Fires in the 21st Century under Different Shared Socioeconomic Pathways (SSPs) using CESM/WACCM ensemble projections

Abstract:

Fire is an important component of the Earth system. Fires directly impact climate through emitting radiatively and chemically active trace gases and aerosols to the atmosphere, and causing alterations to the terrestrial ecosystem, such as changing vegetation distribution and structure, disturbing the carbon and water cycle, and changing surface albedo. Fire is also impacted by climate and human activities. Previous studies have suggested that in the future global fire risk may increase but with large uncertainty. Thus, this study quantifies the change of fire behavior in the 21st century under different Shared Socioeconomic Pathways (SSPs) and two geoengineering scenarios. Specifically, we analyze the global burned area and fire carbon emissions based on the Whole Atmosphere Community Climate Model Version 6 (WACCM6) simulations during 2015-2100. The model simulations were conducted under the forcing driven by SSP scenarios and provided for CMIP6. For most scenarios there are multiple ensemble simulations, leading to a total of 23 simulations analyzed in this study. Note that though the burned area and fire carbon emissions are simulated by the fire scheme in the model, the WACCM6 simulations still used specified CMIP6 fire emissions of trace gases and aerosols.

Our preliminary results show that (1) the modeled global total burned area does not differ among the scenarios at the end of the 21st century, except for that under the scenario SSP5-8.5, which has significantly higher burned area; (2) Different regions have very different (even opposite) trends under the same SSP scenario (for example, burned area and fire carbon emissions increase over North America while decrease over South America), and different regions benefit from different SSP scenarios in terms of burned area; (3) burned area and fire carbon emissions under the geoengineering SSP5-8.5 scenarios in the year 2100 are similar to the SSP1-2.6 over many regions such as North America; (4) burned area and fire carbon emissions increase in the year 2100 at Northern Hemispheric middle-to-high latitudes under all scenarios. We are also quantifying the driving factors (e.g., soil moisture, changes in temperature, humidity, precipitation, wind, etc.) of these fire trends globally and regionally.