Unraveling the Dynamics of Irrigation Water Use in North China: Patterns and Influencing Factors over the Early 21st Century

Abstract: The Haihe River Basin (HRB) in North China, characterized by a warm and humid environment, has witnessed a transformation in agricultural water supply patterns, influenced by both climatic changes and groundwater withdrawal restrictions. Despite the impact of these changes on irrigation activities, comprehensive monitoring of irrigation water use (IWU) is lacking, with existing studies predominantly focusing on the influence of irrigation on climatic factors and crop yield. Few studies address the effects of warming and humidification on IWU, and the impacts of human activities associated with groundwater withdrawal restrictions remain underexplored. This study introduces a novel IWU estimation method and examines changes in IWU across the HRB from 2003 to 2022. By quantifying the contribution of irrigation water to different destinations (evapotranspiration consumption, root zone soil water increment, and groundwater recharge), key drivers of IWU change are revealed. The accuracy of IWU estimates proves high, effectively reflecting spatiotemporal changes in irrigation activities. Results demonstrate declining trends in irrigation water intensity and the proportion of irrigation area, with changes in irrigation water intensity dominating overall IWU variations. Shifts in cropping patterns, such as the southward relocation of winter wheat planting and increased drought-tolerant corn cultivation after 2012, explain regional disparities in IWU values. The proportion of irrigation water consumed by evapotranspiration and root zone water increment was 0.58 and 0.39, respectively. Utilizing the least partial square regression method, cropping pattern changes emerge as common drivers for irrigation water intensity in the three main administrative regions (Hebei Province, Beijing, and Tianjin). Irrigation management factors prevail in Hebei Province and Tianjin, while climate factors, particularly in Beijing, play a significant role. Increased water supply and a wetter climate over the past 20 years contributed to decreased irrigation water intensity, particularly in Hebei Province and Beijing. Additionally, optimization of cropping patterns and the adoption of water-saving agriculture further reduced irrigation water intensity in the HRB. This study provides a thorough understanding of the evolving irrigation landscape and associated mechanisms in the HRB over the past two decades. The findings offer insights into combatting climate change and groundwater depletion, informing strategies for sustainable water resource management. Keywords: Irrigation water use; drivers; cropping patterns; North China Plain