Revealing the inherent relationship between urban water systems and carbon emissions has important theoretical and practical significance for promoting “water conservation and carbon reduction” in cities. This study utilizes the 2021 social water cycle statistical data of Yiwu City to quantify the carbon emissions of urban water systems. It analyzes the “water–carbon” related characteristics and carbon emission intensities under different water sources and stages and explores the carbon reduction potential of urban water systems under different scenarios. The results show that the operational phase is the main contributor to the carbon emissions of the urban water system in the research area, accounting for approximately 86% of the total carbon emissions. Over the entire process, the carbon emissions from the water supply and drainage stages are the largest, accounting for 39% and 31% of the total carbon emissions, respectively. In terms of carbon emission intensity, the carbon footprint of the water cycling process using reclaimed water as the water source is higher than that of high-quality water and conventional water sources. This is primarily due to the significantly higher carbon emission intensity in the reclaimed water phase compared with the other phases. In terms of influencing factors, the differences in the “water–carbon” correlation characteristics of different links in the water system in the research area are mainly affected by changes in urban water consumption, water treatment methods and processes, and other related factors. For the coordinated development of “water conservation and carbon reduction” in urban areas, future efforts should focus on improving the reuse rate of reclaimed water in urban life and industry, reducing the leakage rate of water distribution networks, and enhancing water treatment processes. These measures aim to increase water efficiency in urban water systems and reduce carbon emissions.

Poyang Lake, the largest freshwater lake in China, is an important regional water resource and a landmark ecosystem. In recent years, it has experienced a period of prolonged drought. Using appropriate drought indices to describe the drought characteristics of the Poyang Lake Basin (PLB) is of great practical significance in the face of severe drought situations. This article explores the applicability of four drought indices (including the precipitation anomaly index (PJP), standardized precipitation index (SPI), China Z-index (CPZI), and standardized precipitation evapotranspiration index (SPEI)) based on historical facts. A systematic study was conducted on the spatiotemporal evolution patterns of meteorological drought in the PLB based on the optimal drought index. The results show that SPI is more suitable for the description of drought characteristics in the PLB. Meteorological droughts occur frequently in the summer and autumn in the PLB, with the frequency of mild drought being 17.29% and 16.88%, respectively. The impact range of severe drought or worse reached 22.19% and 28.33% of the entire basin, respectively. The probability of drought occurrence in the PLB shows an increasing trend in spring, while in most areas, it shows a decreasing trend in other seasons, with only a slight increase in the upper reaches of the Ganjiang River (UGR). One of the important factors influencing drought in the PLB is atmospheric circulation. The abnormal variation of the Western Pacific Subtropical High was one of the key factors contributing to the severe drought in the PLB in 2022. This study is based on a long-term series of meteorological data and selects the drought index for the PLB. It describes the spatiotemporal distribution characteristics and evolution patterns of drought and investigates the developmental path and influencing factors of drought in typical years. This study provides a reliable scientific basis for similar watershed water resource management.

The treatment of rural domestic sewage is essential for the comprehensive improvement of the rural environment. At present, the rate of resource utilization of rural domestic sewage is generally low in China, which fits with the actual situation of rural areas, and low cost is becoming the requirement for the development of rural sewage treatment technologies. Adopting a tailored approach based on local conditions for utilising sewage resources is the best option for rural sewage management. Therefore, it is very important and urgent to explore and evaluate the mode of rural domestic sewage resource utilisation. This paper analyzes the current status of sewage resource utilization in rural China. It researches and explores sewage treatment technology and resource utilization models based on 10 study sites in Yongkang City, Zhejiang Province. At the same time, this article evaluates pollution control effectiveness and environmental emission reduction benefits. The results show that the effluent quality of the treated wastewater by the skid-mounted resource utilization equipment met the reuse requirements and maintained stable water quality. The project can save 251,900 tons of high-quality water resources annually, reducing COD by 78.51 tons, reducing NH₃-N and TP by 5.62 tons and 0.39 tons, respectively, and reducing carbon emissions by more than 134 tons. The project has achieved significant comprehensive benefits in water conservation, pollution reduction, and carbon reduction.

