Damaging thunderstorm winds increasing in central U.S.
Analysis shows impact of climate change on outflow from thunderstorms
Destructive winds that flow out of thunderstorms in the central United States are becoming more widespread with warming temperatures, according to new research by the U.S. National Science Foundation (NSF) National Center for Atmospheric Research (NCAR).
The new study, published this week in Nature Climate Change, shows that the central U.S. experienced a fivefold increase in the geographic area affected by damaging thunderstorm straight line winds in the past 40 years. The research uses a combination of meteorological observations, very high-resolution computer modeling, and analyses of fundamental physical laws to estimate the changes in the winds, which are so short-lived and localized that they often are not picked up by weather stations.
The work was funded by NSF, which is NCAR’s sponsor, and by the MIT Climate Grand Challenge on Weather and Climate Extremes.
“Thunderstorms are causing more and more of these extreme wind events,” said NCAR scientist Andreas Prein, the author of the new study. “These gusts that suddenly go from no wind at all to gusts of 60 to 80 miles per hour can have very damaging impacts on buildings, power grids, and even human safety.”
Capturing small-scale events
Straight line winds are caused by powerful downdrafts that flow from the base of thunderstorms. The National Weather Service classifies such winds as damaging if they exceed 50 knots, or about 57 miles per hour. The winds likely cause about $2.5 billion in damage annually in the US, based on insurance industry estimates. In 2020, a particularly powerful derecho — a widespread, straight-line windstorm associated with fast-moving thunderstorms — caused an estimated $11 billion in damage in the Midwest.
Scientists have long been interested in the impact of climate change on straight line winds. Until now, however, simulations of climate conditions run on computer models have been too coarse to capture such brief and small-scale events. Further clouding the picture, weather observations appear to show that there are more periods of little to no wind worldwide (a phenomenon known as global stilling), even though, paradoxically, maximum wind speeds can rise simultaneously.
To determine if damaging straight line winds are becoming more widespread, Prein turned to a high-resolution, computer model simulation that NCAR scientists recently produced in collaboration with the U.S. Geological Survey. The advanced simulation is named CONUS404 because it simulates climate and hydrological conditions at a resolution of 4 kilometers (2.5 miles) across the continental United States, or CONUS, over the past 40-plus years.
Prein focused on summertime conditions in the central U.S., a global hotspot for straight line winds. The high-resolution modeling enabled him to get a much more fine-grained picture of winds than relying on sparse atmospheric observations, and to expand his analysis from 95 weather stations to 109,387 points in the simulation. The simulation showed that the area affected by straight line winds has increased in the last 40 years by about 4.8 times.
Prein verified the accuracy of the simulation by comparing it with measurements of selected winds in the past, such as the 2020 derecho. His analysis showed that the CONUS404 simulations were reliably capturing straight-line winds, as opposed to previous, coarser simulations that failed to capture many such events.
This left the question of whether climate change could be responsible for the increase in winds. Prein approached this question by analyzing the thermodynamics of straight line winds and how actual wind events such as the 2020 derecho would have been affected by different atmospheric conditions based on first-order physical principles.
Straight line winds result when rain and hail at high altitudes evaporate and cool the ambient air, which then plummets and, at the surface, spawns intense winds that rush outward. In studying this process, Prein’s calculations showed that climate change is likely altering the picture by increasing the temperature difference between the cool air in downdrafts and the warm surrounding air. This larger temperature difference lets the cold air descend even faster, making it more likely for a thunderstorm to generate damaging winds.
“As these findings show, it is crucial to incorporate the increasing risk of straight line winds when planning for the impacts of climate change so we can ensure the future resiliency of infrastructure to this frequently neglected peril,” Prein said.
This material is based upon work supported by the National Center for Atmospheric Research, a major facility sponsored by the National Science Foundation and managed by the University Corporation for Atmospheric Research. Any opinions, findings and conclusions or recommendations expressed in this material do not necessarily reflect the views of the National Science Foundation.
About the article
Title: “Thunderstorm straight line winds intensify with climate change”
Author: Andreas F. Prein
Journal: Nature Climate Change
On the web: news.ucar.edu
On X: @NCAR_Science
JOURNAL
Nature Climate Change
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Thunderstorm straight line winds intensify with climate change
ARTICLE PUBLICATION DATE
2-Nov-2023
Study links changes in global water cycle to higher temperatures
Over last 2,000 years, rising and falling temperatures have altered the way water moves around the planet
Peer-Reviewed PublicationIt’s a multi-billion dollar question: What will happen to water as temperatures continue to rise? There will be winners and losers with any change that redistributes where, when and how much water is available for humans to drink and use.
