Posts Tagged ‘Flood’

Floods and Global Warming is fashion not science

February 18, 2011

There is the attempt to link current weather to long term climate, to use computer models to achieve the evidence, and to alarm the public and policy makers that climate change is real and here.

Roger Pielke Jr. points out:

Nature published two papers yesterday that discuss increasing precipitation trends and a 2000 flood in the UK.  I have been asked by many people whether these papers mean that we can now attribute some fraction of the global trend in disaster losses to greenhouse gas emissions, or even recent disasters such as in Pakistan and Australia. I hate to pour cold water on a really good media frenzy, but the answer is “no.”  Neither paper actually discusses global trends in disasters (one doesn’t even discuss floods) or even individual events beyond a single flood event in the UK in 2000.  But still, can’t we just connect the dots?  Isn’t it just obvious?  And only deniers deny the obvious, right? ….

In short, the new studies are interesting and add to our knowledge.  But they do not change the state of knowledge related to trends in global disasters and how they might be related to greenhouse gases.  But even so, I expect that many will still want to connect the dots between greenhouse gas emissions and recent floods.  Connecting the dots is fun, but it is not science.

And Andrew Revkin goes to town in his New York Times blog about how uncertainties and caveats disappear when a political corner is being fought:

….. In scientific literature you rarely see statements so streamlined and definitive. For climate science, this is the equivalent of a smoking gun. News indeed. Add in the extreme floods last year (a period not included in the study) and you have more relevance, although Roger Pielke Jr. this morning notes the importance of distinguishing between analysis of certain kinds of extreme precipitation events and disastrous flooding.

The problem is that the Nature paper is not definitive at all, as you’ll see below.

None of this detracts from the importance of this work, or the overall picture of an increasingly human-influenced climate, with impacts on the frequency of gullywashers.

But this does raise big questions about the standards scientists and journals use in summarizing complex work and the justifiable need for journalists — and readers — to explore such work as if it has a “handle with care” sign attached.

This is not about “ false balance.” This is about responsible reporting.

A previous instance occurred in 2006, when a paper in Science on frog die-offs in Costa Rica included this firm and sobering statement:

Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming.

Things were far more complicated, of course, as you can read in my 2008 piece on Vanishing Frogs, Climate and the Front Page.

Iceland volcano watch stands down

November 6, 2010

Jökulhlaup from Grímsvötn subsides

The earlier concern about meltwater flooding from the Grimsvotn glacial lake in Iceland which could have signalled that the volcano underneath was about to erupt has subsided.

Bridge over Gígjukvísl

Figure 1. The jökulhlaup from Grímsvötn: image

The jökulhlaup (glacial outburst flood) from Grímsvötn that began near the end of October is now coming to an end. The flood reached a maximum level shortly after noon on November 3, and scientists from IMO visited the site on that day to study the effects of the flood on the region adjacent to the ice margin. Two IMO technicians have performed regular discharge measurements on the bridge over the river Gígjukvísl throughout this week (Figure 1) and the results from their measurements are shown in Figure 2.

Figure 2. Discharge (m3/s) measurements at Gígjukvísl bridge: From the curve the total amount of floodwater is estimated 0.45 km3

The discharge curve is typical for jökulhlaups from Grímsvötn that do not result from volcanic activity: Over the course of several days, the amount of water flowing through an ice tunnel at the glacier bed steadily increases. Loss of frictional heat from the floodwater causes melting of the tunnel walls, thereby increasing the flow capacity of the tunnel.

In past centuries, most jökulhlaups from Grímsvötn have entered the course of the river Skeiðará. This time, however, floodwater that emerged from beneath the eastern part of the glacier went westwards along the glacier margin and then entered the river Gígjukvísl. Skeiðará has deposited very large amounts of sediment on the eastern part of Skeiðarársandur plains over the centuries, increasing the elevation of the sandur area there relative to the central part. In addition, the glacier has carved a trench during times of advance. Thus, it was clear that retreat of the glacier over the past 15 years would sooner or later lead to a drastic shift in the direction of meltwater flow from this part of the glacier. In the summer of 2009, this shift occurred and water has ceased to enter the course of Skeiðará.


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