On the Increased Precipitation Recycling by Large-Scale Irrigation over the Haihe Plain

Irrigation not only plays an important role in global food security, but it also affects aspects of the regional climate, including precipitation. In this study, we proposed a simple and convenient method to quantify the contribution of large-scale irrigation to precipitation by distinguishing the amount of evaporation generated by irrigation from local evaporation based on the precipitation recycling method. A case study was presented to show the increased precipitation recycling ratio and the contribution of irrigation to precipitation during the main irrigation period in the Haihe Plain from 1961 to 2016. We found that the average precipitation recycling rates in the Haihe Plain are 8.32%, 9.74%, and 10.36% in April, May, and June, respectively. The contribution rates of irrigation to precipitation in the Haihe Plain are 3.76%, 5.12%, and 2.29% in April, May, and June, respectively. The total contribution of irrigation to precipitation during the main irrigation period is 3.77 mm; the respective contributions in April, May, and June are 0.72, 1.70, and 1.35 mm. The contribution of irrigation to local precipitation is relatively small as the inflow of atmospheric moisture during the irrigation period is still the main factor affecting local precipitation. Nevertheless, this part of the precipitation during the irrigation period alleviates the water shortage in the Haihe Plain to some extent.