Image: Post-wildfire simulations of the Cosumnes watershed in California showing spatial variability in the changes to surface water storage and groundwater storage (Maina and Siirila-Woodburn, 2019).
Two recent exercises in modeling the hydrological effects of forest thinning and wildfire are yielding intriguing insights.
Hydrogeologist Fadji Maina and colleague Erica Siirila-Woodburn of the Lawrence Berkeley National Laboratory ran simulations of wildfire effects in the Cosumnes River watershed (see map)
. “We chose the Cosumnes because it’s one of the largest rivers that has no dam in California,” explains Maina. The most significant findings concerned the way wildfire affects groundwater recharge and storage. “It depends on where the wildfire occurs,” says Maina. The underlying rocks—foothill volcanics or High Sierra granites—make a difference. Consistent with earlier studies, the model also showed more snow accumulation after wildfire, but unexpected results include a post-fire increase in evapotranspiration in some downslope areas. Another study focused on the effects of forest thinning on snowpack on the west side of Lake Tahoe. A team led by University of Nevada, Reno ecohydrology professor Adrian Harpold used lidar (three-dimensional radar) to map a patch of forest, then simulated how removing trees of different heights affects snowpack accumulation and melt. “In forest that’s more dense relative to height, results show that taking out some of the smaller trees really can show a net benefit to the amount of snowmelt,” Harpold says. Effects of thinning vary with elevation and which way a slope faces, but thinning appears to have the greatest payoff on some south-facing slopes at low to mid-elevation. The snowmelt simulation is part of a larger multidisciplinary effort for the Lake Tahoe West Restoration Project
, “a comprehensive look at how to restore the forest for multiple uses: fire management, wildlife habitat, recreation.”