Spatio-temporal pattern and prediction of agricultural blue and green water footprint scarcity index in the lower reaches of the Yellow River Basin

Agricultural production is the largest water-using sector in the lower reaches of the Yellow River Basin (YRB). However, water shortages seriously restrict the high-quality development of the local economy and society. This study assessed the temporal and spatial patterns of the agricultural blue (WFblue) and green (WFgreen) water footprints of six crops in the lower reaches of the YRB based on Penman-Monteith method, established composite agriculture water (AWS), agricultural blue water (AWSblue), and agricultural green water (AWSgreen) footprint scarcity indexes to evaluate the agricultural security level of blue and green water resources in the lower reaches of the YRB. And the Spatial pattern of blue and green water footprint scarcity indexes for 2030 was predicted. The results showed that in 2020, the total WFgreen of six crops in the lower reaches of the YRB was 58.45 billion m³, of which the WFgreen of maize accounted for 47.53%, followed by winter wheat (32.01%). The total agricultural blue water footprint (WFblue) of six crops was 46.12 billion m³, and the winter wheat had the highest WFblue (32.00 billion m³) and accounted for 69.39%, followed by maize (8.19 billion m³, 17.76%). The total blue water evapotranspiration (ETblue) of crops in the northwestern lower reaches of the YRB was generally higher than that in the southeastern region. However, the ETgreen spatial layout showed the opposite trend. From 2010 to 2020, the WS decreased overall, and the proportion of regions with a WS greater than 1 decreased from 73.5% in 2010 to 61.76% in 2020. By 2030, AWS in the lower reaches of the YRB will further intensify. Compared to 2020, in 76.47% of cities the AWS showed an increasing trend, 58.82% of cities will be in extreme insecurity, and the proportion of areas with the AWSblue in an insecure state will be 35.29%, green water resources are relatively abundant and will be in a safe and relatively safe state in 2030. Although the AWSgreen of 91.18% of cities in 2030 showed an increasing trend compared to that in 2020. AWSgreen showed that the lower reaches of the YRB are still in a safe and relatively safe state. However, rational development and utilization of surface water and groundwater resources should be strengthened. To ensure the rational supply and sustainable use of blue water resources, the lower reaches of the YRB should strengthen the construction of water conservancy projects through water diversion, transfer, and storage.