Evaluating the Performance of GPM IMERG Products for Precipitation Estimation in the Volta River Basin of Ghana

Abstract The Volta River basin in West Africa, covering a substantial area of Ghana, faces significant water management challenges due to highly variable rainfall and limited availability of high temporal resolution rain gauges. This study, developed under the 2024 Global Precipitation Measurement (GPM) Mission mentorship program, evaluates precipitation in the Volta River basin using high-resolution satellite-derived data from the Integrated Multi-satellite Retrievals for GPM (IMERG). In the absence of sub-daily rainfall data, comparisons were made between daily precipitation from local rain gauges and IMERG version 06 and version 07 (Early, Late, and Final) runs. Results indicated a very weak correlation between daily precipitation estimates from IMERG and gauge data, but a significantly improved correlation for monthly estimates. In addition, version 07 performed better than V06 in many of the metrics used including, higher r-squared, lower root mean square error, and improved bias. Extreme precipitation days and no rain days were also compared to determine how well IMERG estimated occurrences. While IMERG failed to accurately estimate extreme precipitation, version 07 estimates performed better than version 06 estimates. IMERG also consistently estimated light precipitation when rain gauges observed no precipitation. While this study shows that IMERG did not perform well in the region, it also highlights the improvements from version 06 to 07. This study contributes to our understanding of precipitation estimates from satellite remote sensing in the Volta River basin which can enhance disaster risk management and climate resilience in Ghana.