In the early 2000s, Inez Fung had reached an impasse. She had just been named to her current professorship in atmospheric science at the University of California, Berkeley, and was working with colleagues to formulate a mathematical model of how warming feeds warming in Earth’s climate system—that is, how the decreasing capacity of land and ocean to take up carbon dioxide accelerates overall temperature increases. A major uncertainty involved the resilience of vegetation in the face of climate change.
The uncertainty, recalls Fung, arose from a lack of cross-disciplinary knowledge about the fate of rainwater, which made it difficult to assess how well trees could sustain droughts. “All we had were assumptions about water underfoot,” she explains. “Atmospheric people were done when rain hit the ground. Tree people perked up only after the rain fell, and the stream and geology people didn’t start thinking about it until the tree people were done.”
Fung proposed a digital sensor network to track rainwater as it moved through soil, rock, tree roots, and sap, until it departed via creek or transpiration. She got private foundation funding to install it on a Northern California hillside, where it has generated the insights that 30 percent of the rainfall gets trapped in weathered bedrock some 20 to 50 feet below the surface, and that trees with deep roots can tap this “rock moisture” through the summer. Thus, the resilience of trees may be linked to local geology. The project still operates with National Science Foundation support.
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