Highest minimum temperature: Why Delhi’s warm nights are cause of worry

Sub: Geography

Sec : Climatology

Context:

Delhi recorded its highest minimum temperature since 1969 on Tuesday, reaching 35.2°C.

Details:

The city is experiencing unusually high day and night temperatures, with seven heatwave days in June and six consecutive warm nights.
The previous highest minimum temperature was 34.9°C on May 23, 1972. Records before 1969 are not analyzed, so it’s unclear if this is the highest ever. Two Haryana stations recorded even warmer mornings.

What is a ‘warm night’?

A warm night is when the minimum temperature is 4.5 to 6.4°C above normal; a severe warm night exceeds this by more than 6.4°C. The day temperature must be 40°C or higher for these conditions.
Northwest India is experiencing a significant rain deficit and consistently high temperatures. Increased night temperatures are causing more heat stroke cases, as people find no respite from the heat.

Urban Heat Island effect in Delhi:

IMD data shows June 2024 has had 12 days with minimum temperatures over 30°C, a first since 2011.
The urban heat island effect, where densely built areas trap heat, is contributing to the rising temperatures.
Studies indicate that cities now cool down more slowly than between 2001 and 2010, leading to warmer nights.

What us Urban Heat Island effect?

Urban heat island may be defined as the local and temporary phenomenon in which certain pockets within a city are experiencing higher heat load than its surrounding area.
This rise of heat basically happens due to buildings and houses of cities made up of concrete where the heat is trapped and not able to dissipate easily.
Urban heat island is basically induced due to trapped heat between establishments made up of concrete.
The temperature variation can range between 3 to 5 degrees Celsius.

Source: IE