“The Tibetan Plateau is about 4,000—5,000 metres high and due to certain atmospheric and thermodynamic processes, climate warming is dependent on elevation. Hence, the higher plateau gets significantly warmer than the surrounding areas in a global warming scenario,” says R. Krishnan, a scientist with the Indian Institute of Tropical Meteorology (IITM), Pune.
This difference in warming amplifies phenomena like western disturbances, Krishnan tells ScDev.Net. Western disturbances are defined as extra-tropical storms originating in the Mediterranean that bring sudden winter rain and snow to parts of northwest India.
Significantly, a study by Krishnan and others appeared in Climate Dynamics in May 2014 showed how the warming of the Tibetan Plateau increases the instability of westerly winds. These western disturbances, in turn, result in an increase in instances of heavy winter rainfall in north and northwest India.
“The greater the intensity of the disturbance, the more intense the rainfall,” explains Krishnan.
Krishnan adds that while temperatures at elevations of 4,000 metres were found to increase at a rate of 0.80 degree Celsius per decade, temperatures in the plains were found to increase at the rate of 0.10 degree Celsius during the same period, and this difference in temperature increase intensifies the disturbances.
Recent years have witnessed several instances of intense winter rains.
In December, western disturbances lashed the Indian states of Jammu and Kashmir, Himachal Pradesh, Uttarakhand and western Uttar Pradesh for about 48 hours. Similar instances of heavy rain due to western disturbances also occurred in 2013.
Scientists at IITM carried out the study by comparing instances of heavy rainfall between 1901 and 2011 to case studies of western disturbances in India Meteorological Department’s (IMD) daily and weekly weather reports.
In order to analyse the reason behind the increasing intensity of the disturbances, the surface temperature trends between 1961 and 2006 over meteorological stations in the eastern Tibetan Plateau were assessed. Wintertime temperatures at sites above 2,000 metres were found to increase at a rate of 0.61 degree Celsius per decade.
However, IMD scientists do not see any trend of increased intensity of western disturbances. “This year, there have been certain instances of heavy winter rainfall. That does not mean that we will have it next year. We do not have sufficient data yet to predict a trend,” says L. S. Rathode, director-general, IMD.
Link to abstract in Climate Dynamics
This article has been produced by SciDev.Net's South Asia desk.