Monday, May 19, 2008

Delhi Thunderstorms : An Analysis

Every May, Delhi is lashed by thunderstorms of high-speed squalls and rain that cool down the city drastically. And just as suddenly, the clouds part and it’s scorching hot again.

“Actually, May has been like this almost every year. In fact, Delhi has seen more dust storms with greater intensity in the past,” said SC Bhan, director of the IMD’s Safdarjung observatory.

The Met office is never impressed or surprised. But it did admit that this May has been a far more active this year than the last — it has had six thunderstorms already, compared to the seven in all of last May.

But the ferocity of the squall and the intensity of the rain has been in the past — the highest wind speed recorded this year was 98 kmph (at Safdarjung) on Saturday, against 111 kmph last year.

“The strongest ever was 152 km per hour on May 23, 1976,” he said. That’s shade faster than the fastest ball bowled by cricketer speedsters Shoaib Akhtar and Brett Lee — and we are talking about winds of that speed here.

Is it because of climate change, global warming? Some experts say these thunderstorms and Cyclone Nargis that hit Myanmar are because of global warning. But others say they want more proof.

But here is how the Delhi thunderstorms happen according to the Met office. As temperatures begins to rise, air over Rajasthan, which is the hottest of the northern states because of the large expanse of deserts, gets lighter and rises and cold air from neigbouring regions rush in fill up that empty space.

The neighbouring regions in this case happen to be the Arabian Sea or the cooler hilly states of Himachal Pradesh and Jammu & Kashmir. This air is not cooler but is also heavy with moisture.

This cool, wet air rushes in take the space vacated by hot rising air and creates cyclones of high speed winds and rain — and that brings rain and squalls to Delhi, and some welcome relief from summer.

But these squalls can get quite destructive — uproot or break large number of trees which have known to have killed and injured people and damaged vehicles and houses in their vicinity.

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