Mumbai’s minimum temperature at night surpassed 25°C for 623 days between 2014 and 2023: Study

Night temperature below 25 degrees is considered to be healthy and normal. However, during the analysis, the 25 degree mark was kept as a benchmark, considering that human health and sleep cycles are affected in a negative manner if the night temperature rises 25 degrees.

According to the data furnished by the research groups, the maximum number of days when Mumbai recorded high night temperature was in 2021 with 74 days, followed by 73 days in 2022, 68 days in 2017 and 64 in 2018.

The research data furthermore states, if heatwave conditions and factors like global warming stayed within controlled limits then the number of days when night temperature would surpass 25 degrees mark would have been 16 and 19 days in 2021 and 2022, 22 days in 2017, and 22 days in 2018.

Data also shows that Mumbai’s night temperature has increased by an average 65% between 2018 and 2023, which is the third-highest in Maharashtra.

Ulhasnagar and Kalyan have seen the highest increase in night temperature by 72.7% by recording 705 days of night temperature, surpassing 25 degrees, followed by Thane which has recorded a 70.3% increase by recording 674 days of high night temperature during the past decade.

Meanwhile, experts have attributed the rapid concretization of mega-cities behind the changing trend of increasing night temperature.

Roxy Mathhew Koll, climate scientist from the Indian Institute of Tropical Meteorology (IITM), Pune, said urban heat island effect is most visible in the night-time temperatures since cities turn into urban heat islands when buildings, roads, and other infrastructure absorb and re-emit heat, causing cities to be several degrees hotter than surrounding rural areas.

“The high-rise buildings and concrete setup in the cities do not let the excess heat escape during the night. As the temperatures do not cool down, the heatwave continues into the nght. Open green spaces and natural environments with trees can help release the heat faster at night. However, in India, we do not appreciate natural space as much as we appreciate skyscrapers. Add some haphazard city planning, poor architecture and unsustainable construction to it, the recipe for an urban heat island is complete.” Koll said.

Aarti Khosla, director of Climate Trends said, “Like day temperatures, night temperatures have also shown constant and steady rise over the last few years. Warm nights have been punishing this summer with several cities shattering five decades of records. It’s evident that cities will bear the highest brunt, which will get worse due to urban heat island effect. Several studies have already established that by the turn of the century, without very large reductions in fossil fuel burning, night-time temperatures will not fall below 25°C in some places during hot weather, impacting one’s ability to recover for the next day. If we do not act now, nights would continue to be hotter, longer and sleepless, especially for the vulnerable.”

Furthermore, data shows that cities such as Pune and Nashik have recorded an increase by a paltry 0.7% and 3% between 2018 and 2023.