The time of year has arrived when red weather alerts become a daily feature in forecasts. High temperatures and dry air pose a danger related to a phenomenon once considered seasonal and mostly local—but which has now become global. Wildfires, which over the past few decades—and especially the last 15 years—have caused devastating consequences, are no longer just a threat to forests and air quality. New findings show that their impact on water quality is far more prolonged than previously assumed.
The most affected region facing recurring wildfires is the western United States, where fires typically occur between June and October, peaking in August and September. However, even the beginning of 2025 was marked by terrifying scenes from Los Angeles. Canada is also among the countries most affected by wildfires, having lost several million hectares of forest to flames in 2023. Similar trends are seen in the southern hemisphere, with Australia facing fires most often from December to March.
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Study Conducted in the U.S.
A new study conducted by CIRES (Cooperative Institute for Research in Environmental Sciences) at the University of Colorado Boulder revealed that river contamination can persist for up to eight years after a wildfire.
This research represents the first large-scale analysis of post-fire water quality across the entire western United States. Scientists examined over 100,000 water samples from 500 river basins—half from areas affected by wildfires, and the other half from unaffected regions.
The most significant increases in pollution levels occur within the first five years after a fire, although elements such as nitrogen and sediments remain elevated for up to eight years. Areas with dense forest vegetation are especially vulnerable, while extreme weather events like heavy rains often worsen the situation by triggering waves of toxic runoff into river systems.
Although earlier research had already pointed out that ash and soil erosion degrade water quality, those findings were typically based on local studies. The new CIRES analysis offers a continental perspective, with the study’s authors emphasizing that watersheds react differently—some show massive increases in sediment levels, while others remain nearly unaffected. This variability makes planning more difficult and highlights the need for resilience strategies tailored to local conditions.
The CIRES study clearly illustrates the serious consequences of climate change and wildfires, underscoring the urgent need for proactive, preventive measures—not merely reactive ones once the damage is already done.
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