Effects of climate change on suitable rice cropping areas, cropping systems and crop water requirements in southern China

Agricultural Water Management 159 (2015) 35–44

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Effects of climate change on suitable rice cropping areas, cropping systems and crop water requirements in southern China Qing Ye a,b , Xiaoguang Yang b,∗ , Shuwei Dai c , Guangsheng Chen d , Yong Li e,b , Caixia Zhang a a

College of Forestry, Jiangxi Agricultural University, Nanchang 330045, PR China College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, PR China c School of Natural Resources, University of Nebraska–Lincoln, Lincoln 68583, USA d Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge 37831, USA e Guizhou Key Laboratory of Mountainous Climate and Resources, Guiyang 550002, PR China b

a r t i c l e

i n f o

Article history: Received 29 August 2014 Received in revised form 18 May 2015 Accepted 23 May 2015 Available online 5 June 2015 Keywords: Climate change Rice cropping system Crop water requirement Irrigation water requirement Suitable planting area for rice

a b s t r a c t Rice is one of the main crops grown in southern China. Global climate change has significantly altered the local water availability and temperature regime for rice production. In this study, we explored the influence of climate change on suitable rice cropping areas, rice cropping systems and crop water requirements (CWRs) during the growing season for historical (from 1951 to 2010) and future (from 2011 to 2100) time periods. The results indicated that the land areas suitable for rice cropping systems shifted northward and westward from 1951 to 2100 but with different amplitudes. The land areas suitable for single ricecropping systems (SRCS) and early double rice-cropping systems (EDRCS) decreased, whereas the land areas suitable for middle double rice-cropping systems (MDRCS) and late double rice-cropping systems (LDRCS) expanded significantly. Among the rice-cropping systems, the planting area suitable for SRCS was the largest during the historical period (1951–1980), whereas the suitable planting area for LDRCS was the largest during the future period (2070–2100). Spatially, the water requirement of rice during the growing season exhibited a decreasing trend from southeast to northwest from 1951 to 2010. Temporally, the regional water requirement of rice during the growing season decreased from 720 mm (1951–1980) to 700 mm (1981–2010) as a result of solar radiation and evapotranspiration. However, the water requirement was predicted to increase from 1027 mm (2011–2040) to 1150 mm (2071–2100). During the past six decades, the planting area suitable for double rice-cropping systems increased by 2.7 × 104 km2 and, consequently, the CWR and irrigation water requirement (IWR) increased by 1.1 × 1010 and 8.8 × 109 m3 , respectively. In addition, under A1B scenarios, the CWR and IWR of double rice-cropping systems are expected to increase by 1.6 × 1011 and 1.2 × 1011 m3 , respectively, from 2071–2100 compared with the historical period of 1951–1980. The regional CWR and IWR were predicted to increase respectively by 8% and 6% from 2011 to 2040, by 17% and 19% from 2041 to 2070, and by 20% and 24% from 2071 to 2100 compared with 1951–1980. These increases can be attributed to climate warming, which expands the suitable planting area for multiple-cropping systems and extends the growing season for late-maturing rice varieties. Our study aims to provide a scientific guide for planning future cropping systems and optimizing water management in the southern rice cropping region of China. © 2015 Elsevier B.V. All rights reserved.

1. Introduction China contains 19% of the world’s population but only 7% of the global farmland, only approximately 0.093 ha of farmland per person (Liu et al., 2011). Accelerated urbanization in combination with explosive economic growth has further worsened the

∗ Corresponding author. Tel.: +86 10 62733939; fax: +86 10 62733939. E-mail address: [email protected] (X. Yang). http://dx.doi.org/10.1016/j.agwat.2015.05.022 0378-3774/© 2015 Elsevier B.V. All rights reserved.

shortage of agricultural land (Chen, 2007). Cultivated land decreased by 2120 km2 per year from 2000 to 2009 because of urbanization (Cai et al., 2009; Yao et al., 2012). The conflict between farmland reduction and population growth is intensifying (Yang and Li, 2000). Meanwhile, grain production in China has increased in the past 10 years due to improved agricultural techniques, especially the adoption of multiple-cropping systems (Liu and Wang, 2013). In 2005, 46% of the cultivated land was multiple-cropped (Zhuo et al., 2013), yielding 67% of the total grain production in China (Chen, 2012). Multiple cropping is one of the simplest ways

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to increase grain production and plays an important role in maintaining food security in China. Global warming has advanced the start date and delayed the end date of the crop growing season, resulting in a longer growing season (Frich et al., 2002; Linderholm et al., 2008; Parmesan and Yohe, 2003; Root et al., 2003; Song et al., 2010). The extended crop growing season has made it possible to improve multiple-cropping indices and to extend the boundaries of multiple-cropping systems (Yang et al., 2011b; Zhang, 2000; Zhao et al., 2010). In the southern rice growing area of China, the length of the growing season has been extended by 17.9 days per year, and the double rice-cropping area has shifted northward by 300 km from 1961 to 2009 (Song et al., 2011b). The CWR differs among cropping systems (Han and Qu, 1991; Liu and Han, 1987) and could be significantly impacted by climate change (Cao et al., 2008; Liu and Lin, 2004; Ma et al., 2006; Sun et al., 2013). Under future climate scenarios, the crop water requirement is predicted to increase by 4.89% and 6.06% during 2046–2065 and 2081–2100, respectively, compared with 1961–1990 (Cong et al., 2011). In addition, a 1 ◦ C increase in temperature is predicted to increase the crop water requirement by 4–4.5% (Wang et al., 2007). Further, reports have indicated that climate warming has already resulted in changes in cropping systems in southern China (Chen et al., 1999; Long et al., 2010; Lu et al., 2007; Wang et al., 1999). To date, many studies have investigated the water requirements of rice with respect to climate change (Han et al., 2011; Li et al., 2010; Luo et al., 2009; Song et al., 2011a; Wang et al., 2012a,b; Zulu et al., 1996). However, climate change affects various aspects of rice cultivation systems in addition to the CWR, including cultivation land and the length of the crop growing season (Yoo et al., 2013). The variability of the CWR based on potential changes in the distribution of rice cropping systems has not been well documented.

