In order to assess the water resources carrying capacity (WRCC) of Hubei province, an improved catastrophe progression method based on M-K test and correlation analysis was established. This model includes evaluation, abrupt change test and correlation analysis. It can make a comprehensive assessment of water resource carrying capacity in a certain area. The evaluation results of this model are clear and can effectively avoid the effects of subjective weight and, in addition, it can also streamline the index system. We applied the model to study the WRCC of Hubei province from 2005 to 2016, considering the supply and demand of water resources, ecological environment, economy and society. The results showed that the WRCC of Hubei province is at the ‘weak’ level, presenting a certain development and utilization potential, but it must be strictly controlled and moderately developed. The WRCC of Hubei province is improving, but must be adjusted by water conservation facilities and long-term management policies to prevent the foreseeable deterioration. Water supply and demand systems and ecological environment systems were found to be the driving factors of WRCC through correlation analysis. This approach gives the decision-makers suggestions about water resource sustainable utilization.

Due to the importance and complexity of water resources regulations in the pond irrigation systems of the Jiang-Huai hilly regions, a water allocation simulation model for pond irrigation districts based on system simulation theory was developed in this study. To maximize agricultural irrigation benefits while guaranteeing rural domestic water demand, an optimal water resources regulation model for pond irrigation districts and a simulation-based optimal water resources regulation technology system for the pond irrigation system were developed. Using this system, it was determined that the suitable pond coverage rate (pond capacity per unit area) was 2.92 × 10⁵ m³/km². Suitable water supply and operational rules for adjusting crop planting structure were also developed the water-saving irrigation method and irrigation system. To guarantee rural domestic water demand, the multi-year average total irrigation water deficit of the study area decreased by 4.66 × 10⁴ m³/km²; the average multi-year water deficit ratio decreased from 20.40% to 1.18%; the average multi-year irrigation benefit increased by 1.11 × 10⁵ RMB (16,128$)/km²; and the average multi-year revenue increased by 6.69%. Both the economic and social benefits were significant. The results of this study provide a theoretical basis and technological support for comprehensive pone governance in the Jiang-Huai hilly regions and promote the establishment of a water allocation scheme and irrigation system for pond irrigation districts, which have practical significance and important application value.

Stable isotopes of lake waters are widely used to identify the relative importance of hydrological processes on the lake water balance across the ungauged landscape via the coupled-isotope tracer model. The isotopic compositions of twenty shallow freshwater lakes across the mid-lower reaches of Yangtze floodplain (MLY) were investigated in January and May of 2018. The lake-specific input water (δ_I) and evaporation-to-inflow (E/I) ratios were estimated to explore the specific lake hydrology across the MLY. Results showed that distinct isotopic enrichment trends in May compared with those in January, which was indicative of stronger evaporation in May. The δ¹⁸O_I values of specific lakes exhibited large variability across the MLY, which may be related to the watershed properties, such as watershed area and elevation, and rainfall. The estimated E/I ratios of lakes across the MLY were below 1, which suggested that these lakes (code 1–15) are flood-dominated in the middle reaches of Yangtze River where lakes are susceptible to Three Gorges Dams regulations. By contrast, the relatively lower variability of lake E/I ratios were observed from the Yangtze River Delta (code 17–20) because these lakes with developed river network systems are highly exchanged by artificial regulation. Our investigation of lake types and corresponding isotopic evolution patterns are likely typical of other floodplain landscapes and their identification could be used to better predict hydrological responses to ongoing climate change and artificial regulations by dams.