Strong Influence of Irrigation on Water Budget and Land Surface Temperature in Indian Subcontinental River Basins

Irrigation modulates the terrestrial water budget in intensively irrigated regions. However, the influence of irrigation on water budget and land surface temperature (LST) has not been quantified in Indian subcontinental river basins. Here, using the in situ and satellite-based observations and the Variable Infiltration Capacity model with irrigation scheme, we show that the presence of irrigation substantially alters water budget (especially evapotranspiration, ET) and LST in the subcontinental river basins. While irrigation results in increased ET in all the 18 subcontinental basins, mean annual ET of Indus and Ganges basins increases by 47% and 12%, respectively, due to irrigation. Total runoff has increased in the most basins due to irrigation. Irrigation has a remarkable influence on LST with cooling of 0.2-0.65 degrees C. Compared to other basins, irrigation water demand is high in Indus and Ganges basins during the postmonsoon season (October-January). Our results show that between 1951 and 2012, irrigation demand has decreased in 13 out of the 18 basins during the premonsoon season (February-May). However, irrigation water demand increased in 12 out of the 18 basins in the postmonsoon season. Changes in irrigation demands are largely driven by changes in soil moisture due to weakening/strengthening of the summer monsoon precipitation. Our findings have implications for water budget estimation over intensively irrigated basins where ET might be substantially underestimated in the previous studies that do not consider the role of irrigation.