Only about one-third of global rivers (or tributaries) remain in a nearly natural condition, known as climate-sensitive rivers. We lack clear evidence on the changes in streamflow volume and timing of these rivers, which significantly compromises our capacity for protection. Here, we analyse alterations in streamflow and centre of timing at 1017 stream gauges across 812 climate-sensitive rivers and tributaries worldwide from 1950 to 2022. We observed increasing trends in streamflow volume (Q) at just over half of our sites (512), biased towards earlier changes in centre of timing (CT) (⩾−2 d yr−1), with more than 65% of records reflecting this trend. At over 80% of gauges, we found that rising Q and earlier CT are sensitive to increasing precipitation (P) and earlier centre of timing of precipitation (PCT). More than 60% of significant gauges show moderate to severe changes in Q and CT. We identified 104 global climate-sensitive rivers, located in subtropical, temperate and arctic regions, that have experienced large and severe changes based on long-term changes in Q seasonality (CT > ±15 d). Long-term changes in Q and CT may persist in rivers experiencing large and severe changes and intensify in those with minor and moderate changes. These changes will increase flooding, alter storage, cause water shortages, and degrade river health. We recommend proactive strategies including better streamflow monitoring, adaptive infrastructure (e.g. reservoirs, flood control), flexible flood management protocols, water-sharing agreements during droughts, and prioritised protection of ecosystems to buffer against variations in Q and CT.

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