Comparing the impacts of irrigation patterns on the near-surface climate

Abstract

Previous studies have shown that irrigation can impact the near-surface climate, but none refer to the differences in the impacts of irrigation types such as flooding and spraying. In this study, we add a novel irrigation module to the recently released community land model 4.0 and simulate irrigation in two ways: first, by spraying water above a canopy similar to precipitation to simulate spray irrigation; second, by directly adding water on the ground to simulate flood irrigation. Differences between coupled irrigation and control runs and differences between two irrigation patterns are analyzed globally and in three heavily irrigated countries: The USA, India, and China. Our results show that spray irrigation has greater impacts than flood irrigation on nearsurface climate. Spray and flood irrigation respectively increase evapotranspiration by 4.33 w/m2 and 3.36 w/m2 and 2 m relative humidity by 0.36% and 0.14%. In addition, spray and flood irrigation respectively decrease sensible heat flux by 2.86 w/m2 and 2.43 w/m2, ground temperature by 0.13 K and 0.12 K, daily maximum of average 2 m temperature by 0.1 K and 0.04 K, soil temperature in top 10 cm of soil by 0.22 K and 0.12 K, and vegetation temperature by 0.12 K and 0.06 K averaged over irrigated land. Among the above three heavily irrigated countries, impacts of both flood and spray irrigation are greatest in India.