Nick Rosen | |

What goes up when the rain comes down?

Brace yourself!  Worldwide, 2010 was the wettest year since records began. And it was not just the amount of rain and snow, but the intensity which increased.

Choosing where to live in the future will be much more to do with protecting yourself against flooding than worrying about warmer weather and rising sea levels.

Australia, Pakistan, Tennessee, China, the Philippines, Thailand, Brazil, the Balkans, Bangladesh, Indonesia, Colombia, Sri Lanka, France and the UK all experienced devastating rainfall last year. And there was unusually heavy snowfall in some of those regions.

Why is this happening and what should you do about it? There is a list of tips at the end of the story.

Every scientist agrees that temperatures are rising, and that as warmer air expands it holds more moisture. Each 1 degree centigrade rise in global temperature adds 7% of moisture to the air. It is this that has made rainfall, when it occurs, more intense.

. “The pervasive increase in water vapour changes the intensity of precipitation events with no doubt whatsoever,” Kevin Trenberth of the US National Center for Atmospheric Research announced in January. “Yes, all events. Even if temperatures or sea surface temperatures are below normal, they are still higher than they would have been, and so too is the atmospheric water vapour amount and thus the moisture available for storms.”

Cycles of rainfall are also changing. In the US, Kenneth Kunkel of the National Climatic Data Center in Asheville, North Carolina, analysed data from more than 1000 rain gauges across the country. Over the past 100 years, the intensity of extreme rainstorms that occur once per year on average has risen 1.4 per cent per decade, he found.

he says that in 2000, a “once a year” storm was dumping 14 per cent more rain on average than it would have done in 1900. “It would be wise for society to take this into account when building a dam to last 50 or 75 years, or a new housing development,” says Kunkel. “That’s not really done right now.”

At its most devastating, the intensity of once in 20 years” extreme rainstorms is increasing even faster, by about 3 per cent per decade, although for these rare events the statistics are more patchy. The overall increase also seems to be accelerating. Most of it happened in the last three decades, and Kunkel hasn’t even included 2010 in his analysis yet. “I’m guessing that when the data come in, they are going to be high,” he says.

Other studies show that heavy rainfall has been increasing in intensity in most other parts of the world too These results can’t be put down to changing methods or issues with scientific instruments, as almost all the figures come from the humble rain gauge, unchanged over the decades. “It is basically an 8-inch bucket– so simple that you almost can’t call it technology,” says Kunkel.

Insurers agree They are seeing a rise in claims for flooding. Claims for flood damage are rising faster than claims for other natural disasters such as earthquakes and eruptions, says Gerd Henghuber, a spokesman for insurance firm Munich Re. “The growing number of weather-related catastrophes most probably cannot be fully explained without climate change.”

So warmer weather is leading to wetter weather, empirical evidnece confirms that more rain is falling and at least one insurer says that the rain is causing more destruction– welcome to Global Storming

In 2007,Nature magazine compared the results of 14 different models of rainfall data for the 20th century. The models that included greenhouse gas emissions matched the overall global pattern seen so far, with increased rainfall in most regions (Nature, vol 448, p 461).

Still, that study looked only at total precipitation. When it comes to flooding, what really matters is whether climate change is making extreme events even more extreme. This is a harder question to tackle, partly because extreme events are rare and so our information on them is limited.

In another recent study, a team led by Allen looked at one specific event– the floods that occurred in the UK in autumn 2000, causing £1.3 billion worth of damage. With the help of computer time loaned by volunteers via climateprediction.net, they did thousands of model runs simulating the weather in 2000, with initial conditions both as they were and as they could have been without global warming. They found that climate change had nearly doubled the likelihood of this kind of flood (Nature, vol 470, p 382).

As the world continues to warm, we can expect each year to bring a more fearsome storm.  “You can have a situation where mean rainfall decreases but the extremes increase,” forecasts Kendon. Other computer models suggest that the amount of rainfall on the worst 5 per cent of rainy days will increase by 50 per cent.

What’s more, how much rain falls is only part of the story. Warmer weather will dry out soils faster, for instance, which reduces the risk of flooding. “The relationship between precipitation and flooding is immensely complex,” says Gale. “Variation in a single factor, such as soil moisture, might mean that the same precipitation event could remain in channel or could generate a significant flood.”

On top of this, we are changing the physical nature of river valleys enormously. “What we do is take all the agricultural land around cities, pave it, build houses and put in storm-water sewers, all of which stops water from infiltrating the ground where it can be stored and percolate slowly into rivers,” says Gale. Instead, rainwater is funnelled rapidly into main rivers. So part of the problem with forecasting future flooding is not knowing how the landscape will change.

Trouble is that scientists are not ready to say exactly which parts of the world will have the worst increase in floods, so there is no reason to choose one part over another

All the same there are seven things that off-grid dwellers could do.

 

1. Avoid previously flood-prone areas.

2. Find out what would happen in the event of a flash flood near you – would water cascade towards you, or away from you.  Would you need to move to higher ground, or leave altogether (if there is time)?

3. Will the local sewage works be flooded?  That would pose a serious health risk and be a reason to leave.

4. Will power lines be cut?  Probably yes. So no point in heading in to town to check your email.

5, Make sure your building is secured in the event of a violent storm. If wind pulls the roof  off you might just get wet, or the rood might land on you.

6. Check the FEMA web site for updates

7. Fuel and Food will run out – have your supplies laid down. Ironically a flood will probably render the water undrinkable – make sure accessible backup water -is stored above ground level.

Thanks to Permaculture Activist

Buy our book - OFF THE GRID - a tour of American off-grid places and people written by Nick Rosen, editor of the off-grid.net web site

2 Responses to “Global Storming”

  1. fu

    However, a warming effect is even better than a global cooling. It is to late to act and the earths population too big, uninformed and anyway too egaged with other issues like simply surviving. My opinion is, that one cannot change the basic aspect of an so called autopoetic system – called as well human being. Such systems follow certain rules: one of them is just to act in order to guarantee the stability of the system itselve. As long as we have other problems to solve, that concern us more serious, we won’t be motivated to tackle any greenhouse-gas-reduction.

    The nature will play the “survival-of-the-fittest-game” with us and just the best adapted/situatet and smartest folks/peoples/individuals will last.

    Reply
  2. Earthling

    It has taken 160 years for the global temperature to ‘allegedly’ rise 0.8ºC, so if one full degree C of warming only adds an extra 7% of moisture to the air, there isn’t much to panic about.
    Is Tennessee a country?

    Reply

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