Compound hot-dry 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.

由气候变暖与人为活动共同驱动的湖泊缺氧现象，对水生生态系统构成严重威胁。然而，复合干热极端事件（compound dry-hot extremes, CDHEs）对湖泊缺氧过程的影响仍有待厘清。本研究依托机器学习模型与多源数据集，探究了2000至2020年复合干热极端事件对中国湖泊溶解氧（dissolved oxygen, DO）动态的调控作用。本研究重构了11789个湖泊的月溶解氧浓度序列，并基于历史气候资料识别出复合干热极端事件。研究发现，中国湖泊普遍出现且持续加剧的缺氧现象：52.2%的湖泊溶解氧浓度呈显著下降趋势（平均速率为-0.12 mg/L/十年），其中青藏高原与云贵高原区域的降幅最为显著。复合干热极端事件的发生频次与强度持续升高，尤其在干旱与半干旱区域，其持续时长与严重程度为关键驱动因子。复合干热极端事件会加剧湖泊缺氧过程，在小型湖泊与高海拔湖泊中表现尤为突出。至本世纪末，在SSP2-4.5与SSP5-8.5情景下，全国湖泊溶解氧浓度预计将下降0.76~1.25 mg/L；在高排放情景下，青藏高原湖泊的溶解氧浓度降幅将超过1.2 mg/L。气温升高与干旱时长延长的复合效应，预计将加速溶解氧流失，对湖泊生物多样性与生态系统服务构成风险。本研究强调，在受复合干热极端事件影响的脆弱区域制定针对性湖泊管理策略具有紧迫性；同时指出，需将气候极端事件纳入未来水质规划体系，以切实保护淡水资源。