Many previous studies estimated the suitable planting area for rice based solely on the accumulated air temperature data; however, it is also necessary to incorporate crop information (e.g., rice varieties, cropping system types, and sowing dates), geographic information (e.g., latitude) and climate data (e.g., precipitation, solar radiation, and air temperature). In this study, we aim to: (1) investigate the changes in the main rice-cropping systems in southern China under historical and future climate change; (2) analyze the spatio-temporal variations in the CWR and IWR during the growing season; and (3) evaluate the possible effects of climate change on the CWR and IWR of different rice-cropping systems. This research will provide scientific evidence for planning cropping systems and water management in the rice cropping area of southern China.

2. Data and methods 2.1. Study area and data The research area is located in southern China (99–123◦ E and 18–34◦ N). The borders of this region were delineated by Liu and Han (1987) based on similarities in natural resources (e.g., characteristics of the terrain, radiation and water resources), socio-economic conditions, and crop varieties, structures, and maturity types. In addition, the integrity of the county-level administrative division was considered in subarea divisions (Fig. 1). The cropping systems in this region are rice-based, (e.g., double-cropping rotation of middle rice and winter wheat, triple-cropping rotation of double rice and winter wheat/oilseed rape). The paddy land area in this region accounts for 83.5% of the total paddy land area in China (Hu, 2009). In particular, the regional double rice-cropping system

Fig. 1. Overview of the research area. The upper right picture shows the distribution of arable and non-arable land in southern China (2005), and the lower right picture shows the elevation and distribution of meteorological stations in southern China.

Q. Ye et al. / Agricultural Water Management 159 (2015) 35–44

area accounts for 66% of the total paddy land area and contributes to 61.3% of the national rice production (Xin and Li, 2009). A better understanding of how multiple rice-cropping systems respond to climate change in the past and future can provide insights into adaptation strategies to ensure China’s food security. Historical climate data for 1951–2010 from 254 meteorological stations (Fig. 1) were acquired from the China Meteorological Science Data Sharing Service (http://cdc.cma.gov.cn) and included atmospheric pressure; maximum, minimum, and average temperatures; relative humidity; precipitation; wind speed; and number of sunshine hours. Gridded climate data for 2011–2100 under the A1B scenario (Nakicenovic and Swart, 2000) were originally obtained from the National Climate Center (http://cdc.cma.gov.cn) at a spatial resolution of 25 km and were downscaled using the regional climate model RegCM3 nested within the global model M2ROC 3.2-hires (Gao et al., 2010, 2012; Shi, 2007). According to the World Meteorological Organization, one climatological period is suggested as 30 years (WMO, 1989). Therefore, we divided the entire research period 1951–2100 into five periods, including (a) 1951–1980, (b) 1981–2010, (c) 2011–2040, (d) 2041–2070, and (e) 2071–2100. To ensure that the results of the future scenarios were comparable to the historical period, we selected the gridded data based on the geographical locations of the meteorological stations. The phenology data were obtained from the China Meteorological Bureau agricultural meteorological observatory (http://cdc.cma. gov.cn), and the digital elevation model (DEM) data (Version 4.1) were downloaded from the CIAT-CSI SRTM website (http://srtm. csi.cgiar.org). 2.2. Suitable distribution indices for the main rice cropping systems In this study, we used the growing season utilization rate to evaluate the suitability of the growing season for various rice cropping systems. The growing season utilization rate (UGS ) is defined as the ratio of the potential growing season length (PGSL) to the theoretical growing season length (TGSL) for each rice cropping system (e.g., single rice-cropping system, double rice-cropping system). If the UGS equals 1.0, the potential growing season perfectly satisfies the theoretical growing season of the rice cropping system. If the UGS is less than 1.0, the potential growing season does not satisfy the theoretical growing season, and if the UGS is greater than 1.0, the potential growing season is more than sufficient to satisfy the theoretical growing season of the rice cropping system. The UGS was calculated using the following equation: UGS =

PGSL TGSL

(1)

where UGS is the growing season utilization rate (unitless); PGSL is the length of the potential growing season (days) and TGSL is the length of the theoretical growing season (days). We defined the suitable distribution indices for the main rice cropping systems based on Gao et al. (1983) (Table 1). The PGSL is the duration from the beginning (sowing date) to the end (maturity date) of the climatological growing season. The beginning of the climatological growing season is specified as the first occurrence of a five-day moving average daily temperature greater than 10 ◦ C with an 80% probability. The end of the climatological growing season is specified as the last occurrence of a five-day moving average daily temperature greater than 15 ◦ C with an 80% probability (Gao and Li, 1992; Gao et al., 1983, 1987; Yan et al., 2004). The TGSLs for different rice varieties were simulated using a climatic-ecological model for rice developed by Gao et al. (1983); these values are listed in Table 2.

