Increase in Reported UK Floods Due to Population Growth, Not Climate Change – Study

For years, University of Colorado Prof. Roger Pielke, Jr. has been demonstrating that damages due to hurricanes are not increasing once economic data are adjusted (‘normalized’) for increases in population, wealth, and the consumer price index.

More people with more valuables at higher prices incur greater combined monetary losses when disaster strikes. There is no “greenhouse signal” in properly-adjusted hurricane loss data — no trend reflecting a potential warming-induced increase in hurricane frequency or power.

Source: R. Pielke, Jr. Normalized U.S.  Hurricane Damages: 1900-2012. The gray bar indicates estimated damages from Hurricane Sandy.

University of Amsterdam Prof. Laurens M. Bouwer reviewed 22 studies of damages from tropical storms, thunder storms, tornados, floods, hail, brushfires, and earthquakes over multiple decades in the U.S., Europe, Asia, Latin America, and Australia. He came to the same conclusion:

The studies show no trends in losses, corrected for changes (increases) in population and capital at risk, that could be attributed to anthropogenic climate change. Therefore, it can be concluded that anthropogenic climate change so far has not had a significant impact on losses from natural disasters.

If that seems counterintuitive, it’s because detection and reporting of extreme weather has increased. The improved density and spatial coverage of monitoring systems coupled with round-the-clock weather news makes extreme weather seem much more common today than it was perceived to be, say, in the 1970s.

Apparent increases in one type of extreme weather — flooding — may have an even simpler explanation: more people living in places where floods occur.

A new study by scientists at the University of Southampton Tyndall Center for Climate Change Studies finds that population growth and urban expansion account for the reported increase in damaging floods in the UK over the past 129 years. In the words of lead author Andrew Stevens, a growing population means “more properties exposed to flooding and more people to report flooding.”

From the University’s press release:

A rise in the number of reported floods in the UK over the past 129 years can be related to increased exposure, resulting from urban expansion and population growth, according to new research by the University of Southampton.

In one of the most comprehensive studies of its kind, scientists have discovered that although the number of reported floods has gone up during the 20th and 21st Century, this trend disappears when the figures are adjusted to reflect population growth and increased building numbers over the same period.

Published in the journal Hydrological Sciences, the study looks at data sets from 1884 to 2013 and found an upward trend in reported flooding, with flood events appearing more frequently towards the end of the 20th century, peaking in 2012 when annual rainfall was the second highest in over 100 years.

The rise in UK flood reports over the 20th Century coincides with population growth from 38.2 million to 59.1 million and a tripling in the number of houses, from 7.7 million to 24.8 million.

“As a result there were more properties exposed to flooding and more people to report flooding,” says lead author Andrew Stevens. “A higher exposure to flooding will result in more reported flood events and larger potential damages.”

The study, Trends in reported flooding in the UK: 1884-2013, is available in PDF here.