more-extreme years
6
Frequency%
4 2
y = 0.8718x - 5.6669 R² = 0.666
2
(b2). less-extreme years y = 0.1002x - 0.6511 R² = 0.0518
1 0
-2
-1
-6
163 164 165
3
0
-4
162
4
-2 -3 -4
Fig. 1. (a) Decadal changes and (b) anomaly variations in the frequency of winter extreme precipitation in the Northern Hemisphere in 1901–2017.
166
The Northern Hemisphere was divided into low latitude, middle latitude, and high latitude
167
regions, with boundaries of 0–30°N, 30–60°N, and 60–90°N, respectively. Table 1 shows that
168
extreme precipitation exhibited varying characteristics with latitude. In the past century, the
169
frequencies of more-extreme years as well as those of less-extreme years were higher in middle
170
and high latitudes than in low latitudes, indicating that the interannual variations of extreme
171
precipitation in middle and high latitudes were higher than in low latitudes. In the past century, 6
172
the frequency of more-extreme years in high latitudes exhibited significantly increased (P < 0.01),
173
and the increasing rate of the frequency of more-extreme years in high latitudes was higher than
174
that in middle latitudes. The frequency in low latitudes were minimal changes (P > 0.05).
175
However, the frequency of less-extreme years were minimal changes in middle and high
176
latitudes (P > 0.05), and increased significantly in low latitudes (P < 0.01). Overall, these results
177
reveal that the number of more-extreme years in middle and high latitudes increased significantly,
178
while the number of less-extreme years in low latitudes increased significantly. The increasing
179
rate of the frequency of more-extreme years in high latitudes was higher than that of
180
less-extreme years in low latitudes.
181
It can be seen from the anomaly distribution (Figure 2) that after the 1950s the
182
more-extreme years displayed positive anomalies at all latitudes, indicating that after the 1950s
183
the frequency of more-extreme years over terrestrial Northern Hemisphere was high. The
184
variation of less-extreme years differed with latitude. In the middle and high latitudes changes
185
occurred after the 1970s and 1980s, while in low latitudes changes occurred after the 1950s. The
186
frequency of less-extreme years in the middle and high latitudes was low after the 1970s and
187
1980s, respectively, while in the low latitudes it was high after the 1950s. The above result shows
188
that, relatively speaking, since the middle of the 20th century the number of more-extreme years
189
in the Northern Hemisphere has increased, while the number of less-extreme years has decreased
190
in middle and high latitudes, and increased in low latitudes.
191 192 193 194
Table 1 Frequency and decadal variation trend of winter extreme precipitation at high, middle, and low latitudes in the Northern Hemisphere (** indicates P < 0.01). Total Years with more winter Years with less winter frequency
extreme precipitation
extreme precipitation
Frequency
Variation trend
Frequency
Variation trend
(%)
(%/10a)
(%)
(%/10a)
High latitudes
18.26
9.70
1.50**
8.56
−0.11
Middle latitudes
18.91
10.52
0.80**
8.39
0.09
Low latitudes
12.02
8.04
0.23
3.98
0.37**
7
195 (a1).High latitudes
14
Frequency%
9
196
3 1
4 -1 -1 -3 -6
-5
-11
-7
5
(b1).High latitudes
Frequency%
(b2).Middle latitudes
2
2
0
0
-1
-1
-2
-2
-3
-3
-3
-4
-4
-4
-2
(b3).Low latitudes
y = 0.3699x - 2.4046 R² = 0.5322
1
0 -1
y = 0.231x - 1.5016 R² = 0.1693
3 y = 0.0911x - 0.592 R² = 0.0288
2 1
1
(a3).Low latitudes
5 4 3 2 1 0 -1 -2 -3 -4
4
3 y = -0.1078x + 0.7009 R² = 0.0276
3
198 199 200 201
y = 0.7969x - 5.1797 R² = 0.6744
4
4
197
(a2).Middle latitudes
5
y = 1.5049x - 9.7816 R² = 0.6747
Fig. 2. Decadal anomaly variations in the frequency of winter extreme precipitation at different latitudes in the Northern Hemisphere in 1901–2017.(a1、a2、a3)more-extreme years and (b1、 b2、b3)less-extreme years.
