Optimization of crop irrigation strategies using modeling in Haihe Plain under climate change

The Haihe Plain has made a great contribution to national food security in the world. The stable production of grain crops can rely mainly on groundwater extraction for irrigation, thus leading to the overexploitation of groundwater in the region. Additionally, the ever-increasing global climate can also threaten water resources and food production. Deficit irrigation can be expected to serve as a water-saving technique under current climate conditions, in order to significantly improve water use efficiency. However, much more irrigation water can be required to fully meet the normal growth needs of crops, particularly with the general increase in temperatures. It is a high demand to quantitatively assess the changes in crop water use and crop yields under future climate scenarios. Adaption irrigation can be used to explore climate change for the sustainable development of agriculture in the major food-producing regions with scarce water resources. In this study, an enhanced SWAT model was combined with the multiple general circulation models (GCMs) from CMIP6, in order to simulate the climate and irrigation scenarios. The improved SWAT model included some enhancements in two aspects: one was an automatic irrigation using MAD (management allowed depletion), and another was the dynamic CO₂ input. Additionally, three shared socioeconomic pathways (SSPs) were selected, namely SSP1-2.6, SSP2-4.5, and SSP5-8.5. Firstly, the enhanced SWAT model and multiple GCMs were applied to simulate the actual evapotranspiration (ET_a), irrigation, net groundwater use (NGU), and crop yields under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios in the future period (2041-2070). Furthermore, the appropriate irrigation strategies were explored for the future scenarios of climate change. The results showed that: 1) Annual ET_a increased by 5.5%, whereas, the annual irrigation and NGU decreased by 5.9% and 25.8%, respectively, in the future period, compared with the historical period (1971-2000); Under the SSP5-8.5 emission, the annual ETa increased the least, whereas, the annual irrigation and NGU decreased the most. 2) The winter wheat and summer maize yield increased by 14.3% and 6.5%, respectively; There was the declined yield of summer maize under the greenhouse gas emission scenario. 3) In the future climate, the appropriate schedule of irrigation was achieved in the jointing stage of winter wheat with the rainfed summer maize, indicating the maximum groundwater recovery. In food security, it is recommended irrigation during the jointing and filling stages of winter wheat with the rainfed summer maize. 4) In terms of grain production and groundwater resource recovery, the irrigation strategies can be recommended to vary among different zones. In Baoding, Shijiazhuang, Xingtai, and Hengshui zones, irrigation can be applied during both the jointing and filling stages. In the Handan zone, irrigation can be recommended only during the jointing stage, while in the Langfang zone, it should be during the filling stage. Finally, irrigation can be advised before winter and during the filling stage of winter wheat in the Cangzhou zone. The findings can provide for the rational planning of regional agricultural water resources and sustainable food production.