Diminished vegetation cover following wildfires  and tree mortality  can reduce long-term water infiltration, increase soil erosion and flash floods and release sediment that degrades drinking water quality. Widlfires increase impacts of extreme precipitation events due to climate change, which contribute to increased surface runoff and hence increased risks of land erosion, landslides and flooding . Under current conditions, nearly half the global land area is at a moderate-to-high risk of water scarcity due to wildfires . From 1984 to 2014, wildfires in the western USA affected 6-11% of stream and river length . Under a high-emissions scenario of a 3.5℃ temperature increase, post-fire erosion across the western USA could double sedimentation and degrade drinking water quality in one-third of watersheds by 2050 . In Brazil, post-fire vegetation loss tends to increase runoff, reduce infiltration and reduce groundwater recharge and flow of springs . Runoff from wildfires can contain DOC precursors for the formation of carcinogenic trihalomethanes during chlorination of water for drinking  as well as chromium, mercury, selenium and other toxic trace metals .
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report