In recent years, wildfires in the western United States have occurred with increasing frequency and scale. Climate change scenarios in California predict prolonged periods of drought with potential for conditions even more amenable to wildfires. The Sierra Nevada Mountains provide up to 70% of the state’s water resources, yet there is little known on how wildfires will impact water resources in the future.

A new study by scientists at Lawrence Berkeley National Laboratory (Berkeley Lab) uses a numerical model of an important watershed in California to shed light on how wildfires can affect large-scale hydrological processes, such as stream flow, groundwater levels, and snowpack and snowmelt. The team found that post-wildfire conditions resulted in greater winter snowpack and subsequently greater summer runoff as well as increased groundwater storage.

The study, “Watershed Dynamics Following Wildfires: Nonlinear Feedbacks and Implications on Hydrologic Responses,” was published recently in the journal, Hydrological Processes.

“We wanted to understand how changes at the land surface can propagate to other locations of the watershed,” said the study’s lead author, Fadji Maina, a postdoctoral fellow in Berkeley Lab’s Earth & Environmental Sciences Area. “Previous studies have looked at individual processes. Our model ties it together and looks at the system holistically.”

The researchers modeled the Cosumnes River watershed, which extends from the Sierra Nevadas, starting just southwest of Lake Tahoe, down to the Central Valley, ending just north of the Sacramento Delta. “It’s pretty representative of many watersheds in the state,” said Berkeley Lab researcher Erica Woodburn, co-author of the study. “We had previously constructed this model to understand how watersheds in the state might respond to climate change extremes. In this study, we used the model to numerically explore how post-wildfire land cover changes influenced water partitioning in the landscape over a range of spatial and temporal resolutions.”

Using high-performance computing to simulate watershed dynamics over a period of one year, and assuming a 20% burn area based on historical occurrences, the study allowed them to identify the regions in the watershed that were most sensitive to wildfires conditions, as well as the hydrologic processes that are most affected.

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