Unusually high temp points to early onset of summer
NEW DELHI: Has summer arrived early in 2022?
The last few weeks have been unusually hot in large parts of India. An HT analysis of Indian Meteorological Department (IMD) data shows that average maximum temperature in the country has reached levels which were historically breached in mid-April.
The reason for this kind of weather is the lack of rain. IMD data also shows that so far, this has been India’s driest March since 1901.
India’s average maximum temperature reached 35.27°C on March 18, as per data from IMD’s gridded database. A grid in this database corresponds to a box of latitude and longitude a degree apart. India is covered by 383 such grids.
The average maximum temperature reading for March 18, 2022 was 9.6% more than the historical average or normal, which is based on the average values between 1981 and 2010. A comparison with the historical average series also shows that average temperatures above the 35°C mark are only seen around the middle of April, suggesting that 2022 might be a year of remarkably early onset of summer. The average maximum temperature between March 16 to 18 this year is higher than historical averages for maximum temperature up to April 13.
In fact, the average maximum temperature of 35.27°C for March 18, 2022 is only 1.54° below the highest value of the historical average for daily maximum temperature on any day of the year, which arrives on May 26, just before the start of official monsoon season on June 1.
To be sure, the headline historical average value hides the regional variation in summer temperatures in India. Out of 30 states for which this calculation is possibly using the gridded database, the highest value of the historical daily maximum temperature is more than 40°C in eight states..
NEW DELHI: Has summer arrived early in 2022?
The last few weeks have been unusually hot in large parts of India. An HT analysis of Indian Meteorological Department (IMD) data shows that average maximum temperature in the country has reached levels which were historically breached in mid-April.
The reason for this kind of weather is the lack of rain. IMD data also shows that so far, this has been India’s driest March since 1901. India’s average maximum temperature reached 35.27°C on March 18, as per data from IMD’s gridded database. A grid in this database corresponds to a box of latitude and longitude a degree apart. India is covered by 383 such grids.
The average maximum temperature reading for March 18, 2022 was 9.6% more than the historical average or normal, which is based on the average values between 1981 and 2010. A comparison with the historical average series also shows that average temperatures above the 35°C mark are only seen around the middle of April, suggesting that 2022 might be a year of remarkably early onset of summer. The average maximum temperature between March 16 to 18 this year is higher than historical averages for maximum temperature up to April 13.
In fact, the average maximum temperature of 35.27°C for March 18, 2022 is only 1.54° below the highest value of the historical average for daily maximum temperature on any day of the year, which arrives on May 26, just before the start of official monsoon season on June 1.
To be sure, the headline historical average value hides the regional variation in summer temperatures in India. Out of 30 states for which this calculation is possibly using the gridded database, the highest value of the historical daily maximum temperature is more than 40°C in eight states.
This early heat has turned the March 1 to March 20 interval of 2022 the 14th hottest by maximum temperature since 1951. The March 14-March 20 week of 2022 is the third hottest since 1951. As is expected, the 2022 temperatures for all days from March 14 to March 19 were the among the top five for those days since 1951.However, none of these days in the past week was the hottest since 1951 for India.This is perhaps only because not all states experienced their hottest day of the year on the same day. Kerala’s hottest day this year was on March 14 (35.8°C), while Bihar’s hottest day was on March 20 (36.6°C). Even at these early dates in the year, however, 11 states -- Kerala, Karnataka Gujarat, West Bengal, and all North-East states except Sikkim -- have already experienced a daily maximum temperature higher than normal.Another five states – Maharashtra, Rajasthan, Odisha, Telangana, and Tamil Nadu – have experienced a daily maximum temperatures less than a degree below the highest value that normal maximum temperature takes in a year.
Rajasthan, Telangana, and Maharashtra have also experienced daily maximums that correspond to a normal maximum further ahead in the year. The 40.49°C average maximum experienced in Rajasthan on March 17, for example, arrives in the normal chart earliest on May 13. Corresponding dates for Telangana and Maharashtra are April 28. The region of the national capital experienced its hottest day of the year on March 20, with maximum temperature reaching 37.72°C. While this was still 3.69°C less than the highest daily value in the 19812010 averages (41.41°C), it was the hottest March 20 since 1951. In the historical average chart, Delhi breaches the 37°C figure from April 14 onwards. The March 16-March 20 week this year was the 2nd hottest since 1951.
What explains this unusually hot March?
A large and unprecedented deficit in rainfall is one reason. In the 1961-2010 period (called the Long Period Average or LPA),
India received 16.9 mm rainfall on average in the March 1-March 20 interval. This year, it has received just 2.5 mm of rainfall in this interval, the lowest since 1901. The trend of large deficiency is reflected across states to such an extent that the state with the best rainfall (compared to LPA) this March so far is Rajasthan, which has a 2% surplus compared to its LPA. All states except Rajasthan, Karnataka (13% deficit), Kerala (28% deficit), and Tamil Nadu (56% deficit) have a deficit higher than 60%, which is considered a “large deficient” by IMD.
These trends in rainfall themselves are a result of a lack of active western disturbances this month and anti-cyclonic activity over central and western India, according to Mrityunjay Mahapatra, director general Meteorology at IMD. The former is a Mediterranean storm that brings rainfall in the winter months of India. The latter is, as the name suggests, the opposite of a cyclone. Instead of rising, an anti-cyclone is the case of the air sinking and getting warm and therefore becoming capable of holding more moisture, preventing rainfall.