Near-record temperatures in Pakistan have claimed hundreds of lives and devastated crops in the third major heatwave in four years. But as temperatures on Friday dipped to under 38C (100F), signalling the end of nearly four weeks of blistering heat, leading meteorologists warned that the country could expect longer, more intense and more frequent events in future.

Qamar-uz-Zaman Chaudhry, a vice-president of the World Meteorological Organisation (WMO) and former director of Pakistan's Met Office, said the recent extreme summer temperatures that are commonly followed by massive floods could largely be attributed to climatic warming. "If we look at the frequency and the trend of the extreme weather events impacting Pakistan then it is easy to find its link with climate change," he said.

Chaudhry, who wrote Pakistan's climate change policy, authored a report in 2013 that showed the number of heatwaves in Pakistan had increased from 1980 to 2009 and that average temperature in the Indus delta was steadily rising.

In 2010, the May temperature in Mohenjo-daro, a semi-ruined city in Sindh province, reached 53.5C (128F), the fourth highest temperature ever recorded in the world and the highest ever in Asia.

Babar Hussain, who runs the Pakistan Weather Portal, said: "In 2013 the maximum was 51C/52C. The heatwave started on 12 May in Sindh province and gripped the entire country by 15 May. It lasted, with only a minor break, until 10 June. In that time, it reached 51/52C in Larkana, [a city of 2 million people in southern Sindh province] while Lahore, Punjab province's capital of about 15 million population, recorded 47C on 23 May, its hottest temperature since 1954."

The effect of the heatwaves on human life has been devastating. Newspapers in Pakistan have reported hundreds of deaths because of the heat since early May, but no official numbers have been released.

"With the coming of the monsoon rains this year, we have already begun to see an increase in cases of diarrhoea. This is because of contaminated drinking water," said Isaac Chikwanha, medical co-ordinator for Médecins Sans Frontières in Pakistan. "Heat strokes and dehydration are common among children and adults before the monsoon season when the temperature rises."

"The rise in vector-borne diseases including diarrhoea, cholera, gastroenteritis, typhoid and hepatitis is due to environmental factors and the effects of climate change," said Iqbal Memon, president of the Pakistan Paediatric Association. "The Indus River used to flow at full strength prior to the monsoon season and freshwater was abundantly available. Now there is no water in the Indus River. Ponds and riverines in Sindh have become contaminated, but people have no other option but to use that water for drinking and cooking. This lack of freshwater is purely due to environmental reasons," Memon told Dawn newspaper.

Farming has been badly affected, with cows giving less milk and not enough water for some crops. "The heat actually helped the cotton crop because it came when it was flowering and it quickly turned into fruit," said Mustafa Talpur of Oxfam in Islamabad. "But it badly hit the sugarcane, rice and chilli crops. The lack of irrigation water has affected the yield, but the exact impact wont be known until the harvest is over."

The heatwave may have affected people in cities more than in rural areas, partly because of the "heat island effect" which sees temperatures in urban areas 5-8C higher than in the countryside. Urban conditions were particularly bad because the heatwave led to power cuts which in turn led to violent protests. Many families were unable to pump water or run air conditioners. Officials at one point turned off the air conditioning in government offices.

Pakistan is, along with Bangladesh, highly vulnerable to natural disasters, and has experienced massive floods in the last three years, droughts and heatwaves.