- Email: [email protected]
Annual Variability of Precipitation of the North West of Algeria
Available online at www.sciencedirect.com
APCBEE Procedia 5 (2013) 373 – 377
ICESD 2013: January 19-20, Dubai, UAE
Annual Variability of Precipitation of the North West of Algeria Hind Meddi , LGEE, Blida - ALGERIA
Abstract This study of the variability and change in annual rainfall in the North West of Algeria is based on the analysis of 25 stations with more than 50 years of data. The charts and analysis show that during the last century, the north west of Algeria show an alternation of dry and humid periods. We have used several methods to study the non-stationarity and trend in the series of studied stations. The results show generally upward trend covering the Thirties and the Fifties. The pluviometry fall was observed during the beginning of the Forties and the middle of the Seventies. The reduction of pluviometry exceeds 36 % in the Mascara region and in the extreme west. On the other hand, the decrease of rainfall is about 20 % in the centre of Algeria. The test on trends sequential confirmed the existence of three major trends during the last century. An increase of rainfall since 1945-46, which followed by a relatively dry phase and a decrease in
©2013 2013The Published ElsevierbyB.V. Selection © Authors.by Published Elsevier B.V. and/or peer review under responsibility of Asia-Pacific Chemical, Environmental Engineering Society Selection andBiological peer review&under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords : Drought; rainfall; stationarity; West; Algeria
1. Introduction Water has always been an essential factor for the development of agriculture and it has become a strategic issue. Repeated episodes of drought, especially since the decade of the 70's when a change in the rainfall regime in the reduction sense became a reality, especially for the central and western region. Algeria and especially the western region have experienced several droughts during this century, the 40s and 70s until
Corresponding author. E-mail address:[email protected]
2212-6708 © 2013 The Authors. Published by Elsevier B.V. Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2013.05.064
374
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
today. The most recent one was characterized by its spatial extent, its intensity and its major significant impact and the decrease of water resources. The purpose of this study is to characterize possible changes in climate in the central and western part of Algeria, to do, a statistical analysis of long time series data of rainfall at annual scale in different stations was conducted. 2. Material and method 2.1. Presentation of the study area The study area covers 89 420 km2. It is located between 2 ° 10'10''west and 3 ° 10'11''east of longitude and between 34 ° 18'54''and 36 ° 48'12''N of latitude (Fig. 1). The study area stretches on 250 km from south to north and about 500 km from west to east. 2.2. Climate and rainfall variability The northern part of Algeria is characterized by a Mediterranean climate with a relatively cold winter and rainy and hot dry summers. The rainfall reached 400 mm in the west, 700 mm in the center and 1000 mm in the east near the coast. This type of climate also affects the range of the mounts of the Tellian Atlas, where we recorded at the level of Eastern summits total of rainfalls ranging from 800 to 1600 mm, while those values are lowered in the Center (700 to 1000 mm) and in the Western (600 mm). 2.3. Data The climate research and monitoring of its evolution requires many long series of observations. Unfortunately, we do not have a perfectly reliable and continuous data. Representative sample, in statistical terms is a long process fraught with pitfalls and in which many errors are very different nature could be committed. Furthermore, it is necessary, before using data sets, to be concerned about their quality and their representativeness. The data represent a major element in the study of spatial and temporal variability of rainfall and drought. Data taken from the two organizations responsible for network rainfall namely the National Agency of Hydraulic Resources (ANRH) and the National Meteorological Office (ONM). The stations were selected according to the length of available rainfall records and their geographical positions in order to better cover the whole region, and the different climatic influences. Forty-eight (48) stations were selected on the studied region (Fig. 2). After critical and homogenization of monthly and annual data, the period 1930/31-2003/04 (ie 74 years) was chosen
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
Fig. 1. Location
of rainfall stations studied
