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Climate Change May Mean More Trees and Less Water, Researchers Say

With Californians working to reduce their water consumption and increase supply in response to the ongoing drought, researchers are giving a reminder that people are not the only water users in the state.

A recent study by Michael Goulden and Robert Bales of the University of California shows that another set of thirsty California residents, trees in the Sierra Nevada, are likely to consume more water as the climate warms.  The study, published in the Proceedings of the National Academy of Sciences, measured the effects of temperature on evapotranspiration (ET), the amount of water that evaporates or is absorbed by plants, in the upper Kings River basin of California.  Their findings indicate that as elevation increases, cold weather becomes a progressively significant limiting factor for ET.

The scientists’ concern is that as the climate warms, this limiting factor will be weakened.  Warmer temperatures may allow vegetation to expand to higher elevations and grow more densely, increasing ET and diminishing stream flows. Based on current climate change models, flow in the Kings River could decrease by nearly 30% by 2100.

Goulden and Bales note that this figure could overestimate the effects of climate change, as other factors might affect ET or slow the spread of vegetation.

In addition, people could potentially mitigate the effects of warming by managing forests to thin vegetation.  UC scientists have previously suggested that thinning forests to bring them in line with historical conditions, when periodic fires checked growth, might result in more water in rivers.  UC Berkeley’s Sierra Nevada Watershed Ecosystem Enhancement Project (SWEEP) hopes to measure the effects of targeted forest management on water supply in certain test areas.

It is important to note that trees also serve important roles in protecting water supplies.  For instance, after a major fire destroyed a swath of forest in Colorado’s Front Range in 2012, the US Forest Service arranged to plant nearly 150,000 trees to stabilize the mountainside and prevent eroded soil from filling reservoirs.  Thus, while Goulden and Bales show that ever-denser forests may have a negative impact on water supplies, going too far in the opposite direction would do real damage as well.

Written by Stratecon Staff