202
The results of MK test show that there are mutation points of more-extreme years in the
203
northern hemisphere land and in high, middle and low latitudes (Figure 3). The mutation point of
204
more-extreme years in northern hemisphere is the 1930s, while the mutation point of
205
more-extreme years in high, middle and low latitudes is 1930s, 1940s and 1910s respectively.
206
The mutation point of less-extreme years only appears in low latitudes, which is the 1940s. The
207
more-extreme years increased significantly after the 1950s, and the less-extreme years increased
208
significantly in low latitudes after the 1950s, and their changes all occurred after the mutation
209
point. (a1).Northern Hemisphere
(a4).Low latitudes 4
(a2).High latitudes 4
2
3
3
3
1
2
2
2
1
1
1
0
0
0
-1
-1
-1
0 -1 -2
210
(a3).Middle latitudes
3
-3
4
-2 UF
UB
-3
-2
UF
UB
-3
8
-2 UF
UB
-3
UF
UB
(b2).High latitudes 4
(b1).Northern Hemisphere 3
3
2
(b2).Middle latitudes 4
(b3).Low latitudes 4
3
3
2
2
1
1
2 1
1 0
0 -1 -2 -3
-1
0
0
-2
-1
-1
-3 -4
-2
-2
-3
211 212 213 214 215
Fig. 3. The results of the Mann-Kendall test in the frequency of winter extreme precipitation at different latitudes in the Northern Hemisphere in 1901–2017. (a1、a2、a3、a4)more-extreme years and(b1、b2、b3、b4)less-extreme years.
216
3.2 Spatial distribution Pattern and Variation Characteristics of Winter Extreme
217
Precipitation Over Terrestrial Northern Hemisphere
218
3.2.1 Spatial pattern distributions and variations of more-extreme years
UF
UB
UF
UB
-3
UF
UB
UF
UB
219
In the past century, the spatial distribution of the frequency of more-extreme years in the
220
Northern Hemisphere is shown in Figure 4. It can be seen that the frequency of more-extreme
221
years in the Northern Hemisphere ranged 0–38.33%, and the spatial distribution was not uniform.
222
The data were tallied in 5% increments. As shown in Figure 5, the frequency of more-extreme
223
years in most regions was distributed in the range of 5–10% and 10–15%, with 10–15% being
224
the most common. The regions with frequencies of more-extreme years > 15% were mainly
225
distributed in northeastern and eastern Canada, the western United States, northeastern Mali,
226
southern Egypt, central Russia, northern Kazakhstan, and northern India.
227 228 229 230
Fig. 4. Spatial distribution of the frequency of more-extreme years in the Northern Hemisphere in 1901–2017(unit: %).
9
231 232 233 234 235
Fig. 5. Number of grid points for the frequency of winter extreme precipitation in the Northern Hemisphere in 1901–2017.
236
Northern Hemisphere. As shown in this figure, the grid points that exhibited an increasing trend
237
in the frequency of more-extreme years accounted for 71.68% of the Northern Hemisphere’s land
238
area, while those displaying a decreasing trend accounted for 21.50%, and those that were
239
unchanged accounted for 6.82%. It can be seen that in the past century the grid points of nearly
240
2/3 of the land areas in the Northern Hemisphere had an increasing trend in the frequency of
241
more-extreme years. Among them, 20.54% exhibited a significant increasing trend (Figure 7),
242
with an average linear trend value of 2.57%/10a, while 1.37% showed a significant decreasing
243
trend, with an average linear trend value of −2.03%/10a. The overall proportions of grid points
244
showing significant increases in high, middle, and low latitudes were 34.31%, 19.09%, and
245
6.31%, respectively. It can be seen that the proportion of the area with significant increases was
246
the largest in high latitudes. The proportions of grid points with significant decreases in high,
247
middle, and low latitudes were 0.02%, 1.88%, and 2.14%, respectively, revealing that the
248
proportion of the area with significant decreases was the largest in the low latitudes. The areas
249
with significant increases in the frequency of more-extreme years were primarily located in
250
western Alaska, northeastern Canada, the vicinity of Greenland, most of Iceland, and
251
northwestern and central Eurasia. The areas with significant decreases in the frequency of
252
more-extreme years were mainly in the northern part of the Indian peninsula, central Kazakhstan,
Figure 6 shows the linear trend distribution of the frequency of more-extreme years in the
10
253
and southern Africa.
