Evaluating hydrologic impact from concurrent insect and fire disturbances

Abstract

Study RegionRio Grande Headwaters Study FocusIn the western US wildfires are increasing in duration and frequency, insect inducted forest mortality is widespread, and both wildfires and forest mortality are exacerbated by drought. These forest disturbances have hydrologic implications that are not always evident in the post-disturbance water budget – especially at the watershed outlet. In this study we evaluate two snow dominated paired catchment systems in the forested Rio Grande headwaters – where each impacted site was severely burned by the 2013 West Fork Complex (WFC) fire, and all sites (including control sites) were severely impacted by spruce beetle induced forest mortality from approximately 2005 to 2010. A combination of observed runoff, reanalysis precipitation, and remotely sensed evapotranspiration and vegetation metrics are used to evaluate the post-fire surface water budget (runoff and evapotranspiration) in paired catchments. New hydrological insights for the regionSignificant changes in post-fire surface water budget partitioning are not detectable, which is likely the result of decreased evapotranspiration due to insect-induced vegetation change in all study catchments prior to the fire. Our findings highlight the importance of considering overlapping disturbances, especially in paired catchment studies, and in alpine and subalpine forest regions like the Rio Grande headwaters that are increasingly prone to drought, insect mortality and wildfire. Our results also illustrate that insect induced forest mortality has significant implications for post-fire hydrology studies that rely on control-impact or before-and-after comparisons.