Modeling the Hydrological Impacts of the Yarnell Hill Fire Using the Automated Geospatial Watershed Assessment (AGWA) Tool

Abstract

The highly publicized 2013 Yarnell Hill Fire is the deadliest wildfire in Arizona history, killing 19 members of the Granite Mountain Hotshots firefighting crew. Wildland fires like Yarnell Hill have immediate effects on human life and property, but they can also increase the frequency and severity of flooding events due to loss of vegetation and hydrophobicity of soils and ash. This study seeks to model hydrological impacts due to land cover change following the Yarnell Hill Fire using the Automated Geospatial Watershed Assessment (AGWA) Tool. AGWA can enable hydrologic modeling using the Soil & Water Assessment Tool (SWAT) or the Kinematic Runoff and Erosion Model (KINEROS2) and can help land and water resource managers make quick decisions regarding flood mitigation strategies following a wildfire. In this study, AGWA is used to model the change in land cover due to the Yarnell Hill fire based on a burn intensity map created using the differenced Normalized Burn Ratio (dNBR) and based on pre- and post-fire Landsat 8 Operational Land Imager (OLI) imagery. Storm conditions included in the model represent a variety of storm recurrence intervals based on National Weather Service (NWS) data for the town of Yarnell. For all post-fire storm conditions modeled, flooding increases more rapidly and with greater volume as compared to pre-fire conditions.