IDENTIFYING POST-FIRE VEGETATION GROWTH TRENDS IN THE LOS ANGELES SAN GABRIEL MOUNTAINS: A CASE STUDY OF THE 2020 BOBCAT FIRE

Wildfires drastically change the ecologic landscape in just a few days while it takes years of post-fire recovery for vegetation to return to its former pre-fire state. Assessing changes in vegetation can help understand how the hydrological components in the wildfire-affected areas contribute to potential shifts in vegetation. This case study of the 2020 Bobcat Fire in Los Angeles River Basin of Southern California uses Google Earth Engine (GEE) and ArcGIS Pro to monitor vegetation changes by calculating Difference Normalized Burn Ratio (dNBR), Normalized Difference Vegetation Index (NDVI), OpenET’s Evapotranspiration (ET), and changes in National Land Cover Database (NLCD) between the years 2020 and 2023. Time series were created for this fire event by isolating areas of high, moderate, and low dNBR severity classes. Our results show a decrease in combined high and moderate dNBR severity areas within the Bobcat perimeter of over 55% while low severity areas fluctuate based on declining high and moderate burn severity areas due to vegetation growth. Average NDVI in high severity areas had the largest growth to its pre-fire conditions at an increase of about 0.4 compared to moderate and low severity areas at about 0.25 and 0.15, respectively. Evergreen Forest and Scrub/Shrubs show growth trends in all burn severity areas with Scrub/Shrub in the moderate severity areas having the highest growth at over 120% from 2021 to 2023. Additionally, moderate and low severity areas have seen drops in ET levels a year after the fire but have seen peak ET values grow halfway to their pre-fire conditions in 2022 and remain steady in 2023. Overall, we observed the increasing post-fire vegetation growth characterized by a decrease in burn severity and increases in both average NDVI and ET levels. Using GEE, ArcGIS Pro and currently available satellite imagery shows the accessibility of vegetation data for wildfire studies. This approach enables the investigation of evolving vegetation components in burned areas, enhancing our understanding of the impacts wildfires have on ecosystems.