Post-fire Vegetation and Hydrologic Recovery in a Mediterranean Climate

Abstract

Accurate field data are required to predict elevated runoff and sediment transport to aid post-fire planning. This is especially significant at the small catchment scale, where these runoff processes occur disproportionately, occurring at a higher magnitude and higher frequency. Sources of elevated runoff include soil hydrophobicity, in-channel sediment loading through dry ravel, extensive rill networks, and exposed bare soil. Recovery of these processes are related to vegetation conditions before, during, and after fire. This can be quantified using satellite-based vegetation indices to understand the recovery of the burned area and resulting hydrologic response. The main objective was to demonstrate potential for ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) evaporation measurements in post-fire hydrology by linking to hydrologic signatures (flashiness index and runoff-ratio) to highlight changes and improve vegetation assessments after fire. A case study of the 2018 Holy Fire is presented using a control catchment and a burned catchment. Results show that areas containing higher proportions of montane hardwood and montane hardwood conifers burned at high soil burn severity, a result of the normal to moderately dry period (2012-2016, 2018) that decreased annual evapotranspiration and increased water stress leading up to fire. For 1-year post-fire, ECOSTRESS measured the highest variation between burned and control during the peak dry months (3 to 4 mm/day), which explained the comparatively higher dry-season flows observed for the burned catchment. Summer field visit also showed vegetation regrowth that consisted of mostly annual grasses following a moderately wet year. Preliminary results were adequate; however, not enough time has passed for the system to fully recover, and thus, we present a Google Earth Engine application to help track recovery.