When the heat makes waves

The weathermen, certainly, don8217;t have very good news. Apprehension is writ large on the faces of baffled meteorologists who are worried by the fact that this year heat waves have started their assault right from the second half of March as against the month of May last year.

Although the commencement of heat waves so early is being described as a meteorological variability observed in certain regions, it is the dry spell gettingprolonged from March right up to April which has raised serious concern over these vagaries in weather. The thundershowers, which are the only natural way such heat waves are suppressed have failed to strike so far and the situation is progressively worsening.

A shocking 33 out of the 35 sub-meteorological sub-divisions in the country have fallen in the deficient rainfall category, for the period March 1 to April 7 as per the weather report of the India Meteorological Department IMD.

Except for the Andaman and Nicobar Islands and Lakshadweep, the entire country has drawn a blank on thundershower activity, which ideally starts with the onset of summer in the month of March. For the common people, it is the early8217; onset of summers that makes their lives miserable.

8220;This year the thundershower activity has been subdued so far and this is making us worry,8221; says Dr U.S. De, the additional director general of meteorology at the Central Observatory of IMD in Pune. 8220;We cannot rule out the repetition oflast year8217;s developments. Even the Gangetic West Bengal region has not seen rainfall activity so far,8221; he points out.

Meanwhile the mystery question remains: why is it that Orissa suffers from such sweltering heat that takes such a high toll of lives in the region? Not only did the state record the maximum number of sun-stroke cases last year, this year too the coastal state has already opened its death account. Meteorologists are certainly perplexed about this and prefer to pin the blame on the lack of adaptability of the local people to withstand such high temperatures.

8220;The people residing at a place for a sufficiently long time get more or less acclimatised to the normal weather conditions of that place. In Orissa the death toll was more last year as the local people were not acclimatised to such high temperatures,8221; says Dr D.S. Desai, director, weather forecast division, IMD. But so far no concrete reasons have been found to explain why the coastal region is experiencing such hightemperatures.

Heat waves are generally described as spells of abnormally hot weather conditions observed in the summer season from March to June and which move progressively from one region to another. In India, a heat wave is considered to be severe when the maximum temperature remains 5 celsius above the normal value for a region with the standard maximum of above 40 degrees and 7 degrees for a region with standard maximum of 40 degrees or less.During summer, the surface of the earth heats up and subsequently the air close to the surface becomes warmer and thus lighter in weight and rises in the atmosphere. As a result the air from the surrounding area rushes to one point to create a convergence current. The air which rises up gets mixed with the incoming air containing moisture like those from coastal areas and gives rise to thundershowers. This phenomenon is essential for cooling the surface and atmosphere and a prolonging in its activation increases the severity of hot weather conditions.

In1998, major parts of the country, extending from north India, parts of northeast India and the northern parts of peninsular India experienced severe heat wave conditions during the second half of May.

These conditions initially prevailed over northwest India. It then extended in a south-southeast direction towards Orissa and coastal Andhra Pradesh.A detailed study of last year8217;s severe heat wave carried out by U.S. De and R.K. Mukhopadhyay of IMD and published in Current Science, tries to explain the global reasons behind the calamity.

8220;In the last two decades, it can be seen that the maximum number of the heat wave days and the human lives lost during May and June over the Indian subcontinent are comparatively large during the years 1983, 1988, 1995 and 1998. These years are preceded by warm ENSO years El Nino Southern Oscillation. The year 1997 was the severest warm ENSO year of the century. Hot and dry weather conditions were not only experienced in India in 1998 summer but the drought and delugesprevailed in almost every part of the globe,8221; they observed in the study. The first five months of 1998 were the planet8217;s hottest on record, according to the scientists of the USA-based National Oceanographic and Atmospheric Administration.

8220;It is too premature to say that the unsual phenomenon of excessive heat waves is due to global warming,8221; says De. He does add however that further studies in this subject are needed to understand and predict such extreme events which are hazardous to life on earth. The renowned meteorologist, R.H. Kripalani from Indian Institute of Tropical Meteorology IITM, also points to the El Nino as the possible reason for this phenomenon.

According to Kripalani, 8220;During El Nino excess heat is concentrated in the waters of the tropical Pacific. In 1998 El Nino reached its maximum peak around December 1997, when sea surface temperature SST anomalies were maximum.8221; According to him, SSTs continued to decrease sharply after May 1998. However, after June 1998 moderate coldepisode La Nina the reverse of El Nino effected by cooling of SSTs over the tropical pacific commenced. Thus, the weakening of warm episode El Nino and the entry of cold episode La Nina must have liberated a huge amount of heat from the tropical Pacific. The reason then for the unprecedented heat wave of 1998 could possibly be the effects of this heat carried by atmospheric circulation.It seems then that there is more to an Indian summer, with its severe heat waves, than we ever dared to imagine!