Quantcast

Have Floods Changed with Increasing CO2 Levels?

U.S. Geological Survey

Only one of four large regions of the U.S. showed a significant relationship between carbon dioxide (CO2) in the atmosphere and the size of floods over the past 100 years. This was in the Southwestern region, where floods have become smaller as CO2 has increased.

This does not mean that no strong relationship between flooding and greenhouse gases will emerge in the future.

An increase in flood magnitudes remains one of the most anticipated impacts of climate change, and land and water resource managers are asking questions about how to estimate future flood risks and develop effective flood mitigation strategies for the future.

A new report published by U.S. Geological Survey (USGS) scientists in the Hydrologic Sciences Journal looks at this potential linkage using historical records of floods throughout the nation. Scientists studied flood conditions at 200 locations across the U.S. looking back 127 years through 2008.

"Currently we do not see a clear pattern that enables us to understand how climate change will alter flood conditions in the future, but the USGS will continue to collect new data over time and conduct new analyses as conditions change," said USGS scientist and lead author Robert Hirsch. "Changes in snow packs, frozen ground, soil moisture and storm tracks are all mechanisms that could be altered by greenhouse gas concentrations and possibly change flood behavior. As we continue research, we will consider these and other factors in our analyses."

The decrease of floods in the Southwest is consistent with other research findings that this region has been getting drier and experienced less precipitation as a likely result of climate change.

"The relationship between greenhouse gas concentrations and floods is complex, demonstrating the need for long-term streamflow data to help guide future flood hazard mitigation and water resources planning," said Matthew Larsen, USGS associate director for Climate and Land Use Change. "USGS streamgages provide real-world data to help scientists understand this relationship. Planning for water supplies and flood hazards should be informed by a combination of predictive modeling approaches as well as statistical approaches such as this study."

The USGS operates more than 7600 streamgages across the U.S., collecting data on the amount of water flowing in streams and rivers. This study used data from 200 of these USGS streamgages, each of which had between 85 and 127 years of data through 2008.

Climate changes that could influence flood magnitudes include shifts in the intensity and tracks of various types of storms and changes in the type of precipitation (rain versus snow). The conditions on the landscape when large storms arrive can also change (for example, smaller snowpacks, less soil moisture and less frozen soil). All of these can influence the size of floods. Of course, human activities within the watershed can also have a major influence in the size of floods. These include urbanization, building of dams and levees, and shifts in vegetation types and drainage of soils and wetlands. At the present time, we see much larger changes in flooding from these causes than we can see from greenhouse forcing.

In this study, the U.S. was divided into four large regions, and research showed some regional differences in the way that flood magnitudes have varied with CO2 concentrations over the past century. In the Northwest and Southeast, there is virtually no evidence of increases or decreases in flood magnitudes over the study period. The Northeastern region (which stretches from the middle of the Dakotas and Nebraska all the way east to the New York and New England area) shows a tendency towards increases in flooding over this period.

Has the Magnitude of Floods across the USA Changed with Global CO2 Levels is available online. The article contains a map of the results and extensive tables, which identify the streamgages used in the study and the site-specific findings for each of them.

To learn more about USGS streamgages, click here.

For more information, click here.

EcoWatch Daily Newsletter

Ryan Hagerty / USFWS

It's become a familiar story with the Trump administration: Scientists write a report that shows the administration's policies will cause environmental damage, then the administration buries the report and fires the scientists.

Read More Show Less
Valerie / Flickr / CC BY-NC-ND 2.0

A coalition of some of the largest environmental groups in the country joined forces to file a lawsuit in federal court challenging the Trump administration's maneuver to weaken the Endangered Species Act.

Read More Show Less
Sponsored
beyond foto / Getty Images

By Kimberly Holland

Children who eat a lot of gluten in their earliest years may have an increased risk of developing celiac disease and gluten intolerance, according to a new study published in JAMATrusted Source.

Read More Show Less
Joe Raedle / Getty Images

By Jake Johnson

Calling the global climate crisis both the greatest threat facing the U.S. and the greatest opportunity for transformative change, Sen. Bernie Sanders unveiled today a comprehensive Green New Deal proposal that would transition the U.S. economy to 100 percent renewable energy and create 20 million well-paying union jobs over a decade.

Read More Show Less
orientalizing / Flickr

The Parties to CITES agreed to list giraffes on Appendix II of the Convention on International Trade in Endangered Species (CITES) today at the World Wildlife Conference or CoP18 in Geneva. Such protections will ensure that all giraffe parts trade were legally acquired and not sourced from the poached giraffes trade and will require countries to make non-detriment findings before allowing giraffe exports. The listing will also enable the collection of international trade data for giraffes that might justify greater protections at both CITES and other venues in the future.

Read More Show Less
Sponsored

The WHO stressed that more research is needed on the potential health risks of microplastic ingestion. luchschen / iStock / Getty Images Plus

The UN's health agency on Thursday said that microplastics contained in drinking water posed a "low" risk at their current levels.

However, the World Health Organization (WHO) — in its first report on the potential health risks of microplastic ingestion — also stressed more research was needed to reassure consumers.

Read More Show Less

Brazil's right-wing President Jair Bolsonaro is giving President Trump a run for his money in the alternative facts department.

Read More Show Less
Washington Gov. Jay Inslee delivered his 2019 State of the State address on Jan. 15. Governor Jay and First Lady Trudi Inslee / Flickr

Washington Gov. Jay Inslee, who made solving the climate crisis the center of his presidential campaign, is dropping out of the 2020 Democratic primary race.

Read More Show Less