Climate and Land Surface Changes in Hydrology 183 Proceedings of H01, IAHS-IAPSO-IASPEI Assembly, Gothenburg, Sweden, July 2013 (IAHS Publ. 359, 2013).
Hydro-climatic variability in two Moroccan basins: comparative analysis of temperature, rainfall and runoff regimes
KENZA KHOMSI1, GIL MAHE2, MOHAMED SINAN3 & MARIA SNOUSSI4 1 Direction de la Météorologie Nationale, cité de l’air, aéroport Casa Anfa, Maroc [email protected] 2 IRD et Université Mohamed V-Agdal, Rabat, Maroc 3 Ecole Hassania des Travaux Publics (EHTP) Km 7, Route d'El Jadida, BP. 8108, Casablanca, Maroc 4 Université Mohamed V-Agdal, Faculté des Sciences Département des Sciences de la Terre Rabat, Maroc
Abstract The increase of temperature over Morocco, projected by climate models, should affect hydro- climatic regimes and ecological and socio-economic systems. In order to investigate the evolution of these regimes in the large basins of Tensift and Bouregreg, we compared the trends of observed temperature, rainfall and runoff variability. Annual temperature time series show significant increasing trends ranging between 0.07 and 0.25°C per decade in both basins. Shifts in annual and monthly temperature trends were recorded between the mid-1970s and mid-1980s and also in the early-1990s. In both basins, total annual rainfall decreased and changed its regime in the late-1970s, monthly rainfall regime changed only in the Tensift basin between early and mid-1970s. Runoff in both basins showed no significant trend for most of the stations, but a consistent decreasing trend since the early-1970s in the Tensift basin and the late-1970s and the early-1980s in the Bouregreg basin. Significant hydro-climatic changes occurred first in the southern basin (Tensift). Ruptures are most frequent in the spring and summer monthly time series. Key words temperature; rainfall; runoff; hydro-climatic regime; variability; trend; rupture; Tensift; Bouregreg; Morocco
INTRODUCTION Climatic changes have now become a pressing issue on the world’s attention and concerns over their impacts are greatly increasing because they are likely to affect natural, social and economic systems at local and regional scales (Del Rio et al., 2011). One of the most important requirements of research about climate change is to analyse historical changes in the climatic system (Houghton, 1996). Several authors have carried out analyses of temperature trends at different spatial scales to quantify rates of climate warming, for instance: Moberg et al. (2006) for all Europe, Del Rio et al. (2011) in Spain, Hulme et al. (1995) for all Africa, Elagib & Mansell (2000) in Sudan, Rosell (2011) in Ethiopia and Speth &Fink (2010) in Benin. Temperature increase was also confirmed in Morocco and other North African countries (Schilling et al., 2012). Whereas the temporal evolution of temperature presents a clear warming pattern worldwide, precipitation does not show any generalized trend. Mosmann et al. (2004) studied summer precipitation in mainland Spain between 1961 and 1990; he found that July and August rainfall increased in 20% of the southern areas, while it declined in June and September in 10% of the territory. Significant decreasing precipitation trends were recognized by De Luis et al. (2000) in the region of Valencia (east Spain) while neither trends nor abrupt changes were found in a semi-arid area in the southeast of the country between 1967 and 1997 (Lazaro et al., 2001). Decreasing rainfall trends were detected in many countries in West and Central Africa, in particular after the 1970s (Mahé et al., 2001; Conway et al., 2009), such as in Nigeria (Oguntunde et al., 2011), Congo (Samba & Nganga, 2011), Botswana (Batisani et al., 2010) and Benin (Speth & Fink, 2010). Decreasing precipitation trends were also observed for North African regions, such as Algeria (Meddi et al., 2010) and Morocco (Schilling et al., 2012; Singla et al., 2010). Changes in precipitation regimes and increasing temperatures are likely to affect river runoff (Zhao et al., 2009). In West and Central Africa, the runoff of many rivers has decreased since 1970 (Paturel et al., 2007) while the runoff of others has increased (Oguntunde et al., 2006). The diverse studies cited above show that climate change will induce varied environmental responses depending on the areas involved. Thus, it is important to deal with the issue of global change at a local or regional scale. Hydroclimatic trends in Morocco have not been extensively investigated. Sebbar et al. (2011) studied recent evolution and ruptures in the annual rainfall regime in northern Morocco between 1935 and 2004. He showed that the region underwent a substantial rainfall reduction and that the
