Using CESM-RESFire to understand climate–fire–ecosystem interactions and the implications for decadal climate variability
Authors: Zou Yufei , Wang Yuhang , Qian Yun , Tian Hanqin , Yang Jia , Alvarado Ernesto 
Published: January 2020

Abstract. Large wildfires exert strong disturbance on regional and
global climate systems and ecosystems by perturbing radiative forcing as
well as the 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 fully
integrated in previous climate model studies, and the resulting effects on
the projections of future climate change are not well understood. Here we
use the 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), reproduces the
observed aerosol optical depth (AOD) from space-based Moderate Resolution
Imaging Spectroradiometer (MODIS) satellite products and ground-based
AErosol RObotic NETwork (AERONET) data; it agrees well with carbon budget
benchmarks from previous studies. We estimate the global averaged net
radiative effect of both fire aerosols and fire-induced LCC at -0.59±0.52 W m−2, which is 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 increases 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
considerably enhanced radiative effect is 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 increases 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
in fire aerosols could counter the projected decrease in anthropogenic
aerosols due to air pollution control policies in many regions. We also
evaluate two distinct feedback mechanisms that are associated with fire
aerosols and fire-induced LCC, respectively. On a global scale, the first
mechanism imposes positive feedbacks to fire activity through enhanced
droughts with suppressed precipitation by fire aerosol–cloud interactions,
while the second one manifests as negative feedbacks due to reduced fuel
loads by fire consumption and post-fire tree mortality and recovery
processes. These two feedback pathways with opposite effects compete at
regional to global scales and increase the complexity of
climate–fire–ecosystem interactions and their climatic impacts.