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Table 1 Suitable distribution indices for the main rice cropping systems. Rice cropping system

Cropping pattern

Suitable distribution indices

Single rice cropping system (SRCS) Early double rice cropping system (EDRCS)

Hybrid rice

UGS ≥ 1.0 for SRCS UGS < 1.0 for EDRCS UGS ≥ 1.0 for EDRCS UGS < 1.0 for MDRCS

Middle double rice cropping system (MDRCS) Late double rice cropping system (LDRCS)

Medium maturity early indica + medium maturity japonica Late maturity early indica + hybrid rice Hybrid rice + hybrid rice

UGS ≥ 1.0 for MDRCS UGS < 1.0 for LDRCS UGS ≥ 1.0 for LDRCS

2.3. Determination of the length of the rice growing season We divided the rice growing season into three stages: the early stage (from sowing to booting), middle stage (from booting to flowering) and late stage (from flowering to maturity) (Allen et al., 1998; Li et al., 2010). The methods suggested by Gao et al. (1983) were used to calculate the PGSL and TGSL during the five periods (1951–1980, 1981–2010, 2011–2040, 2041–2070 and 2071–2100). For rice varieties with early and middle maturation, the sowing date was specified as the date with an 80% probability of an average daily temperature equal to or greater than 10 ◦ C, and the length of the growing season (from sowing to maturity) was calculated using a climatic-ecological model (Gao and Li, 1992). For late-maturing rice varieties, the sowing date (the beginning of the seedling stage) was specified as 30 days earlier than the maturation date of the earlymaturing varieties, and the transplanting date was specified as 5 days (harvesting time) after maturity of the early-maturing varieties. The maturation date was derived from the climatic-ecological model. We used the mean lengths of the phenological stages during the period of 1980–2010 to interpolate the booting and heading stages, based on the FAO approach (Allen et al., 1998). The mean phenological dates for 1951–2010 for the various rice cropping systems are listed in Table 3. 2.4. Water requirements of rice 2.4.1. Crop water requirement The CWR is the total amount of water required for transpiration by a well-managed crop grown under optimal conditions without water or nutrient stress. The CWR was calculated as the potential crop evapotranspiration using the crop coefficient (Kc ) and reference crop evapotranspiration rate (ET0 , mm day−1 ) recommended by the FAO (Allen et al., 1998): CWR = ET0 · Kc ET0 =

0.408(Rn − G) + (900/(T + 273))U2 · (ea − ed )  + (1 + 0.34U2 )

(2) (3)

where CWR is the crop water requirement (mm day−1 ); ET0 is the reference crop evapotranspiration rate, mm day−1 ; Rn is the net radiation at the crop surface (MJ m−2 day−1 ); G is the soil heat flux density (MJ m−2 day−1 ); T is the daily mean air temperature at a height of 2 m (◦ C); U2 is the wind speed at a height of 2 m (m s−1 ); ed is the saturation vapor pressure at the air temperature (kPa); ea is the actual vapor pressure (kPa);  is the slope of the saturation water vapor pressure-temperature curve (kPa ◦ C−1 );  is the psychometric constant (kPa ◦ C−1 ). Rn , G,  and U2 can be calculated using climate data from meteorological stations. The crop coefficients for the early, middle and late stages of the growing season were obtained from previous studies (Allen et al., 1998; Li et al., 2010) (Table 4).

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Table 2 The theoretical rice growing season length (TGSL). Variety type

Representative varieties

TGSL (days)

Hybrid rice Medium maturity early indica Late maturity early indica Medium maturity japonica

Shanyou II Yuanfengzao Guangsi Nanjing 34

N = 101.56 − 3.52T + 0.16(T)2 + 0.16D + 3.28˚ N = 71.82 − 2.42T + 0.14D + 1.49˚ N = 71.73 − 3.826T + 0.088D + 1.856˚ N = 122.64 − 3.13T + 0.39D + 1.09˚

Note: “N” is the theoretical growing season length (TGSL, days); “T” is the difference between 25 ◦ C and the average temperature from the beginning of the climatological growing season to the full-heading stage (◦ C); “D” is the number of days between April 1 and the climatological beginning date; “˚” is the difference between the station latitude and 30◦ N. Table 3 Mean phenological dates (month/day) for various rice varieties (early, middle, and late maturity) in the main rice cropping systems (single and double rice-cropping) in southern China. Period

Cropping system

Rice variety

Sowing date

Transplanting date

Booting date

Flowering date

Maturity date

Growing season length (days)

