Interesting article from Water Deeply, and if the results are implemented into policy, we will have yet another reason to build Auburn Dam.
A century of fire suppression has left Western forests overgrown. That has interrupted nature’s regular fire cycle and means that when fires do happen, they become catastrophic because there is plentiful fuel to burn. It also means forests are sucking up more water than they did historically.
How much more water? That’s always been difficult to estimate. But making this calculation could go a long way toward fixing the overgrown forest problem. If we know how much water could be freed up by thinning forests to reduce fire danger, it could create a new financing mechanism to do the expensive work of cutting trees and staging controlled burns.
A team of scientists from the University of California and the National Park Service now has some answers. In a new study, they combined sensors that measure evapotranspiration – how much water trees exhale – with satellite images of “greenness” on the landscape to estimate the additional freshwater runoff that could be created by thinning overgrown forests.
Results vary depending on local climate and geography, of course. But across California’s entire Sierra Nevada, the research suggests that forest thinning could increase freshwater runoff by 10 percent. That’s not small potatoes in a state where drought is common.
To explain the results further, Water Deeply spoke with Roger Bales, a coauthor of the study and director of the Sierra Nevada Research Institute at the University of California, Merced.
Water Deeply: What water supply benefits did you attribute to forest thinning work?
Roger Bales: One thing we found is that medium-intensity fire is approximately equal to the restoration treatments the Forest Service and others are trying to do. And when you have that medium-intensity fire or the restoration treatment, you can reduce evapotranspiration, which means more runoff.
In the American River basin, the highest we saw was a net evapotranspiration reduction equal to about 55,000 acre-feet of water per year. This is for all of the American River basin. So when you add up all the fires in the American River basin over that time period, from 1990 to 2008, by 2008 you had gained 55,000 acre-feet more runoff compared to 1990.
People would love to have that amount of water. And that does not get us into the most recent decade of more high-intensity fires. This was just the period when we had the best data.