WILDFIRE
Wildfire is increasing across the United States and the world due to climate change, whether measured by the number of fires, the area burned, or the length of the fire season. In addition to incurring substantial costs in lives and property, wildfires substantially alter watershed hydrology and downstream water resources. Wildfire can increase flood risk by altering vegetation water use and changing soil infiltration through hydrophobic burn layers; it can also impair water quality from both chemical residues of the burn processes and from contaminant loads due to increased surface runoff and soil erodibility. However, the response of watersheds to wildfire depends on the details of both the watershed and the fire. Our current understanding of watersheds' response to wildfire remains limited, so the WRElab uses computational simulation and measurements of water quality to better understand and plan for the effects of these hazards on critical water resources.
Caldor Fire
In August 2021, the Caldor Fire started in California's Cosumnes Watershed, the site of ongoing mountain ecohydrology research. Over the next 10 weeks the fire burned nearly 900 square kilometers and destroyed more than 1,000 homes, leaving behind a drastically changed landscape. A group from Lawrence Berkeley National Laboratory partnered with the American River Conservancy, a local citizen science group, to collect water samples from a series of established sampling points within the watershed to investigate the effects of the fire and monitor potential water quality concerns.
We are using both measurements and modeling to better understand how the Caldor Fire affected watershed function in the Cosumnes Watershed. Water samples allow us to directly investigate the concentrations of water quality components that might exceed safety standards, and to directly compare with pre-fire water chemistry. The watershed model built for pre-fire conditions has been adapted to investigate how watershed function was altered by the fire relative to how it would have functioned in a no-fire counterfactual. We are exploring how fire conditions altered flood risk and the flow paths of water through the watershed. We are combining the models and measurements to quantify the loss of nutrients and carbon from the ecosystem and the loads of these and metals into downstream rivers and the Sacramento-San Joaquin Delta.
Lawrence Berkeley Lab personnel, UC Davis students, and USFS staff collected samples from the burn scar only weeks after fire activity.
The organic carbon concentration was positively correlated with streamflow in the few months after the Caldor Fire (October 1, 2021 - June 1, 2022). The higher organic carbon concentrations generally came from less-burned subwatersheds.
Recent papers & presenations
Dennedy-Frank, P.J., M. Newcomer, J. Peña, E.R. Siirila-Woodburn (2022), Understanding Post-fire Water Quantity and Quality Changes With a Rapid-response Field Campaign and Integrated Hydrologic Model, presented at Frontiers in Hydrology Meeting 2022, AGU, 19-24 June.
Siirila-Woodburn, E.R., M.E. Newcomer, J. Peña, P.J. Dennedy-Frank, K. Kang, D. Brook, E. DeLacy V. Pacific (2022). Biogeochemical Response of a Sierra Nevada Watershed Following Compounding Extremes: Drought, Wildfire, and Atmospheric Rivers, presented at 2022 Fall Meeting, AGU, 12-16 Dec.