Temporally compounding extreme fire weather and extreme precipitation risk over the western United States

Abstract:

An extreme precipitation event after a wildfire can multiply damages to natural and human systems through flash floods, debris flows and mudslides. One example are the destructive mudslides that occurred in Southern California during a brief but severe storm over the burned area of the 2017 Thomas Fire, leading to 21 deaths and over $200M in damages. Anthropogenic forcing is expected to drive increases in wildfire risk and amplify extreme wet events, possibly increasing the risk of concurrent wildfire-extreme precipitation events. First, we examine the characteristics of temporally compounding extreme fire weather events and extreme precipitation events on daily, seasonal, and annual timescales over the western US. We use the 40-member CESM Large Ensemble experiment to quantify the impact of internal climate variability and anthropogenic activity in 20th and 21st century simulations. Then, we isolate the roles of variability and trends in extreme fire weather risk from those of extreme precipitation risk in driving changes in the frequency and magnitude of the compounded events. Moreover, we investigate atmospheric dynamics and land processes that create conditions that underlie temporally compounding extreme fire weather and extreme precipitation events on multiple time scales. Our analysis will provide insight to adaptation efforts focused on preventing devastating impacts in wildfire-prone regions.