Understanding Climate-Fire-Ecosystem Interactions UsingCESM-RESFire and Implications for Decadal ClimateVariability

Abstract. Large wildfires exert strong disturbance to regional and global climate systems and ecosystems by perturbing radiative forcing as well as carbon and water balance between the atmosphere and land surface, while short- and long-term variations in fire weather, terrestrial ecosystems, and human activity modulate fire intensity and reshape fire regimes. The complex climate-fire-ecosystem interactions were not included in previous climate model studies, and the resulting effects on the projections of future climate change are not well understood. Here we used a fully interactive REgion-Specific ecosystem feedback Fire model (RESFire) that was developed in the Community Earth System Model (CESM) to investigate these interactions and their impacts on climate systems and fire activity. We designed two sets of decadal simulations using CESM-RESFire for present-day (2001–2010) and future (2051–2060) scenarios, respectively and conducted a series of sensitivity experiments to assess the effects of individual feedback pathways among climate, fire, and ecosystems. Our implementation of RESFire, which includes online land-atmosphere coupling of fire emissions and fire-induced land cover change (LCC), reproduced the observed Aerosol Optical Depth (AOD) from space-based Moderate Resolution Imaging Spectroradiometer (MODIS) satellite products and ground-based AErosol RObotic NETwork (AERONET) data and agreed well with carbon budget benchmarks from previous studies. We estimated the global averaged net radiative effect of both fire aerosols and fire-induced LCC at −0.59 ± 0.52 W m−2, which was dominated by fire aerosol-cloud interactions (−0.82 ± 0.19 W m−2), in the present-day scenario under climatological conditions of the 2000s. The fire-related net cooling effect increased by ~ 170 % to −1.60 ± 0.27 W m−2 in the 2050s under the conditions of the Representative Concentration Pathway 4.5 (RCP4.5) scenario. Such greatly enhanced radiative effect was attributed to the largely increased global burned area (+19 %) and fire carbon emissions (+100 %) from the 2000s to the 2050s driven by climate change. The net ecosystem exchange (NEE) of carbon between the land and atmosphere components in the simulations increased by 33 % accordingly, implying that biomass burning is an increasing carbon source at short-term timescales in the future. High-latitude regions with prevalent peatlands would be more vulnerable to increased fire threats due to climate change and the increase of fire aerosols could counter the climate effects of the projected decrease of anthropogenic aerosols due to air pollution control policies in many regions. We also evaluated two distinct feedback mechanisms that were associated with fire aerosols and fire-induced LCC. On a global scale, the first mechanism imposed positive feedback to fire activity through enhanced droughts with suppressed precipitation by fire aerosol-cloud interactions, while the second one manifested negative feedback due to reduced fuel loads by fire consumption and post-fire tree mortality and recovery processes. These two feedback pathways with opposite effects competed at regional to global scales and increased the complexity of climate-fire-ecosystem interactions and their climatic impacts.