20 August 2014

New UK Flood Normalization

There are lots of interesting new studies emerging on trends in disasters and extreme events, and their possible relation to changes in climate, human-caused or otherwise. A new paper in the Hydrological Sciences Journal (Stevens et al. here in PDF) finds no evidence for an increase in UK flooding, once the data is normalized for exposure. 

The authors conclude:
Consequences are the combined results of high river flows, pluvial flooding and coastal  flooding, the numbers of people and property exposed to flooding and the effects of flood defence construction and floodplain management policies. The increase in the total number of reported flood events in the 20th century in the UK appears to be a function of the gradual increase in exposure due to urban expansion and population growth. However there is also greater capacity to report flood events. The number of reported ‘Class 3’ flooding events has remained static or decreased slightly over the 20th Century. This is despite the UK population almost doubling and the number of dwelling houses tripling over the same time period.

There is no clear underlying trend in flood reports present in the UK flood data when it is normalised for exposure. Pielke Jr. and Landsea (1998) studied damage caused by hurricanes in the USA. They also found that normalising damage reports to take account of exposure removed the upward trend of losses over time and only left a large decade to decade variation in losses. The lack of a systematic trend in the normalised UK total flood count mirrors these findings. It is also in agreement with studies of trends in river flows (Robson 2002).
As frequent readers here will appreciate, the best way to evaluate the fidelity of any normalization approach is to compare trends in the normalization with trends in the geophysical events. That checks out in this study.

Add Stevens et al. 2014 to the large and growing academic literature indicating that increasing disaster losses cannot at present be attributed to human-caused climate change.