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184 Kenza Khomsi et al. main ruptures are recorded between 1968 and 1984. According to Singla et al. (2010), a diminution of rainfall was observed over the major part of the kingdom from 1976 to 1980; runoff rupture dates are identical to that of the rainfall. Schilling (2012) described the climate variability for the 21st century of five North African states, including Morocco, and reviewed the vulnerability of the country to the confirmed increasing temperature and decreasing precipitation. Very locally, Riad et al. (2006) studied hydroclimatic variability in the high Atlas basins; the study showed the important seasonal and inter-annual variability of mean rainfall and the general decreasing of mean runoff between 1980 and 1986. Most previous studies carried out in Morocco have focused on large-scale areas and were interested in only one hydro-climatic variable at a time. In this study, three climatic parameters are considered (temperature, rainfall and runoff) to provide a comparative overview of climatic variations and their impacts at the local and regional scales. The study deals with hydro-climatic trends and ruptures, during the last decades, in two large catchments of Morocco: Tensift and Bouregreg, using statistical approaches. The trends’ magnitudes and their significance were evaluated using Sen’s slope method and the Mann-Kendall test, respectively. Four methods were used for rupture detection: The tests of Pettitt, Buishand, Lee & Heghinian and the segmentation procedure of Hubert. The t-test was used for rupture significance. The main objective of this work is to: (a) examine the long-term annual trends and annual and monthly ruptures of mean air temperature, precipitation and runoff during the last decades, from the 1960s to the end of the 2000s for most of them, in two large basins of Morocco: Tensift and Bouregreg; (b) test if the trends and ruptures are statistically significant; and (c) compare the variables’ trends and ruptures, according to various methods (see Table 2), within each basin and between the basins.
STUDY AREA AND DATASETS Study area Morocco is the extreme northwest African country, situated between 1.5 and 17°W longitude and 20.5 and 36°N latitude. The Bouregreg River basin (located between 5.4°–6.8°W and 32.8°– 34°N), occupies almost all of the central plateau of Morocco. It is a combination of monotonous plateaus, deep gorges and basins partitioned by steep ridges over an area of 9656 km2 (Marghich, 2004) thus 1.3% of the surface of the country. The elevation rises to 1627 m and 50% of the surface is located between 500 and 1000 m (SIGMED 1, 2009). The climate is semi-arid and average annual rainfall is about 400 mm in coastal regions to 760 mm in the western part of the basin. The number of rainy days per year is 75–100 in the mountainous regions and 60–75 else- where.The Tensift River basin (7.2°–9.4°W and 30.8°–32.2°N), covers an area of 19 400 km2, thus 2.7% of the surface of the country. The rainfall distribution is influenced by the relief of the High Atlas. Rainfall is low in the plains where the yearly total does not exceed 350 mm, whereas in the mountains it can reach more than 500 mm. The number of rainy days is 25–50 per year for coastal areas and the Haouz central plain, and 45–70 in the mountains (CID2, 2004).
Temperature, rainfall and runoff data Temperature and rainfall data were obtained, respectively, from 5 and 10 meteorological stations of the synoptic network of the Moroccan Meteorological Office (Fig. 1). Runoff data were collected from 18 flow gauges of the Hydraulic Basin Agency of Bouregreg and Chaouia and the Hydraulic Basin Agency of Tensift,in Morocco. Each station provided at least 27 years of data. The hydrological year begins in September and ends in August. Data underwent a quality control before being made publiclyavailable andmissing values do not exceed 3% of the series. Figure 1 and Table 1 present the location of the meteorological stations and the periods analysed.
1The SIGMED project stands for “Spatial approach of the impact of agricultural activities in the Maghreb on sediment transport and water resources in large river basins” – http://armspark.msem.univ-montp2.fr/sigmed/ 2CID stands for the department research “Consulting, Engineering and Development” Hydro-climatic variability in two Moroccan basins 185
(a) (b)
Fig. 1 Location of temperature, rainfall and runoff stations in Bouregreg (a) and Tensift (b) catchments.
