Changes in the area and water consumption of winter wheat under limiting groundwater exploitation in the Hebei Plain

The shortage of water resources and long-term high-intensity agricultural production have further intensified the water crisis in the Hebei Plain, an important grain production region. The local government has implemented a limiting groundwater exploitation policy since 2014 to alleviate the contradiction between water and food security. Measures such as seasonal fallow, rain-fed agriculture, and water-saving agriculture have been implemented in terms of agricultural production. To explore the impact of this policy on agricultural water use, the changes in planting area and water consumption characteristics for winter wheat in the Hebei Plain during the years before and after the implementation of the policy were analyzed. Based on the spectral variation characteristics of winter wheat, distribution maps of winter wheat from 2009 to 2019 were retrieved using MODIS NDVI data. Combined with the TSEB (two-source energy balance model) evapotranspiration dataset and agricultural production statistics, the water consumption characteristics of winter wheat before and after the policy were compared, and the driving factors for these changes were investigated. Our study found that the planting area of winter wheat in the Hebei Plain increased by 183 700 hm² from 2009 to 2019. Five years after the implementation of the policy, the total planting area of winter wheat increased by 104 000 hm², mainly concentrated in the east; while it decreased in the west. In terms of water consumption of winter wheat, the level of evapotranspiration and total water consumption of winter wheat increased by 32.58 mm and 1.09 billion m³ compared with those before the policy. Compared with the winter wheat field, seasonal fallow land reduced evapotranspiration by 73 mm in addition to not pumping groundwater for irrigation. During the study period, the annual average water use efficiency of winter wheat was 1.67 kg∙m⁻³. After the implementation of the policy, the water use efficiency of winter wheat in 2/3 regions of the Hebei Plain had been increasing annually. The main reason for the decrease in winter wheat area was the change in planting structure caused by farmers’ pursuit of higher agricultural economic benefits and urbanization. The support policy from the government to ensure food security and improve the mechanization degree of winter wheat planting promoted an increase in its planting area. The fragmentation of farmland, the unstable transfer of farmland management rights, and the lack of initiative and pressure to save water led to the low popularity of water-saving irrigation for winter wheat. Facing the contradiction between water shortage and food production, it is still necessary to strengthen water-saving agriculture and significantly reduce the water consumption of evapotranspiration to alleviate the contradiction.