Echoes of Fire: Geospatial Analysis of Terrain, Legacy Burns, and Wind-Aligned Severity During the 2025 Forsyth Fire, Pine Valley, Utah

Abstract

This study investigated how topography, vegetation moisture, and legacy fire perimeters influenced burn severity and directional spread during the 2025 Forsyth Fire in Pine Valley, Utah. The analysis integrated remote-sensing, topographic, and meteorological data within ArcGIS Pro 3.5.3 to quantify spatial controls on fire behavior. Differenced and relativized Normalized Burn Ratio (dNBR, RdNBR) indices derived from pre- and post-fire Landsat 8 OLI composites were used to map burn severity. In contrast, Normalized Difference Vegetation and Moisture Indices (NDVI, NDMI) were used to assess pre-fire fuel conditions and post-fire canopy moisture changes. Topographic derivatives from the 10 m National Elevation Dataset—slope, aspect, and elevation—were summarized using zonal statistics. Mean burn severity increased from reburn to control zones, with dNBR ranging from 88 to 174. Steeper slopes (20.18 ± 0.95°) and south-facing aspects (southness = –0.14 ± 0.08) were associated with higher dNBR (r = 0.57) and greater moisture loss (r = –0.69), confirming the influence of solar exposure and terrain inclination. Wind-alignment analysis indicated that approximately 70 percent of perimeter expansion occurred within 30° of the dominant southwest-to-northeast wind vector (mean azimuth = 41.1° ENE), linking burn severity to directional spread. Overall, the Forsyth Fire exhibited enhanced intensity along steep, south-facing ridges intersecting the 2016 Saddle Fire scar, suggesting that residual fuels and terrain channeling amplified severity toward the Pine Valley community. The results demonstrate that integrated geospatial modeling effectively characterizes the interactions among terrain, wind, and fuel that control wildfire behavior.