Why are temperatures in Mumbai set to rise by up to 5 degrees on two consecutive days?

The metropolis is home to two IMD weather observatories – one in Santacruz and another in Colaba – which recorded maximum temperatures of nearly 35 degrees Celsius on Friday afternoon. A heatwave warning is issued in Mumbai when the two observatories record daytime temperatures of over 37 degrees Celsius, or 4-5 degrees above normal, for at least two consecutive days. For instance, the first heatwave alert of the season was sounded last month when the city sweltered at more than 37 degrees Celsius for at least four consecutive days.

Why are the temperatures expected to see a deviation of 4-5 degree Celsius in the coming days?

Weather experts have attributed the predicted spike in temperatures to an anticyclone system that is expected to develop over the region. According to Nitha Sasidharan, scientist from IMD Mumbai, this system is expected to usher in strong easterly winds from the interior parts of the country. “Since these easterlies are strong, they will delay the westerly winds, i.e. the sea breeze, from setting in. Owing to this, the city can expect a spike of over 4-5 degree Celsius above the normal from Sunday,” said Sasidharan.

Such spikes are not atypical for the city in March. Data furnished by the IMD shows that while the city’s highest March temperature in 2024 was 38.8 degree Celsius, the maximum temperature had soared to 39.4 degree Celsius in 2023, 39.6 degree Celsius in 2022 and even 40.9 degree Celsius in 2021.

Why are heat waves becoming the new normal for Mumbai?

An analysis of the meteorological data from IMD Santacruz in the Mumbai Climate Action Plan of 2022 shows that while the city recorded 12 heatwave events between 1973 and 2020, Mumbai has shown a warming trend over a period of 47 years with an increase of 0.25 degree Celsius per decade.

According to projections by the National Oceanic and Atmospheric Administration (NOAA) and Climate Lab, 60 per cent of a year will comprise high heat days in Mumbai by 2040. High heat days, as per the study, are those when the city records a maximum temperature of 32 degree Celsius or more.

Mahesh Palawat, Vice President of meteorology and climate change, Skymet Weather, said, “Typically, heatwaves are a result of the change in wind directions which are common during summers. However, there has certainly been an increasing trend in the number of heatwaves over the years. This is a result of global warming and climate change whose impacts on the global temperatures have become more visible in recent years. As the air temperatures have risen owing to the greenhouse gases, the heating has also increased. During the winters, too, we observed that there were fewer cold waves in India, with even the northern parts of the country experiencing shorter spells of winter.”

What precautions must one take during a heatwave?

Since heatwaves are characterised by a prolonged period of hot weather along with high humidity, they pose health risks such as heatstroke and dehydration. According to IMD, while its current ‘yellow’ heatwave alert means that the temperatures can be tolerated by the general public, it can lead to potential health concerns among vulnerable groups such as infants, people with chronic diseases, etc.

Dr Mohan Joshi, dean of Sion Hospital, told The Indian Express, “Besides avoiding the sun, people must drink water to ensure adequate hydration. Children and extremely old people should particularly avoid heat as it can cause heat strokes, viral fever, and even renal stones, which are caused due to dehydration.”

To prevent health risks, the weather bureau advises the public to avoid heat exposure, especially between 11am and 4pm. In its advisory, the IMD states that people must exercise caution by wearing lightweight, light-coloured and loose cotton clothes while covering one’s head using a cloth, hat or an umbrella.