Prolonged Drought in a Mediterranean EcoRegion Suppresses Wildfire Impacts on Hydrology
Abstract
Wildfires are a natural and changing component of many landscapes around the world, however they are undergoing rapid regime shifts in the face of climate change. Despite the emphasis in the literature on the most severe and catastrophic hydrological responses (i.e. debris flow and flooding), there remains a significant knowledge gap on the range, gradients, and thresholds of wildfire size and severity required to initiate hydrological responses. We investigated changes in hydrological conditions in the Russian River Watershed (RRW), California, a Mediterranean, drought prone, fire-adapted ecosystem, following eleven fires that occurred during the years 2017-2020. We find that sub-watersheds of the RRW have not burned beyond an intrinsic, and still unknown, threshold required to initiate substantial changes in hydrological response. Using a series of paired burned/unburned catchments nested within the larger watershed, we examined temporal and spatial patterns of pre-and-post fire water hydrology using a rainfall runoff hydrological model. Despite the extent of these successive fires burning between 1-50% of each sub-watershed, little evidence of fire-related shifts in hydrology were found. As a function of percent of area burned, wildfire imposed a limited effect on runoff ratios (runoff/precipitation) and runoff residuals (observations minus model simulations) with an asymptotic effect beyond 30% area burned. Disturbance thresholds (percent of watershed area burned) of 20% have previously been suggested, yet only moderate disturbance response was observed even when wildfires accounted for >40% in a single year. Using measurements of discharge compared to modeled discharge, drought and event-scale storm conditions largely account for the variability observed in RRW streamflow. The lack of hydrological response could be attributed to many factors that are unique to this Mediterranean ecoregion. These larger intrinsic thresholds could result from millennia of fire-history/adaptation, and/or prolonged drought that buffers the watershed hydrological response to repeated wildfires.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.H45A..08N