Interannual Variability of TRMM RADAR Precipitation over West Africa and the Sahel

Abstract

Precipitation is an important part of the hydrological cycle in West Africa and the Sahel that impacts on water resources, food security and disaster management. Long term satellite observations provide an unprecedented record that helps us determine rates of change in rainfall. The Tropical Rainfall Measuring Mission (TRMM) satellite radar precipitation is important in capturing rain rates at their pixels along its footprint. Daily data has been smoothen using FIR filter to remove spurious signals due to storms. The data is averaged to 3-daily means to allow investigations at shorter time scales. Results show strong interannual spatial variability across the latitudes. Positive rain rates in West Africa corresponds with positive rain rates in the Sahel, even though climatologically the regions are different. Strong positive anomalies corresponds to period of flood, while negative to drought in both the regions. The Guinea coasts experiences rainfall year round with maximum values in June-July months. Short spells of dryness were observed across the timeseries for periods less than 2 weeks. This could be attributed to the impact of anomalous winds akin to westward African Easterly jets (AEJ) that emanates from the east and perturbs the monsoon system. The central aim is to charaterise interannual spatial changes in rainfall across the two regions, and the results herewith serves as useful background conditions to coupled ocean-atmosphere models as well in the assessment of local climate scenarios.