Friday, January 31, 2014

Is the flooding on the Somerset Levels down to climate change?

RL 27/1/2012

The Somerset Levels flooded for four solid (liquid?) weeks.
We have had the wettest January in UK for 100+ years.

Is this due to global warming/climate change?
Everyone knows that we cannot take any one event and say "That is due to climate change". What we can do is say that climate change has made this event, and many other extreme weather events, more probable.

Climate science predicts that as air warms it will hold more water vapour, which will cause rainfall to be more extreme.

This prediction is borne out by observation. Westra, Alexander and Zwiers of Adelaide University studied water precipitation records of 8000+ good quality weather stations covering more than a century. They published in the Journal of Climate 2013. Two thirds of the stations, especially those near the tropics, showed an increase in extremes of rainfall - either more or less than the average expected. This increase was proportional to air temperature, so that a 1C increase in air temperature was associated with a 7% increase in rainfall extremes.

The value of this study lies in its simplicity and its extent. Rain gauges are the simplest of all weather measurements. And 8000 stations going back 109 years are difficult to argue with.
Flood patterns and river flows are difficult to estimate accurately. Rain gauges are not.

Pall et al. generated several thousand climate model simulations of UK autumn 2000 weather, comparing actual conditions, and cooler conditions with the greenhouse gas component removed. Results were fed into a precipitation-runoff model that is used to simulate severe daily river runoff events in England and Wales (proxy indicators of flood events). In nine out of ten cases the model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%. 

Here's the local evidence:
It has been found that there are general trends of increased volume of rainfall and runoff in winter.
Flood risk and vulnerability are increasing with increased frequency of occurrence of extreme events due to climate change &c.
It found that there are general trends of increased volume of rainfall and runoff in winter.
We have so far experienced 0.8C of warming, compared to pre-industrial levels. Environment Secretary Owen Paterson believes that 2.0C of warming is something that can be shrugged off as trivial. That is why he has cut the budget low carbon climate change initiatives from £26.9 million/yr to £17.2 million/yr. Here he is not denying that he has cut the funding of flood defences.

Paterson is clearly wrong. He should resign.

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