Assessing the accuracy and applied use of satellite-derived precipitation estimates over Nepal

Accurate observational precipitation data supplied at a fine spatial resolution is vital for informing sustainable water resources management in Nepal. Livelihoods in Nepal are acutely impacted by precipitation. The amount of monsoon precipitation determines water available for drinking, hydropower and irrigation. Extreme precipitation events often result in landslides, flash flooding and crop damages. Freely available satellite-derived precipitation data products have the potential to substantially inform water policy. Such products could advocate sustainable use of water resources and enhance the adaptive capacity of rural populations in Nepal to future precipitation changes. In this research, statistical measures were used to assess the accuracy of Tropical Rainfall Measuring Mission satellite-derived precipitation estimates (TRMM 3B42) relative to ground-based precipitation data (APHRODITE), seasonally from 2001 to 2007. In all seasons the majority of satellite precipitation estimates were significantly correlated with ground-based precipitation. However, satellite precipitation estimates consistently overestimated the amount of precipitation, with error greatest in the monsoon season. The satellite precipitation product inaccurately detected extreme precipitation events, 'rainy days' and precipitation intensity in the monsoon season. Results suggest that precipitation estimates derived from this satellite product have limited use in agricultural planning, water resource management and developing mitigation measures to the impacts of extreme events in Nepal. Currently, ground-based precipitation measurements still provide the most accurate information for use in water resources management. Maintaining and developing precipitation gauge networks in Nepal, particularly in regions of high relief, is extremely important for increasing the accuracy of both ground-based and satellite-derived precipitation products.

► Satellite-derived and ground-based precipitation were well correlated for Nepal.
► TRMM generally overestimated precipitation in all seasons.
►  Precipitation extremes were not well-detected by TRMM in Nepal.
► APHRODITE offers a more accurate product for informing water policy and management.
► More gauges are needed in the High Mountain to increase accuracy of both products.