Study of Drought in Seven Algerian Plains

During the past century, Algeria has been subject to frequent periods of drought, which were recorded first in 1944 and then successively in 1981, 1989, 1990, 1992, 1994, 1996 and 1999. The northwestern and central Plains of the country were particularly affected by this phenomenon, resulting in significant decrease of yields and water resources with severe damages to crops. The most important water deficit periods were recorded in 1981 and 1989 at the Chellif Plain (136 %) and in 1990 at the plains of Ghriss, Mitidja and Sidi Bel Abbes. The most common indexes used to evaluate the drought severity are (1) Palmer drought severity index and (2) the standardized precipitation index, which are useful tools in studies concerned with the long-term forecasting of water resources and management of water in agriculture, giving valuable results about the water balance within a specific system. The analysis of the relationship between annual precipitation and these three indices showed that during the period 1930–2007, precipitation was strongly related to AMO and NAO. The ENSO and NAO indices are negatively correlated with precipitations. The period of deficit starting from 1975 corresponds to a phase of increasing AMO index to reach a positive phase. On the seasonal scale, the evolution of this index is similar to that of the annual scale. The use of Markov chains for studying the interdependency of rainfall series through a long-term period showed a strong trend for a dry year to be followed by another dry period. This trend is higher in the western plains than in the centre. The results show also that the probability for a wet year to be succeeded by another wet year exceeds 50 %. These results hold for winter and spring seasons.