干旱区生态环境知识资源中心

Using precipitation data from the Climatic Research Unit and the cluster analysis method, the northern Africa (0-30 degrees N; 20 degrees W-40 degrees E) was sub-divided into four homogenous climatic zones for the base period (P0) 1901-1940. The four climatic zones were distributed into Saharan, Sahelian, wet tropical and equatorial climate types. The application of a segment of 15 years with overlap going from 1901-1940 (P0) and 1961 to 2000 (P4) throughout the periods 1916-1955 (P1), 1931-1970 (P2) and 1946-1985 (P3), shows important spatio-temporal modifications of rainfall zones south of 15 degrees N. The semi-arid lands (Sahelian) which govern the dynamics of this zone doubled at the end of the twentieth century, while the wet tropical and equatorial zones decreased at the half. Temperature trends have a magnitude of up to 1.5 K per century in all the four climatic zones. This warming was mainly observed during the last three decades. During these same three decades, regional precipitation trends were less significant. The extreme conditions in temperature and the precipitation were analysed in terms of their persistence. The sporadic long-lasting extreme conditions appear for several years to over 10 years during the last century.