254
255 256 257 258
259 260 261 262 263 264
Fig. 6. Linear trend distribution of the frequency of more-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a).
Fig. 7. Linear trend distribution of the frequency of more-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a). Color areas indicates P < 0.05.
3.2.2 Spatial pattern distribution and variations of less-extreme years
265
Figure 8 illustrates the spatial distribution of the frequency of less-extreme years in the
266
Northern Hemisphere from 1901 to 2017. It can be seen that the frequency of less-extreme years
267
in the Northern Hemisphere over the past century ranged 0–20.83%, and the spatial distribution
268
was not uniform. The frequency was mainly between 5–10%, accounting for 57.12% of the grid
269
points, while the frequencies of 0–5% and 10–15% accounted for 22.57% and 10.86% of all grid
270
points, respectively (Figure 5). The regions in which the frequency of less-extreme years was >
271
15% were mainly distributed in eastern and northeastern Canada, western Norway, western
272
Romania, and northern and central Russia.
11
273
274 275 276 277 278
Fig. 8. Spatial distribution of the frequency of less-extreme years in the Northern Hemisphere in 1901–2017 (unit: %).
279
Hemisphere in the past century is shown in Figure 9. As seen in this figure, the grid points
280
exhibiting an increasing trend in the frequency of less-extreme years accounted for 47.45% of
281
the Northern Hemisphere’s land area, those exhibiting a decreasing trend accounted for 38.68%,
282
and those that were unchanged accounted for 13.87%. Among them, 8.43% of the grid points
283
showed a significant increasing trend (Figure 10), with a trend value of 2.15%/10a, while 5.47%
284
showed a significant decreasing trend, with a trend value of −2.47%/10a. The proportions of grid
285
points with significant increases in high, middle, and low latitudes were 10.26%, 7.56%, and
286
7.71%, respectively, while the proportions of grid points with significant decreases in high,
287
middle, and low latitudes were 11.81%, 3.84%, and 0.58%, respectively. It can thus be seen that
288
the high latitude region had the largest area of increase as well as the largest area of decrease in
289
the frequency of less-extreme years. Therefore, high latitudes experienced the most significant
290
changes in less-extreme years. In the middle and low latitudes, the overall area with a significant
291
increase in the frequency of less-extreme years was larger than the overall area with a significant
292
decrease. The areas with a significant increase were mainly located in northeastern North
293
America, central and eastern Eurasia, Central Asia, northern China, and southern Mongolia; the
294
areas with a significant decrease were mainly distributed in western Greenland, as well as
295
northwestern, north central, and northeastern Eurasia.
The linear variation trend of the frequency of less-extreme years over terrestrial Northern
12
296 297 298
299 300 301 302 303
Fig. 9. Linear trend distribution of the frequency of less-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a).
Fig. 10. Linear trend distribution of the frequency of less-extreme years in the Northern Hemisphere in 1901–2017 (unit: %/10a). Color areas indicates P < 0.05. Based on the above analysis, we can see that the frequencies of more-extreme years and
304
less-extreme years in the Northern Hemisphere ranged from 5% to 15%, and the spatial
305
distribution was not uniform. The grid points that had an increasing trend of more-extreme years
306
and less-extreme years both accounted for a large proportion, and the number of grid points with
307
a significant increase was larger than the number with a significant decrease. The proportion of
308
grid points with a significant increase in the frequency of more-extreme years was the largest in
309
the high latitude region, and the proportion of grid points with a significant decrease in the
310
frequency of less-extreme years was the largest also in the high latitude region, indicating that
311
the high latitudes of the Northern Hemisphere experienced the largest variation in extreme
312
precipitation.
