The Main Cause of the Persistent Drought in Sahel and the Increasing Trend of El Niño Events During Recent Years

The persistent drought of Sahel since 1986 is a major problem of climatic anomalies during recent years. Many scientists have searched for its casuses. Winstanley (1973) suggested that it was related with the strengthening of cold air from the North Atlantic, which forced the Azore high and ITCZ normally located at Sahel to shift southward. Charney (1975) has pointed out that overgrazing may be the main cause, and through a series of bio- geophysical feedback processes, it would result in the persistent drought of Sahel.Present study has found that successive decreasing of direct radiation in the Northern Hemisphere since 1960s may be the principal factor producing this climatic anomaly.