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Project aims to improve accuracy of climate change models

There’s broad scientific consensus that, because of climate change, the western U.S. will have less water and the northeastern U.S. will have more. But how much less and how much more is deeply uncertain, presenting a critical challenge for the scientists, policymakers and public servants tasked with ensuring the nation’s water supply.

Flavio Lehner, assistant professor of earth and atmospheric sciences, is working to reduce that uncertainty, by improving the climate models on which future water projections are based. Lehner won a three-year, $500,000 grant from the National Oceanic and Atmospheric Administration (NOAA) to do that work, beginning this fall.

Flavio Lehner

Dan Barrie, a program manager in NOAA’s Climate Program Office, said Lehner’s work will improve NOAA’s climate models and enable the agency to make better short-term predictions of floods and droughts and better long-term projections of how surface water systems will evolve in the 21st century.

“The United States is experiencing profound changes in its regional water resources,” Barrie said. “It is more urgent than ever to have the best modeling tools to provide a vision of these future changes so that we can take cost-effective measures now to mitigate and adapt to them.”

Lehner’s research, which will improve climate modeling globally, was based on similar research he began in the Colorado River. Current estimates predict that for every degree Celsius of global warming, the Colorado River will lose between 3 to 15% of its streamflow.

Lehner compared the differences in climate models to the disparity in human reactions to COVID-19 – assessing whether an individual has COVID-19 is relatively simple, but predicting how sick the virus will make each person is much more difficult. A similar principle is at play in climate modeling, he said.

“For example, for the Colorado River, all of the numbers point in the same direction – in a warmer climate, there will be less water. But the big uncertainty is how much less,” Lehner said.

To test the sensitivity of climate models, Lehner’s group is studying 70 years of data on precipitation, temperature and streamflow, to assess how well current models would have predicted what actually happened.

“The most important question to us is: How sensitive are these models to changing environmental factors, such as changes in temperature and atmospheric greenhouse gases? And is their sensitivity consistent with what we see in reality?” he said.

The models Lehner and colleagues are using are more complicated and ultimately more useful because they take into account multiple interacting systems. Rather than just measuring rainwater or groundwater, Lehner is examining how atmospheric, terrestrial and hydrologic systems interplay, in the presence of increasing temperatures and atmospheric greenhouse gases. For example, there is now 40% more carbon dioxide in the air today than there was 100 years ago, and the earth is 1 degree Celsius warmer.  Even if precipitation remained neutral, those changes would cause plants to alter their behavior – consuming more groundwater to prevent parching, and thus leaving less to become stream runoff available to humans. But with added complexity comes added uncertainty.

“We already have a sizable uncertainty because we don’t know how much precipitation is going to change, but if you go one step further and say, how does runoff or streamflow change? The uncertainty becomes even larger,” Lehner said.

Modern climate modeling expanded dramatically in the 1980s and has provided useful and accurate information to help scientists and policymakers plan and adapt, Barrie said. Since 1980, the U.S. has experienced an average of 7.1 major weather or climate disasters per year, each causing losses of more than $1 billion. But in the past five years, the annual average of major disasters has jumped to 16.2, according to NOAA.

“Improving climate models is one step to ensuring that equitable adaptation efforts can be implemented to minimize net negative impacts on people and the economy. The cost of investments like Dr. Lehner's research project pales in comparison to the magnitude of the potential benefits,” Barrie said.

Krisy Gashler is a writer for the College of Agriculture and Life Sciences.

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