Forests will grow faster, suck up more moisture
After taking a big-picture look at the water cycle, U.S. Forest Service researchers say global warming may decrease the amount of water produced by forests and grasslands across the country — even with increases in precipitation.
National forests and grasslands contribute about 14 percent of the national water supply. Global warming may spur growth on those lands, while water yield simultaneously decreases, as forest water use (through evaporation and transpiration) increases dramatically with higher air temperatures, according to a new study.
By 2100, this elevated water use could increase ecosystem productivity — the growth of trees and other vegetation — by 8 to 24 percent, leading to a projected 4 to 7 percent decrease in water yield. The most severe declines in water yield could be seen in the Northwest, West North Central, and Southwest regions of the United States.
“A notable tradeoff between water yield and productivity is expected to intensify under higher greenhouse gas emissions and associated climate change in the future, posing greater challenges to managing these lands and balancing these important ecosystem services,” said Kai Duan, a North Carolina State University postdoctoral researcher working with the Forest Service Eastern Forest Environmental Threat Assessment Center and the study’s lead author.
The study modeled the water cycle on 170 U.S. national forests and grasslands based on projections from 20 global climate models.
“From a long-term perspective, the major threat that climate change poses on forest ecosystems is the large rise in air temperature and altered patterns in water balance,” said Ge Sun, Eastern Threat Center research hydrologist and corresponding author of the study. “A better understanding of water and carbon responses to climate change is vital for land managers and decision makers to develop appropriate mitigation and adaptation strategies to sustain the broad variety of ecosystem services provided by our national forests and grasslands.”
The article is available online at http://www.nature.com/articles/doi:10.1038/srep24441.