Streamflow plays an important role mainly for hydropower and irrigation in Bhutan. River discharge composed with precipitation and glacier melt has a large temporal change because the climate in the country is monsoon. Some studies indicate that water scarcity could get serious in the future because glaciers in Bhutan would decrease or disappear. However, such studies focus on only the annual water amount without evaluating seasonal fluctuation. In this study, we aim to predict present (1998-2007) and future (2071-2100) river discharge on daily time scale by using a hydrological model incorporated a glacier model. The hydrological model named “H08 water resource model” calculates runoff and river discharge based on natural water circulation with the contribution of glacier melt by combining a glacier model. Glacier runoff and river discharge are simulated with meteorological data and geospatial data. These data are interpolated into 1 minute spatial resolution. APHRODITE and WFDEI reanalysis data are used as present data. Three GCMs from RCP 8.5 emission scenario are used as future data. We compared present and future river discharge on monthly time scale. As a result, in several river basins, river discharge will decrease in dry season. On the other hand, river discharge will increase in wet season. Furthermore, glacier melt could decrease because of shrinkage of glaciers. Hence, severe drought may occur in winter when the amount of precipitation is smaller than that of usual winter.
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