Comprehensive Assessment of Water Resource Carrying Capacity Based on Improved Matter–Element Extension Modeling

The evaluation of water resource carrying capacity (WRCC) is crucial for guiding regional water management. This study established a WRCC evaluation index system and standards for the middle and lower Yangtze River, covering four subsystems: water resources, and social, economic, and ecological dimensions. The study improved the matter–element extension model by introducing triangular fuzzy numbers. The enhanced model was then used to assess the WRCC of seven provinces in the middle and lower Yangtze (2015–2023). Furthermore, GIS was used to examine the spatiotemporal variations and driving factors of WRCC. The main conclusions are as follows: (1) from 2015 to 2023, the evaluated level of WRCC in the Yangtze River’s middle and lower reaches remained stable and improved overall. Among them, the WRCC of Shanghai rose most significantly, from level III to level I. Zhejiang’s WRCC remained stable at level II, while Hubei and Hunan remained stable at level III, but with a trend toward improvement. Jiangsu’s WRCC fluctuated significantly. (2) The evaluation values of the subsystems in each region show a certain level of volatility. The water resource subsystem remained relatively stable in most regions, the social subsystem showed some variability, and both the economic and ecological subsystems developed well, showing positive effects in economic development and ecological protection in various regions. (3) The water resource subsystem had the greatest influence on WRCC. Per capita water resources, the urbanization rate, the greening coverage rate in built-up areas, and per capita GDP have the most significant impact on the WRCC in the Yangtze River’s middle and lower reaches.