TEMPORAL AND SPATIAL VARIATIONS OF THE ATMOSPHERIC DUST LOADING THROUGHOUT WEST-AFRICA OVER THE LAST 30 YEARS

The dust haze conditions, typical of the African atmosphere south of t he Sahara, are a result of wind-generated dust from arid lands. The ma gnitude of the dust haze is evaluated for the 30-year period beginning in 1957 by calculating the number of occurrences where the observed v isibility was reduced below threshold values of 10 km and 5 km. The fr equency of low visibility was several times greater for the 1977-1986 period than for the 1957-1966 period. Large decreases in visibility ar e observed after the severe droughts of 1972-1973 and 1982-1984. Contr asting regional differences of the dustiness evolution are noticed. Th ese differences are closely related to the differences in the regional rainfall evolution. The increase in dustiness is believed to arise fr om dust produced in new desertic areas which result from rainfall shor tages along the southern border of the Sahara.