Table 1 Spatial location of used stations by basin. Station Basin Parameter Latitude N Longitude E Data period Rabat-Salé Bouregreg Temperature 34.05 –6.77 1951–2004 Rainfall 1951–2007 Kenitra Bouregreg Temperature 34.30 –6.60 1951–2005 Rainfall 1916–2007 Kasba Tadla Bouregreg Temperature 32.87 –6.27 1983–2009 Oued Zem Bouregreg Rainfall 32.87 –6.57 1956–1984 Ain Loudah Bouregreg Runoff 33.55 –6.7 1973–2008 Lalla Chafia Bouregreg Runoff 33.7 –6.3 1971–2008 Ouljet Haboub Bouregreg Runoff 33.08 –6.04 1973–2008 Sidi Jabeur Bouregreg Runoff 33.38 –6.29 1972–2008 Sidi Med Chrif Bouregreg Runoff 33.56 –6.54 1971–2008 Marrakech Tensift Temperature 31.62 –8.03 1941–2005 Rainfall 1934–2005 Safi Tensift Temperature 32.28 –9.23 1955–2005 Rainfall 1956–2007 Ait Ourir Tensift Rainfall 31.47 –7.72 1969–2002 Amizmiz Tensift Rainfall 31.22 –8.23 1976–2002 Chichaoua Tensift Rainfall 31.60 –8.83 1976–2002 Saada Tensift Rainfall 31.63 –8.17 1969–2002 Tahanaout Tensift Rainfall 31.33 –7.95 1969–2002 Tahanaout Tensift Runoff 31.29 –7.96 1963–2003 Tafériat Tensift Runoff 31.54 –7.6 1963–2003 Aghbalou Tensift Runoff 31.32 –7.75 1970–2003 Takerkoust Tensift Runoff 31.36 –8.14 1936–2003 Nkouris Tensift Runoff 31.06 –8.14 1975–2003 Imine Tensift Runoff 31.22 –8.11 1967–2003 Abadla Tensift Runoff 31.72 –8.57 1970–2003 Iloudjane Tensift Runoff 31.18 –8.8 1976–2003 S Rahal Tensift Runoff 31.64 –7.48 1965–2003 Talmest Tensift Runoff 31.87 –9.27 1971–2003 Igrounzar Tensift Runoff 31.35 –9.57 1976–2003 Zelten Tensift Runoff 31.34 –9.57 1976–2003 Adamna Tensift Runoff 31.46 –9.68 1971–2003 186 Kenza Khomsi et al.
METHODOLOGY The magnitudes of trends in the time series of temperature, rainfall and runoff have been calculated using the Sen’s slope estimator proposed by Theil (1950) and Sen (1968). For n pairs of data points this estimator is given by equation (1): x − x β = i j Median (1) ti − t j where xi and xj are data values at times ti and tj (i > j), respectively (Shifteh Some'e et al., 2012). The statistical significance of trends was investigated using the Mann-Kendall non parametric test, applied with a confidence level of 95%. The test was recommended by the World Meteor- ological Organization (1988) as a standard procedure for detecting trends in hydrological data. Discontinuities in the studied datasets were analysed using the rupture tests of Pettitt, Buishand & Lee & Heghinian and the segmentation procedure of Hubert (Lubès-Niel et al., 1998). The null hypothesis tested is that there is no rupture in the series and a rupture is considered as very likely when it is statistically significant and is detected by two tests or two stations. These procedures are well defined by Maftei et al. (2011). The statistical significance of the resulting ruptures was assessed using the two-tailed t-test, considering a significance level of 95%.
RESULTS AND DISCUSSION Hydro-climatological series were examined for trends, slopes and ruptures on an annual basis. Some results for monthly ruptures are also presented, but they will be largely displayed in a further paper, as they deserve a detailed analysis.
Temperature regime Generally increasing trends of annual temperature are found for the studied catchments. In both basins, increase rates are of the same order of magnitude (0.07° and 0.25°C per decade) (Table 2). Significant upward trends were noted for four of the five stations investigated; only the station in Marrakech had no significant trend. According to tests for rupture, significant change in tem- perature regime of the Bouregreg basin was identified around 1986 and 1994. In 1986, trend change of 0.07 and 0.35°C per decade was recorded in Rabat-Salé and Kenitra, respectively. In 1994, the stations of Kenitra and Kasba Tadla registered trend changes of –0.09° and 0.41°C per decade, respectively. For the Tensift basin, trend changes of 0.63° and 0.38°C per decade were observed, respectively, in Marrakech and Safi in 1982. As for monthly data and for both basins, significant changes were observed in the months of March, April, June, September and December; the years of change are, respectively, 1992, 1994, 1993, 1976 and 1975 for the Bouregreg basin, and 1986, 1981, 1993, 1977 and 1974 for the Tensift basin. The temperature regime of July changed in the Bouregreg basin around 1983, 1986 and 2002, while changes are noticed in November 1980 in the Tensift basin.
