Implementation and Evaluation of Irrigation Techniques in the Community Land Model.

Several previous studies have highlighted the irrigation‐induced impacts on the global and regional water cycle, energy budget, and near‐surface climate. While land models are widely used to address this question, the implementations of irrigation in these models vary in complexity. Here, we expand the representation of irrigation in Community Land Model to enable six different irrigation methods. We find that using a combination of irrigation methods, including default, sprinkler, flood and paddy techniques performs best as determined by evaluating the simulated irrigation water withdrawals against observations, and therefore select this combination as the new irrigation scheme. Then, the impact of the new irrigation scheme on surface fluxes is evaluated and detected using single‐point simulations. Finally, the global and regional irrigation‐induced impacts on surface energy and water fluxes are compared using both the original and the new irrigation scheme. The new irrigation scheme substantially reduces the bias and root‐mean‐square error of simulated irrigation water withdrawal in the USA and other countries, but considerably overestimates withdrawals in Central China. Results of single‐point experiments show that different irrigation methods have different effects on surface fluxes, while the magnitudes are small. At the global scale, the new scheme enlarges the irrigation‐induced impacts on water and energy variables relative to the original scheme, with varying magnitudes across regions. Overall, our results suggest that this newly developed scheme is a better tool for simulating irrigation‐induced impacts on climate, and highlight the added value of incorporating human water management in Earth system models. Plain Language Summary: Knowing the effects of irrigation on the water and energy cycle is important, as it helps us to understand better how irrigation may affect the near‐surface climate such as dampening heat extremes and increasing local air humidity. Land models are widely used for this purpose. However, in most of these models, different irrigation techniques are currently not considered. In this study, we develop a new irrigation scheme for the Community Land Model, and evaluate it by comparing modeled and observed irrigation water withdrawals and surface energy and water fluxes. Results show that this new scheme performs better in simulating irrigation water withdrawals in most countries. Results of one‐dimensional simulations show that different irrigation methods have small but varying impacts on surface fluxes. At the global and regional scale, incorporating more realistic irrigation methods enlarges the effects of irrigation on water and energy variables. We therefore conclude that improving the realism of irrigation in models can help us to improve our understanding of how irrigation affects climate through altered water and energy fluxes. Key Points: A newly‐developed irrigation module considering different irrigation methods is implemented in Community Land ModelThe new irrigation scheme shows a better performance of simulating irrigation water withdrawal against the original moduleDifferent irrigation methods have different effects on water cycle and energy budgets, changing regional irrigation‐induced impacts [ABSTRACT FROM AUTHOR]