1951–1980

SRCS EDRCS

MM EM LM EM LM EM LM

3/25 3/19 6/11 3/9 6/6 1/20 5/4

4/25 4/18 7/11 4/8 7/6 2/19 6/3

7/15 5/31 9/8 5/24 8/30 4/16 7/24

7/25 6/9 9/20 6/2 9/10 4/26 8/4

9/4 7/6 10/31 7/1 10/20 5/29 9/10

162 109 142 114 136 130 130

MM EM LM EM LM EM LM

3/25 3/24 6/17 3/13 6/11 1/20 5/4

4/24 4/23 7/17 4/12 7/11 2/19 6/3

7/9 6/5 9/13 5/29 9/5 4/16 7/24

7/18 6/14 9/25 6/8 9/17 4/26 8/4

8/26 7/12 11/5 7/6 10/27 5/29 9/11

154 109 141 116 138 130 130

MM EM LM EM LM EM LM

3/18 3/3 5/21 2/17 5/8 1/14 4/16

4/17 4/2 6/20 3/18 6/7 2/13 5/16

7/4 5/11 8/22 4/28 8/12 4/2 7/8

7/14 5/20 9/4 5/7 8/25 4/12 7/19

8/22 6/12 10/16 6/2 10/8 5/11 8/29

160 105 149 106 153 118 133

MM EM LM EM LM EM LM

3/21 3/8 5/28 2/17 5/7 1/13 4/15

4/20 4/7 6/27 3/18 6/6 2/12 5/15

7/9 5/18 8/31 4/27 8/19 4/1 7/6

7/19 5/27 9/13 5/6 8/28 4/11 7/17

8/28 6/22 10/27 6/1 10/5 5/10 8/25

160 106 152 105 151 118 131

MM EM LM EM LM EM LM

3/17 3/8 5/28 2/18 5/6 1/13 4/15

4/16 4/7 6/27 3/19 6/5 2/12 5/15

7/6 5/18 8/28 4/27 8/8 3/31 7/5

7/16 5/27 9/10 5/5 8/21 4/10 7/16

8/25 6/22 10/24 5/31 10/3 5/10 8/22

161 106 149 103 150 118 130

MDRCS LDRCS 1981–2010

SRCS EDRCS MDRCS LDRCS

2011–2040

SRCS EDRCS MDRCS LDRCS

2041–2070

SRCS EDRCS MDRCS LDRCS

2071–2100

SRCS EDRCS MDRCS LDRCS

Note: SRCS: single rice-cropping system; EDRCS: early double rice-cropping system; MDRCS: middle double rice-cropping system; LDRCS: late double rice-cropping system. MM: medium maturity; EM: early maturity, and LM: late maturity.

2.4.2. Irrigation water requirement The IWR is the amount of water required to meet the CWR, beyond that supplied by rainfall. Typically, the IWR is calculated as the difference between the CWR and the actual crop evapotranspiration under rainfed conditions (i.e., PE during the growing season) (Brouwer and Heibloem, 1986; Li et al., 2010): IWR =

N  n=1

CWRn −

N 

PEn

Table 4 Crop coefficients for different growth stages during the rice growing season. Crop

Crop stage

Kc

Rice

Sowing – booting Booting – flowering Flowering – maturity

1.05 1.20 1.00

(4)

n=1

where IWR is the irrigation water requirement (mm); N is the length of the growing season (days); n is the Julian day of the year during the growing season; CWRn is the crop water requirement on the nth day (mm day−1 ); PEn is effective precipitation on the nth day (mm day−1 ). We calculated the effective precipitation during the growing season in the southern rice cropping area of China using the USDA

recommended method (Döll and Siebert, 2002; Li et al., 2010; Smith, 1992):

 PE =

P(4.17 − 0.2P)/4.17

P < 8.3

4.17 + 0.1P

P ≥ 8.3

(5)

where PE is effective precipitation (mm day−1 ); P is daily precipitation (mm day−1 ).

Q. Ye et al. / Agricultural Water Management 159 (2015) 35–44

3. Results 3.1. Changes in the suitable planting area for the main rice cropping systems The utilization ratio of the rice growing season (i.e., the PGSL to TGSL ratio) with a value ≥1.0 was used as an index for suitable planting areas of the various rice cropping systems. A spatial distribution model was developed using the regression between geographic information (e.g., longitude, latitude and elevation) and the UGS . Then, we used ArcGIS and geostatistical methods to map suitable planting areas for the various rice cropping systems. The suitable planting areas for the various cropping systems have been shifting northward during the research period (1951–2100) (Fig. 2 and Table 5). In general, suitable planting areas for SRCS and EDRCS decreased, while suitable planting areas for MDRCS and LDRCS expanded significantly. The suitable planting area for SRCS had the greatest coverage from 1951 to 2010, whereas the suitable planting area for LDRCS had the greatest coverage over the following nine decades (2011–2100). The suitable planting area for SRCS was mainly distributed within 25–34◦ N and 98–111◦ E from 1951 to 1980 (Fig. 2A) and within 30–34◦ N and 111–122◦ E from 1981 to 2010 (Fig. 2B). The suitable planting areas for SRCS, EDRCS, MDRCS, and LDRCS from