Rainfall regime Annual rainfall trends for all basins stations are generally towards drier conditions (Table 3). Especially strong and statistically significant precipitation trends were noticed at Tahanaout, Oued Zem and Rabat Salé. For the 10 stations investigated, trend magnitudes are different. Rainfall regimes change significantly around 1979 in Rabat-Salé (Bouregreg basin) and in 1976 and 1978 in Tahanaout and Ait Ourir, respectively (Tensift basin). A rainfall trend of decrease by –17.39 mm/decade occurs in the station of Rabat-Salé. A trend of increase of 40.1 mm/decade was observed in the rainfall of Ait Ourir and of 41.6mm/decade in Tahanaout. As for monthly data, no significant trend change was noticed in the Bouregreg basin, while in the Tensift basin, significant trends were observed in June and April (around 1976), January (1971), November and December (1973). Hydro-climatic variability in two Moroccan basins 187
Table 2 Trends and ruptures in air temperature time series. Site Basin Trends Ruptures Trend change (°C/decade) Sen’s slope Pettitt Lee & Hubert Buishand Year of Differences (°C/decade) Heghinian rupture Sen’s slope Rabat-Salé Bouregreg 0.1 1986 1986 1962, 1979 R 1979 0.44 1986 0.07 Kenitra Bouregreg 0.15 1986 1994 1994 R 1986 0.35 1994 –0.09 Kasba Bouregreg 0.25 1999 1994 1994 R 1994 0.41 Tadla 1999 –0.45 Marrakech Tensift 0.07 1982 1999 1970,1972,1993 R 1982 0.63 1993 0.74 1999 –0.24 Safi Tensift 0.21 1982 NP 1982 NP 1982 0.38 P (N): Positive (Negative), Bold Character: Result is statistically significant, R: Rupture, NP: Not performed because of data non normality, Significance level = 0.05, trend change is calculated for significant ruptures only.
Table 3 Trends and ruptures in rainfall time series. Site Basin Trends Ruptures Trend change (mm/decade) Sen’s Slope Pettitt Year of Trend Buishand Year of Differences of (mm/decade) rupture change rupture Sen’s Slope Rabat-Salé Bouregreg –25.4 1979 1979 NR NR 1979 –17.39 Kenitra Bouregreg –3.4 NR 2006 NR NR - - Oued Zem Bouregreg –64.7 NR 1979 NR NR - - Ait Ourir Tensift –40.9 NR 1978 1978 R 1978 40.1 Amizmiz Tensift –6.87 NR 1999 NR NR - - Chichaoua Tensift –5.37 NR 1999 NR NR - - Saada Tensift –15.12 NR 1971 NR NR - - Tahanaout Tensift –81.07 1978 1976 1976 R 1976 41.06 Safi Tensift –14.04 NR 1956 NR NR - - Marrakech Tensift –6.3 NR 1999 NR NR 1999 48.9 P (N): Positive (Negative), Bold Character: Result is statistically significant, R: Rupture, NR: No Rupture, Significance level = 0.05, trend change is calculated for significant ruptures only.
Runoff regime In contrast to the predominantly positive temperature and negative precipitation trends throughout the Bouregreg and the Tensift basins, no generalized runoff trend has been observed (Table 4). A combination of positive and negative, high and low trends was found. Magnitudes of negative trends are larger than those of positive ones and only three stations out of 18 showed statistically significant trends. In the Bouregreg catchment, no significant change occurred in the runoff regime. Significant ruptures were found around 1974 and 2000 in the Tensift catchment where, apart from Taferiat that recorded an upward runoff trend of 1.01 m3 s-1 per decade, most of the stations recorded a downward runoff trend. Regarding monthly data, February and May runoff regimes changed in the Bouregreg basin around 1979 and 1982, respectively, while in the Tensift basin changes of the April, May, June and July regimes occurred around 1971.
