Climatic effects of irrigation over the Huang-Huai-Hai Plain in China simulated by the weather research and forecasting model

The climatic effects of irrigation over the Huang-Huai-Hai Plain (3HP) in China are investigated by using the weather research and forecasting model coupled with an operational-like irrigation scheme. Multiple numerical experiments with irrigation off/on during spring, summer, and both spring and summer are conducted. Results show that the warm bias in surface temperature and dry bias in soil moisture are reduced over the 3HP region during the growing seasons by considering the irrigation in the model. The air temperature during nongrowing seasons is also affected by irrigation because of the persistent effects of soil moisture on land-air energy exchanges and ground heat storage. Irrigation can induce significant cooling in the planetary boundary layer (PBL) during the growing seasons and lead to a relatively wet PBL with increased low-level clouds during spring but a relatively dry condition in summer. Further analyses indicate that irrigation leads to increased summer precipitation over the Yangtze River Basin and decreased summer precipitation in southern and northern China. These responses are associated with the changes in the large-scale circulation induced by irrigation. Irrigation tends to cool the atmosphere and forces a possible southward shift of the upper level jet that can further affect the precipitation distribution. Our model results suggest that in addition to local-scale processes, large-scale impacts should also be considered when studying the precipitation response to irrigation over East Asia.