A thunderstorm over Sydney, Australia.
Credit: Wikimedia
As you sink a bogey putt on the first hole, the sun is intense and the air is close and sticky. The forecast is for thunderstorms later; the sooner you finish this round of golf the better.
Back in the clubhouse, you notice a shroud of high cloud has blocked out the Sun and on the horizon you see a dark, ominous mass of cloud over the city, almost certainly a thunderstorm. The wind has picked up too. Golfers begin to stream in from the course as the cloud thickens and a few large drops of rain hit the clubhouse windows.
Then the heavens open. Heavy rain floods the car park. There's a flash of lightning and five seconds later the thunder arrives. "About a mile away," you think, remembering the calculation your grandfather taught you.
That's when the hail starts. Golf ball sized chunks of ice begin to blanket the course, collecting several birdies and a few holes in one.
And in less than an hour it's all over.
You've just experienced a severe thunderstorm, which released more than 1015 joules of pent up energy. An equivalent amount of electricity could power all of the U.S. for about five hours.
The National Severe Storms Laboratory (NSSL) run by NOAA in the U.S. estimates that at any given moment there are 2,000 thunderstorms in progress around the world.
When a thunderstorm contains tornados, hail over 18mm in diameter or winds faster than 90 km/h, it's classed as severe by the NSSL. Severe thunderstorms cause over two billion dollars worth of property damage and kill more than 100 people each year in the U.S. alone.
The infrastructure and activity in our cities is affecting the weather around us: the concrete and asphalt heat up the ground relative to the countryside; the buildings obstruct airflow; and, depending on the exact conditions, the particles in pollution can enhance or delay weather events. Even short term activities such as traffic jams can have an effect.
What's more, cities are set to explode, with the U.N. predicting the number of city dwellers will almost double to 6.4 billion by 2050, and changes in global climate are going to lead to stronger thunderstorms in regions that are already affected.
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