A concise comparison of two rainfall onset definitions using convective properties derived from TRMM precipitation radar data

Most rainfall onset definitions in West Africa were estimated using station-based data. These data and hence the rainfall onset definitions may, however, not be a good representative for the entire climatic zone of the station. Based on existing definitions, a new rainfall onset definition is developed from the Tropical Rainfall Measurement Mission 3B42 gridded rainfall observations. 16 years of data were analyzed, which were taken between mid-April to mid-July over rainforest zones (west coast rainforest, dry rainforest and Nigeria–Cameroon rainforest) and between mid-May to mid-August over savannah zones (Nigeria savannah, and “Central African and South Sudan savannah”). While both definitions yield rather similar results in west coast rainforest, Nigeria–Cameroon rainforest and Nigeria savannah zones; results differ, however, substantially over dry rainforest and the Central African and South Sudan savannah. The new onset definition is further justified using an event-based analysis of mesoscale convective systems, flash counts and other convective parameters. Results have proved the new onset definition to be reliable and relevant for applications in agricultural productivity.