Development of Flood Forecasting System for the Wangchhu River Basin in Bhutan

In mountainous countries like Bhutan, floods are potentially serious dangers for communities since they triggersubsequent hazards such as landslides. The countries lying in the Himalayan Mountain are exposed to floodsowing to the heavy rainfall and glacial lake outburst floods. The forecasting of catastrophic flood hazards iscrucial for the sustainability of these mountainous countries. At the same time, the hydro-met observation systemis inadequate to set up a robust flood-forecasting model in Bhutan. This paper focuses on developing a floodforecasting model for the Wangchhu river basin in Bhutan, by assimilating the hydrological gauge data andsatellite rainfall, and by providing stream flow frequency, rating curve and stream characteristics of theWangchhu basin. The study depicts the poor efficiency without upstream rainfall gauges. Using satellite databasewith proxy stations in the upper catchments increase the accuracy of the model. The Weather Research Forecast(WRF) model generated 3-day rainfall forecasts, which were used to generate flow forecasting. The WRF resultfor Bhutan is poor; thus, other sources of rainfall prediction need to be incorporated in the model. The model hasbeen calibrated for 2003-2004 and validated for 2005, 2009 and 2010 data.