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1951–1980 were 9.63 × 105 km2 (44% of the total research area), 3.21 × 105 km2 (14% of the total research area), 4.47 × 105 km2 (20% of the total research area), and 4.88 × 105 km2 (22% of the total research area), respectively. The 1981–2010 coverage of suitable planting areas for the various rice cropping systems ranked in decreasing order is SRCS (accounting for 41% of the total research area), LDRCS (accounting for 23% of the total research area), MDRCS (accounting for 21% of the total research area) and EDRCS (accounting for 15% of the total research area) (Fig. 2B). The suitable planting area for SRCS was reduced by 6.2 × 104 km2 , whereas the suitable planting areas for EDRCS, MDRCS, and LDRCS increased by 0.7 × 104 km2 , 2.3 × 104 km2 , and 3.2 × 104 km2 , respectively, from 1981 to 2010 compared with 1951–1980. The suitable planting areas for all cropping systems shifted northward over the period 2011–2040 compared with 1951–1980, but with different amplitudes: the SRCS and EDRCS planting areas were significantly reduced by 5.32 × 105 km2 (accounting for 24% of the total research area) and 1.18 × 105 km2 (accounting for 5.3% of the total research area), respectively, whereas the suitable planting areas for MDRCS and LDRCS increased by 2.48 × 105 km2 (accounting for 11% of the total research area) and 4.02 × 105 km2 (accounting for 18% of the total research area), respectively (Fig. 2C).

Fig. 2. Coverage of suitable planting areas for various rice cropping systems during 1951–1980 (A), 1981–2010 (B), 2011–2040 (C), 2041–2070 (D), and 2071–2010 (E). The pie charts indicate the proportions of suitable planting areas for the various rice cropping systems relative to the total research area.

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Table 5 Suitable planting area (SPA, unit: × 104 km2 ) for various rice cropping systems in southern China during five periods (1951–1980, 1981–2010, 2011–2040, 2041–2070, and 2071–2100), and the percent changes relative to the total research area (, unit: %). Cropping system

SRCS EDRCS MDRCS LDRCS

1951–1980

1981–2010

SPA

SPA



SPA

2011–2040 

SPA



SPA



96.3 32.1 44.7 48.8

90.1 32.8 47.0 52.0

−2.8 0.3 1.0 1.4

43.1 20.3 69.5 89.0

−24.0 −5.3 11.2 18.1

22.2 8.8 66.3 124.5

−33.4 −10.5 9.7 34.1

11.2 4.2 47.8 158.7

−38.4 −12.6 1.4 49.5

During the period of 2041–2070, the suitable planting areas for SRCS and EDRCS were predicted to continue to decrease by 1.83 × 105 and 2.32 × 105 km2 , respectively, and the planting areas for MDRCS and LDRCS were predicted to continue to increase to 30% and 56% of the total research area, respectively, compared with 1951–1980 (Fig. 2D). From 2071 to 2100, the total suitable planting area for SRCS and EDRCS accounted for 6.9% of the total research area (Fig. 2E). Meanwhile, the suitable planting area for LDRCS expanded to the northern limit of EDRCS from 1951 to 1980, which is the largest area (accounting for 71% of the total research area) among the rice cropping systems. These analyses indicate that under the background of climate warming, a significant northward shift in the suitable planting areas of various rice cropping systems will have occurred in southern China over the period 1951–2100. This shift would affect the effectiveness of local climate resources for various rice cropping systems (Ye et al., 2013) and ultimately affect the potential rice yield (Ye et al., 2014). In the following sections, we explore the impacts of this change on the total crop water requirement and crop water deficit during the rice growing season in southern China. 3.2. Temporal and spatial characteristics of the CWR, PE and IWR The CWR (Fig. 3A and B), PE (Fig. 3F and G) and IWR (Fig. 3K and L) decreased from southeast to northwest from 1951 to 2010. These three agrometeorological indicators were higher for the double rice-cropping area than for the single rice-cropping area. The regional mean CWRs for 1951–1980 and 1981–2010 were 760 and 740 mm, respectively. In general, the CWR and IWR for MDRCS were higher than those of the other cropping systems, and the PE for LDRCS was higher than that of the other cropping systems. Areas with a relatively low CWR (below 500 mm) expanded from 1981 to 2010, whereas areas with a relatively high CWR (above 800 mm) contracted compared with the period of 1951–1980. Under the A1B scenario, the regional mean CWR from 2011 to 2100 was predicted to be 774 mm. Among the cropping systems, the CWR for MDRCS and LDRCS was relatively high, whereas the CWR for SRCS was relatively low (Fig. 3C–E), and the IWRs for MDRCS and LDRCS were relatively high (Fig. 3M–O). The PE exhibited a spatial zonal distribution, with lower values in the southwest and northeast regions of the research area and higher values in the center (Fig. 3H–J). Significant temperature increases and the northwestern expansion of multiple-cropping systems resulted in a significant increase in the CWR and IWR of the late-maturing rice variety during 2011–2100. The CWR increased slightly prior to 1970 and then decreased slightly until 2010 (Fig. 4). Under the A1B scenario, the CWR was predicted to increase significantly until 2070 and then decrease slightly. The PE during the growing season accounted for 30–50% of the CWR, and the remaining 50–70% was from irrigation. During 1951–2010, 61% of the CWR was from irrigation. Under the A1B scenario, the IWR of rice increases, primarily because the PE does not increase as much as the CWR. On average, the IWR

