Regionalization of rainfall in North-Western Algeria

Mohamed MEDDI, Hind MEDDI, Samir TOUMI, Madjid MEHAIGUEN

ABSTRACT: Our study focuses on the regionalization of rainfall in northwestern Algeria. This region is the most affected by rainfall reduction since the second half of the 1970s. The regionalization of spatial variability of precipitation is studied over two separate periods in order to improve the quality of information. Two statistical techniques were used, i.e., the Principal Components Analysis with rotation and the non-hierarchical clustering (k-means clustering). The regionalization of rainfall using 46 stations with 74 years of observations (1930-2004) allowed us to identify four groups characterizing the different climatic regions in the studied area. To refine this regionalization, we have introduced new stations (182 stations) with a shorter period of observation (36 years, from 1968 to 2003). This new procedure allowed us to highlight new regional groups. The homogeneity test of Krauss (1977) improved by Fernandez Mills et al. (1994) showed some weakness in the homogeneous structure of rainfall fields of these groups, especially the temporal component. The major element in limiting these groups is the longitude (the correlation coefficient between this parameter and rain is of the order of 0.66). To show the influence of the distance from the Mediterranean Sea and the altitude, the K-means clustering technique was applied on each one of these six groups. This procedure allowed us to divide the region into twelve groups. The homogeneity became clearer except in the groups where the temporal variability of rainfall is significant, which caused the reduction of Krauss coefficient value. When using this technique in these groups, we have demonstrated the importance of the longitude, the distance from the Mediterranean Sea and the topography characterized by its altitude in the regionalization of rainfall on an annual basis.

Keywords: Regionalization, rainfall, North-western, Algeria. .

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