Abstract
Wildfires can dramatically alter water quality with severe implications for human and freshwater systems. Although regional assessments of these effects can aid water managers in mitigation efforts, analyses to date have been limited by water quality data availability. Here, we unify observations from 245 burned catchments across the western U.S., applying a novel analytical framework to compare post-fire signals to baseline levels from 293 unburned basins for the period 1984–2021. Carbon, phosphorus, and turbidity exhibit significantly elevated levels (p ≤ 0.05) in the first 1–6 years post-fire, while nitrogen and sediment show significant increases up to 8 years post-fire. In each constituents’ peak post-fire response year, average loads of carbon, nitrogen, and phosphorus are 7–110 times pre-fire levels and sediment and turbidity 25–500 times greater than pre-fire. Higher responses are linked with greater forested and developed areas, with these characteristics respectively explaining up to 75 and 45% of inter-basin response variability. Overall, this analysis provides strong evidence of multi-year water quality degradation following wildfires in the U.S. West, as well as the influence of basin and wildfire features. These insights will aid in assessing watersheds’ vulnerability to the impacts of future wildfires.