Impact of Wildfire on Surface Energy Balance in Six California Case Studies

Abstract:

This study investigates the impact of wildfires on surface energy exchange through the assessment of six California wildfires that occurred in the last 20 years. A burned-unburned binary mask was generated from the MODIS approximate date of burn product and implemented into the Simplified Simple Biosphere model for a series of simulations. Model performance was evaluated against the North American Land Data Assimilation System and was found to simulate surface temperature and net radiation accurately. Simulations show a decrease in latent heat flux in every case study except the Rush fire which occurred in Lassen County in August 2012. Post-fire changes in net radiation and sensible heat followed similar trends, decreasing in each of the domains except for the Rush and Cedar fires. The greatest changes in temporally averaged net radiation occurred in the Rim (-41.7 W/m2), Basin-Complex (-31.6 W/m2), and Rush (26.5 W/m2) fires. Initial increases in sensible heat flux, caused by the decrease in albedo from ash deposition, are balanced by decreases in latent heat flux in the Zaca, Rim, and Basin- Complex case studies. Results also indicate a relationship between decreases in average sensible heat flux and LAI change. Wildfires that burn in sparsely vegetated areas are associated with increases in sensible heat flux, an effect that is magnified by long ash deposition periods (i.e. Rush fire), while wildfires that burn in densely vegetated areas are associated with large decreases in sensible and latent heat flux (i.e. Rim, Basin-Complex fires).