Rain is expected to fall in large parts of northern and eastern India this week, according to forecasts issued by the Indian Meteorological Department on Monday. This follows similar weather patterns in April and May so far. This indicates that this summer season is likely to be one of the coldest. How cool exactly? IMD gridded data show this is the 18th coldest summer since 1951, the first year the IMD has published gridded data. However, it appears colder if we exclude the first part of the summer months, when temperatures are usually low in absolute terms.
Before discussing summer temperature trends further, it is important to note that the IMD does not clearly define the summer season. The months of January and February are called “winter”, which is followed by the “pre-monsoon” season from March to May, the “southwest monsoon” from June to September (sometimes called the summer monsoon), and the post-monsoon season in October and December. Even these definitions are not without disagreement. For example, the IMD releases its forecast for the “cold weather season” – December to February – around December 1, which can only be interpreted as a winter forecast.
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For the sake of simplicity – and because this period is generally among the warmest periods of the year – Hizb ut-Tahrir considered the period from March to May to be the summer season. This shows that the period from March 1 to May 10 this year had an average maximum temperature of 33.08 degrees Celsius, the lowest average of 18 degrees since 1951. This was also 0.51 degrees Celsius colder than the average of these days in the period 1981-2010, which is considered normal. This leaves no doubt that this summer has been colder than usual.
This summer would certainly be colder if we excluded the first 15 days of March from the analysis. This is because only 30 days recorded temperatures above normal during the 71-day period from March 1 to May 10; And 14 of them are among the first 15 days of May. Another 14-day stretch occurred in the second half of April, but with a much smaller upward skew than in the first half of March. In other words, the biggest reason this summer doesn’t rank among the coolest summers is the trend in the first half of March. If this period is excluded from the analysis, the average maximum for the period from March 16 to May 10 is 33.31°C, the eighth lowest since 1951 and 1.16°C below normal.
Chart 1
However, just because India is experiencing one of its most wonderful summers, does not mean that all parts of the country are experiencing it. Even from March 16 to May 10, average maximum temperatures in about two-thirds of the country were below normal. Only 44% of the country saw an average at least 0.5°C colder than normal, and only 31% of the country saw an average at least 0.5°C colder than normal. As the accompanying map shows, a relatively small portion of the country — the northern and northwestern regions, the Indo-Gangetic plains, and the northeastern regions — makes this summer look cooler than average for India. Most of the central, western and peninsula regions were somewhat warmer than normal.
Map 1
As expected in summer, these trends are driven by precipitation trends. The more days of extra rain a place has, the more likely it is to experience cooler than normal temperatures on average. For example, places that had a cooler-than-normal summer so far saw more rain than normal for at least seven days in the period after March 15.
Map 2
