New Delhi, which endured one of its worst heatwaves in history earlier this month, has now faced the biggest downpour in decades, with rainfall over a 24-hour period surpassing the city's average for the entire month of June.

The downpour caused a fatal airport roof collapse, disrupted flights, closed a metro station, blocked underpasses, and led to massive traffic jams.

WHAT'S HAPPENING?

Delhi's main Safdarjung weather station recorded 228.1 mm (9 inches) of rainfall in the 24 hours ending 8:30 a.m. (0300 GMT), its highest 24-hour rainfall in June in 88 years, according to the India Meteorological Department (IMD).

Areas around Delhi airport had 148.5 mm (5.85 inches) of rain over a three-hour period on Friday, compared with 101.7 mm (4 inches) for all of June last year.

The seasonal monsoon rain, which slowly covers the country beginning from its southern tip at the end of May, brought respite from heatwave conditions that had persisted in Delhi until last week.

Temperatures this summer have neared 50 degrees Celsius (122 Fahrenheit) in the city and Delhi has recorded at least 40 consecutive days of temperatures at or above 40 C (104 F) up to June 22, according to IMD data.

An IMD official, speaking on condition of anonymity, said the progress of the monsoon was stalled for a week, which led to lower rainfall and heatwaves in northern India, but sudden thunderstorms last week in the region pushed the monsoon clouds back on track.

He said this would help the monsoon cover the entire country on time or even a few days ahead of the normal schedule.

WHY THE EXTREMES?

For every degree increase in earth's temperature, the amount of water vapour in the atmosphere can increase by about 7%, according to a NASA article in 2022. Experts say that can lead to heavy rains in a short period of time.

"Because of climate change, you will get more extreme rain events, which means more rain in a fewer number of rainy days, rainy hours," Sunita Narain, director general of Indian research body Centre for Science and Environment, said in a video post on social media this week.

"If you look at the data from across India, you will find that many weather stations are already reporting that they are breaking the record of 24-hour rainfall, which means that a city, a region, can get its annual rain, as much as a whole year's rain, in a matter of a few days or even one day."

DEALING WITH ERRATIC MONSOONS

Delhi has endured erratic monsoon patterns over the last 40 years, facing both deficient and excessive rainfall, said Vishwas Chitale, at the Indian think tank Council on Energy, Environment and Water.

"Such skewed distribution of rainfall impacts infrastructure and people severely, which re-emphasises the importance of climate proofing infrastructure and the economy," he said.

Experts say India needs to dig more lakes and ponds to store heavy rainfalls and prevent massive water shortages in heavily populated cities like Delhi and Bengaluru. Municipalities need to ensure drains and canals are un-clogged to avoid heavy flooding and major disruptions.

The country also needs to substantially increase its green cover and raise public awareness about the impacts of heat, stagger work hours and change schoolday timings, the experts say.

(Reporting by Krishna N. Das, Shivam Patel and Rajendra Jadhav Editing by Raju Gopalakrishnan and Frances Kerry)