This study characterizes the hydrological regime of the Upper Ayeyarwaddy River Basin (UARB) of Myanmar under current and future climate change scenarios by using the Soil and Water Assessment Tool (SWAT). The model simulation results show that the annual precipitation, actual evapotranspiration and water yields are 1,578, 524 and 1,010 mm, respectively. These will increase by 13–28%, 11–24% and 42–198% under two representative concentration pathways (RCPs), RCP 4.5 and RCP 8.5, for the future. There is seasonal variability across the cool, hot and rainy seasons in the agro-ecological regions – mountains, hills and inland plains. As in other Asian regions, the model shows that the wet (rainy) season is becoming wetter and the dry (cool) season is becoming drier in the UARB too.

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Hydrological models have been used to analyze the hydrological processes and availability of water in different watersheds. It is one of the most significant aspects of water resources management and development programme to use different hydrological models for predicting the flow of river basins. Calibration and validation of the developed hydrological model is also important so that the model users can be confident while estimating the flow of the watershed. In this study, a semi-distributed hydrological model was developed for 0.176 million km2 Upper Blue Nile river basin using Soil and Water Assessment Tool (SWAT). The applicability of SWAT was assessed for rainfall-runoff simulation in Upper Blue Nile basin. The model was calibrated and validated using 10 years of discharge data. Model calibration and sensitivity analysis were performed with sequential uncertainty fitting (SUFI-2), which is one of the programs interfaced with SWAT, in the package SWAT-CUP. The most and least sensitive parameters were CN2 (curve number) and GW_DELAY (ground water delay time) respectively. Performance of the model was evaluated based on Nash Sutcliff Efficiency (NSE) and Coefficient of Determination (R2) which were 0.71 and 0.66 respectively for calibration. Overall, the model demonstrated good performance in producing the patterns and trend of the observed discharge which assures the suitability of the SWAT model for future scenario analysis. Uncertainty analysis of the SWAT model of upper Blue Nile basin, consideration of other parameters and incorporating more flow data from other stations within the basin is recommended for future studies.