Comparison of ET₀ Estimation Methods in a Humid Tropical Region: The Kuranji Catchment, Indonesia

Many studies have evaluated various evapotranspiration (ET₀) estimation methods globally; however, it is necessary to assess how accurately these methods can function in tropical catchment area (DAS), especially in areas with limited data, such as the Kuranji catchment in Padang, Indonesia. This study aims to the performance of four ET₀ estimation methods—FAO-56 Penman-Monteith (PM), Hargreaves-Samani, Priestley-Taylor, and MOD16A2 satellite-derived ET₀—under varying data constraints typical of humid tropical environments. Using ground observations from BMKG’s Padang station, ERA5-Land reanalysis, and streamflow records from the Kuranji weir, we compute daily ET₀ (2015–2022) and assess impacts on hydrological modeling. Results show that while FAO-56 PM remains the most accurate (MAE = 0.0 mm/day, NSE = 0.82), Priestley-Taylor performs best among simplified methods (MAE = 0.3 mm/day, NSE = 0.79) when radiation data are available. Hargreaves-Samani overestimates ET₀ by 12–14% due to humidity neglect, while MOD16A2 exhibits higher uncertainty (±0.4 mm/day) from cloud contamination. This study recommends hybrid approaches combining ground and reanalysis data to improve accuracy in data-scarce tropical catchments, supporting climate-resilient water management in Padang and similar regions.