2041–2070

2071–2100

accounted for 65% of the CWR from 2011 to 2100. Because of the northward expansion and westward shifting of multiple-cropping systems, the CWR for 2011–2100 increased by 140 mm compared with 1951–1980, resulting in a regional increase in the IWR of 120 mm. 3.3. Growing-season CWR for the main rice cropping systems The CWR of single rice-cropping systems from 1951 to 2010 was 290 mm lower than that of double rice-cropping systems. The CWR varied slightly between the early and late cropping systems; the CWR for late-maturing varieties was approximately 140 mm higher than for early-maturing varieties. Under the future climate scenarios, temperature increases during the growing season resulted in higher CWRs compared with the past six decades (Cong et al., 2011). During the period 2011–2040, the CWR ranked from high to low is as follows: MDRCS, LDRCS, EDRCS, SRCS. The CWRs for 2041–2070 and 2071–2100 were highest for MDRCS, followed by EDRCS, LDRCS, and SRCS (Fig. 5). Under future climate scenarios, the CWR exhibited a significantly greater spatial difference compared with the historical climate data. We estimated the suitable planting areas for the various cropping systems using 2005 land-use information and the proportions of suitable planting areas for the main rice cropping systems (Table 5). Then, we multiplied the planting areas by the mean CWR of the various cropping systems to obtain the total CWR during the growing season. The difference between the total CWR and PE (Eq. (5)) is the total IWR (Table 6). During the past six decades, suitable planting areas for SRCS and EDRCS have been significantly reduced under climate warming. Therefore, the total CWR and IWR of these cropping systems are decreasing in southern China. However, suitable planting areas for double rice-cropping systems increased by 2.7 × 104 km2 ; consequently, the CWR and IWR increased by 1.1 × 1010 and 8.8 × 109 m3 , respectively. Over the next nine decades, the suitable planting area for LDRCS is predicted to expand significantly. The CWR and IWR of double rice-cropping systems are expected to increase by 9.1 × 1010 and 5.7 × 1010 m3 , respectively, from 2011 to 2040, 1.4 × 1011 and 9.5 × 1010 m3 , respectively, from 2041 to 2070, and 1.6 × 1011 and 1.2 × 1011 m3 , respectively, from 2071 to 2100 when compared with the historical period of 1951–1980. This would lead to a considerable increase in the total CWR in the research area. The total CWR and IWR for 2011–2040 are predicted to be 2.98 × 1011 and 1.89 × 1011 m3 , respectively. The total CWR and IWR are anticipated to reach 3.44 × 1011 and 2.35 × 1011 m3 , respectively, during 2071–2100. 4. Discussion 4.1. Impacts of climate change on suitable planting areas for rice Previous reports have indicated that the length of the growing season could be extended by climate warming and that the suitable growing area could shift northward for many vegetation types in

Q. Ye et al. / Agricultural Water Management 159 (2015) 35–44

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Fig. 3. Crop water requirements (A–E), effective precipitation (F–J) and irrigation water requirements (K–O) of rice during 1951–1980 (A, F, K), 1981–2010 (B, G, L), 2011–2040 (C, H, M), 2041–2070 (D, I, N), and 2071–2010 (E, J, O) in southern China.

the northern hemisphere (Frich et al., 2002; Linderholm et al., 2008; Parmesan and Yohe, 2003; Root et al., 2003), including rice (Song et al., 2011b). Paddy land is largely influenced by anthropogenic management; however, impacts of climate change on the distribution of various rice cropping systems could still be significant. Yang

et al. (2011b) reported that the suitable planting boundary for double rice-cropping systems has shifted northward by 50 km between 1951–1980 and 1981–2010, and Zhao et al. (2010) reported that suitable planting boundaries for MDRCS and LDRCS have shifted northward by 64 and 20 km, respectively. These studies suggest

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1200

Crop water requirement (mm) Effective precipitation (mm) Irrigation water requirement (mm)

1000

800

600 400

200 Historical climate 0 1951

A1B scenario

1980

2010

2040

2070

2100

Fig. 4. Variations in regional mean crop water requirement (CWR), effective precipitation (PE) and irrigation water requirement (IWR) of rice growing in southern China during 1951–2100. Note: irrigation water requirement is calculated as (crop water requirement – effective precipitation).

Crop Water Requirement (mm)

1400 1200 1000

1951-1980

1981-2010

2011-2040

2041-2070

2071-2100

R1 R2 R3 R4

R1 R2 R3 R4

Middle maturity rice Late maturity rice Early maturity rice

800 600 400 200 0

R1 R2 R3 R4

R1 R2 R3 R4

R1 R2 R3 R4

Fig. 5. Crop water requirement (mm) of rice during the growing season (mean value with 80% probability) for the main rice-cropping systems during five periods in southern China. R1: single rice-cropping system; R2: early double rice-cropping system; R3: middle double rice-cropping system; R4: late double rice-cropping system.

