Validation of TRMM Radar Rainfall Data over Major Climatic Regions in Africa

Abstract

The Global Precipitation Climatology Center global-precipitation-analyses rain gauge data have been used to validate the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) data over the major climatic regions in Africa. The threshold-matched precipitation index and the TRMM-and-other-sources “best-estimate” data (3B43) have also been compared with rain gauge data and with the TRMM PR rainfall product. In the 36-month climatological assessment of the satellite products at a grid spacing of 1.0°, continental Africa has been categorized into five distinct climatic regions: arid, semiarid, savanna, tropical wet, and the South Atlantic Ocean. Zonal mean analysis shows that TRMM PR has a large overestimation in the tropical-rain-forest region of Africa in December–January–February and in March–April–May. The bias is minimized in June–July–August and September–October–November. Bias is generally high for all algorithms in the dry seasons when rainfall is minimal but is less pronounced in the dry seasons of southern African climatic regions. In general, 3B43 has the closest agreement with rain gauge data. The derived standard errors of the algorithms in the climatic regions of Africa are used as a measure of reliability and show that quantitative climatological estimates of TRMM PR are reliable only in the wettest season of the northern savanna and southern semiarid regions when the mean precipitation is greater than 120 mm month^–1. The study also shows that TRMM PR has the closest agreement with 3B43 over the South Atlantic Ocean. Over land, all the satellite estimates showed significant seasonally and regionally dependent bias.