Monday, August 16, 2010

More on Leh Rainfall and cloudburst

13th August, 2010 - Times of India

The cloudburst has again brought out the glaring lack of adequate documentation on such sporadic weather events. J Srinivasan, chairman of Divecha Centre for Climate Change and head of Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, tells TOI's Jayashree Nandi about the need for extensive research on extreme weather events like the cloudburst. Excerpts:

What do you think of the cloudburst disaster at Leh?
Cloudbursts are events in which high rainfall occur over a very small area, in a very short time span (typically more than 100 mm/hour for a few hours). We do not have much data about this phenomenon. However, such events have occurred earlier in Uttarakhand and Himachal Pradesh. For instance, many people were killed in a cloudburst at Pithoragarh (Uttarakhand) on August 7, 2009. These events are rare in Jammu and Kashmir and hence the Leh cloudburst was unexpected. Extreme rainfall events (rainfall more than 100 mm/day) have increased by 50% during the past 50 years. This year we had floods in Pakistan, Gujarat and now in Jammu and Kashmir.

How long did it rain in Leh and across how much area?
India Meteorological Department data says it rained between 1.30 am and 2 am in Leh on August 6. A weather station near Leh recorded only 12.8 mm of rainfall in 24 hours. These events are extremely localized in an area probably less than 30 square kilometres. In August, the normal rainfall in Leh is 15.4 mm and the highest recorded in this season was 51 mm. But this time, the rainfall was probably much higher than that.

Have such events taken place earlier? Is it similar to 2005 Mumbai floods?
Such events occur every year in mountainous regions. Many events are not reported because of insufficient data. For instance, if it happens in some remote areas of Himachal Pradesh and if there is no a weather station close by and there is no habitation in those areas, the event doesn't get reported. Leh cloudburst is comparable to Mumbai floods because it rained for over 12 hours in Mumbai.

Could this be due to climate change?
IMD observations show that events of extreme rainfall have increased by 50% during the past 50 years. And, most climate models predict that global warming will increase such events. We cannot claim that a specific extreme event is due to global warming although we know that the probability of such events will increase as the earth becomes warmer.

Have any new observations been made on climate science recently?
In March, this year a disputed island on the Bangladesh-India border called Talpatti disappeared completely. Such events will occur more often in the future. The impact of sea level rise will not be seen in one or two years because the changes are slow. Similarly in case of temperature rise, IPCC predicts that there will be three degrees rise in 100 years. So that means a .03 degrees rise every year. We will not notice these changes easily unless we look at the long-term trend.

Do you think our policies are robust enough to deal with climate change?
Global warming will have serious impact on our life within 30 to 40 years. We have to act immediately because the transition from the present fossil-fuel dependent economy to one based on renewable energy will take many decades. Sadly, the vision and leadership on global warming has been lacking.

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