Feeling like nights are getting too uncomfortable? New report confirms that nighttime temperatures aren’t dipping enough

As the fast-approaching southwest monsoon gradually drowns out the summer, it will also help ease and then erase the memories of a brutal season past. Even then, an unease is expected to continue lingering in the minds of most Indians: something just wasn’t right this year.

Studies have already shown time and again that deadly heat is becoming a frequent phenomenon in India. With temperatures expected to touch a scorching 54°C, extreme conditions are rendering an increasing number of places unliveable. This includes India’s highly developed metro cities, which are dealing with their own set of unique heat troubles.

Delhi-based think tank Centre for Science and Environment (CSE) has shed light on an alarming trend: not only are heatwaves are becoming deadlier in India’s major cities, temperatures aren’t dropping enough to provide sufficient respite at night either.
Deadlier heatwaves
Spanning over 23 years from January 2001 to April 2024, the study meticulously analysed data from Delhi, Mumbai, Kolkata, Hyderabad, Chennai, and Bengaluru. While their air temperatures haven’t witnessed a dramatic rise during the specified period, these areas have continued to witness an increase in their relative humidity. The researchers think that this may also be heightening the heat stress — a measure combining air and land temperatures along with relative humidity — and intensifying the discomfort and health risks for the city’s inhabitants.

Another of the main culprits behind the discomfort in Indian metros may be due to the way urban sprawl has spread massively in the past few years. The CSE study found that the rapid expansion of urban areas has led to a significant reduction in green cover, coupled with a surge in concrete surfaces. In cities like Chennai, green spaces have dwindled by nearly 14% over the past two decades, while concrete infrastructure has doubled. Even Bengaluru, a city earlier famed for its abundance of garden-like spaces, has only 7% green cover left, an earlier IISc study had found. This transformation contributes to the "urban heat island effect," where concrete-trapped heat is making urban regions notably warmer than their rural counterparts.
Minimums on the rise
However, what’s particularly concerning is the decline in nighttime cooling. Historically, cities would cool down considerably at night, providing much-needed relief from the daytime heat. However, the study reveals that this cooling effect has substantially decreased, exposing residents to prolonged periods of high temperatures without respite. The continuous exposure to heat, compounded by high humidity, exacerbates health risks, making heat stress and related illnesses more prevalent and potentially deadly at lower temperatures.

The health implications are dire. The study observed an increase in the number of days with a heat index — what the weather “feels like” — surpassing 41°C in cities such as Kolkata and Chennai. Furthermore, the monsoon season, once a period of relief, now brings hotter and more humid conditions in some cities compared to the pre-monsoon months. As most might know, high humidity undermines the body’s ability to cool itself through sweating, increasing the risk of heat stress and related illnesses

In response to these findings, CSE Executive Director Anumita Roychowdhury highlighted the necessity for in-depth assessments of heat trends, relative humidity, land surface temperatures, and diurnal temperature variations. These assessments are crucial for developing effective heat management plans that extend beyond emergency responses to encompass long-term strategies, such as expanding green spaces, enhancing water bodies, and improving thermal comfort in buildings.

The study also called for reversing detrimental land use patterns and implementing scientifically grounded measures to monitor and mitigate urban heat stress. The time for action is now, as the repercussions of inaction could be devastating for millions residing in India's rapidly growing urban centers.

The CSE report can be found here.