Heat waves strike Gujarat, Rajasthan

With summers setting in and temperatures soaring, heat waves struck Gujarat and Rajasthan in west and north India. The temperature in Gujarat and Rajasthan crossed 40oC in the last week of March. In Maharashtra day temperature rose up to 39oC in the first week of April.

The temperature rise in the northern regions of Madhya Pradesh was higher at 43oC but the India Meteorological Department (IMD) says there was no heat wave in the state. “Heat wave occurs when the temperatures are above 40oC and four to five degrees above the normal temperature for the region,” says Ajay Shukla of the meteorological department in Madhya Pradesh.

IMD cautions that the temperature would continue to rise in the months to follow. “The temperatures will, though, drop in the plains from Sunday as the direction of the wind is changing,” says B P Yadav, spokesperson for IMD in New Delhi. “The wind was coming from the southern region, now it will blow from the Himalayas,” he adds.

The number, duration and area of spread of heat waves in India increased sharply during 1991-2000 in comparison to the earlier two decades, according to a study by IMD. The department has clubbed its observation centres into 35 sub divisions. On compiling daily data on heat wave conditions over sub divisions, the researchers found that between 1991 and 2000 an average of 22.7 sub divisions in the country were hit by heat waves per year, while between 1971 and 1980 an average of 9.9 sub divisions were hit by heat waves per year. During 1981-1990 the average was 7.3.

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The study, published in the April 2004 issue of IMD journal Mausam, showed more areas suffered frequent heat waves in 1991-2000 compared to earlier decades. Twenty-five subdivisions went through more than 15 spells of heat waves in 1991-2000, while in the previous two decades two sub divisions received more than 15 spells of heat waves. It is the same with the duration of heat waves. During 1991-2000 the highest duration of a heat wave was 16 days, while in the previous decade the longest heat wave was of nine days and a decade before that, 11 days.

Another study said the number of heat wave days per year in central and north-west India increased from three to 12 between 1969 and 2005. But scientists are yet to find the reason behind the increase. One reason could be different parts of the earth warming at different rates; it is likely to bring frequent changes in air circulation (see 'Rain Shocked', Down to Earth, March 1-15, 2009). The different rate of heating could be due to both local factors and global warming. The decade 1991-2000, during which the frequency of heat waves increased sharply, was the warmest in the past 140 years.

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