To find answers and make informed predictions, scientists look to the past. Reconstructions of past climate change using geologic data have helped to show the far-reaching influence of human activity on temperatures since the Industrial Age. But assembling hydroclimate records for the same timeframe has proved to be much harder.
A study from the Past Global Changes (PAGES) Iso2k project team, led by Bronwen Konecky at Washington University in St. Louis, takes an important step toward reconstructing a global history of water over the past 2,000 years. Using geologic and biologic evidence preserved in natural archives — including 759 different paleoclimate records from globally distributed corals, trees, ice, cave formations and sediments — the researchers showed that the global water cycle has changed during periods of higher and lower temperatures in the recent past.
“The global water cycle is intimately linked to global temperature,” said Konecky, an assistant professor of earth, environmental and planetary sciences in Arts & Sciences at Washington University and lead author of the new study in Nature Geoscience.
“We found that during periods of time when temperature is changing at a global scale, we also see changes in the way that water moves around the planet,” she said.
The water cycle is complex, and rainfall in particular has geographic variations that are much more drastic than air temperature. This has made it difficult for scientists to evaluate how rainfall has changed over the past 2,000 years.
“We decided to start with water isotope records because they reflect holistic signals and because they’re recorded in all kinds of different natural archives,” Konecky said. “This is a first step toward reconstructing drought or rainfall patterns at the global scale during the past 2,000 years.”
An intertwined cycle
The global water cycle is vast and intertwined. Water evaporates from the surface of the Earth, rises into the atmosphere, cools and condenses into rain or snow in clouds, and falls again to the surface as precipitation. Each water molecule that is part of the cycle has a certain isotopic ‘fingerprint,’ or composition, which reflects small variations in the atomic weight of the oxygen and hydrogen atoms that comprise the molecule. So, individual water molecules can be heavier or lighter.
With this new study, the scientists found that when global temperature is higher, rain and other environmental waters become more isotopically heavy. The researchers interpreted these isotopic changes and determined their timeline by synthesizing data from across a wide variety of natural archive sources from the past 2,000 years of Earth history.
The PAGES Iso2k project team — which includes more than 40 researchers from 10 countries — collected, collated and sometimes digitized datasets from hundreds of studies to build the database they used in their analysis. They ended up with 759 globally distributed time-series datasets, representing the world’s largest integrated database of water isotope proxy records.
Piecing together signals from many different types of natural archives can be like piecing together apples and oranges. Konecky and the project team knew, however, that water isotopes record climate signals in specific ways in different natural archives. Carefully assembled, this common thread could help them to compare a tree ring to an ice core.
“Every archive is different,” Konecky said. “To make matters more complicated, datasets from different archives are generated by different scientific communities with their own terminology, norms and reference materials. We came up with data description fields (metadata) for the database that translate each record’s particularities into a common tongue that makes it possible to compare variations in one archive to variations in another. This process took years!”
The team met once in person and then did everything afterward by teleconference. They organized co-working sessions at odd hours to accommodate time zones from Hawaii to Japan to Australia to Europe and in between. “We even spent one New Year’s Eve working on the database and the analyses that led to this paper,” Konecky said.
More water cycle changes to come
Global scale relationships between temperature and the isotopic composition of certain environmental waters, like seawater and glacial ice, have long been recognized as the planet moves in and out of ice age cycles. Local scale relationships with temperature on timescales of minutes to months are also well established.
But this study provides the first evidence that temperature and the isotopic composition of environmental waters go hand in hand at timescales in between these two — that is, over decades to centuries.
It’s a rapid adjustment, Konecky said. “As the planet warms and cools, it affects the behavior of water as it leaves the oceans and the vigor of its motions through the atmosphere,” she said. “The isotopic signals in these waters are very responsive to temperature changes.”
The scientists found that global mean surface temperature exerted a coherent influence on the isotopic composition of global precipitation and “meteoric water” (water in lakes, rivers and ice melts) throughout the past 2,000 years. The changes they observed were driven by global ocean evaporation and condensation processes, with lower values during the period of time known as the Little Ice Age (1450-1850) and higher values after the onset of human-caused climate warming starting around 1850.
When it comes to the specific impact of these changes on future rainfall and water availability, it is too early to predict who will win and who will lose. But this study’s data from the last 2,000 years suggest that more water cycle changes are likely as global temperatures continue to increase. June, July and August 2023 were the hottest months on record for our planet.
“The way water behaves when it leaves the oceans and moves around the atmosphere and rains out — that behavior is strongly impacted by changes in atmospheric temperature,” Konecky said.
JOURNAL
Nature Geoscience
ARTICLE TITLE
Globally coherent water cycle response to temperature change during the past two millennia
ARTICLE PUBLICATION DATE
2-Nov-2023
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