Burned area in the Sierra Nevada mountain range has increased over the last half-century, with recent fires having catastrophic impacts on ecosystems and rural communities. We investigated the impact of climate change on summer wildfire in the Sierra Nevada using daily time series of the observed number of fires from the California Dept. of Forestry and Fire Protection and burned area from NASA satellite imagery. We used these observations, along with daily weather observations from PRISM, to quantify relationships between daily temperature and fire activity. We then used these relationships to model decadal trends in wildfires from the 1980s to the 2050s caused by observed and projected changes in summer surface air temperature.
Results/Conclusions
Over 90% of the burned area and 80% of fires in the Sierra Nevada occur during the hot and dry summer season (June through September). During this season, we found that anomalously warm days had a disproportionate effect on fire number probability and burned area. A 1°C increase in daily temperature caused an 18% increase in fire number probability and a 20% increase in the satellite-derived burned area, with the magnitude of the fire response varying between early and late summer. Combining these relationships with climate observations, we found that between the 1980s and 2010s burned area increased by 30% and the number of fires by 25% as a consequence of warming trends. Similar future changes in fire activity were estimated through the middle of the 21st century using climate projections from the Community Earth System Model. Our results highlight the relatively high sensitivity of the burned area and the number of fires in the Sierra Nevada to small changes in summer temperature and provide a data-driven assessment of near-term changes in fire activity expected in the next few decades as a consequence of climate change.