Summary Specifically the study has shown that: − During the observation periods in the basins of Tensift and Bouregreg, temperature rose by between 0.07° and 0.25°C per decade, while precipitation decreased by between –3.4 and –81.1 mm/decade. Runoff showed no significant generalized trends yet magnitudes of negative trends, which reached –15.1 m3 s-1 per decade (Abadla), are larger than those of positive ones;
188 Kenza Khomsi et al.
Table 4 Trends and ruptures in runoff time series. Site Basin Trends Ruptures Trend change (m3s-1/decade) Sen’s slope Pettitt Lee & Hubert Buishand Year of Differences of (m3.s-1/decade) Heghinian rupture Sen’s Slope Ain Loudah Bouregreg 2.33 NR 2007 1994 NR - - Lalla Chafia Bouregreg –6.96 NR 1979 1978 NR - - Ouljet Bouregreg –2.61 NR 2007 NR NR - - Haboub Sidi Jabeur Bouregreg –0.2 NR 2007 2007 NR - - Sidi Med Bouregreg 0.62 NR 2007 NR NR - - Chrif Takerkoust Tensift 0.36 NR 2000 NR NR 2000 –52.7 Tafériat Tensift –9.75 1974 1974 1974 R 1974 1.01 Aghbalou Tensift –5.45 NR NP NR NP - - 1996 –21.67 Tahanaout Tensift –2.92 NR 2000 1996 NR 2000 –16.48 Nkouris Tensift 3.25 NR 2000 NR NR 2000 –72.53 Imine Tensift –6.19 NR 2000 NR NR 2000 –125.9 Abadla Tensift –15.1 NR 1974 1972 NR - - Iloudjane Tensift 0.44 NR 1977 NR NR - - S Rahal Tensift –4.33 NR 1974 NR NR - - Talmest Tensift –6.98 NR 1971 1971 NR - - Igrounzar Tensift 0.19 NR 1995 NR NR - - Zelten Tensift –0.16 NR 1998 NR NR 1998 –1.21 Adamna Tensift 0.46 NR 1971 NR NR - - P (N): Positive (Negative), Bold Character: Result is statistically significant, R: Rupture, NR: No Rupture, NP: Not performed because of data non normality, Significance level = 0.05, trend change is calculated for significant ruptures only.
− Magnitudes of trends in both basins are of the same order, no discernible spatial trend appears in datasets. − In the Bouregreg catchment, change in the annual rainfall regime appeared around 1979. This change is significant only in the station of Rabat-Salé where a rainfall downward trend appeared. An increasing temperature trend appeared around 1986 and 1994. No significant changes affect the annual runoff regime. Changes in monthly temperature regimes were recorded in the mid-1970s for the months of September and December and early-1990s for March, April and June. No changes appeared in monthly rainfall while the February and May runoff regimes changed between late-1970s and early-1980s. − In the Tensift basin, the rainfall regime changed between mid and late-1970s; the trend is increasing. An upward temperature trend is recorded in the catchment around 1982. Runoff trend decreased significantly in 2000, the increasing trend of 1974 appeared only in Taferiat. Changes in monthly temperature trends were noticed in the mid-1970s for the months of September and December, and between the early and mid-1980s for the months of March, April and November. The rainfall trend regime changed between early and mid-1970s for the months of January, April, June, November and December. Runoff regimes of April, May, June and July changed in 1971. − Changes in hydro-climatic regimes began in the early-1970s for the southern basin (the Tensift) while they have reached the northern basin (the Bouregreg) in the late-1970s.
