Map of Water Utilities’ Vulnerability to Harmful Water Quality from Wildfires in the Pacific Northwest

Abstract:

Water utilities in the Western U.S. are vulnerable to climate change because of wildfires and the detrimental cascading effects that follow such as declining water quality. Wildfires are increasing in number and size as summers become hotter and drier, and these disturbances have the potential to increase post-fire runoff-induced erosion and sediment loads to rivers and reservoirs which can overwhelm water treatment plants. Additionally, post-fire soil erosion can increase the concentration of contaminants such as heavy metals, organic carbon, and nutrients which can be difficult for water utilities to remove before delivery to their customers. This research couples a wildfire and a water quality vulnerability index at the watershed scale to better understand which water utilities are most at risk to wildfire in the U.S. Pacific Northwest. Here, wildfire vulnerability metrics rely on climatic and geographical characteristics to estimate the likely risk of fire in a given watershed. The water quality metrics aim to capture potential post-fire water quality changes by accounting for landscape and land use data, land ownership, water utility intake location, water source diversity, and fire preparedness plans. Combining these data for each watershed yields a vulnerability score for the 47 Pacific Northwest water utilities included in the study. These results can be used to inform water utility managers of vulnerable municipal watersheds as well as which areas should be prioritized for forest management and post-fire erosion mitigation if a wildfire occurs. Forest management could be forest thinning and prescribed fire which will help reduce the risk of catastrophic wildfires.