ANNUAL VARIABILITY OF PRECIPITATION OF THE NORTHWEST OF ALGERIA

Drought has characterized the West of Algeria since the end of the Seventies, it is characterized by a remarkable severity, an extent and a persistence of the pluviometric deficit. 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 decrease of rainfall has consequences for water resources availability. The observation period of the various stations frames the possible period of climatic fluctuation and made it possible to retain a sufficient number of reliable data to allow an interesting comparative analysis from the regional point of view even if the distribution of the stations is not always homogeneous on the whole of the study zone. The charts and analysis show that during this 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 plain of Mitidja). The drought recorded during the two last decades knew of equivalent, neither in duration, nor in intensity on the whole of the studied period and region. 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 precipitation from the 70’s.