Performance Evaluation of a Subseasonal to Seasonal Model in Predicting Rainfall Onset Over West Africa

Abstract

The present study evaluates the performance of a Subseasonal to Seasonal (S2S) model (called The China Meteorological Administration) in simulating rainfall onset dates (RODs) over West Africa. Using two ROD definitions, we compared the model's ROD at six lead‐time forecasts (10, 20, 30, 40, 50, and 60 days) with the observed ROD from satellite data sets, statistically quantified the model's capability to reproduce the interannual variability of RODs over the climatological zones in the subcontinent, and investigated how well the model links RODs with the dynamics of monsoon system over the subregion. The results show that the mean RODs follow a latitudinal progression and the dates increases northward from the coast. The performance of the S2S model in reproducing RODs largely depends on the definition used. For instance, the ability of the model to replicate the observed spatial pattern of RODs and all the essential features over the three zones in West Africa is stronger with DEF1 than DEF2. Regardless of the ROD definition used, the 20‐ to 60‐day forecasts produced more realistic simulation than the 10‐day forecast. We also found that the performance of the model in reproducing the interannual variability of RODs depends on the zones (Guinea, Savanna, and Sahel). Moreover, the model could reproduce the three main phases of the West African Monsoon (the onset, the peak, and the southward retreat of rainfall) and other dynamics. The results of the study have application in improving S2S forecasting over West Africa.