Recent trends in selected extreme precipitation indices in Senegal – A changepoint approach

Precipitation regime is the number one factor in food productivity in the Sahel region. Recurrent droughts have caused several food crises in the region during the three last decades. The situation may not improve as a recent special IPCC report states that West Africa will likely experience longer and more intense droughts () in the near future. As drought adversely affects food security, Sahelian decision-makers need to understand past and current trends in Sahelian precipitation to have some insight in what can be expected for the next five years. In this paper, time series of selected precipitation indices were calculated using 1950–2007 daily precipitation data from 31 stations across Senegal and analyzed for changes in temporal trends using a Bayesian multiple change point detection procedure. The selected indices are the mean (M) and the standard deviation (SD) of precipitation, the frequency of wet days (precipitation using threshold of ⩾ 1 mm, Prcpl), the maximum number of consecutive dry days (precipitation < 1 mm, CDD), the greatest maximum amount accumulated over the 3 day (R3d), the mean intensity per wet day (SDII) and the 90th percentile of daily rainfall (Prec90p). They were calculated and averaged over four different regions: the entire country (R0), the Southern Sahelian Region (R1), the Northern Sudanian Region (R2), and finally the Southern Sudanian Region (R3).The Bayesian changepoint detection procedure detects whenever a trend in the data is inverted, from increasing to decreasing or vice versa. Results show that significant changes in trend were almost always consistent across Senegalese regions, with a few years’ differences in the dates of occurrence of the changes. A decreasing trend followed by an increasing trend was found for M, SD, Prcpl, R3d, SDII and Prec90p. An increasing trend followed by a decreasing trend was observed for CDD in regions R0, R1 and R2, but not for R3 where the trend is increasing during the study period. Changes in Prec90p were not consistent across regions, presumably because it is very sensitive to noise in the data. Most changes at the national scale occurred in the 1980s, except for SDII for which the changes occurred in the 1970s. Prec90p displayed a trend change (from a decreasing trend to an increasing trend) in the mid-1990s. Modest to significant increases in SDII were observed for almost all regions while Prcp1 was stable during the last two decades. These results suggest that the continuous rainfall deficit that was observed since 1950 in this part of the Sahel has (at least temporarily) come to an end and that the next few years will be wet.