What were the physical factors involved in the 2007 floods of the River Severn area?

Question

I understand about the human factors such as people building on flood plains etc, environment agency not putting out warnings etc etc.

What i want to know is what really caused the floods, and how far is global warming to blame? or is it not?

Answer 1

The main reason for the exceptionally wet weather in the UK this summer has been that the Jet Stream is located further south than usual. Normally during the summer it woulld pass between Scotland and Iceland, this year it's been running across Wales, Central England and out across the North Sea to Scandinavia.

The jet stream is a high altitude, fast moving stream of air and it can act as a barrier to other weather systems. Normally in the UK summer arrives from southern Europe but this year it's arrival was blocked. At the same time, the jet stream brings in a series of depressions from the Atlantic bringing rain with them.

Global warming has a part to play in that warmer temps mean greater evapouration of water from the seas and oceans, this subsequently falls as rain (or snow). Globally rainfall levels have increased and it's a trend that's set to continue. A few years ago the Met Office predicted a nine fold increase in flooding events by the end of the century, now is probably a good time to move to a house on a hill, away from streams and rivers.

Answer 2

When you get exceptionally heavy rain, the main river is carrying much more water than normal. The Severn is one of the fastest flowing rivers in the UK. (That's why there is the Severn Bore, the river and the incoming tide meet at the estuary). Tributary rivers and streams can't force their way into the fast flowing main river and start to back up. Result: flooding. Of course, continuous heavy rainfall over a few days also contributes, since the surrounding areas are sodden and can't absorb any more water when the smaller rivers and streams overflow their banks.