A University of Connecticut climate scientist confirms that more intense and more frequent severe rainstorms will likely continue as temperatures rise due to global warming, despite some observations that seem to suggest otherwise.

In a research paper appearing this week in the journal Nature Climate Change, UConn civil and environmental engineering professor Guiling Wang explains that data showing the intensity of severe rainstorms declining after temperatures reach a certain threshold are merely a reflection of climate variability. It is not proof that there is a fixed upper temperature limit for future increases in severe rains, after which they would begin to drop off.

“We hope this information puts things in better perspective and clarifies the confusion around this issue,” Wang told UConn Today.  “We also hope this will lead to a more accurate way of analyzing and describing climate change,” said Wang, who led an international team of climate experts in conducting the study, funded by the National Science Foundation’s Division of Atmospheric and Geospace Sciences.

Climate scientists and policymakers closely monitor severe and prolonged rainstorms as they can have a devastating impact on local environments and economies. These damaging storms can cause catastrophic flooding; overwhelm sewage treatment plants; increase the risk of waterborne disease; and wipe out valuable crops.

Wang says the peaks seen in the observational data and climate models simply reflect the natural variability of the climate. As Earth warms, her team found, the entire curve representing the relationship between extreme precipitation and rising temperatures is moving to the right. This is because the threshold temperature at which rain intensity peaks also goes up as temperature rises. Therefore, extreme rainfall will continue to increase, she says.

“In general, extreme precipitation increases with higher temperatures because the air can hold more moisture — although that depends on moisture availability. But beyond a certain point, it is the other way round: the temperature responds to the precipitation, or more strictly speaking, the conditions leading to the precipitation, [such as extensive cloud cover or surface moisture],” explained Kevin Trenberth, an expert on global warming and the lead author of several reports prepared by the Intergovernmental Panel on Climate Change (IPCC), who joined Wang in the study.

Trenberth is currently a Distinguished Senior Scientist in the Climate Analysis Section at the National Center for Atmospheric Research. He shared the 2007 Nobel Peace Prize with former Vice President Al Gore as a member of the IPCC.

“The most obvious example of this is in a drought where there is no precipitation. Another example is in cloudy, stormy conditions, when it is wet and cool. By relating the changes in precipitation to the temperature where the relationship reverses — instead of the mean temperature as in previous studies — we can make sense of the differences and the changes. Moreover, it means there is no limit to the changes that can occur, as otherwise might be suspected if there were a fixed relationship.”

All of which adds up to a soggy future, as climate change continues.

The mission of Dr. Guiling Wang’s Hydroclimatology and Biosphere-Atmosphere Interactions Lab at UConn is to understand and quantify the terrestrial hydrological cycle, its variability, changes, and interactions with the society. With a special focus on water, the lab’s research spans the disciplines of climate and atmospheric sciences, hydrology, and plant ecology. They take “an earth system approach, viewing the Earth’s biosphere, atmosphere, and hydrosphere as dynamically coupled components linked through water, energy, and CO2 exchanges,” according to the website summary.

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