ABSTRACT
ABSTRACT: For well over three decades controversy has surrounded the characteristics of environmental degradation in the Sahel. One reason for this prolonged debate is the dearth of uncertainty in previous Sahelian rainfall work. Global Historical Climatology Network summer rainfall data between 1930 and 1990 were used in sequential indicator simulations to reproduce global statistics over local accuracy to provide a complete assessment of uncertainty. The traditional area-weighted technique showed the characteristic decline in rainfall but represented the extreme of the simulation mean distribution. Annual estimates of the 5th and 95th percentiles of the simulated rainfall mean distribution quantified uncertainty and showed that there is no longer unequivocal evidence of desiccation in the region between the late 1960s and 1990. The probability of exceeding rainfall was calculated for 200 mm and 500 mm and presented using maps for selected years between 1930 and 1990. The results demonstrated that simple isoline thresholds did not adequately represent the boundaries for vegetation and agriculture, respectively.
