Increase in Fire Intensity with Elevation Gain
Abstract
Elevational gradients of water, energy and vegetation, along with anthropogenic controls, govern fire regimes (e.g., return interval, severity, size), generally culminating in high-elevation mesic forests observing less frequent, but higher severity fires. Although fire severity - i.e., ecosystem outcome - and intensity - i.e., released heat energy - are correlated, our quantitative understanding of fire intensity across the elevation gradient at large spatiotemporal scales is limited. Here, we used fire radiative power (FRP) from the MODIS sensor aboard Terra and Aqua satellites from 2000-2021 as a proxy to assess elevational trends and patterns of fire intensity and its biophysical controls in 15 mountainous ecoregions of the Western United States. For each detected active fire pixel, we also derived coincident climate aridity, fire danger indices, topographical measures, and tree cover. We report that the mean FRP was approximately 48% (31 MW) higher at higher-elevations (>3rd quartile, Q3) than at lower elevations (<1st quartile, Q1) for 13 of the 15 studied ecoregions (range: -58% to 128%). While generally positive across elevations, the largest rates of FRP increase with elevation gain was observed in the uplands with a median slope of 26 MW/km for Q3 of elevation as compared to 3.4 MW/km for Q1. To investigate the drivers of this pattern, we conducted a correlation analysis between mean FRP and coincident biophysical covariates in 250 m elevation bands. A majority of ecoregions (10 of 15) showed significant Pearson correlation between elevation-band mean FRP and fire danger indices, climate aridity, and slope, but this relationship was less evident between mean FRP and tree cover, except for generally warmer and drier ecoregions with lower forest cover. This nuanced understanding of elevation-dependent fire intensity helps managers improve fire response in high elevations as more frequent high-elevation fires occur in a warming climate.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMNH45F0492S