CONCLUSION The main aim of this paper was to detect and compare trends in the annual hydro-climatological time series, and ruptures in the annual and monthly series of the Bouregreg and Tensift basins. From this analysis it is concluded that magnitudes of trends in both basins are of the same order. Rainfall followed a decreasing trend since the mid/late-1970s over both basins, and several stations even show a significant rupture in time series. Runoff time series of the Bouregreg basin Hydro-climatic variability in two Moroccan basins 189 show no station with significant ruptures, but many of them show a decreasing trend, while many stations of the Tensift basin show a significant rupture, mostly by the end of 2000 or in the late 1990s. All the temperature time series studied show a significant rupture, with increasing temperatures beginning between 1982 and 1999 in both basins. Results indicate that ruptures in time series of rainfall and temperature began earlier in the southern basin of Tensift, and later in the northern Bouregreg basin. The ruptures in the series occurred from the mid-1970s to 2000 according to the variable and the basin. Dissimilarities in the results between basins may be due to their geographical location and their different topography. These results suggest the need for further work before reaching generalized conclusions regarding recent hydro-climatic trends in Morocco, especially regarding extreme values, which are not presented here. It is recommended, for instance, to transfer this study to other basins from different geographic locations, especially the extreme north and south of the country. Also, it is of utmost importance to perform a comprehensive trend analysis on a monthly basis and assess conclusions about annual ruptures using monthly data. Such analyses can help improve our understanding of climate variability in the studied areas, which remain of special interest due to their climatic and topographic features, the vulnerability of their water resources to climate change and the importance of the socio-economic activities within them.
REFERENCES Batisani, N.J. & Yarnal, B. (2010) Rainfall variability and trends in semi-arid Botswana: Implications for climate change adaptation policy. Appl. Geogr. 30, 483–489. Conway, D., Persechino, A., Ardoin-Bardin, S., Hamandawana, H., Dieulin, C. & Mahe, G. (2009) Rainfall and water resources variability in Sub-Saharan Africa during the twentieth century. Journal of Hydrometeorology 10, 42–59. Del Rio, S., Herrero, L., Pinto-Gomes, C. & Penas, A. (2011) Spatial analysis of mean temperature trends in Spain over the period 1961–2006. Global Planet Change.78, 65–75. De Luis, M., Raventos, J., Gonzalez-Hidalgo, J.C., Sanchez, J.R. & Cortina, J. (2000) Spatial analysis of rainfall trends in the region of Valencia (East Spain). Int. J.Climatol. 20, 1451–1469. Elagib, N.A. & Mansell, M.G. (2000) Recent trends and anomalies in mean seasonal and annual temperatures over Sudan. J Arid Environ.45(3), 263-288. Houghton, J.T., Meira Filho, L.G., Callander, B.A., Harris, N., Kattenberg, A. & Maskell, K. (1996) Climate Change 1995: The Science of Climate Change. Cambridge: Cambridge University Press. Hulme, M., Conway, D., Kelly, P.M., Subak, S. & Down, T.E. (1995) The Impacts of Climatic Change in Africa. Stockholm: Stockholm Environmental Institute. Lazaro, R., Rodrigo, F. S., Gutierrez, L., Domingo, F. & Puigdefabregas, J. (2001) Analysis of a 30 year rainfall record (1967– 1997) in semi-arid SE Spain for implications on vegetation. J. Arid Environ. 48, 373–395. Lubès-Niel, H., Masson, J.M., Paturel, J.E. & Servat, E.