Non-linear relationships between air temperature and river water quality revealed by a panel dataset of 276 Chinese cities

The impact of air temperature on water quality is typically mediated through its influence on water temperature, evaporation, and physicochemical processes. A comprehensive understanding of air temperature’s effects on river pollution is imperative, particularly given rising water scarcity and the increasingly frequent extreme temperature events in China. Here, we employ the fixed effects model to estimate the effects of air temperature on river water quality and elucidate inverted U-shaped responses through 276 Chinese cities from 2014-2020. Our results demonstrate that both single-day high temperatures (>37 °C) and heatwaves (four consecutive days above 35 °C) significantly increase river permanganate index (CODMn) concentration, worsening organic pollution. Additionally, these extreme temperature events contribute over 67% and 10% to quality-based water scarcity, presenting considerable challenges to water withdrawals in cities. Our findings necessitate incorporating temperature-related considerations into contemporary and prospective river governance, contributing to the development of targeted adaptation strategies and enhancing water resource management. Both single-day high temperatures and heatwaves significantly increase river permanganate index, worsening organic compound pollution, and contribute to quality-based water scarcity, according to an analysis of air temperature on river water quality in 276 Chinese cities from 2014- 2020.