Raingauge vs IMERG precipitation data for SWAT modelling: balancing accuracy and cost for reliable hydrological observatories in a tropical river basin

Reliable hydrological monitoring is essential for water resource management but challenging in remote areas with extreme weather. This study evaluated the Soil and Water Assessment Tool (SWAT) model’s performance using various precipitation data sources in the Sahafihitry catchment, northeastern Madagascar. We compared ground-based rain gauge networks of different densities (one, two, and five gauges) with satellite-derived IMERG data. Results showed that denser rain gauge networks (two and five gauges) captured rainfall variability more effectively than single gauges or IMERG data, leading to superior SWAT model performance. Rain gauge configurations outperformed IMERG in simulating both flood events and low-flow periods. While IMERG offers low-cost, readily available data, it introduces significant uncertainty into hydrological modelling. The two-gauge network achieved satisfactory streamflow simulations and represents the most cost-effective option for establishing reliable observatories in this study area.