3. Statistical approaches and analysis of rainfall data Stationarity or nonstationarity of the rainfall data interest many users of these in different applications (hydrology, agronomy, water management, etc..). The detection of one or more breaks give information on the evolution of rainfall in the region. This failure may be regarded as due to a change of parameters of the law of probabilities of random variables whose successive realizations constitute studied time series. In Algeria, the climate changes in the recent decades have had a negative influence on the water resource (groundwater recharge, filling of reservoir dams and on agricultural yields). We hope here to show this evolution by determining the year or years of break of rainfall data. The methods to highlight these break are: The U Buishand statistics [1,2], the test of Pettitt [3,4], the Bayesian method of Lee and Heghinian and the segmentation procedure of Hubert [5], whose power and robustness where shown in a review by Lubes-Niel et al. in 1998 [6] and applied in Algeria [7]. To facilitate the description of regional changes in rainfall patterns, we have based our work on the results of the regionalization of the annual precipitation [9]. The used groups correspond to the homogeneous areas found in this study. 4. Results Applied to each group, these tests give results which are generally consistent. Group I: In the series of annual precipitation, rupture is identified in the year 1966 by the Pettitt test, the procedure of Lee Heghinian corroborates these results by proposing the same dates between which the average rainfall increases by 16% for the station of Boughzoul. Stil in Group I: The station of Sougueur
375
376
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
shows a rupture, by the procedure of Lee Heghinian in 1940 with a decrease of 22%. The Medrissa station has experienced a break in 1993 confirmed by the segmentation procedure of Hubert with an average increase of 25%. Group II: There has been a break in 2002 with an increase of the average rainfall of nearly 49% Group III: For Ain Boucif station, an identified rupture by the procedure of Lee Heghinian and is confirmed by the segmentation procedure in 1935 with a decrease of nearly 51%. For other stations of this group, a break is identified in the year 1976 by the Pettitt test. The procedure of Heghinian Lee and the segmentation of Hubert is consistent with results by suggesting the dates 1972 et1976 with a downward trend in average over than 20%.
Fig. 2. Variations
in both average rainfall data on an annual basis
Group IV: In this chronic of annual precipitation a break is identified between the years 1975 and 1980 by the test of Pettitt and the procedure of Lee Heghinian with a clear reduction of rainfall with an average from 20 to 35%. Group V: For this group, the break was identified, on all stations, from 1975 till 1980. It is confirmed by the two procedures with the exception for the station of Benserkrane situed in the Mountains of Tessala where we identify a break before 1964. The annual rains have decreased between 25 and 45%. Group VI: This region has almost witnessed the same bitch break dates from 1973 to 1980 this failure is identified by the three tests for all stations with a decrease in rainfall between 16 and 40%.
377
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
5. Conclusion The study of the break detection has allowed to localize a change in the rainfall mode during the decade 1970-1980 for the most studied rainfall stations. However, it is the role of climate scientists to find the causes for this phenomenon. better manage. Water resources which is constantly decreasing against a demand which is constantly increasing. These changes are currently pushing policymakers to rethink about the types of crops that can adapt to the new climate of certain regions of the country, particularly in western Algeria. Acknowledgements The authors wish to thank the ONEDD and the National Agency of Water Resources for providing material help and data on which reported analyses are based on. References [1] Buishand T.A. Some methods for testing the homogeneity of rainfall records. Journal of hydrology 58, pp 11-27, 1983. [2] Buishand T.A. Tests for detecting a shift in the mean of hydrological time series. Journal of hydrology 73, pp 51-69, 1984. [3] Pettitt A.N. A non-parametric approach to the change-point problem applied statistics , 28,n° 2, pp 126-135, 1979 [4] Servat, E., Paturel, J.E., Lubès-Niel, H., Kouamé, B., Travaglio, M. & Marieu, B. De la diminution des écoulements en Afrique de l'Ouest et Centrale. C. R. Acad. Sci., Paris, 1.325, série H a, 6 7 9 - 6 8 2, 1997. [5] Hubert P., Carbonnel J-P. et Cchaouche A. Segmentation des séries hydrométéorologiques
application à des séries de
-367, 1989. [6] Lubes H., Masson J-M., Servat E., Paturel J-E. et Servat E. Variabilité climatique et statistique : Etude de simulation de la , 1998 ; 3 : 383-408. [7] Meddi M. et Hubert P. Impact de la modification du régime pluviométrique sur les ressources en eau du NordHydrology of the Mediterranean and semiarid Regions. IAHS, 2003; 278 : 1-7. [8] Meddi H. Régionalisation des precipitations dans le Nord-
Ph.D. Univ.
, 2009.
