Evolution of Pluviometric Regimes in Various Stations of the Northern Algerian Sahara

Abstract

At the end of the 1970s, south-western Algeria was marked by a severe, wide-ranging and persistent drought due to its extraordinary rainfall deficit. Rainfall in this region is characterized by taking into consideration the annual data of a certain number of rainfall stations with more than 60 years of observations (1930– 1999). For each station we analyzed a series of annual rainfall (P) and considered their coefficient of variation (CV). This coefficient expresses the rate of rainfall in time and can be used for comparative studies. We noted that in this region, rainfall was very low with the greatest variability. In order to study the evolution of the total rainfall for winter and spring, we employed two methods: the moving average and the average of accumulated variations. We noted that the winter and spring rains evolved differently; however, from the 1980s to the present, these seasonal totals are the lowest and show the greatest deficit. For each of the stations selected, a rainfall index was calculated defined as a reduced central variable. We established a cartography of the average for each decade of these indexes with a view to revealing the contrast between the different periods studied. Generally speaking, it seems that there is an upward trend in the 1930s and mid-1940s. From the 1950s, we note an increase in rainfall deficit at the level of the zone studied. The fall in total annual precipitation is greatest during the two decades that follow. However, the most sudden and significant fluctuation (in the statistical sense) was observed around the 1980s. This period of deficiency has since been characterized by its intensity and duration.