Shorter Recovery Periods Between Smoke Waves: A Spatio-Temporal Analysis in California (2006-2020)

The increasing frequency of wildfires in California, fueled by climate change through hotter, drier conditions, poses uncertain public health risks due to repeated wildfire smoke exposure. This study explores the "recovery period," the time between smoke waves, which may offer respite from smoke impacts, including health risks and adaptation demands. We examine trends in wildfire smoke wave frequency, duration, and recovery periods in California from 2006 to 2020, aiming to assess repeated exposures and develop a framework to evaluate associated health risks via recovery periods. We define a smoke wave as two or more consecutive days with wildfire-specific fine particulate matter (PM_2.5) > 1 μg/m³, at the census tract level. Recovery periods are calculated as the days between smoke waves, ending with the first wave of 2021. We also examine community characteristics such as income, race, and education. From 2006 to 2010 to 2016-2020, we observed a 60% reduction in recovery periods, an 85% increase in smoke events, and longer durations. Spatial variability was substantial across census tracts, with the greatest reductions in recovery periods in Southern and Central Valley regions. Northern California, with the shortest recovery periods, showed minimal changes. Communities with higher proportions of minority race groups, single female householders, and lower incomes experienced the largest reductions in recovery period length. This study introduces a framework to assess the repeated impacts of smoke waves, highlighting changing spatio-temporal patterns. Incorporating recovery periods into health risk assessments can guide public health strategies to address compounding risks from wildfire smoke.