4.3. Trends in rainfall from 1960 to 2007
Cumulative annual rainfall over the 48-year study period
(annual average 540 mmyr_1) was characterized by two phases
(Fig. 6): 1960e1969 was relatively wet, with an annual average of
757 mmyr_1, and 1970e2007 was drier, with an annual average of
482 mmyr_1. The change in precipitation rate in 1970 (Fig. 6)
coincided with the beginning of the drought in the Sahel (Faure
and Gac, 1981). Since 1970s, the temporal trend in overall
rainfall has been a decrease in rainfall duration and volume,
indicating a drier climate.