Guest essay by Eric Worrall
Paris, France recently suffered severe flooding. Naturally Climate Scientists have blamed the May 2016 Paris floods on Climate, though it was admitted the floods fell well short of the Great Flood of 1910.
Flooding began first on smaller rivers including the Yvette and Loing — south of Paris (Figure 1). The Loing River, a tributary of the Seine, rose to levels not seen since 1982 but still short of the catastrophic January 1910 Paris floods when the Seine reached 8.0 meters (26.2 feet). The Seine – which runs directly through the heart of Paris – peaked at 6.1 meters (20 feet ) above its normal height during the night of June 3rd — a 34-year high. Farther south, in the heart of the Loire basin, tributaries of the Loire River, including the Retreve and the Sauldre Rivers, reached 50-year highs between May 31st and June 1st, flooding highways and the historic 16th-century Chambord castle. The timing of this flood was quite unusual as virtually all previous floods along the Seine and Loire River basins have occurred during winter (as opposed to spring) due to buildup of excess water over several months during the winter. Only two instances in the historical record — July 1659 and June 1856 — show flooding in months other than December, January, February or March. Clearly, this event appears to be a combination of a very wet month of May in general, coupled with very high 3-day rainfall totals in particular. Managing resulting flood risk is particularly challenging at this time of year because many reservoirs are already close to full to prepare for a typically dry summer season.
This year’s May rainfall amounts were exceptional at some stations in France (see Figure 2). The Paris-Montsouris station, recording 179 mm (7 inches), received roughly 3 months worth of rain in one month. The previous record of 133 mm (5.2 inches) was set in 1992. Orleans saw 181 mm (7.1 inches), also about 3 months of precipitation in one month. The old record was 148 mm (5.8 inches) set back in 1985.
What is the history of flooding in Paris? Information on floods is a little difficult to find, perhaps because I don’t speak French, but the following from a critical OECD report on Parisian flood risk preparedness is revealing;
While the possibility of a major flood of the Seine River may initially seem remote, it comes back regularly and arouses public attention as was the case during the spring of 2013 when floods took place upstream of the Seine River basin. Even though the flooding did not cause any major damage, it reopened the question of risk management and the region’s vulnerability to flooding. The prospect of a historic event is a key concern for French risk management stakeholders. The 1910 flood was particularly destructive in the context of an era marked by industrial and technological progress. Such events illustrate the difficulties societies have in compromising between economic development and the management of increased vulnerability of society and multiple economic sectors.
1924 and 1955 also saw major flood events in the Paris region and in the entire Seine basin. Nevertheless, the lack of a significant flood for more than 60 years tends to lessen the memory of risk. Seine floods are characterised by their slow progression and, following on a period of submersion which may be very long. For instance, the waters took almost two months to subside in 1910. Even if the effect of climate change on the frequency and extent of the Seine floods is still uncertain, greater floods than the one of 1910 are still possible, such as the one that occurred in 1658. In other countries, many recent floods significantly exceeded the 100-year levels. This was the case with the floods in Queensland, Bangkok, and Pakistan; as well as during the coastal flooding following hurricane Sandy in New-York, and the 2013 floods in Germany. The EU Floods Directive uses the 1000-year frequency as a reference for extreme events.
On the basis of the OECD report, the claim that the 2016 flood was climate related seems a little thin. Not only was the 2016 flood significantly less severe than a comparable flood which occurred in 1910, the 2016 flood occurred after a 60 year absence of major Paris floods, after major floods in 1910, 1924 and 1955.
There does not appear to be any evidence which supports the theory that climate is somehow exacerbating the frequency or severity of flooding in Paris.
UPDATE: They say a picture says a thousand words, this one not only does that, but speaks with authority. Thanks to Josh for the image, originally sourced from the BBC here. – Anthony