Hotspots and Blind Spots in Global River Temperature Science: Implications for Evidencing Climate Adaptation

Rising river water temperatures ( T w ) pose threats to freshwater ecosystems, water quality and water‐dependent sectors. Yet the evidence needed to support adaptation to higher T w remains uneven. This systematic review synthesises 529 studies published between 1990 and 2025 to assess how T w science has developed and where it can most effectively support adaptation. We show that the field has expanded substantially, but remains concentrated in high‐income, temperate regions, with the United States, Canada and the United Kingdom accounting for approximately 70% of all studies. Much of the research is local or catchment‐scale, based on daily data, and oriented towards empirical modelling, ecological responses and broad thermal‐risk screening. These studies provide a solid foundation for understanding river thermal regimes, particularly in data‐rich temperate systems, but their geographic bias limits transferability to under‐represented regions, river types, sectors and decision contexts. The current evidence base is strongest for ecological and cooling‐oriented adaptation, but weaker where decisions apply to event‐scale risk assessment, water‐quality thresholds, operational triggers, or integration with urban, agricultural and infrastructure pressures. We assert that the main challenge is not simply a shortage of T w studies, but a mismatch between a historically hydro‐ecological evidence base and the wider adaptation decisions now required under climate change. Future research should therefore prioritise transferable monitoring and modelling frameworks, event‐relevant metrics, stronger integration with water‐quality indicators and clearer translation of T w evidence into sector‐specific adaptation guidance.