APCBEE Procedia 5 (2013) 373 – 377
ICESD 2013: January 19-20, Dubai, UAE
Annual Variability of Precipitation of the North West of Algeria Hind Meddi , LGEE, Blida - ALGERIA
Abstract This study of the variability and change in annual rainfall in the North West of Algeria is based on the analysis of 25 stations with more than 50 years of data. The charts and analysis show that during the last century, the north west of Algeria show an alternation of dry and humid periods. We have used several methods to study the non-stationarity and trend in the series of studied stations. The results show generally upward trend covering the Thirties and the Fifties. The pluviometry fall was observed during the beginning of the Forties and the middle of the Seventies. The reduction of pluviometry exceeds 36 % in the Mascara region and in the extreme west. On the other hand, the decrease of rainfall is about 20 % in the centre of Algeria. The test on trends sequential confirmed the existence of three major trends during the last century. An increase of rainfall since 1945-46, which followed by a relatively dry phase and a decrease in
©2013 2013The Published ElsevierbyB.V. Selection © Authors.by Published Elsevier B.V. and/or peer review under responsibility of Asia-Pacific Chemical, Environmental Engineering Society Selection andBiological peer review&under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society Keywords : Drought; rainfall; stationarity; West; Algeria
1. Introduction Water has always been an essential factor for the development of agriculture and it has become a strategic issue. Repeated episodes of drought, especially since the decade of the 70's when a change in the rainfall regime in the reduction sense became a reality, especially for the central and western region. Algeria and especially the western region have experienced several droughts during this century, the 40s and 70s until
Corresponding author. E-mail address:[email protected]
2212-6708 © 2013 The Authors. Published by Elsevier B.V. Selection and peer review under responsibility of Asia-Pacific Chemical, Biological & Environmental Engineering Society doi:10.1016/j.apcbee.2013.05.064
374
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
today. The most recent one was characterized by its spatial extent, its intensity and its major significant impact and the decrease of water resources. The purpose of this study is to characterize possible changes in climate in the central and western part of Algeria, to do, a statistical analysis of long time series data of rainfall at annual scale in different stations was conducted. 2. Material and method 2.1. Presentation of the study area The study area covers 89 420 km2. It is located between 2 ° 10'10''west and 3 ° 10'11''east of longitude and between 34 ° 18'54''and 36 ° 48'12''N of latitude (Fig. 1). The study area stretches on 250 km from south to north and about 500 km from west to east. 2.2. Climate and rainfall variability The northern part of Algeria is characterized by a Mediterranean climate with a relatively cold winter and rainy and hot dry summers. The rainfall reached 400 mm in the west, 700 mm in the center and 1000 mm in the east near the coast. This type of climate also affects the range of the mounts of the Tellian Atlas, where we recorded at the level of Eastern summits total of rainfalls ranging from 800 to 1600 mm, while those values are lowered in the Center (700 to 1000 mm) and in the Western (600 mm). 2.3. Data The climate research and monitoring of its evolution requires many long series of observations. Unfortunately, we do not have a perfectly reliable and continuous data. Representative sample, in statistical terms is a long process fraught with pitfalls and in which many errors are very different nature could be committed. Furthermore, it is necessary, before using data sets, to be concerned about their quality and their representativeness. The data represent a major element in the study of spatial and temporal variability of rainfall and drought. Data taken from the two organizations responsible for network rainfall namely the National Agency of Hydraulic Resources (ANRH) and the National Meteorological Office (ONM). The stations were selected according to the length of available rainfall records and their geographical positions in order to better cover the whole region, and the different climatic influences. Forty-eight (48) stations were selected on the studied region (Fig. 2). After critical and homogenization of monthly and annual data, the period 1930/31-2003/04 (ie 74 years) was chosen
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
Fig. 1. Location
of rainfall stations studied
