Analysis on Flow and Water Balance Parameters of Teesta River Basin due to Climate Change and Upstream Intervention

Teesta, one of the prominent trans-boundary rivers of Bangladesh, possessed significant annual runoff during pre-barrage period (1967–1990) ranging between 3674 cusecs to 139 cusecs during high flood season (HFS) to mean monthly minimum flow (MMN). But the availability of water has significantly reduced due to a number of developments upstream in India, making dry season scarcity of water in Bangladesh a vulnerable issue. Also, flow in this river varies greatly due to the high variation in the intensity of rainfall, an issue which is expected to be worsen as a result of climate change. To understand the impacts of climate change on the river basin, this study employs a semi-distributed hydrological model of the Teesta river basin, developed using the Soil Water Assessment Tool (SWAT). The whole study area including India and Bangladesh is divided into 83 sub-basins for addressing the impact of land use and soil type pattern better. The developed hydrologic model has been calibrated by using SWAT-CUP for 2001 to 2007 and validated for 2008 to 2016 using the available stream flow at a location named Dalia, upstream of Teesta barrage within Bangladesh. The validated hydrologic model has been used to evaluate the change of flow and water balance parameters for the 2020s, 2050s, and 2080s using RCP 2.6 and 8.5 scenarios for two specific selected model named as MIROC-ESM-CHEM and HADGEM2-ES. Comparative analysis of future flow scenarios at Dalia shows that the change in discharge was 187% for the model MIROC-ESM-CHEM for RCP 8.5 depicting the maximum increase. On the other hand, the least percentage change in discharge was found to be 4.83% around 2020s for model HADGEM2-ES of RCP 2.6. Overall analysis on flow depicted increased availability of flow in future with drier dry seasons and wetter monsoon seasons. Conclusions have been drawn on the comparative analysis of water balance parameters.