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False Alarm, Part 356: Study Finds No Evidence That Climate Change Caused More Severe Flooding

A new study conducted by federal scientists found no evidence that climate change has caused more severe flooding in the United States during the last century.

But scientists at the U.S. Geological Survey (USGS), who published their findings in the Hydrologic Sciences Journal Monday, said they will continue to examine the issue, noting that more research is necessary to better understand the relationship between climate change and flooding.

Scientists have long raised red flags about the impacts of climate change, including sea level rise, desertification and drought. In recent years, scientists have increasingly turned their attention to the effect of climate change on severe weather like hurricanes and tornadoes.

USGS scientists warn that the study does not indicate there is no relationship between flooding and climate change. Instead, they say, it underscores the complexity of the issue. The study comes after the United States faced major flooding this year.

The USGS study — titled “Has the magnitude of floods across the USA changed with global CO2 levels” — found no clear relationship between the increase in greenhouse gas emissions blamed for climate change and the severity of flooding in three of four regions of the United States.

There is “virtually no evidence of increases or decreases in flood magnitudes” during the last 100 years in the northwestern and southeastern United States, USGS said. The study found that the northeastern United States “shows a tendency towards increases in flooding over this period.”

But the study was able to identify a clear relationship between flooding and climate change in the southwestern portion of the United States. In that region, floods have become less severe as greenhouse gas emissions have increased, the study says.

“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 Robert Hirsch, a USGS scientist who was the lead author of the study, in a statement.

Hirsch said USGS scientists will examine a number of other factors including “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.”

The study shows that scientists need more information about the flow of various U.S. streams and rivers, USGS Associate Director for Climate and Land Use Change Matthew Larsen said.

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