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| Last Updated::05/12/2014

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CLIMATE WATCH 2013: Precipitation trends

 - Brajakumar, Ph.D. (brajakumar_t@yahoo.com)

Basic theory, climate model simulations and empirical evidence all confirm that warmer climates, owing to increased water vapour, lead to more intense precipitation events even when the total annual precipitation is reduced slightly, and with prospects for even stronger events when the overall precipitation amounts increase. The warmer climate, therefore, increases risks of both drought - where it is not raining - and floods - where it is - but at different times and/or places." The unfolding disaster raises many questions like is this extreme rainfall due to global warming? And what issues does it flag? Do rising temperature really pushing up the frequency of incidents of extreme rainfall?

 

As an example, the disaster in Uttarakhand was aggravated by the large number of landslides in the area between June16 and 17, which had record rainfall of 120 mm in 24 hours before the flash flood of June 16 at Kedarnath and 745 landslides were occurred along the river valleys of Mandakini, Mandani, Kali and Madhyamaheshwar. It is believed that a massive landslide occurred upstream in the north-east region of the Kedar valley. At the same time, heavy rainfall occurred and formed a small lake in the north-west of the valley. The debris from the landslide and water from the lake travelled down the slope, channelled into the glacier, and came down to Kedarnath town.  In climate literature, rainfall of more than 150 mm in a day is termed a very heavy rain event. “Dehradun, on Monday morning registered a record rainfall of 340 mm. This amount of rain in June is seen almost after five decades,” said the Regional Director of the India Meteorological Department (IMD) (Source :The Hindu, June 18, 2013). Eyewitness accounts report the appearance of 'a wall of water'. It was rumoured that a glacial lake had burst because of the rains, a phenomenon called “glacial lake outburst flood” (GLOF). However, it is now confirmed that the disaster was not caused by GLOF, but indeed by a combination of factors, namely early rainfall, movement of southwest monsoon winds, and the formation of a temporary lake.

 

A study by scientists at the National Atmospheric Research Laboratory, Tirupati, showed a six per cent increase in the frequency of very heavy rain events in India over 1901-2004. The more recent period 1951-2004 shows a 14.5 per cent rise per decade. They lay this at global warming's door: the study talked of a “coherent relationship” between the increasing trend of extreme rainfall events in the last five decades and the increasing trend of Indian Ocean sea surface temperature. read more>>