Cities boosted rain, sent storms to the suburbs during Europe's deadly
summer floods

Date:
January 7, 2022
Source:
University of Texas at Austin
Summary:
A study used computer models to investigate how cities and climate
change influenced the destructive and deadly rainstorm that struck
the Rotterdam-Brussels-Cologne metropolitan region on July 14,
2021. The study found that the interplay of large-scale climate
and local-scale urbanization intensified the storm, causing more
rainfall than either climate or urbanization on its own.



FULL STORY ==========================================================================
When it comes to extreme weather, climate change usually gets all the attention. But according to a study from The University of Texas at
Austin and two universities in China, the unique effects of cities --
which can intensify storms and influence where rain falls -- need to be accounted for as well.


==========================================================================
"In addition to cutting emissions we need to recognize that understanding
the effects of urbanization is part of the solution," said Dev Niyogi,
a professor in the UT Jackson School of Geosciences and Cockrell School
of Engineering.

Niyogi is a co-author on a study published in Geophysical Research Letters
that used computer models to investigate how cities and climate change influenced the rainstorm that struck the Rotterdam-Brussels-Cologne metropolitan region on July 14, 2021.

The model found that the interplay of large-scale climate and local-scale urbanization intensified the storm, causing more rainfall than either
climate or urbanization on its own.

The severe weather system was part of a storm complex that dropped heavy
rain across Western Europe in the summer of 2021, causing destructive
and deadly flooding that killed at least 242 people, making it one of
the deadliest floods in European history.

The research team also included scientists from Nanjing University and
Tsinghua University.



========================================================================== Urbanization is known to impact local climate and invigorate storms. City buildings are taller and closer together, which can stall storm systems
while directing them away from the city center. And cities' warmer
relative temperatures and higher levels of pollution can often increase moisture in clouds.

In the new study, researchers found that interplay between a warmer
climate and city environment focused the rainstorm on suburban areas
and boosted rainfall by 50% when compared to the influence of the city
alone. That means that of the near 6 inches of rainfall that fell on
the metropolitan region on July 14, about three inches of it can be
attributed to these interactions.

To conduct the study, the scientists created a storm computer model that included the effects of the environment, city and climate. The model of
the storm proved to be representative of the actual event. The storm
centered over the same regions in eastern Belgium and western Germany
and unfolded over the same timeline with the simulation running from
July 13 -17 with the most rain falling on July 14. The model slightly overestimated the total amount of rain that fell, simulating 7.2 inches
instead of the near 6 inches measured by rain gauges.

In addition to simulating the actual storm environment, the researchers
also created simulation models that replaced cities with undeveloped
land and lowered the temperatures to pre-industrial levels. Doing this
helped the researchers determine how cities and climate each influenced
the storm, as well as their combined impact.

Although the influence of the climate and the city together had the
greatest impact, lead author Long Yang, an associate professor at Nanjing University, said that, when viewed individually, the influence of the
city equals or outweighs that of climate change.



==========================================================================
"We are the first group to reveal that the regional impacts through land- atmosphere interactions on extreme rainfall is comparable or more critical
than that induced by climate-scale processes," Yang said.

The models apply to one extreme storm. Nevertheless, Niyogi said that
the results conform with different urban rainfall studies and show the importance of incorporating the influence of urbanization and regional landscapes into climate models in general.

He also added that adapting to climate change provides an opportunity
to plan more resilient communities that can help shape desired climate outcomes, such as cities that can send storms away from flood-prone
regions.

"At more local scales, there are immediate ways to develop climate
resiliency where you don't have to wait for 100-plus nations signing on to declarations," Niyogi said. "It's something you can do at the city scale,
the regional scale." The study's additional co-authors are Professor
Guangheng Ni and Fuqiang Tian from Tsinghua University in China.

========================================================================== Story Source: Materials provided by University_of_Texas_at_Austin. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Long Yang, Guangheng Ni, Fuqiang Tian, Dev Niyogi. Urbanization
Exacerbated Rainfall Over European Suburbs Under a Warming Climate.

Geophysical Research Letters, 2021; 48 (21) DOI:
10.1029/2021GL095987 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220107084317.htm
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