From China to Europe and North America, rivers are being transformed by intensifying droughts, floods and heatwaves with mounting consequences for biodiversity and water security, according to a new global review published in The Conversation.
Researchers from institutions including the University of Canterbury, the University of Washington, and Inrae say extreme climatic events are pushing river ecosystems beyond their limits, often causing irreversible damage.
Rivers Under Pressure
In 2022, unprecedented heat and drought reduced sections of the Yangtze River the world third-longest river to critically low levels. While the economic impacts on hydropower, shipping and industry were widely reported, scientists say the ecological fallout was less visible but equally severe.
Plankton populations collapsed during the drought, affecting the broader food web. And the Yangtze is not alone.
Across the globe, extreme events are no longer isolated shocks. Instead, they are compounding, cascading through river systems and disrupting habitats far downstream from where they begin.
A drought in upstream headwaters can alter flows for months. When rains eventually return, accumulated debris and pollutants may trigger oxygen crashes and mass fish deaths.
The study highlights the growing threat of “compound events” when multiple climate extremes occur together or in rapid succession.
In Europe’s Rhône River, a record heatwave in 2003 enabled invasive species to thrive, a shift amplified by subsequent flooding. In the United States, wildfire followed by heavy rainfall in 2022 devastated stretches of California’s Klamath River, triggering extensive fish die-offs.
Similarly, post-wildfire rains in 2011 degraded water quality in New Mexico’s Rio Grande, with effects felt far downstream.
Scientists warn that the ecological damage from such compound events is not always proportional to the severity of the initial disaster. Instead, the sequence of events and existing stressors such as pollution, dams and water extraction often determines how catastrophic the outcome will be.
Repeated extremes in Alaska’s Wolf Point Creek, for example, altered invertebrate communities for more than a decade.
Tipping Points and Permanent Change
Because rivers are highly connected systems, impacts rarely remain local. Species unable to migrate to cooler or safer refuges may be permanently lost, particularly in fragmented river networks.
In some cases, ecosystems cross tipping points after which full recovery becomes unlikely. Even large-scale restoration efforts may struggle to reverse biodiversity losses if extreme events continue to intensify under climate change.
From Reactive to Proactive
The authors argue that current river management strategies are largely reactive, responding after disasters strike. They call instead for proactive, catchment-scale approaches designed to build resilience before extreme events occur.
One widely discussed strategy involves protecting natural refuges such as shaded tributaries, deep pools and cold-water streams that offer species temporary relief during heatwaves or droughts. However, researchers caution that even these refuges may degrade under prolonged or repeated extremes.
Innovative solutions are emerging. Engineered thermal refuges, including groundwater-fed cooling systems and gravel trench designs, are showing promise in early trials. Restoring river connectivity, safeguarding groundwater recharge zones and giving rivers more room to flood naturally are also identified as critical steps.
The researchers emphasize that a mix of nature-based solutions and engineered interventions will be required to prepare rivers for a more volatile climate future.
Rivers sustain billions of people, supplying drinking water, food, transport and energy. Yet they remain among the least protected ecosystems worldwide.
As extreme weather events become more frequent and intense, scientists say the challenge is no longer simply restoring rivers to past conditions but preparing them for a fundamentally altered future.
Without decisive action, the world’s rivers may not just change. They may cross thresholds from which there is no easy return.