Researchers have evidence that California’s forests are especially vulnerable to multi-year droughts because their health depends on water stored several feet below ground.
“Each year our forests, grasslands and shrublands depend on water stored underground to survive the dry summers, but during multi-year dry periods there is not enough precipitation in the wet winter season to replenish that supply,” said Joseph Rungee, UC Merced graduate student and lead author on a new paper published in the journal Hydrological Processes.
Trees typically need about the same amount of water every year — more in hotter years. During a drought, that subsurface store of water is gradually depleted, causing stress to trees and other vegetation. If the drought is long enough and especially hot, as was the case from fall 2011 through 2015, large numbers of trees run out of water and die.
By analyzing data from the National Science Foundation’s network of Critical Zone Observatories, Rungee worked with UC Merced Professor Roger Bales, with the School of Engineering and the Sierra Nevada Research Institute, to get a better understanding of where and to what extent the below-ground weathered bedrock provides multi-year drought resilience. The researchers delved into data from sites across the semi-arid West to determine the amount of water storage available in the root zones of different areas.
Bales, Rungee and their colleagues wanted to know how dependent different areas in the West are on that subsurface water storage and how many dry years the plants can survive.
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