Irrigation‐Induced Crop Growth Enhances Irrigation Cooling Effect Over the North China Plain by Increasing Transpiration

Abstract

AbstractThe large‐scale irrigation is demonstrated to significantly affect regional hydroclimatic regime by changing underlying surface (e.g., crop growth and soil moisture), yet the contribution of irrigation‐induced crop “greening” to climatic effects is not well understood. In this study, we use a window‐searching algorithm to evaluate the irrigation effects on vegetation with leaf area index (LAI) as a vegetation index, and further conduct three regional climate simulations to investigate the comprehensive effects of irrigation on surface fluxes and local climate over the North China Plain. We find that irrigation leads to a more significant greening in March‐May (MAM) than in June‐September (JJAS). Especially in April and May, the irrigation‐induced change in LAI (ΔLAI) exceeds 0.4 m2 m−2 in intensively irrigated areas. Irrigation induces a cooling effect in air temperature at 2 m with decreasing magnitudes of 0.58°C in MAM and 0.43°C in JJAS, respectively, in which ΔLAI contributes about 34.5% (0.20°C) and 14.0% (0.06°C). Likewise, the irrigation‐induced changes in latent heat flux, sensible heat flux, and transpiration are all enlarged via the irrigation greening effect. Whereas the increase in soil evaporation is alleviated, because the greening‐triggered enhancement of crop root uptake reduces the increase in soil moisture. Moreover, irrigation effects on net radiation depend on the competing influences of irrigation‐triggered cooling and cloud formation. This study provides beneficial references to understand the impact of irrigation on regional energy balance and water cycle, and highlights that in modeling hydroclimatic feedback to irrigation, the greening effect induced by irrigation should be considered.