Compound dry-hot events intensify widespread lake deoxygenation in China

Lake deoxygenation, driven by climatic warming and anthropogenic influences, poses a significant threat to aquatic ecosystems. Yet, the effects of compound dry-hot extremes (CDHEs) on deoxygenation in lakes remains unclear. This study investigates the role of CDHEs on dissolved oxygen (DO) dynamics in Chinese lakes from 2000 to 2020, using machine learning models and a multi-source dataset. We reconstruct monthly DO concentrations for 11,789 lakes and identify CDHEs based on historical climate data. We find widespread and continuous deoxygenation across lakes in China, where 52.2% of lakes showing significant declines (mean rate: -0.12 mg/L/decade), with the most pronounced reductions in regions such as the Tibetan Plateau and Yungui Plateau. CDHEs increasingly intensified, especially in arid or semi-arid regions, with their duration and severity as key drivers. CDHEs contributed to intensified deoxygenation, especially in smaller and high-altitude lakes. By the end of century, it is projected that the nationwide lake DO decline by 0.76–1.25 mg/L under SSP2-4.5 and SSP5-8.5 scenarios, with Tibetan Plateau lakes losing over 1.2 mg/L in high-emission scenarios. The compounded impacts of rising temperatures and extended dry conditions are expected to accelerate DO loss, posing risks to lake biodiversity and ecosystem services. This study underscores the urgency of tailored lake management strategies in regions vulnerable to CDHEs, and emphasizes the need to integrate climate extremes into future water quality planning to safeguard freshwater resources.