313 314 315 13
316
4 DISCUSSION AND CONCLUSIONS
317
4.1 Discussion
318
(1) In theory, an increase in temperature will lead to an increase in water vapor content and
319
precipitation (Wentz et al., 2007). Observational data have also confirmed the theoretical
320
inference of increasing air moisture content due to increasing temperature (Trenberth et al.,
321
2005). Global warming is an important reason for the increase in extreme heavy precipitation
322
(Goswami et al., 2006). Therefore, under the influence of global warming, the effect of
323
temperature change on the variation of spatiotemporal patterns of extreme precipitation is
324
non-negligible. This study utilized CRU data to analyze the distribution and variation of the
325
frequency of the years with winter extreme precipitation over terrestrial Northern Hemisphere in
326
the past century. This analysis could provide a new basis for the study of extreme precipitation
327
change under the background of climate warming, and in particular, it enriches the study of
328
winter extreme precipitation change as influenced by climate warming.
329
(2) The Fifth Assessment Report of the IPCC pointed out that extreme precipitation changed
330
significantly in the 20th century, during which time it increased significantly in the middle and
331
high latitudes (Stocker et al., 2013). In addition to the significant increase in the frequency of
332
more-extreme years in the middle and high latitudes, it was further discovered in the current
333
study that the frequency of less-extreme years in low latitudes also significantly increased. Chen
334
and Zhang (2016) reported that the frequency of winter extreme heavy precipitation events
335
increased significantly during 1901–2012 in the northern coastal areas across the entire Eurasian
336
continent. In the present study, it was shown that the frequency of more-extreme years increased
337
significantly in 1/5 of the land area of the Northern Hemisphere over the past century, covering a
338
relatively large region including the entire northern coastal areas of the Eurasian continent.
339
López-Moreno et al. (2011) used a regional climate model to simulate the frequency and
340
intensity of heavy snow events at an altitude of 1000 m under the condition of future temperature
341
rise, and found a significant decrease. Moreover, a study by Kenneth et al. (2009) revealed that
342
the frequency of extreme snow years in the United States has decreased due to climate warming.
343
These conclusions differ from those drawn in the present study, which deduced that the
344
frequency of more-extreme years increased at high latitudes of the Northern Hemisphere over the
345
past century.
346
(3) It is concluded in this study that over the past century the frequency of more-extreme
14
347
years in the Northern Hemisphere increased significantly (P < 0.05). The frequency of
348
less-extreme years were minimal changes (P > 0.05). Since 1901, wintertime land temperatures
349
in the Northern Hemisphere exhibited an extremely significant increasing trend (Figure 11), with
350
an increase rate of 0.15°C/10a (P < 0.01). Winter temperatures in the high, middle, and low
351
latitude areas have all displayed significant increasing trends, among which the rate of increase
352
was highest in the high latitude area, averaging approximately 0.19°C/10a (P < 0.01), followed
353
by that in the middle latitudes (0.16°C/10a; P < 0.01) and low latitudes (0.07°C/10a; P < 0.01).
354
The rate of temperature increase in the high latitudes was the greatest, while that in the low
355
latitudes was the smallest. The results show that the areas with a higher increase in temperature
356
exhibited a greater increase in the frequency of more-extreme years, while the areas with a lower
357
rate of temperature increase displayed a greater increase in the frequency of less-extreme years.
358
The spatial distribution of the tendency rate of winter average temperature in the past century
359
(Figure 12) reveals that winter temperatures in the terrestrial Northern Hemisphere generally
360
increased significantly, with greater increases in the middle and high latitude areas than in the
361
low latitude areas. This further proved that the temperature change was related to the variation of
362
extreme precipitation, although the temperature change was not highly consistent with the
363
change in extreme precipitation spatially.
364 -4 (a).Northern Hemisphere
Temperature\℃
-5 -6
-23
y = 0.015x - 8.0008 R² = 0.4698
-25
366 367 368
-6 y = 0.0191x - 28.171 R² = 0.3329
-7
(d).Low latitudes
21
-27
y = 0.0069x + 19.291 R² = 0.3291
20
-8
-10 1901
22
y = 0.0166x - 9.527 R² = 0.342
-8
-10
-29
-9
365
(c).Middle latitudes
(b).High latitudes
1930
1959
1988
2017
-31 1901
1930
1959
1988
2017
-12 1901
19
1930
1959
1988
2017
18 1901
1930
1959
1988
2017
Fig. 11. Interannual change in winter temperatures over terrestrial Northern Hemisphere in 1901–2017.