(1998) Variabilité climatique et statistiques. Etude par simulation de la puissance et de la robustesse de quelques tests utilisés pour vérifier l’homogénéité de chroniques. Rev. Sci. Eau. 3, 383–408. Mahé, G., L’Hote, Y., Olivry, J.C. & Wotling, G. (2001) Trends and discontinuities in regional rainfall of West and Central Africa, 1951–1989. Hydrol. Sci. J. 46, 211–226. Maftei, C., Bărbulescu, A., Buta, C. & Şerban, C. (2011) Change points detection on variability analysis of some precipitation series, MAMECTIS/NOLASC/CONTROL/WAMUS'11. In: Proc. the 13th WSEAS International Conference on Mathematical Methods, Computational Techniques And Intelligent Systems, 232–237. Marghich, A. (2004) Le bassin versant de Bouregreg (Maroc Central) : Etudes hydrologique, hydrogéologique et hydrochimie des eaux. PhD Thesis, Université Sidi Mohammed Ben Abdellah-Faculté des sciences DharLmahraz, Fes. Meddi, M., Assani, A. & Meddi, H. (2010) Temporal variability of annual rainfall in the Macta and Tafna catchments, Northwestern Algeria. Water Resour Manage. 24, 3817–3833. Moberg, A., Jones, P.D., Lister, D.,Walther, A., Brunet,M., Jacobeit, J., Alexander, L.V., Della-Marta, P.M., Luterbacher, J., Yiou, P., Chen, D., Tank, A.M.G.K., Saladie, O., Sigro, J.,Aguilar, E., Alexandersson, H., Almarza, C., Auer, I., Barriendos, M., Begert, M., Bergstrom, H., Bohm, R., Butler, C.J., Caesar, J., Drebs, A., Founda, D., Gerstengarbe, F.W., Micela, G., Maugeri, M., Osterle, H., Pandzic, K., Petrakis, M., Srnec, L., Tolasz, R.,Tuomenvirta, H., Werner, P.C., Linderholm, H., Philipp, A.,Wanner, H. & Xoplaki, E. (2006) Indices for daily temperature and precipitation extremes in Europe analyzed for theperiod 1901–2000. J. Geophys. Res.-Atmos.111(D22), 1–25. Mosmann, V., Castro, A., Fraile, R., Dessens, J. & Sanchez, J.L. (2004) Detection of statistically significant trends in the summer precipitation of mainland Spain. Atmos. Res. 70, 43–53. Oguntunde, P.G., Abiodun, B.J. &Lischeid, G. (2011) Rainfall trends in Nigeria, 1901–2000. J. Hydrol.411(3-4), 207–218. Oguntunde, P. G., Friesen, J., Van de Giesen, N. &Savenije,H.H.G. (2006) Hydroclimatology of the Volta River Basin in West Africa: Trends and variability from 1901 to 2002. Phys. Chem. Earth 31, 1180–1188. Paturel, J.E., Barrau, C., Mahé, G., Dezetter, A. & Servat, E. (2007) Impact of the climatic variability on water resources in West and Central Africa. Hydrological Sciences Journal 52, 1, 38–48. Riad, S., Mania, J. & Bouchaou, L. (2006) Variabilité hydroclimatique dans les bassins versants de du Haut Atlas de Marrakech (Maroc). Sécheresse17(3), 443–446. Rosell, S. (2011) Regional perspective on rainfall change and variability in the central highlands of Ethiopia, 1978–2007. Appl.Geogr.31, 329–338. 190 Kenza Khomsi et al.
Samba, G. & Nganga, D. (2011) Rainfall variability in Congo-Brazzaville 1932–2007. Int. J.Climatol. 32(6), 854–873. Schilling, J., Freier, K., Hertig, E. & Scheffran, J. (2012) Climate change, vulnerability and adaptation in North Africa with focus on Morocco. Agric. Ecosyst. Environ. 156, 12–26. Sebbar, A., Badri, W., Fougrach, H., Hsaine, M. &Saloui, A. (2011) Étude de variabilité du régime pluviométrique au Maroc septentrional (1935–2004). Sécheresse. 22(3), 139–148. Sen, P.K. (1968) Estimates of the regression coefficient based on Kendall’s tau. J. Amer. Statistical Assoc. 63, 1379–1389. Shifteh Some'e, B., Ezani, A. & Tabari, H. (2012) Spatiotemporal trends and change point of precipitation in Iran. Atmos. Res. 113, 1–12. Singla, S., Mahé, G., Dieulin, C., Driouech, F., Milano, M., El Guelai, F.Z. & Ardoin-Bardin, S. (2010) Evolution des relations pluie-débit sur des basins versants du Maroc. In: Global Change: Facing Risks and Threats to Water Resources (ed. by E. Servat et al.) (Proc. of the Sixth World FRIEND Conference, Fez, Morocco, October 2010). IAHS Publ. 340, 679–687.IAHS Press, Wallingford, UK. Speth, P. & Fink, A.H. (2010) Introduction.In: Impacts of Global Change on the Hydrological Cycle in West and Northwest Africa (ed. by P. Speth, M. Christoph & B. Diekkrüger), 4–11. Springer, Heidelberg, Germany. Theil, H. (1950) A rank-invariant method of linear and polynomial regression analysis, I, II, III. Nederl. Akad. Wetensch Proc 53, 386–392, 512–525, 1397–1412. World Meteorological Organisation (1988) Analysing long time series of hydrological data with respect to climate variability.Tech. Rep. WCAP-3, Geneva, Switzerland. Zhao, F.F., Xu, Z.X., Zhang, L. & Zuo, D. (2009) Streamflow response to climate variability and human activities in the upper catchment of the Yellow River Basin. Sci. China Ser E-Tech Sci. 52(11), 3249–3256.