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.

Commonly used indices completely disagree about the relative effect of moisture on heat stress

“…These relationships point to the conclusion that a drier land surface leads to worsened heat stress. Conversely, some recent studies have argued that droughts generally decrease heat stress because of the effect of reduced humidity 11 , while irrigation increases heat stress because of the effect of increased humidity [12][13][14][15] . This discrepancy has potentially major implications, as some climate adaptation actions intended to reduce heat stress, such as urban greening, rely on conversion of sensible heat to latent heat through evapotranspiration of water.…”

Spring Irrigation Reduces the Frequency and Intensity of Summer Extreme Heat Events in the North China Plain

“…Previous studies have mainly focused on the irrigation cooling effect on mean temperatures, aiming to reveal the contribution of irrigation to climate warming mitigation on global or regional scales (e.g., Cook et al., 2015; Qian et al., 2013; Sacks et al., 2009; Wu et al., 2018; Yang et al., 2016, 2020). With extreme heat events frequently occurring, a growing body of literature has attempted to evaluate the irrigation cooling effect on extreme temperatures, and it has been concluded that the impact on extreme temperatures is much more pronounced than that on mean temperatures, highlighting the role of irrigation in modulating extreme temperatures (e.g., Ambika & Mishra, 2022; Hauser et al., 2019; Hirsch et al., 2017; Mishra et al., 2020; Mueller et al., 2016; Thiery et al., 2017).…”

“…Irrigation is an important anthropogenic activity that accounts for approximately 70% of the total freshwater withdrawals globally (Wada et al., 2013) and generates distinct climate impacts (McDermid et al., 2023; Singh et al., 2018; Thiery et al., 2020). Numerous observational and modeling studies have explored the climatic effect of irrigation and yielded considerable achievements, showing that irrigation strongly affects the partitioning of surface turbulent heat fluxes, soil moisture, crop growth, and the coupling strength of land‐atmosphere interactions and therefore climate impacts (e.g., Ambika & Mishra, 2022; Bonfils & Lobell, 2007; Chen & Dirmeyer, 2019; Hirsch et al., 2017; Jha et al., 2022; Kang & Eltahir, 2018; Liu & Wang, 2023; Liu et al., 2021a, 2023; Mishra et al., 2020; Ozdogan et al., 2010; Qian et al., 2013; Thiery et al., 2017, 2020; Wang et al., 2021; Yang et al., 2020). Of the climatic effects of irrigation, the cooling effect is the most famous since it counteracts greenhouse‐gas‐induced warming (Bonfils & Lobell, 2007).…”

Comment on “Improved Water Savings and Reduction in Moist Heat Stress Caused by Efficient Irrigation” by Anukesh Krishnankutty Ambika and Vimal Mishra

“…In a recent article in this journal, Ambika and Mishra (2022), hereafter AM22, employ modeling capabilities to investigate how a shift toward efficient irrigation (surface drip irrigation, specifically) will change moist heat stress regimes and water savings over the Indo‐Gangetic Plains of India. AM22 continues a useful stream of research oriented toward thermal comfort in a densely populated region globally, and how agricultural water management practices dictate these regimes in the region (Ambika & Mishra, 2019, 2020, 2021; Mishra et al., 2020).…”