Assessing economic and hydrological effects of water-saving irrigation using a coupled SWAT–MODFLOW–AquaCrop model

Water-saving measures have been adopted worldwide in response to pressures posed by socioeconomic development and climate change. However, assessing the comprehensive economic and hydrological effects of water-saving measures at the irrigation district scale remains challenging because of complicated interactions between large-scale hydrological dynamics and small-scale crop growth processes. To address this challenge, this study presents a coupled hydrological–crop model at the irrigation district scale that integrates the Soil and Water Assessment Tool (SWAT), MODFLOW, and AquaCrop to simulate surface water, groundwater, and crop growth processes. Validation tests demonstrated high accuracy and adaptability of the model. Simulations were conducted in Hedong Irrigation District, Ningxia, under different water-saving scenarios. The results showed that 50 % deficit irrigation reduced rice, maize, and wheat yields by 1.1 %, 17.3 %, and 12.3 %, respectively. Application of additional irrigation measures could enhance crop yields; however, cost–benefit analysis revealed that sprinkler irrigation, land leveling, and drip irrigation were the most cost-effective measured for water-saving percentages < 59 %, from 59–64 %, and > 64 %, respectively. Regarding hydrological effects, planting structure adjustment excelled in mitigating groundwater decline while maintaining high water yield. Other irrigation measures reduced groundwater storage by an average of 3.4 % and water yield by an average of 6.5 % for every 10 % increase in water-saving, below the 70% water-saving threshold. Beyond this threshold, groundwater decline accelerated significantly. These findings provide valuable insights regarding selection of water-saving measures considering both economic and hydrological concerns.