Mumbai's Nights Get Hotter: Twice as Many Unusually Warm Nights

Mumbai is witnessing a significant rise in both hot days and warm nights, with nighttime temperatures increasing at a more rapid pace. An analysis of IMD data by CEEW revealed that 'unusually warm nights' have more than doubled, from an average of 12 nights in 1981-2010 to 26 nights in 2011-2024. Correspondingly, 'unusually hot days' increased from 12 to 18 annually over the same periods.

This warming trend is driven by a combination of global climate change and intensified urbanisation. The 'urban heat island' effect, where city materials like concrete and asphalt absorb and retain heat, amplifies the warming impact. Experts note that poor nighttime cooling disrupts sleep and recovery, particularly for outdoor workers, and can worsen conditions like diabetes and hypertension due to higher humidity in coastal areas.

CEEW's findings also highlight a seasonal pattern, with the sharpest increase in minimum temperatures occurring during the post-monsoon months (October-December). This is potentially linked to increased atmospheric moisture retaining heat at night. Projections indicate that unusually warm nights in Mumbai could nearly double by 2031-2050, even under moderate global warming scenarios.

Addressing this heat risk requires a multifaceted approach, focusing on both daytime and nighttime temperatures, humidity, and urban planning. Experts advocate for expanding green cover and water bodies, known as 'blue and green infrastructure,' to mitigate heat. Studies show neighbourhoods with more green spaces are significantly cooler, offering crucial relief, especially for low-income communities.