Extreme rain rips apart historic Cinque Terre: "Monterosso no longer exists"
A U.S. Environmental Protection Agency study revealed:
In recent years [in USA], a larger percentage of precipitation has come in the form of intense single-day events. Eight of the top 10 years for extreme one-day precipitation events have occurred since 1990. The prevalence of extreme single-day precipitation events remained fairly steady between 1910 and the 1980s, but has risen substantially since then. The percentage of land area experiencing much greater than normal yearly precipitation totals increased between 1895 and 2008.
To try to get a better grasp on the science, I recently read a paper called “THE CHANGING CHARACTER OF PRECIPITATION” by Kevin Trenberth and other leading atmospheric scientists.
The bottom line: As we turbo-charge our climate system with billions of tonnes of heat-trapping, fossil fuel emissions we can expect an increase in extreme rain and a decrease in light rain.
Here are some of the highlights of how global warming will drive extreme rains.
I was surprised to learn that air usually holds only about a third of an inch of rain above any one spot. So how do we get several inches in a few hours?
To pull that off requires a very high energy storm full of very warm air flowing over a very large and warm body of water. And sure enough our fossil fuel pollution is fuelling an increase in all three of these factors.
1: Warmer air. First our climate pollution is warming the air. Warm air holds about 7 per cent more water vapour for every degree C warmer it is. As extreme temperatures become more common they bring the potential for extreme rains to tag along. Measurements show that averaged over the entire globe, our atmosphere now carries 4 per cent more moisture. We have made our basic weather environment both wetter on average and wetter in the extremes.
2: Warmer oceans. Second our climate pollution is warming oceans and lakes. To fully saturate warm air you need a lot of warm water nearby. If the water is cold it will cool the air. As our oceans warm up they pump more water into warmer air.
3: More energetic storms. Third, our climate pollution is pouring energy into our storms. The fuel of big storms is the latent heat released when water vapour condenses into liquid water droplets. This heat creates the towering updrafts that squeeze water out of the air, as well as the powerful winds that sweep them across the landscape. Warmer, wetter air driven by hotter temperatures means more water vapour condensing into rain. That is boosting the latent heat released which in turn cranks up the energy in the storm into a dynamic feedback loop.
Runaway freight train
Picture a storm as freight train. Each train car (column of air) fills with water at the water tank (ocean). It then dumps that water it at the top of a hill (rain as air rises).
Normally the water tank can only put a third of an inch of water into each car. But as we crank up the ocean and air temperature lots more water gets hosed into each train car.
Next, increasing air temperatures increase the energy pushing the train forward.
Instead of a normal slow train dumping a little water per car on the hill, we find ourselves with a speeding train dumping lots more water from each car as they thunder past the dumping spot.
The fuel for this Deluge Express is oil, coal and natural gas emissions.
The brakes? There aren’t any.
You might want to read that twice.
All we can do to stop this Deluge Express from becoming a runaway is to stop shovelling fossil fuels into the firebox and switch to 100 per cent renewables as fast as we can.
As meteorologist and former hurricane hunter Jeff Masters told Climate Progress:
“In my thirty years as a meteorologist, I’ve never seen global weather patterns as strange as those we had in 2010. The stunning extremes we witnessed gives me concern that our climate is showing the early signs of instability.”