Weather Bee: Why India's average maximum is keeping cool despite heat waves
Extending this analysis for the period starting March 21 suggests that the trend seen in early March continued
India’s average maximum temperature was close to normal in March, a trend that has continued in the first three days of April. This might seem at odds with reports of heat waves in parts of the country. What explains this?
An HT analysis had earlier explained the reason behind India’s average temperature appearing benign in March for the month up to March 20. Extending this analysis for the period starting March 21 suggests that the trend seen in early March continued. Some places remained warmer and others cooler throughout the period starting March 21. Others have flipped between being warmer and cooler than normal. This was the result of rainfall and the wind patterns that western disturbances produce in north-western India.
The trends in temperature described above can be seen in the accompanying maps for the weeks ending March 27 and April 3. They show the deviation in average maximum temperature from the average for those weeks during 1981-2010, considered the normal for temperature in India. Parts of Gujarat, Himachal Pradesh, Uttarakhand, western Uttar Pradesh, and north-eastern India were warmer than normal in both weeks. On the other hand, most of peninsular India remained cooler than normal in both weeks. The two trends together cancelled each other out somewhat and kept the average for India close to normal.
To be sure, as the maps also show, large parts of India flipped between being warmer and cooler than normal. Most of north-western India, central India, and Maharashtra made this flip. On the other hand, eastern states such as Bihar, West Bengal, and Odisha were cooler than normal in the week ending March 27 and turned warmer than normal in the week ending April 3.
The impact of the flips can be seen even in the weekly average for India. The average maximum in the week ending March 27 was 0.29°C warmer than normal. In the week ending April 3, when most parts of India were cooler than normal, India’s average maximum was only 0.07°C warmer than normal.
What is the reason behind these trends? Somewhat similar to the trends seen up to March 20. The trends in north-western India were largely the result of wind patterns. After a western disturbance passes, fast and cool winds blow from the hills in the north and cool down temperatures. The cooling in central, peninsular India, and parts of eastern India, on the other hand, was driven by rainfall. This rainfall was brought by cyclone-like circulations and a trough (a low-pressure area) running from Madhya Pradesh to peninsular India.
Another interesting thing about the trends described above is that they are expected to repeat in the next two weeks, almost exactly as the past two weeks, according to the two-week forecast issued by IMD on Thursday. This means that most parts of India will experience at least some days of relief from unusually hot weather in the next two weeks.
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