Aim of the study:
In this study, the spatial and temporal characteristics of drought in the upper and middle Cheliff; a semi-arid region of northwestern Algeria was examined using the standard precipitation index [SPI] at an annual time scale as a tool for measuring the severity of meteorological drought.

Material and methods:
To asses of SPI annual sum of precipitation from 11 precipitation stations covering the period 1970-2009 were used. In order to identify the possible changes in the precipitation trend of the studied series, statistical tests were selected. The extent, severity and duration of the drought in the study area were obtained.

Results and conclusions:
Statistical tests showed that the occurrence of ruptures in the rainfall regime was detected at the end of the 1970s and the beginning of 1980s with a negative trend. The results of the SPI showed a strong existence of dry years after 1979 and 1980. The years 1993, 1999 and 2001 presented an extremely severe drought (SPI <-2). The evolution of SPI showed a dominance of the frequency of normal years (67%) and alternation of dry years (17%) and wet years (16%) over a period of 40 years. The total surface of the study area is affected by drought during severe years (1993, 1999). The study area exhibits irregularity and heterogeneity of drought due to the great variability of precipitation, it can vary from sub-basin to another and from one year to another.