HYDROLOGIC RESPONSE AND VEGETATION RECOVERY IN THE WALDO CANYON FIRE

The Waldo Canyon Fire burned 18,247 acres at the urban-fringe near Colorado Springs, CO in July 2012; destroying 346 homes, evacuating 36,000 people and becoming the second costliest forest fire in the history of the state. To mitigate post-fire consequences that threaten the urban-fringe, aerial heli-mulch and straw treatments were implemented for over 3870 acres of burned area. Hard treatments such as sediment detention basins, hillslope and in-channel handwork have also been implemented to reduce increased sediment yield to streams. The effects of wildfires have been widely analyzed, but typically focus on first year debris flows and plot-scale vegetation recovery. Few studies evaluate treatment effectiveness at the watershed scale and at this magnitude of treatment. This study couples the hydrologic effects of the wildfire with vegetation recovery, evaluated through in-situ instruments and remote sensing. Our work in the Waldo Canyon Fire includes monitoring discharge in ten sub-basins and two unburned, control basins since October 2012 with respect to treatments and geomorphologic parameters. Five USGS rain gages distributed throughout the burn area supplement our hydrologic sensors. We investigate hydrologic response and vegetation recovery for each study basin for the first post-fire storm season (2013 spring and summer) and evaluate vegetation regrowth using Moderate Resolution Imaging Spectroradiometer (MODIS) and Landsat indices. Normalized Differenced Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) are used to estimate spatial and temporal vegetation “greenness”. These indices are a proxy of vegetation biomass to monitor pixel by pixel vegetation recovery throughout the burn area as a function of National Land Cover Database vegetation classes, elevation, and burn severity parameters. Vegetation recovery will likely show a strong correlation to these parameters. We hypothesize that the remote sensing indices will show little vegetation recovery but increases in greenness are likely due to an initial pulse of weeds and grasses. Information garnered will improve post-fire modeling and prediction through the development of a multi-variable rainfall-runoff relationship based on burn severity, slope, aspect, and treatment type.