Assessing the Impacts of Climate and Land Use and Land Cover Change on Freshwater Availability: Applications in the Ganges and the Brahmaputra River Basins

Understanding the effects of projected climate and land use and land cover change on freshwater availability has been viewed as a strategic essential requirement to manage freshwater resources sustainability. Agriculture is the single largest sector of freshwater usage, and scarcity of freshwater has already been observed in many of the world’s major agriculturally important river basins. While the intensification of the hydrological cycle due to climate change may lead to less exposure to freshwater scarcity in some basins, it may worsen the current freshwater scarcity in other basins. Hence, quantifying current and future freshwater availability is a critical aspect of adapting to changing and variable climate because access to sufficient freshwater is linked to food security, human health, ecosystem health, land use change, economic development, and regional conflicts. In this research a framework utilizing appropriate input data and models from the public domain has been developed to quantify freshwater availability with long-term trends at the basin level. In this framework, first the factors governing precipitation variation spatial and temporal have been evaluated. Specific factors that have been emphasized include El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) modes. The analysis provides insight into the variation of basin precipitation by ENSO-IOD interactions. Second, the observed basin precipitation variation were used in calibrating Statistical Downscaling Model (SDSM) connecting global scale predictors and regional scale precipitation dynamics. SDSM was implemented to downscale the 21st century precipitation from Canadian Center for Climate Modeling and Analysis version 3.1 (CGCM3.1) predictor variables. Finally, using this downscaled precipitation along with CO2 concentration, temperature, and land cover land use projections in Soil and Water Assessment Tool (SWAT) hydrology model, water availability in the basin’s hydrological components during the 21st century has been quantified and long-term trends in the hydrological components have been analyzed. Although the framework has been implemented for the Ganges and the Brahmaputra river basins, it has been developed with a broader goal of quantifying future freshwater availability in the agriculturally important major river basins around the world. The research results for the pilot basins suggest that prevailing climate modes ENSO and IOD lead to significant differences in the magnitude and spatial distribution of seasonal precipitation between the Ganges and Brahmaputra basins. Uncertainties were relatively lower in the downscaled projections of monthly precipitation than that of raw CGCM3.1 projections, and impacts of projected changes in climate and land cover land use are expected to increase future freshwater availability with pronounced seasonal variation in the Brahmaputra basin. Hence, this assessment framework holds promise to facilitate well informed decision making in minimizing natural hazard risks and climate impacts on agriculture, and supports development of strategies to ensure optimized use of water resources in best management practices under a changing climate at the basin scale around the world