Gauging the ungauged: estimating rainfall in a West African urbanized river basin using ground- based and spaceborne sensors

Accurate precipitation observations are crucial for hydrological forecasts, notably over rapidly responding
urban areas. This study evaluated the accuracy of three gridded spaceborne rainfall products (Integrated MultisatellitE
Retrievals for GPM (IMERG), Meteosat Second Generation Visible (MSG-VIS), and MSG-Infrared (MSGIR))
and the non-governmental Trans-African Hydro-Meteorological Observatory (TAHMO) gauges across the
Odaw catchment (Accra, Ghana) from January 2020-July 2022. IMERG is hardly able to capture the strong
spatial variability of rainfall required for flood forecasting, but agrees in annual sums with TAHMO and MSG-IR.
MSG-IR has difficulties during the wet season. MSG-VIS, only available during daylight, shows limited accuracy
and gives high estimates while other products do not detect rain. TAHMO gauges effectively record highintensity
events and their strong spatial variability, although some (daily) accumulations are doubtful and data
gaps exist due to technical issues. These findings assist hydrological modelers in selecting appropriate datasets
at suitable spatiotemporal resolutions for their research.