Table 6 Crop and irrigation water requirements (×109 m3 ) of the main rice cropping systems in southern China during the five periods. Cropping system

SRCS EDRCS MDRCS LDRCS Total

1951–1980

1981–2010

2011–2040

2041–2070

2071–2100

CWR

IWR

CWR

IWR

CWR

IWR

CWR

IWR

CWR

IWR

93.8 53.6 78.8 46.6 272.8

62.1 34.9 52.2 29 178.2

74.4 52.3 83.6 54.2 264.4

48 35.5 55.7 33.7 172.9

28.1 44.6 133.1 92.7 298.4

16.4 31.1 89.0 52.8 189.3

11.5 22.2 163.4 132.6 329.7

9.2 15.6 114.9 80.3 220.1

1.9 5.4 140.3 196.2 343.8

1.5 3.7 104.5 125.5 235.1

that climate change has a marked effect on both single and double rice-cropping systems. Our study further investigated the impacts of climate change on various double rice-cropping systems (i.e., EDRCS, MDRCS and LDRCS). We observed that the planting areas suitable for MDRCS and LDRCS expanded northward by 47 and 52 km2 , respectively, between 1951–1980 and 1981–2010, which could primarily be attributed to the increases in air temperature. Under the future climate scenario, we observed a more northward expansion and a westward shift in the planting areas suitable for MDRCS and LDRCS. The planting areas suitable for SRCS and ERCS were reduced by 38% and 13% of the total research area, respectively, between 1951–1980 and 2071–2100. 4.2. Impacts of changes in rice cropping patterns on water requirements Climate change could affect the water consumption of paddy fields (De Silva et al., 2007; Fischer et al., 2007; Thomas, 2008; Yoo et al., 2012). Wang et al. (2012a) reported that under SRA1B

scenarios, the CWR and IWR of rice increased by more than 2% and 5%, respectively, during 2046–2065 and by 5% and 15%, respectively, during 2081–2100. In our study, the, total CWR and IWR of rice in southern China under the A1B scenario increased by approximately 8% and 6%, respectively, during 2011–2040, 17% and 19%, respectively, during 2041–2070, and 20% and 24%, respectively, during 2071–2100 compared with values from 1951 to 1980. Our values are higher than those reported by Wang et al. (2012a) but similar to those of Yoo et al. (2013). This may result from effects of climate change on (i) the water consumption of the paddy field due to increased temperature and (ii) the distribution pattern of the rice cropping system through changes in the potential length of the growing season. Therefore, we considered these two factors in our study for estimates of the CWR and IWR. The regional CWR for 1981–2010 was 34 and 12 mm lower for the single and double rice-cropping systems, respectively, compared with 1951–1980. There are two major reasons for this decrease: first, decreases in solar radiation and evapotranspiration reduced the CWR (Yang et al., 2011a), and second, assuming that rice

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varieties have not changed, the length of the growing season decreased because of increased temperature (Cui, 1995). Consequently, the CWR could decrease. Historically, the multiplecropping indices of rice could be improved by lengthening the potential growing season; however, this effect is trivial. However, under a future climate scenario, this effect becomes more significant than the effect of shortening the growing season and decreasing solar radiation. Thus, the regional CWR is predicted to increase significantly during 2011–2070 when compared with 1951–1980. 4.3. Hypothesis and uncertainty In this study, we assumed that similar rice varieties were used in the various cropping systems; however, the selection of the rice variety depends on breeding technology, governmental policies, the grain market, and extreme weather conditions (e.g., low temperatures and waterlogging) during the growing season. Therefore, the results of the variability in suitable planting areas for the main rice cropping systems in southern China are solely a reflection of the impacts of temperature changes. Because irrigated agriculture is prevalent in southern China, the evaluation of the CWR under a future climate scenario could offer insights into optimal water management. The fact that we only investigated the suitable planting areas for various rice cropping systems with 80% probability may underestimate the impact of climate change. In addition, the simulation of the theoretical growing season for suitable planting areas was based on the assumption that there were no changes in the rice varieties. The maturation date of the theoretical growing season was specified as the date when the daily average temperature was equal to or higher than 10 ◦ C with an 80% probability in addition to the length of the simulated growing season. However, this method only addresses the mean theoretical growing season during each period and fails to reflect inter-annual variation. Therefore, the total CWR of rice during the growing season for various rice cropping systems only reflects the inter-decadal variation. Nevertheless, these predictions can still be used for effective mid- to long-term planning of agricultural water usage in southern China. Under alternative water saving technologies developed for rice cultivation (e.g., crop-regulated deficit irrigation, alternate wetting and drying irrigation) (Rejesus et al., 2011; Zhang et al., 2007), actual evapotranspiration increased and the irrigation water decreased by 6–14% (Belder et al., 2004). These technologies can weaken the effect of climate change on the IWR. In our study, however, the increase in IWR resulting from changes in the cropping systems was higher than that generated by water-saving technology. 5. Conclusions In this study, we used the ratio of PGSL to TGSL to evaluate the trends in suitable planting areas for the main rice cropping systems in southern China. In addition, the spatio-temporal variations in the CWR, PE and IWR of rice during the growing season were investigated. Climate change caused a northward expansion and westward shift in the main rice cropping systems and increased the suitable planting areas for multiple rice-cropping systems and middle- or late-maturity rice varieties. This provides an opportunity to further increase multiple-cropping indices for rice production in southern China. However, changes in the patterns of the rice cropping systems led to increases in the CWR and IWR of rice during the growing season. Over the past six decades, the suitable planting area for double rice-cropping systems increased by 2.7 × 104 km2 , and as a result, the CWR and IWR increased

