Wildfires in earth system: Driver, transport and feedback

Abstract

Wildfires release large amounts of greenhouse gases, carbonaceous aerosols, and other pollutants, therefore having complex impacts on the earth climate, local weather, and air quality. To study the transport of the wildfire emissions, a plume height dataset has been developed. The resulting dataset from 2002 to 2010 captured well the observed MISR plume height distribution. By adding the plume height dataset in the climate model, the plume-rise enhanced AOD downstream of the wildfire spots by 20 to 50%. Moreover, an online plume rise module for CAM5 has been developed, allowing for the feedbacks of climate/weather on fire plume rise. As an application of this developed plume height dataset, the impact of West Canada wildfires (WCWs) on Northeast United States (NEUS) have been investigated. The observed OC/EC ratios over the NEUS show significant correlations with WCWs burned area since 2001. Detailed analysis and modeling simulations show that the strength of wildfire explains 48% variance of OC/EC disturbance while the transport effect explains another 35% variance. Africa wildfires response to half of global wildfire emissions. To investigate the driver of this wildfire variability, this study examined relationship between fire, climate, and ecosystem in arid, intermediate and mesic regions. The results show that the LAI caused fuel limitation dominates the wildfire variability in Africa. As an important feedback from wildfires, the fire-forest interaction is recognized as an important disturbance to produce the savanna-forest landscape in Africa. This study presents new observational evidence, showing significant negative lag correlations between the burned area and the forest amount in both hemisphere Africa. Ensemble runs of a modified ecosystem model have been performed with broad range of parameter values, suggesting that 90% of the fire needs to be reduced compared to 2005 level to reach the RCP4.5 forest target in 2100.