Increased risk of the 2019 Alaskan July fires due to anthropogenic activity

Abstract:

July 2019 saw record-breaking wildfires which burned over 3,600 km² and emitted an estimate of 3.5 Tt Carbon in Alaska, accompanied by extremely hot and dry conditions in June and July. Smoke plumes from July 2019 fires degraded air quality over most of Alaska, inducing the first ever dense smoke advisory (visibility less than a mile) for Anchorage, and some of the world’s worst air quality in Anchorage and Fairbanks. Previous studies use a weather-based index to attribute the increased risk of an extreme Alaskan fire season to warmer temperatures associated with anthropogenic climate change. However, the human-induced increased risk of extreme fires in Alaska is also likely attributed to the elevated abundance and dryness of biofuel and an increased number of human-ignited fires. The present study takes advantage of the modeling capability of the Geophysical Fluid Dynamics Laboratory (GFDL) Earth System Model 4.1 (ESM4.1) to simulate the complex interactions between fire, climate, land ecosystem, and human activity to assess the influence of anthropogenic activities on extreme fires in Alaska. Using historical climate simulations performed with the GFDL ESM4.1 model, the climatological burned area and fire carbon emission during the month of July increased since 1950s in Alaska, resulting in higher occurrence of a 2019-like event during recent decades. The historical increase in the occurrence of an extremely fire-active July was attributed to anthropogenic activity, which caused a three-fold increase in the risk of a 2019-like fire season. The anthropogenic influence on the increased occurrence of an extreme fire season in Alaska was primarily through an increase in anthropogenic ignition, and secondarily through climate-induced biomass abundance.