Improved water savings and reduction in moist heat stress caused by efficient irrigation

Abstract

Intensive agriculture and irrigation play a crucial role in the food security of India. However, irrigation has considerably impacted regional climate and groundwater sustainability. Notwithstanding the profound implications of irrigation on dry and moist heat and groundwater depletion, the role of efficient irrigation on moist heat stress reduction and water savings remains unexplored. Here, we use observations and simulations from the Weather Research Forecasting (WRF) model to examine the impact of efficient (drip) irrigation on moist heat stress and water savings over the Indo-Gangetic Plain. Irrigated area has increased more than 20% over the Indo-Gangetic Plain during the 1970-2005 period. As a result, irrigation water use has increased dramatically over the region. The irrigation expansion partly contributed to the rise of 0.46°C (P-value < 0.05) in the summer (April-May) season wet-bulb temperature over the Indo-Gangetic Plain, which is a measure of moist heat stress. The Indo-Gangetic plain exhibited a strong land-atmospheric coupling between soil moisture and dry and moist heat. WRF simulations conducted using ERA5 as boundary conditions show that switching from the conventional (channel) to the efficient (drip) irrigation leads to a moderate warming (∼0.2°C) and a significant decrease in specific humidity over the Indo-Gangetic Plain. The reduction in specific humidity due to efficient irrigation significantly lowers the moist heat stress (wet-bulb temperature) and increases water savings. Our findings show the double benefits of efficient irrigation to curb the rapidly declining groundwater and increase moist heat stress in the region.