imd officials say the present heat wave is not an unusual phenomenon. "The heat wave will not persist for a longer time," says S R Kalsi, deputy director general of imd . The heat wave is "due to the lack of effective western disturbances and stagnating high pressure in the western part of the country", notes R K Dutta, former head of the National Centre for Medium Range Weather Forecasting in New Delhi.
Western disturbances occur when troughs or lean pressure areas, either at the surface or in upper air, lie in the regimes of prevailing westerly winds, explains an imd official in New Delhi. Widespread rain in winter is generally associated with western disturbances that move across the northern parts of South Asia, where they have a marked control over the weather, notes the official.U S De, additional director general of meteorology at the Central Observatory of imd at Pune, was quoted in the media to have said: "This year the thunder-shower activity has been subdued so far, and this is making us worry. We cannot rule out the repetition of last year's developments. Even Gangetic West Bengal has not seen rainfall activity so far."
While this can explain the weather conditions in the northern and north-western India, it still does not explain the intense spell of heat in Orissa. This year, the heat wave hit Orissa as early as the last week of February. In the first week of April, temperature was rising above 40C. By the end of April, at least 19 people had succumbed to it in the state.
In the absence of a plausible explanation, scientists say the high toll of the heat wave is due to the local people's lack of adaptability to such high temperatures. In a paper entitled Severe heat wave over the Indian Subcontinent in 1998, in perspective of global climate , U S De and R K Mukhopadhyay observe that people living at a place for a sufficiently long time get more or less acclimatised to the normal weather conditions of that place. They add that though the temperature in north-western India, especially Rajasthan, was nearing 50C, the death toll was not as high as that of Orissa. But the question 'why is Orissa experiencing such extreme temperatures' remains unanswered (see 'Heat and Death', Down To Earth , May 15, 1999).
As regional weather patterns do not provide any clues to the heat wave in Orissa, it is natural to look at global climatic events to find explanations. The El Nio phenomenon has been associated with global climatic changes in the past year or so. "(The present heat wave) does not have anything to do with global climate patterns like El Nio," says S R Kalsi. "The heat wave cannot straightaway be linked to global anomalies like El Nio or global warming," says R K Dutta.
But there are imd officials who do see a connection here. In his paper mentioned above, U S De observes that El Nio seems to have a link - though unexplained - with the hot and dry conditions experienced in India in the 1998 summer. In the last two decades, "it can be seen that the maximum number of heat wave days and the human lives lost during May and June over the Indian subcontinent are comparitively large during the years 1983, 1988, 1995 and 1998. These years were preceded by El Nio" (see chart: El Nio's afermath ).
While this may explain the heat wave in 1998 - 1997 was an El Nio year - the present heat wave is difficult to understand. Especially as this year is witnessing La Nia, the reversal of the El Nio phenomenon. If severe heat waves in India are linked to El Nio, there is reason for concern as several scientists fear that El Nios will be stronger and more frequent in the future due to the effects of global warming. And even if there is no connection between El Nio and global warming, there may still be a link between global warming and the heat waves in the Indian subcontinent, some experts point out.
face="Arial" size="2">Lives lost
face="Arial" size="1">Uttar Pradesh, Maharashtra, Tamil Nadu and Andhra Pradesh
face="Arial" size="1">Uttar Pradesh, Madhya Pradesh and Bihar
face="Arial" size="1">Uttar Pradesh
face="Arial" size="1">Uttar Pradesh, Punjab and Maharashtra
face="Arial" size="1">Punjab and Bihar
face="Arial" size="1">Andhra Pradesh, Punjab, Rajasthan, Himachal Pradesh and Bihar
face="Arial" size="1">Orissa, Punjab, Haryana and Uttar Pradesh
face="Arial" size="1">Rajasthan, Madhya Pradesh and Maharashtra
face="Arial" size="1">Rajasthan, Madhya Pradesh, Gujarat and Maharashtra
face="Arial" size="1">Rajasthan, Madhya Pradesh, Haryana, Bihar, Uttar Pradesh and
face="Arial" size="1">Punjab, Haryana, Rajasthan and Uttar Pradesh
face="Arial" size="1">Punjab, Haryana, Rajasthan, Madhya Pradesh, Uttar Pradesh and
face="Arial" size="1">Rajasthan, Haryana and Uttar Pradesh