EMPIRICAL ANALYSIS OF THE RECENT RAINFALL RECOVERY IN WEST AFRICA

Abstract

In this study, daily and monthly rainfall data from 167 and 254 stations, respectively, across West Africa with at least 80% data availability for a 31-year period (1980-2010) and the gridded African Rainfall Climatology- Version 2 (ARC2) data for the period 1983-2013, were used to investigate the monthly, intra-annual and inter-annual rainfall variability over West Africa. Precipitation-related indices of the Expert Team on Climate Change Detection Indices (ETCCDI) were used to investigate the implication of the recovery in terms of the occurrence of precipitation extremes, intensity and frequency. Also, trends in the rainy season onset and retreat dates were analysed to assess the implication of the recovery on monsoon season length. The Standardised Precipitation Index (SPI) for various running time scales was used to assess the consistency of the rainfall recovery with the change from the drought states toward wet or normal conditions. Using the joint global observational dataset from the National Centers for Environmental Prediction (NCEP) and the National Center for Atmospheric Research (NCAR), the study further examined the physical mechanisms and teleconnections that led to the observed recovery in the West African rainfall. This analysis involved the influence of Sea Surface Temperature (SST) Anomaly on West African rainfall variability and the feedbacks from land surface condition changes. A projection for future scenarios of the recovery in West African rainfall was made based on the Empirical-Statistical Downscaling (ESD) applied to the output of the Hadley Global Environment Model 2 (HadGEM2) projections. Results of this study reveal that the majority of stations in the selected Sahelian region show statistically significant positive (increasing) rainfall trend for annual totals. The August- October period shows the largest rainfall recovery in the Sahel and the date of the retreat of the rainy season significantly moved later into the year by 2 days per decade over that region.