Inconsistent linear trends in Senegalese rainfall indices from 1950 to 2007

Abstract

ABSTRACTDaily precipitation data from 31 Senegalese stations spanning the period from 1950 to 2007 were used to examine the inter-annual variations of seven rainfall indices: the annual mean precipitation (MEAN); the annual standard deviation of daily precipitation (STD); the frequency of wet days (PRCP1); the maximum number of consecutive dry days (CDD); the greatest 3-day total of rainfall (R3D); the wet day precipitation intensity (SDII); and the 90th percentile of rain day precipitation (Prec90p). The indices were spatially averaged over three agroclimatic regions in Senegal. Trends in the averaged indices time series were assessed using both visual examination and a modified version of the Mann-Kendall test (MM-K). Initially negative significant trends in all seven indices suggest gradually drier conditions over the three agroclimatic regions between 1950 and 1980. In contrast, no significant trends or even positive significant trends were observed from the mid-1980s to 2007. The MM-K test was applied to all available data (1950-2007) and the period spanning from 1971 to 2000.While several indices were found to have significant suggests trends towards drier conditions for the 1950-2007 period, only PRCP1 showed a positive significant trend for the 1971-2000 period. The MM-K did not detect a significant trend for the remainder of the indices. It was found that the rainfall deficit and therefore drought is no longer intensifying, and that the region may even become wetter. However, the period covered by the observations is still too short to resolve the question of whether there is now a trend towards wetter conditions.ABSTRACTDaily precipitation data from 31 Senegalese stations spanning the period from 1950 to 2007 were used to examine the inter-annual variations of seven rainfall indices: the annual mean precipitation (MEAN); the annual standard deviation of daily precipitation (STD); the frequency of wet days (PRCP1); the maximum number of consecutive dry days (CDD); the greatest 3-day total of rainfall (R3D); the wet day precipitation intensity (SDII); and the 90th percentile of rain day precipitation (Prec90p). The indices were spatially averaged over three agroclimatic regions in Senegal. Trends in the averaged indices time series were assessed using both visual examination and a modified version of the Mann-Kendall test (MM-K). Initially negative significant trends in all seven indices suggest gradually drier conditions over the three agroclimatic regions between 1950 and 1980. In contrast, no significant trends or even positive significant trends were observed from the mid-1980s to 2007. The MM-K test was applied to all available data (1950-2007) and the period spanning from 1971 to 2000.While several indices were found to have significant suggests trends towards drier conditions for the 1950-2007 period, only PRCP1 showed a positive significant trend for the 1971-2000 period. The MM-K did not detect a significant trend for the remainder of the indices. It was found that the rainfall deficit and therefore drought is no longer intensifying, and that the region may even become wetter. However, the period covered by the observations is still too short to resolve the question of whether there is now a trend towards wetter conditions.