Decoding the nexus of surface water and groundwater in Northwestern China: Insights from long-term irrigation activities and numerical modeling

Abstract

Accurately predicting surface water (SW)-groundwater (GW) exchanges is crucial for effective salinization control in arid and semi-arid agricultural areas. In this study, we developed a coupled SW-GW flow model for Qingtongxia Irrigation District (QID), which is the fourth-largest irrigation area in China with over 2,000 years of irrigation history. The model simulated canal diversions, GW level dynamics, and SW-GW fluxes among rivers, canals, ditches, and irrigation zones over the past 23 years. From 2000 to 2022, groundwater levels declined by −0.18, −0.45, and −0.04 m/yr across three major administrative zones, showing significant seasonal fluctuations. Furthermore, irrigation has a substantial impact on temporal changes in groundwater components and major fluxes. The interaction between GW and the Yellow River (YR) displayed highly heterogeneous temporal and spatial characteristics across the regions but showed a noticeable decreasing trend in the total yearly groundwater discharge to the YR, with a reduction of 8.4 × 10⁵ m³/yr. The Tanglai canal recorded the highest yearly diversion at 11.02 × 10⁸ m³, followed by the Huinong, Xigan, Hanyan, and Headwork canals. The average GW discharge to ditches accounted for over 25 % of the total SW-GW drainage to the YR from 2000 to 2022. Multi-scenario predictions indicate that reducing water diversions to 25 % of current levels over the next decade could lower average groundwater levels by up to 0.95 m, with the steepest declines in the Xigan and upper Huinong canals. This study provides a quantitative method for examining SW-GW interaction patterns, supporting sustainable groundwater management in salinization control.