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by 1.1 × 1010 and 8.8 × 109 m3 , respectively. Under the A1B scenario, the CWR and IWR are predicted to increase by 7.1 × 1010 and 5.7 × 1010 m3 , respectively, during 2071–2100 compared with 1951–1980. In particular, regional CWR and IWR are expected to increase respectively by 8% and 6% during 2011–2040, by 17% and 19% during 2041–2070, and by 20% and 24% during 2071–2100 compared with 1951–1980. Although our research methods are limited by the underlying assumptions, the results from this study provide a scientific guide for planning cropping systems and optimizing future water management in the southern rice cropping area of China. Acknowledgements This work is funded by Special Fund for Meteorology-scientific Research in the Public Interest, China (GYHY201106020) and the National 973 Program of China (2010CB951502). References Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop Evapotranspiration Guidelines for Computing Crop Water Requirements-Irrigation and Drainage Paper 56. Food and Agriculture Organization of the United Station, Rome. Belder, P., Bouman, B.A.M., Cabangon, R., Guoan, L., Quilang, E.J.P., Yuanhua, L., Spiertz, J.H.J., Tuong, T.P., 2004. Effect of water-saving irrigation on rice yield and water use in typical lowland conditions in Asia. Agric. Water Manage. 65, 193–210. Brouwer, C., Heibloem, M., 1986. Irrigation Water Management: Irrigation Water Needs. Food and Agriculture Organization of the United Nations, Rome. Cai, Y., Wang, Y., Li, Y., 2009. Study on changing relationship of demand and supply of cultivated land in China. China Land Sci. 23, 11–18. Cao, H., Su, X., Kang, S., Wang, Z., 2008. Effect of climate change on main crop water requirements in Guanzhong Region. J. Irrig. Drain. 27, 6–9. Chen, H., Lin, T., Cai, W., 1999. Climate change on cropping system in Fujian province. Fujian Agric. Sci. Technol., 3–4. Chen, J., 2007. Rapid urbanization in China: a real challenge to soil protection and food security. Catena 69, 1–15. Chen, K., 2012. Exploration on the model and benefit of multi-cropping system in southern China. South China Agric. 6, 13–15. Cong, Z., Yao, B., Ni, G., 2011. Crop water demand in China under the SRA1B emissions scenario. Adv. Water Sci. 22, 38–43. Cui, D., 1995. The scenario analyses of possible effect of warming climate on rice growing period. Q. J. Appl. Meteorol. 6, 361–365. Döll, P., Siebert, S., 2002. Global modeling of irrigation water requirements. Water Resour. Res. 38, 8-1–8-10. De Silva, C.S., Weatherhead, E.K., Knox, J.W., Rodriguez-Diaz, J.A., 2007. Predicting the impacts of climate change—a case study of paddy irrigation water requirements in Sri Lanka. Agric. Water Manage. 93, 19–29. Fischer, G., Tubiello, F.N., van Velthuizen, H., Wiberg, D.A., 2007. Climate change impacts on irrigation water requirements: effects of mitigation, 1990–2080. Technol. Forecast. Social Change 74, 1083–1107. Frich, P., Alexander, L.V., Della-Marta, P., Gleason, B., Haylock, M., Klein Tank, A.M., Peterson, T., 2002. Observed coherent changes in climatic extremes during the second half of the twentieth century. Clim. Res. 19, 193–212. Gao, L., Li, L., 1992. Meteorological Ecology for Rice. China Agricultural Press, Beijing. Gao, L., Li, L., Guo, P., 1983. The length of growing season and climatic and ecologic regionalization for rice in China. Chin. J. Agrometeorol., 50–55. Gao, L., Li, L., Jin, Z., 1987. A climatic classification for rice production in China. Agric. Forest Meteorol. 39, 55–65. Gao, X., Shi, Y., Giorgi, F., 2010. A high resolution simulation of climate change over China. Sci. China Ser. D: Earth Sci. 40, 911–922. Gao, X., Shi, Y., Zhang, D., Filippo, G., 2012. Climate change in China in the 21st century as simulated by a high resolution regional climate model. Chin. Sci. Bull. 57, 374–381. Han, B., Lu, Y., Wang, W., Peng, S., Jiao, X., 2011. Impacts of climate change on rice growing period and irrigation water requirements. J. Irrig. Drain. 30, 29–32. Han, X., Qu, M., 1991. Crop Ecology. China Meteorological Press, Beijing. Hu, Z., 2009. Analysis of the situation of rice production in China. Hybrid Rice 24, 1–7. Li, Y., Yang, X., Dai, S., Wang, W., 2010. Spatiotemporal change characteristics of agricultural climate resources in middle and lower reaches of Yangtze River. Chin. J. Appl. Ecol. 21, 2912–2921. Linderholm, H.W., Walther, A., Chen, D., 2008. Twentieth-century trends in the thermal growing season in the Greater Baltic Area. Clim. Change 87, 405–419. Liu, B., Wang, X., 2013. Analysis of the major contribution factors of nine-year consecutive increasing of China’s grain. Chin. J. Agric. Resour. Reg. Plann. 34, 5–10. Liu, D., Feng, Z., Yan, Y., You, Z., 2011. Characteristics of grain production and spatial pattern of land carrying capacity of China. Trans. CSAE 27, 1–6. Liu, X., Han, X., 1987. Regionalization of Cropping System in China. Beijing Agricultural University Press, Beijing.

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