Record precipitation in the UK

**Xnn** · Nov22-09, 08:45 PM

Recently, extremely heavy rain has fallen in the United Kingdom.
Some locations received over 12 inches of rain within a 24 hour period!
This is likely a UK record for the greatest 24 hr rainfall based on records
going back to 1914.

http://www.metoffice.gov.uk/corporat...r20091120.html

Please note that man made global warming is very likely to result in
increases of extreme precipitation in many regions of the world including northern
Europe:

Extremes of daily precipitation are very likely to increase in northern Europe.

Above quote from page 850 of the following:

http://www.ipcc.ch/pdf/assessment-re...-chapter11.pdf

Also, on page 875, a map indicates that the greatest precipitation increases in
Northern Europe are projected for Scandinavia especially during the winter while
decreases are projected for Southern Europe (Spain, Italy and Greece).

**Evo** · Nov22-09, 10:40 PM

Kurdt was telling me that the flood fortifications back in 2005 were overwhelmed, and then they rebuilt them to 2005 standards with no increase to deal with heavier rain.

I was surprised that the engineers failed to build against predictions of heavier rains. Or even that they didn't increase the fortifications from the level that was breached. They decided that it couldn't happen again.

**turbo-1** · Nov22-09, 10:42 PM

Originally Posted by Evo

Kurdt was telling me that the flood fortifications back in 2005 were overwhelmed, and then they rebuilt them to 2005 standards with no increase to deal with heavier rain.

I was surprised that the engineers failed to build against predictions of heavier rains. Or even that they didn't increase the fortifications from the level that was breached. They decided that it couldn't happen again.

Yeah, and New Orleans can't happen again. Our bureaucrats are idiots, not engineers, and when they control the engineers, really bad stuff happens over and over again.

**Xnn** · Nov23-09, 12:00 PM

Don't know how much of it is just political posturing, but the news
reports are claiming it was a once in a 1000 year event
while the fortifications were built for 100 year events.

When Workington's flood defences were rebuilt following the great storms of 2005, residents were assured they could withstand a "once in a century" flood. What the local authorities hadn't reckoned on was that just four years on, the Cumbrian town, and its near neighbour, Cockermouth, would be deluged by what was described yesterday as a once in a millennium event.

http://www.telegraph.co.uk/news/6616...-defences.html

**mgb_phys** · Nov23-09, 12:06 PM

Clever chaps these politicians,
Based on less than 100years of observation they were able to determine that the previous flood was a 1:100 year event and that the events distribution was random.
Now with only one more data point they can tell that this was a 1:1000 year event.

Presumably next years will be a 1:1,000,000 year event

**Borek** · Nov23-09, 12:42 PM

OTOH: you can't build fortifications that sustain everything, you have to somehow estimate risks and decide how much money you can spend. Now and then something extraordinary will hppen.

**mgb_phys** · Nov23-09, 12:51 PM

Originally Posted by Borek

Now and then something extraordinary will hppen.

And when it does you assure everybody that it could never happen again, when it does happen again next year you assure people that THAT event could never happen again.

**matthyaouw** · Nov23-09, 01:41 PM

It's all well and good saying defences should be higher. I'll bet every flood defence in the world would be better for being a bit higher or a bit stronger. The reality is these things are very very expensive and in places we are struggling to maintain what we've got, nevermind improve them. You have to predict how frequently a flood of a certain magnitude will happen (difficult!) and do the best you can to convince the money givers that it's worth protecting against a flood that is expected to happen only once in 1000 years. People do the best they can in a very difficult situation but they won't get it right all the time.

**turbo-1** · Nov23-09, 01:56 PM

Years back when I was consulting for a mill in Wickliffe, KY, very near the confluence of the Ohio and Mississippi Rivers I flew in on a small plane, and most of the area was under water. They had gotten over 6" of rain in a single day, just before I got there. The levee system had trapped all that water so that it couldn't run off to the rivers. This is the same levee system that channels floods and pushes them farther downstream so that the bottom-land can't serve its historical purpose. By getting flooded and silted, the land had its nutrients replenished, periodically, and the downstream flooding would be lessened. Now the silt and nutrients are driven toward the Gulf, and farmers put chemical fertilizer on the bottom-land so they can farm it. It's a bit perverse. The levee system has produced some predictable and undesirable consequences.

**Astronuc** · Nov23-09, 02:09 PM

Originally Posted by Xnn

Don't know how much of it is just political posturing, but the news
reports are claiming it was a once in a 1000 year event
while the fortifications were built for 100 year events.

When I lived in Houston, the once per 100 year events began occuring more frequently than once/decade. In one 10 year period, we had 3 once/100-yr events.

**mgb_phys** · Nov23-09, 04:23 PM

Originally Posted by matthyaouw

you can to convince the money givers that it's worth protecting against a flood that is expected to happen only once in 1000 years.

Usually these events aren't the result of a random 100year storm.
They have a much more direct local cause:

You build a new freeway bypass past a village, all the rain that would have fallen on farmland now falls on concrete, into drains which overflow into rivers. That's the problem in a lot of cumbria.

You build a new housing estate on what was a river meadow. You can't let the houses flood, so you build embankments along the river and channel the water to whichever town happens to be downstream.
- Tip for town planners. if there is a 1000year old village called Landbeach, and on lower ground there is another 1000year old village called Waterbeach then building a housing estate between this and the river might not be a smart idea.

To improve crop yields (of crops that are sold as a subsidy anyway) you put in better field drains, this water gets diverted straight into the river. That's why York now has record floods every year despite being in the same place on the same river for 2000years.