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What is a tornado and why do they hit America so hard?

With 16 dead already, the US tornado season has already begun.

The devastation of a tornado in the US.
The devastation of a tornado in the US.
Image: AP/Press Association Images

EVERY YEAR, AROUND 1,200 tornadoes hit America.

In 2012, 68 people were killed by tornadoes in the United States, on top of 1,500 injuries and massive damage to whole towns. In Arkansas and Oklahoma, the devastation has already been felt, as 16 people have died following a massive series of tornadoes.

Broadly speaking, a tornado is a column of air that touches both a cloud and the earth. It is caused when two masses of different temperatures and humidity collide. However, it is not fully understand how they form.

The US, or more specifically, the centre of its mainland, is hit by tornadoes throughout the year, with tornado season generally peaking around late spring.

The area between Texas and the Canadian border and between Colorado and western Pennsylvania is known as Tornado Alley.

Tornado_Alley Source: Wikimedia

Unsurprisingly, much of the devastation is located in these states, with Tornado Alley bearing the brunt of the 2011 tornado outbreak that killed over 300 people.

So, why America?

Quite simply, it’s down to climate.

When land is caught between dry air on one side and warm, moist air on another, you get a tornado. Unfortunately for the residents of Tornado Alley, that is exactly what they live in.

Of course, the US isn’t alone in having tornadoes, as this map from the National Climatic Data Centre shows.

globdist Source: Noaa

Nor is the US alone in fatalities from tornadoes. In 1989, 1,300 people died in Bangladesh and in 1984, 400 Russians were killed in a tornado outbreak.

The US is hit every year, in the same rough geographic area, so how do people die year-on-year?

The National Oceanic and Atmospheric Administration (NOAA) says that it comes down to people not being prepared.

Of the 68 people killed in 2012 in the US, just four lived outside a zone that had been alerted to an oncoming twister.

NOAA advises people to get to basements or interior hallways in the event of tornadoes.

Unfortunately, most of those killed live in what NOAA dubs “manufactured homes” or trailers.

PA-9088452 Source: Graham Hughes

These accounted for 48, or 70 per cent of 2012′s deaths. The impact a tornado has on a trailer has been likened to an aluminium can going through a washing machine.

Just last week, Purdue University researchers said that most tornadoes occur in so-called “transition zones”, where towns meet farmland. This is generally where trailer parks are located.

The research analysed more than 60 years of Indiana tornado data. They found 61-percent of touchdowns between 1950 and 2012 occurred within .62 miles of urban areas compared to 43-percent of touchdowns fell within that same distance from forests.

They found the majority of tornado touchdowns occurred near areas where dramatically different landscapes meet – for example, where a city becomes farmland or a forest meets a plain.

Read: “It’s chaos”: At least 16 killed as powerful tornadoes tear across southern US

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