3. Statistical approaches and analysis of rainfall data Stationarity or nonstationarity of the rainfall data interest many users of these in different applications (hydrology, agronomy, water management, etc..). The detection of one or more breaks give information on the evolution of rainfall in the region. This failure may be regarded as due to a change of parameters of the law of probabilities of random variables whose successive realizations constitute studied time series. In Algeria, the climate changes in the recent decades have had a negative influence on the water resource (groundwater recharge, filling of reservoir dams and on agricultural yields). We hope here to show this evolution by determining the year or years of break of rainfall data. The methods to highlight these break are: The U Buishand statistics [1,2], the test of Pettitt [3,4], the Bayesian method of Lee and Heghinian and the segmentation procedure of Hubert [5], whose power and robustness where shown in a review by Lubes-Niel et al. in 1998 [6] and applied in Algeria [7]. To facilitate the description of regional changes in rainfall patterns, we have based our work on the results of the regionalization of the annual precipitation [9]. The used groups correspond to the homogeneous areas found in this study. 4. Results Applied to each group, these tests give results which are generally consistent. Group I: In the series of annual precipitation, rupture is identified in the year 1966 by the Pettitt test, the procedure of Lee Heghinian corroborates these results by proposing the same dates between which the average rainfall increases by 16% for the station of Boughzoul. Stil in Group I: The station of Sougueur
375
376
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
shows a rupture, by the procedure of Lee Heghinian in 1940 with a decrease of 22%. The Medrissa station has experienced a break in 1993 confirmed by the segmentation procedure of Hubert with an average increase of 25%. Group II: There has been a break in 2002 with an increase of the average rainfall of nearly 49% Group III: For Ain Boucif station, an identified rupture by the procedure of Lee Heghinian and is confirmed by the segmentation procedure in 1935 with a decrease of nearly 51%. For other stations of this group, a break is identified in the year 1976 by the Pettitt test. The procedure of Heghinian Lee and the segmentation of Hubert is consistent with results by suggesting the dates 1972 et1976 with a downward trend in average over than 20%.
Fig. 2. Variations
in both average rainfall data on an annual basis
Group IV: In this chronic of annual precipitation a break is identified between the years 1975 and 1980 by the test of Pettitt and the procedure of Lee Heghinian with a clear reduction of rainfall with an average from 20 to 35%. Group V: For this group, the break was identified, on all stations, from 1975 till 1980. It is confirmed by the two procedures with the exception for the station of Benserkrane situed in the Mountains of Tessala where we identify a break before 1964. The annual rains have decreased between 25 and 45%. Group VI: This region has almost witnessed the same bitch break dates from 1973 to 1980 this failure is identified by the three tests for all stations with a decrease in rainfall between 16 and 40%.
377
Hind Meddi / APCBEE Procedia 5 (2013) 373 – 377
5. Conclusion The study of the break detection has allowed to localize a change in the rainfall mode during the decade 1970-1980 for the most studied rainfall stations. However, it is the role of climate scientists to find the causes for this phenomenon. better manage. Water resources which is constantly decreasing against a demand which is constantly increasing. These changes are currently pushing policymakers to rethink about the types of crops that can adapt to the new climate of certain regions of the country, particularly in western Algeria. Acknowledgements The authors wish to thank the ONEDD and the National Agency of Water Resources for providing material help and data on which reported analyses are based on. References [1] Buishand T.A. Some methods for testing the homogeneity of rainfall records. Journal of hydrology 58, pp 11-27, 1983. [2] Buishand T.A. Tests for detecting a shift in the mean of hydrological time series. Journal of hydrology 73, pp 51-69, 1984. [3] Pettitt A.N. A non-parametric approach to the change-point problem applied statistics , 28,n° 2, pp 126-135, 1979 [4] Servat, E., Paturel, J.E., Lubès-Niel, H., Kouamé, B., Travaglio, M. & Marieu, B. De la diminution des écoulements en Afrique de l'Ouest et Centrale. C. R. Acad. Sci., Paris, 1.325, série H a, 6 7 9 - 6 8 2, 1997. [5] Hubert P., Carbonnel J-P. et Cchaouche A. Segmentation des séries hydrométéorologiques
application à des séries de
-367, 1989. [6] Lubes H., Masson J-M., Servat E., Paturel J-E. et Servat E. Variabilité climatique et statistique : Etude de simulation de la , 1998 ; 3 : 383-408. [7] Meddi M. et Hubert P. Impact de la modification du régime pluviométrique sur les ressources en eau du NordHydrology of the Mediterranean and semiarid Regions. IAHS, 2003; 278 : 1-7. [8] Meddi H. Régionalisation des precipitations dans le Nord-
Ph.D. Univ.
, 2009.