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Climate change made Hurricane Harvey's rainfall worse, study finds

Climate change is partly to blame for the record rainfall that fell over Texas and Louisiana in the days after Hurric...

Posted: Dec 13, 2017 8:18 PM
Updated: Dec 13, 2017 8:18 PM

Climate change is partly to blame for the record rainfall that fell over Texas and Louisiana in the days after Hurricane Harvey's landfall on August 25, according to new scientific analysis.

Human-caused climate change made the rainfall from Harvey, which dumped more than 19 trillion gallons of water and brought devastating floods to the Houston area, roughly three times more likely to occur and 15% more intense, according to World Weather Attribution (WWA), an international coalition of scientists led by nonprofit scientific research group Climate Central, in a report published Wednesday.

The question of whether climate change played a role in the disaster came up almost immediately, as it so frequently does after extreme weather events.

It was assumed that climate change contributed to Harvey's rainfall, as intense rainfall events are one of the most often cited consequences of a warming climate. The observational data and computer models used in this study supported that assumption.

As air temperature warms, it can hold more moisture (about 7% more per degree Celsius of warming), which means there is more water vapor in the air that can be squeezed out as rainfall in a world warmed by climate change.

Other factors, such as changes in upper level winds and sea level rise can also contribute to increased flood events.

The WWA study examined extreme precipitation events in the US Gulf Coast region since 1880 and found "a clear positive trend between 12% and 22%." Using computer models loaded with this data and comparing it to similar models that do not show the climate warming, the authors attempted to quantify the role that the warming climate had on the 2017 event.

Harvey, which rapidly intensified to a Category 4 storm just before landfall near Corpus Christi, Texas, stalled after it moved inland and remained nearly stationary for four days. This allowed rainfall totals to add up in and around Houston, reaching levels never before seen in a landfalling tropical system.

Cedar Bayou, about 30 miles east of Houston, recorded 51.89 inches of rainfall by the morning of August 31. That eclipsed the 48-inch rainfall record from Tropical Storm Amelia in 1978 and set a new record for the continental US.

The biblical flooding across Harris and surrounding counties required more than 120,000 people to be rescued or evacuated, and about 80 people died.

Though the economic impact from Harvey is still being calculated, "it is likely a $100 billion disaster," according to Adam Smith, lead researcher at the National Oceanic and Atmospheric Administration's National Centers for Environmental Information.

"Harvey is the closest modern disaster comparison we have in relation to Katrina in terms of damage costs," Smith told CNN.

The WWA study looked only at the role climate change played in the amount of rainfall Harvey produced, ignoring other variables that made Harvey so exceptional, such as the rapid intensification before landfall and the unusual lack of movement it had in the following days.

"It's clear that Harvey's exceptional rainfall was due to the stalling and looping nature of the track of the storm -- which this study does not address in the slightest," Ryan Maue, a meteorologist with weather.us who was not affiliated with the study, told CNN.

But that doesn't mean Maue is refuting its conclusion.

"There's little doubt that global warming has and will continue to enhance rain rates and intensity, but it's not clear that this paper has teased out all of the possible mechanisms that led to Harvey's extreme flooding impacts," Maue said.

Minnesota Coronavirus Cases

Data is updated nightly.

Cases: 448268

Reported Deaths: 6013
CountyCasesDeaths
Hennepin931011480
Ramsey40016739
Dakota33072340
Anoka30999364
Washington20164228
Stearns17871187
St. Louis13690241
Scott1195496
Wright11614104
Olmsted1048475
Sherburne821365
Carver694836
Clay653280
Rice606868
Kandiyohi554371
Blue Earth541033
Crow Wing482774
Otter Tail457167
Chisago452732
Benton420186
Winona389646
Douglas374166
Nobles370846
Mower365529
Goodhue347958
Polk328658
McLeod325345
Morrison311744
Beltrami310347
Lyon302236
Becker284939
Itasca284543
Isanti282841
Carlton280043
Steele27379
Pine266713
Freeborn245321
Todd231730
Nicollet224636
Brown215134
Mille Lacs214246
Le Sueur210015
Cass207623
Meeker199733
Waseca189316
Wabasha17083
Martin170026
Roseau165416
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Renville137539
Houston135913
Dodge13474
Chippewa131332
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Fillmore12355
Wadena120116
Rock110212
Sibley10857
Aitkin108433
Watonwan10668
Faribault105916
Pennington99215
Kanabec97818
Pipestone94423
Yellow Medicine93714
Murray8815
Jackson85610
Swift83418
Pope7385
Marshall70215
Stevens7018
Clearwater68514
Lac qui Parle65716
Lake63715
Wilkin6259
Koochiching59610
Lincoln4841
Big Stone4573
Unassigned43768
Grant4298
Norman4248
Mahnomen4107
Kittson37219
Red Lake3174
Traverse2503
Lake of the Woods1951
Cook1140

Iowa Coronavirus Cases

Data is updated nightly.

Cases: 305606

Reported Deaths: 4278
CountyCasesDeaths
Polk45754449
Linn17795275
Scott15444163
Black Hawk13773236
Woodbury13016175
Johnson1211749
Dubuque11387150
Pottawattamie8992112
Dallas888671
Story869434
Webster469771
Cerro Gordo466768
Sioux455157
Clinton450361
Warren443938
Marshall427761
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Muscatine390477
Des Moines381841
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Wapello344198
Jasper321959
Lee317130
Marion304952
Jones271349
Henry264330
Carroll255434
Bremer245048
Crawford231022
Boone218417
Washington217632
Benton209444
Mahaska193136
Jackson192031
Tama187757
Dickinson186026
Delaware173736
Kossuth173644
Clay168820
Wright164824
Fayette162322
Hamilton160029
Buchanan159923
Winneshiek155719
Harrison155162
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Clayton151448
Butler148224
Page144715
Floyd139636
Cherokee139027
Mills136416
Lyon135332
Poweshiek132724
Hancock130224
Allamakee127928
Iowa125422
Calhoun12279
Grundy121226
Jefferson120724
Madison12039
Winnebago119429
Mitchell116234
Louisa115030
Cass113341
Chickasaw111612
Sac111215
Emmet110831
Appanoose110538
Union108822
Humboldt105519
Guthrie103024
Shelby102926
Franklin102418
Unassigned9310
Palo Alto9079
Montgomery85622
Keokuk85026
Howard84219
Monroe81218
Clarke7957
Pocahontas77611
Ida74630
Greene6927
Davis69121
Adair68820
Lucas6508
Monona64016
Osceola6409
Worth6113
Taylor5949
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Van Buren49712
Decatur4894
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Wayne41421
Adams2963
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