15
369 370 371 372 373
Fig. 12. Linear trend distribution of winter temperatures over terrestrial Northern Hemisphere in 1901–2017 (unit: °C/10a).Shading indicates P < 0.05.
374
Northern Hemisphere, as well as the mutation points of the average winter temperature in high,
375
middle and low latitudes (Figure 13). The results show that there is no intersection between UF
376
and UB in the 0.05 probability range, so the annual average temperature of land in the northern
377
hemisphere in winter has no mutation in 1901-2017, and the winter average temperature in high,
378
middle and low latitudes has no mutation in 1901-2017. Therefore, it can be concluded that the
379
change of extreme precipitation on time scale does not exactly match the change of temperature.
Furthermore, the MK test is used to analyze the winter temperature in the terrestrial
380 (a3).Middle latitudes 9
9
7
7
7
7
5
5
5
5
3
3
3
3
1
1
1
(a1).Northern Hemisphere
-11901
381
1930
-3
9
1959
1988
UF
(a2).High latitudes
2017
UB
(b1).Northern Hemisphere
7 5
-11901
1930
-3
1959
1988
UF
2017
UB
-11901
1 1930
-3
1959
1988
UF
2017
UB
-11901
(b2).High latitudes
(b3).Middle latitudes
9
9
9
7
7
7
5
5
3
3
3
1
1
1
-3
1930
1959
UF
1988
2017
UB
-11901 -3
1930
1959
UF
1988
2017
UB
-11901 -3
1959
1988
UF
2017
UB
(b4).Low latitudes
5
1901
1930
-3
3
-1
382 383 384 385 386
(a4).Low latitudes
9
9
1 1930
1959
UF
1988
2017
UB
-11901 -3
1930
1959
UF
1988
2017
UB
Fig. 13. The results of the Mann-Kendall test in winter temperatures(a) and annual average temperatures(b) in the Northern Hemisphere in 1901–2017. Meanwhile, we analyzed the winter temperature anomaly and annual average temperature
387
anomaly in the northern hemisphere in the past century (Figure 14), and found that the
388
temperature changes occurred in the late 1980s, which was not consistent with the turning point 16
389
of the extreme precipitation frequency anomaly. It is further explained that the distribution and
390
change of extreme precipitation are related to temperature, but not completely affected by
391
temperature, but also by atmospheric circulation and other factors.
392 4
(a1).Northern Hemisphere
3
Temperature\℃
393
Temperature\℃
1901
1930
1959
1988
2017
-1
1930
1959
1988
2017
-1
-2 -3
-3
-3
-4
-4
-4
(b1).Northern Hemisphere 2
1930
1959
1988
1959
1988
2
(b3).Middle latitudes
1959
1988
1930
1959
1988
2017
1
y = 0.0127x - 0.7465 R² = 0.612
(b4).Low latitudes 1
1901
2017
1930
1959
1988
y = 0.0072x - 0.4259 R² = 0.5254
0.5
0 1930
1901
2017
-2
y = 0.0138x - 0.8127 R² = 0.4313
1901
2017
1930
-1
0 1901
-2
1901
(b2).High latitudes
1
0 -1
0
0 1901
-2
y = 0.0116x - 0.6862 R² = 0.5964
y = 0.0069x - 0.4057 R² = 0.3291
1
1
-2
1
y = 0.0166x - 0.9823 R² = 0.342
2
0
0
2
394 395 396 397 398
3
1
1
(a4).Low latitudes
2
(a3).Middle latitudes
4
y = 0.0191x - 1.1292 R² = 0.3329
2
y = 0.015x - 0.8824 R² = 0.4698
2
-1
(a2).High latitudes
4
3
2017
0 1901
-1
-1
-0.5
-2
-2
-1
1930
1959
1988
2017
Fig. 14. Interannual anomaly variations in winter temperatures(a) and annual average temperatures(b) over terrestrial Northern Hemisphere in 1901–2017. (4) The results of this analysis reveal that the frequencies of more-extreme years and
399
less-extreme years in the Northern Hemisphere over the past century in the high and middle
400
latitudes were higher than those in the low latitudes. Since 1901, winter precipitation over
401
terrestrial Northern Hemisphere have shown a significant increasing trend (Figure 15), increasing
402
at a rate of 0.16 mm /10a (P < 0.01). Moreover, winter precipitation in the high and middle
403
latitudes has shown an extremely significant increasing trend, increasing at rates of 0.37 mm/10a
404
(P < 0.01) and 0.14 mm/10a (P < 0.01), respectively. Meanwhile, winter precipitation in low
405
latitudes has decreased at a rate of -0.04 mm/10 a (P > 0.05). It can be seen that the greatest rate
406
of winter precipitation increase occurred at high latitudes, and the smallest occurred at low
407
latitudes. This reveals that the number of more-extreme years increased in the regions with
408
significant increases in winter precipitation over the past century, while the number of
409
less-extreme years increased in the regions with minimal changes in winter precipitation (Figure
410
16).
