Shahid Baloch, a grave digger at a Edhi run cemetery is taking no chances.

Like many people in the city, he was caught out by the severity of last summer's heat wave which killed more than 1,300 people, and has hired a digger to excavate three elongated trenches big enough for 300 bodies.

"Thanks to God, we are better prepared this year," said Baloch, 28, who works with three brothers at the vast Karachi cemetery run by Edhi Foundation.

When the heat wave struck in the summer of 2015, hospitals, morgues and graveyards in the city of 20 million people were overwhelmed, and drug addicts, day labourers and the elderly were the biggest victims of the searing heat.

Temperatures hit 44 degrees Celsius (111 Fahrenheit), their highest since 1981 and above normal summer levels of around 37C (99F).

Intervention by the army and charity groups staved off an even worse disaster, locals said, but the crisis exposed the shortcomings of emergency services in coping with environmental disasters that scientists say will become more common in the future.

Meteorological office is not predicting a repeat of last year's extreme conditions, but, like Baloch in the cemetery, officials are preparing for the worst just in case.

"It will not get out of control the way it happened last year," said Karachi Commissioner Asif Hyder Shah, adding that nearly 60 hospitals now have spare capacity for 1,850 heat wave patients.

Last summer patients slept on ward floors and long queues formed outside Karachi's main state hospitals at the peak of the heat wave.

Shah said nearly 200 first response centres have been set up across the city, offering basic heat-stroke treatment to swiftly stabilise patients. There are also 700 makeshift relief centres, dishing out drinking water and rehydration salts.

A man drinks a cup of water at a water distribution point set up on a street corner as preparations are made in case of another heatwave in Karachi.─Reuters

"This will save lives. It's a comfort," said street vendor Muhammad Mahmood, 32, after downing a cup of water at one centre. Next to him, children in school uniforms queued to quench their thirst.

Efforts to prepare for extreme heat have been limited by decades of under-investment in Pakistan's crumbling electricity grid and water infrastructure, leaving the sprawling city vulnerable in times of crisis.

The problem last year was compounded by power cuts which left people unable to cool themselves with fans and air conditioners, particularly affecting those unable to afford generators.

Some politicians pinned blame on the provincial government and K-Electric, the company that supplies electricity to Karachi, for the high death toll. K-Electric did not respond to requests for comment.

Under-investment hampers plans

Last summer, the Edhi morgue ran out of freezer space after about 650 bodies were brought in the space of a few days. Ambulances left decaying corpses outside in sweltering heat.

Similar macabre scenes plagued Karachi's cemeteries, where grave diggers refused to work in the baking sun and charged up to five times normal rates for burial plots.

"People were not able to buy those graves," said Faisal Edhi, managing trustee of the Edhi Foundation. "They buried their dead in their relatives' graves."

Faisal Edhi, son of Abdul Sattar Edhi, founder of EDHI Foundation, visits the EDHI morgue in Karachi.─Reuters

Some residents said much would depend on whether any future heat wave struck during the fasting month of Ramadan.

Abdul Qayyum Soomro, religious affairs adviser to the chief minister of Sindh province, said officials will meet clerics to discuss whether a fatwa, or religious edict, should be issued allowing people to break the fast for health reasons.

Commissioner Shah said the subject was "extremely sensitive" among a devout population.

"If things get really bad, I may abandon the fast since God says life is most precious," said a fruit vendor selling mangoes and bananas from a push cart.

Last year, his five-year-old son fell ill from the heat but was only treated at the third hospital they visited. The first two, including Karachi's biggest, were full.