Substantial decline in atmospheric aridity due to irrigation in India

Abstract

Compound extremes of soil moisture drought and high vapour pressure deficit (atmospheric aridity) are disastrous for natural and social systems. Despite a significant expansion in irrigated area in India, the role of irrigation on soil moisture and atmospheric aridity is not examined. We used observations, reanalysis datasets, and high-resolution simulations from the Weather Research and Forecasting (WRF) model to show that irrigation significantly modulates soil moisture and atmospheric aridity in India. The Indo-Gangetic Plain, which is one of the most intensively irrigated regions in the world, experienced significant (P-value =0.03) cooling (~0.8�C) and an increase in Solar-induced chlorophyll fluorescence (SIF) during the crop growing season (November-February). Atmospheric aridity has significantly (P-value =0.0002) declined (-1.38kPa) while soil moisture (1.6m3/m3) and relative humidity (2.0%) have increased over the Indo-Gangetic Plain during 1979-2018. We conducted high-resolution simulations using the WRF model to examine the role of irrigation on atmospheric aridity. Irrigation strongly modulates soil moisture drought and atmospheric aridity by increasing latent heat and relative humidity and reducing sensible heat. Our findings have implications as irrigation can influence compound extremes of soil moisture drought and atmospheric aridity. Climate models need to incorporate the influence of irrigation for reliable projections in the intensively irrigated regions.