China has been facing a contradiction between its water supply and demand for a long time, and it is urgent that it builds a “water-saving society”. Previous research on water pricing mainly focused on the policy level, only considering the supply and demand sides and ignoring the participation of local governments. Due to the inconsistent approval mechanisms, different times of cost formation, and lack of a scientific pricing relationship between multiple water sources and multiple users, with the current water pricing in China, it is difficult to solve the complex problem of water resource allocation. This study aimed to promote the qualitative supply of water and the reuse of reclaimed water, achieve a high-quality and low-cost water supply, and explore the role of water-pricing mechanisms in the regulation of multi-source water supply configurations. The mechanism of regulation is constructed for the complex, multi-source, multi-user water resource system, and a three-party game model is established among local governments, water supply enterprises, and water users. A reasonable pricing system with a rational price relationship is obtained, and Pinghu City in Zhejiang Province is taken as the research area. The prices of the external water supply to residential users, non-resident users, and special users are 4.48 CNY/m³, 6.28 CNY/m³, and 7.12 CNY/m³. The external supply prices for resident users, non-resident users, and special users are 3.81 CNY/m³, 5.25 CNY/m³, and 6.05 CNY/m³. The external supply price for non-resident users is 2.62 CNY/m³ for reclaimed water. The results of the study showed that when the government’s contribution did not exceed the amount that it would have been without the inclusion of recycled water and the annual payment of water users did not exceed their ability to pay, the income of water suppliers increased by 69%. The three balanced objectives of rational water resource configuration by the local government, reasonable profit for the water supply enterprise, and reasonable payment by water users have been achieved. This study provides theoretical and methodological support for the implementation of water pricing for multi-source and multi-user water supplies in water-scarce areas.

In this study, the theory of equilibrium water prices is constructed and practiced based on previous research on cooperative game technology and the water price system. The equilibrium water price utilized in this study emphasized solving the unbalanced and unsustainable water supply system, including the reclaimed water resources and the current water price used in numerous Chinese cities. Safety, affordability, and sustainability become the key factors of the equilibrium water price system, which is operated and analyzed in a typical city in southeastern China. The cooperative game model of equilibrium water price is solved by game technology, considering various factors such as the price strategy, the water supply quantity, and the local water demand. The practical application shows that the theoretical system can effectively solve the problem of water price formation mechanisms after the unified allocation of different types of water resources. It not only enhances the enthusiasm and initiative of the public in the utilization of reclaimed water, but also plays an important role in the rational utilization of multiple water resources for different purposes by introducing a reasonable water price ratio and local water resource allocation.

In recent years, flash droughts with a rapid onset and strong intensity have attracted extensive attention due to their impact on agriculture and ecosystems. However, there is still no feasible method for flash drought forecasting and early warning. This paper employs the thresholds of several meteorological variables to identify flash droughts in Zhejiang Province, China, and build a probabilistic flash drought forecasting model through numeric weather forecast (NWF) and the generalized Bayesian model (GBM). The results show that the northern part of Zhejiang Province has the highest risk of flash drought. The NWF is a viable method to provide future information for flash drought forecasting and early warning, but its forecasting accuracy tends to decline with the increase in the lead time and is very limited when the lead time is over 5 days, especially for the precipitation forecast. Due to the low performance of the NWF, the flash drought forecast based on the raw NWF may be unreliable when the lead time is over 5 days. To solve this problem, probabilistic forecasting based on GBM is employed to quantify the uncertainty in the NWF and is tested through an example analysis. In the example analysis, it was found that the probability of a flash drought exceeds 30% from the probabilistic forecasting when the lead time is 12 days, while the deterministic forecasting via the raw NWF cannot identify a flash drought when the lead time is over 5 days. In conclusion, probabilistic forecasting can identify a potential flash drought earlier and can be used to evaluate the risk of a flash drought, which is conducive for the early warning of flash droughts and the development of response measures.