Post-fire impacts on microclimate and convective precipitation

Abstract

Changes in the landscape by fire have been measured and documented during several field projects. In this study the effects of landscape changes on the microclimate of a burn scar are examined and the potential changes in precipitation amount and microphysical characteristics of storms over and near the burn area are investigated. The Colorado State University Regional Atmospheric Modeling System was used to simulate the physical processes at work in the burn scar environment. The model was initialized with an atmospheric sounding from a flash flood event to investigate the effects of the burn scar on the development of precipitation in an atmosphere associated with the development of heavy precipitation. Burn scar regions are more vulnerable to flooding and erosion, and a major goal of this study is to explore whether these already flood-susceptible regions are also regions of enhanced precipitation, therefore increasing the potential for flooding over the burn scar. The results show that the burn scar significantly affected both the microclimate of the environment and the amount of precipitation produced by convection over the burn scar. The increased sensible heat flux and temperatures over the burn scar resulted in convective development and cloud formation. Effects were also seen in externally forced convection in stronger updrafts and greater precipitation. Microphysical changes in the forced convective clouds showed increased number concentration of graupel thus implying greater electrification of these clouds. Sensitivity tests revealed some effects of soil moisture changes in the burn scar while distinct differences were seen with a stronger initialization wind field. The findings of this study suggest that burn scar regions are not only more susceptible to flooding due to increased runoff with changes in surface characteristics, but may also be preferred regions of convective development, increased precipitation, and greater lightning activity.