What Does The IPCC Say About Flooding?

  • Date: 26/02/14
  • Paul Matthews, The IPCC Report

In view of the current wave of hysteria about flooding and the bogus claims from people who ought to know better, it’s timely to have a look at exactly what the IPCC has said about flooding.

IPCC SREX 2011

In late 2011 / early 2012 the IPCC published a Special Report on Extreme Events, known as SREX for short.  This was a joint production of WG1 and WG2. Here is the statement on floods from the SREX SPM:

There is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at regional scales because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes.

So they don’t even know whether flooding is increasing or decreasing – in which case it might have been more logical to say that there is not really any detectable change. On possible future change, they are similarly uncertain:

Projected precipitation and temperature changes imply possible changes in floods, although overall there is low confidence in projections of changes in fluvial floods.

AR5 2013

Turning now to the AR5 report, the first point to note is that the SPM does not include the word “flood” at all. There is an item in Table SPM1 on heavy precipitation events, which says there have been “likely more land areas with increases than decreases”, a less confident statement than in AR4 (“likely over most land areas”).

In the main text, flooding is discussed in chapter 2, section 2.6.2.2. Here is what it says (references removed):

AR5 WGII assess floods in regional detail accounting for the fact that trends in floods are strongly influenced by changes in river management. While the most evident flood trends appear to be in northern high latitudes, where observed warming trends have been largest, in some regions no evidence of a trend in extreme flooding has been found, e.g., over Russia based on daily river discharge. Other studies for Europe and Asia show evidence for upward, downward or no trend in the magnitude and frequency of floods, so that there is currently no clear and widespread evidence for observed changes in flooding except for the earlier spring flow in snow-dominated regions.
In summary, there continues to be a lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.

Roger Pielke provided a useful summary of what the IPCC AR5 actually says about extreme events. His final are words were prophetic:  “Of course, I have no doubts that claims will still be made associating floods, drought, hurricanes and tornadoes with human-caused climate change – Zombie science – but I am declaring victory in this debate. Climate campaigners would do their movement a favor by getting themselves on the right side of the evidence.”

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