Roles of Irrigation and Reservoir Operations in Modulating Terrestrial Water and Energy Budgets in the Indian Subcontinental River Basins

Water management activities affect the terrestrial water cycle by increasing water supply and redistributing the water and energy budgets over irrigated agricultural land. However, the dynamics of how water management activities interact with the terrestrial water and energy budgets have not been sufficiently studied over Indian subcontinental Basins. In this study, we applied a well-evaluated water management model, coupled with a large-scale land surface hydrological model with irrigation and reservoir operation schemes to examine the impacts of irrigation and reservoir operations on terrestrial water and energy budgets over the Indian subcontinental basins. We conducted two simulations: NATURAL (i.e., no irrigation and no reservoirs) and water management scenario (i.e., with irrigation and with reservoir regulations, referred to as MANAGED) over 18 basins from 1951 to 2012. The water management impacts were evaluated by comparing a number of key water and energy budget terms such as evapotranspiration (ET), total runoff, land surface temperature (LST), latent heat flux (LHF), sensible heat flux (SHF), reservoir storage, and discharge. Our results show that water management activities have significant (pvalue <0.05) impacts on ET, LHF, and LST in most of the river basins during the pre-monsoon season (February–May). Comparing to the NATURAL scenario, ET and LHF under the MANAGED scenario are significantly increased in most basins during pre-monsoon and post-monsoon seasons, especially in semiarid regions. Therefore, the influence of irrigation on water and energy budget can be an overestimation in comparison to the constrained irrigation, which is a more realistic scenario.