411
17
(b).High latitudes
Precipitation/mm
(a).Northern Hemisphere
412 413 414 415
y = 0.0164x + 28.25 R² = 0.2203
32 30
27 25
45
y = 0.0371x + 20.039 R² = 0.4613
40
23
37
1959
1988
2017
17 1901
y = -0.0042x + 29.724 R² = 0.005
32
35 27 30
19 1930
(d).Low latitudes
y = 0.0137x + 33.115 R² = 0.0593
21
28 26 1901
(c).Middle latitudes
1930
1959
1988
2017
25 1901
1930
1959
1988
2017
22 1901
1930
1959
1988
2017
Fig. 15. Interannual variation in winter precipitation over terrestrial Northern Hemisphere in 1901–2017.
416 417 418 419
Fig. 16. Linear trend distribution of winter precipitation over terrestrial Northern Hemisphere in 1901–2017 (unit: mm/10a)Shading indicates P < 0.05.
420
4.2 Conclusions
421
(1) During 1901–2017, the frequency of more-extreme years over terrestrial Northern
422
Hemisphere was higher than that of less-extreme years, with specific values of 9.64% and 7.33%,
423
respectively, corresponding to return periods of approximately 10 years and 14 years. The
424
frequency of more-extreme years was higher than that of less-extreme years, and the frequency
425
of more-extreme years had a significant increasing trend, with a trend value of 0.87%/10a. The
426
frequency of less-extreme years also exhibited an increasing decadal trend, albeit not significant.
427
(2) During 1901–2017, the frequencies of more-extreme years and less-extreme years over
428
terrestrial Northern Hemisphere in the middle and high latitudes were higher than those at low
429
latitudes. The frequency of more-extreme years in the middle and high latitudes exhibited a
430
significant increasing trend, with the maximum increase rate of 1.50%/10a appearing at high
431
latitudes. However, the frequency of less-extreme years showed no significant change in the
432
middle and high latitudes, while the frequency at low latitudes displayed a significant increasing
433
trend, with a rate of 0.37%/10a. The frequencies of both the more-extreme years and
434
less-extreme years increased at all latitudes after the 1950s. 18
435
(3) During 1901–2017, the frequencies of more-extreme years and less-extreme years over
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terrestrial Northern Hemisphere ranged 5–15%. In the Northern Hemisphere, an increasing trend
437
in the frequency of more-extreme years was observed at 71.68% of the grid points, and a
438
significant increasing trend was observed at 20.54% of the grid points, with an average linear
439
trend value of 2.57%/10a. An increasing trend in the frequency of less-extreme years was
440
observed at 47.45% of the grid points, and a significant increasing trend was observed at 8.43%
441
of the grid points, with an average linear trend value of 2.15%/10a. Over the past century, the
442
Northern Hemisphere was mainly characterized by an increase in winter extreme precipitation.
443 444
Acknowledgments: This research is funded by the National Natural Science Foundation of
445
China (Grant No. 41771067).
446 447
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Highlights: We analyze characteristics of winter extreme precipitation in the northern hemisphere. The frequency of years with extreme winters in high latitudes exhibited a significant increase. The frequency of less extreme winters in low latitudes exhibited a significant increase.
Conflict of Interest Statement We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript.