Climate warming drives thermal shocks and accelerated freshwater habitat fragmentation

Abstract

Climate change is exposing freshwater fish to warmer temperatures, causing widespread range contraction and population declines. However, how climate-driven disruptions will affect freshwater fish persistence under future thermal extremes remains poorly understood. Here, using weekly water temperature data (1976-2099), we assess the vulnerability of 9,809 freshwater species to short- and long-term thermal extremes and show that gradual warming can trigger abrupt thermal exposure. Tropical regions experience a high proportion of species at risk, whereas non-tropical regions face severe thermal extremes. We introduce the concept of thermal fragmentation exposure to understand how heterogeneous warming fragments freshwater habitat, thereby amplifying local extinction risks. Around 63% of riverine fish will experience more persistent thermal barriers under a high-emissions scenario, with thermal fragmentation accelerating over time. These findings underscore the urgent need for targeted conservation strategies to safeguard freshwater fish biodiversity.