Water resources scarcity has threatened the coordinative development of demographics, society and economy. As a typical rapidly urbanizing area and an emerging megacity in China, Chengdu is confronting the pressure of inadequate water supply. The present study divides the macroeconomic factors that affect the water resource supply and demand balance into six major subsystems: water resources supply, water demand, water drainage, population, ecological environment and economy. The combining variable interaction description and predictive simulation models are applied to simulate the water supply and demand ratio (S:D) from 2005 to 2035. Further, this study designs different development scenarios to simulate the change of S:D ratios by altering the parameter values of driving factors. The results show that: (1) the S:D ratio will decline if the current development scenario continues, implying the serious water resources shortage and the severe water supply-demand conflict in Chengdu; (2) socio-economic water demand and wastewater/rainwater reuse are the key driving parameters of S:D ratio, especially the water consumption per ten thousand yuan of industrial value-added; (3) the S:D ratio will increase from 0.92 in the current baseline scenario to 1.06 in the integrated optimization scenario in 2025, and the long-term planning brings 2035 from 0.71 to 1.03, with the proportion of unconventional water supply rise to 38% and 61%, respectively. This study can provide a decision-making tool for policy-makers to explore plausible policy scenarios necessary for bridging the gap between the water supply and demand in megacities.

The hydrological processes play an important role in stimulating fish spawning behavior. Changes in the natural hydrological processes will alter the populations and distribution of fish, which may have a negative impact on the native aquatic organisms. The aim of this study is to identify the alteration of the water rising process during the fish spawning period and to construct an ecological flow optimization model to restore the water rising conditions for fish reproduction. The Mann–Kendall test and the sliding t-test were used to detect the mutation year of the mean daily flow data sets in the fish spawning period in each monitoring year. Then the data sets can be divided into pre-altered and post-altered periods. The water rising process was characterized by the water rising processes count, the duration, the daily flow increase rate, the date of the water rising process, and the initial water rising flow. The changes in hydrological processes in the middle reaches of the Yangtze River were investigated by comparing the post-altered and pre-altered characteristic parameters. Furthermore, we integrated the statistical values of the five characteristic parameters in pre-altered into an ecological flow optimization model to simulate the natural water rising processes for the spawning of the Four Major Chinese Carps (FMCC) and Chinese Sturgeon (CS). The analysis showed that after the hydrological mutation year, the duration and the initial water rising flow in the FMCC spawning season were increased, with hydrological alteration degrees of 63.10% and 70.16%, respectively; however, the daily flow increase rate was significantly decreased, with hydrological alteration of 86.50%. During the CS spawning season, the water rising processes count and the initial water rising flow were dramatically altered parameters, with hydrological alteration degrees of 50.86% and 83.27%, respectively. The former parameter increased, but the latter decreased significantly in the post-altered period. To induce the spawning activity of FMCC and CS, appropriate ecological flows and hydrological parameters were proposed. These results showed that during the spawning seasons of FMCC and CS, the hydrological processes of the middle reaches of the Yangtze River changed significantly. Therefore, ecological flow must be ensured through ecological operation of upstream reservoirs to provide suitable spawning conditions in target fish spawning grounds.

Introduction: The rapid urbanization and industrialization, accompanied by high-intensive population, energy consumption and transportation activities, have made air pollution an intractable environmental issue in China, especially in most megacities. This study identified the primary air pollutant (PAP) of a Chinese megacity—Chengdu, and analyzed the spatiotemporal changes of PAP concentrations.Methods: The LMDI and GWR models were employed to probe the spatiotemporal drivers of air pollution in Chengdu.Results and discussion: The pollutants of PM₁₀, PM_2.5, O₃, and NO₂ were identified as the PAPs of Chengdu. During the period of 2015∼2021, the concentrations of the four PAPs showed decreasing trends from 90.5 μg/m³, 56.7 μg/m³, 90.0 μg/m³, and 34.0 μg/m³ to 54.2 μg/m³, 33.7 μg/m³, 87.0 μg/m³, and 29.1 μg/m³, respectively. In 2021, the spatial distributions of the PAP concentrations were characterized by being higher in the central areas. The temporal changes in the PAP concentrations were conjointly influenced by population, per capita GDP, urban built-up area per unit GDP, greenery coverage rate, and pollution load intensity of greenery, with positive effects of population, per capita GDP, and greenery coverage rate and negative effects of urban built-up area per unit GDP and pollution load intensity of greenery. In spatial, the geographical factors (including temperature, precipitation, wind speed, cultivated area and vegetation coverage rate) and socio-economic factors both affected the PAP concentrations. However, there were spatial heterogeneities in the driving forces between different districts of Chengdu, due to the disparities in both the socio-economic and geographical context in different areas. This study also highlights possible policy implications for alleviating urban air pollution, and provides scientific insights for building the clean and livable urban environments for cities.

Scaling commonly occurs at pipe wall during landfill leachate collection and transportation, which may give rise to pipe rupture, thus posing harm to public health and environment. To prevent scaling, this study prepared a low surface energy nanocomposite by incorporating silicone-acrylate polymer and hydrophobically modified nano-SiO₂ into the high-density polyethylene (HDPE) substrate. Through the characterization of contact angle, scanning electron microscopy and thermogravimetry, the results showed that the prepared composite has low wettability and surface free energy, excellent thermal stability and acid-base resistance. In addition, the prepared composite was compared with the commercial HDPE pipe material regarding their performance on anti-scaling by using an immersion test that places their samples into a simulated landfill leachate. It was apparent that the prepared composite shows better scaling resistance. The study further expects to provide insight into pipe materials design and manufacture, thus to improve landfill leachate collection and transportation.