Extreme weather events are increasing in frequency and intensity, but their ecological impacts remain less well understood than those of gradual climate change, largely owing to the challenge of studying unpredictable, short-lived events. The 2021 western North American heatwave is among the most extreme on record globally, yet a broad assessment of its ecological consequences is lacking. Here we synthesize meteorological, ecological, hydrological and wildfire data, along with process-based modelling, to quantify the heatwave and its impacts across the region. Our meta-analysis of 32 terrestrial and marine taxa reveals that over 75% were negatively impacted, but species responses ranged widely, from 99% declines to 89% increases. This variability reflects differences in organisms’ thermal sensitivities, response capacities and exposures, with the latter dependent on geography, microclimate and refugia. Impacts tended to be greater for sessile marine invertebrates, algae and plants than for birds and mammals. At the ecosystem scale, changes in gross primary productivity ranged from 30% increases in cooler, wetter areas to 75% decreases in warmer, arid ones. Streamflow from snow and ice melt increased 40% during the heatwave before dropping below average, whereas wildfire activity surged 37% during the heatwave and 395% the following week. Our results underscore the urgent need for enhanced coordinated approaches to predict, detect and manage increasing heatwaves.
We use a mixed-methods approach, leveraging field data from scientists working in the region affected by the 2021 western North American heatwave, remote-sensing and open access datasets, media reports and process-based modelling to advance understanding of how organisms and ecosystems respond to short-term extreme temperature anomalies. We first demonstrate spatial variability in exposure for three different meteorological variables (air temperature, land surface temperature and VPD) across the heatwave’s geographic extent and combine these records with species’ thermal performance curves to show how the same extreme climatic event could affect the performance of different organisms in distinct ways. We then conducted a meta-analysis of published and unpublished datasets from long-term monitoring programs, well-timed experiments or opportunistic observations quantifying ecological responses to the heatwave across taxa. We hypothesized that across the heatwave’s overall negative effects on organisms, sessile organisms would be more negatively impacted than motile ones owing to their inability to access cooler microclimates and that species responses would range from immediate but potentially short-lived behavioural responses (for example, change in activity levels during the heatwave) to mortality and other effects (for example, reproductive failure) with longer-lasting demographic effects. Complementing this meta-analysis with additional literature (that did not meet the criteria for the meta-analysis), field observations and media records, we further document the breadth of ecological responses to the heatwave. Finally, we used process-based models, open-access government datasets and satellite-derived data to quantify the heatwave’s broader ecosystem impacts: changes in gross primary productivity, streamflow and wildfire activity. Our synthesis provides insights into the breadth and variability of extreme heatwave impacts, and factors driving this variability, and ends with recommendations for scientists and policymakers to better prepare for future heatwave events.
Sources:
Nature Ecology & Evolution
https://www.nature.com/articles/s41559-026-02987-6 .
Provided by the IKCEST Disaster Risk Reduction Knowledge Service System
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