As Germany and Spain sweated and London sweltered through its hottest July day on record this week, scientists said it is "virtually certain" that climate change is increasing the likelihood of such heat waves in Europe.

In real-time data analysis released on Friday, a team of international climate scientists from universities, meteorological services and research organizations said the kind of heat waves hitting Europe this week - defined as three-day periods of excessive heat - are becoming much more frequent in the region.

In De Bilt in the Netherlands, for example, a heat wave like the one forecast for the next few days would have been a roughly one-in-30-years event in the 1900s, according to the scientists. It is now likely to happen every three-and-a-half years, they said.

A boy plays at a fountain on a hot summer day in central Brussels on Thursday. Scientists have said it is 'virtually certain' that climate change is increasing the likelihood of heat waves in Europe. (Yves Herman/Reuters) In Mannheim, Germany, a heat wave like that of the last few days would have been a once-in-a-century event in the 1900s, but is now likely to happen about every 15 years, they said.

London also saw its hottest recorded July day on Wednesday, with temperatures at Heathrow Airport hitting 36.7 C, the scientists noted.

As heat waves grow more frequent, "it does resonate with a much wider audience that this is connected to climate change and we're facing a new normal", said Maarten van Aalst, director of the Red Cross Red Crescent Climate Centre.

An orangutan eats popsicles as zoo-keepers gave animals iced food to keep them cool as temperatures soar, at Rome's zoo on Thursday. (Andrew Medichini/Associated Press) The heat wave analysis, which looked at five European cities, is part of a World Weather Attribution programme led by Climate Central, a U.S.-based science journalism organisation, and supported by scientists from organizations around the world, including Oxford University, the University of Melbourne, the Royal Netherlands Meteorological Institute and van Aalst's Climate Centre.

The programme aims to use climate and weather data, forecasting and climate models to show how changing weather patterns are linked to climate change.

It hopes to help cities and countries better understand and prepare for more extreme weather like this week's scorching days in Europe.

Isolated elderly people at risk

The Netherlands Central Bureau of Statistics has predicted that on average 200 more people will die in that country each week during a heat wave, a 10 per cent rise in deaths.

Deaths among the isolated elderly are a particular problem, and accounted for a big share of the estimated 70,000 additional people who died in France and other European nations during a 2003 heat wave.

Residents at a Belgium home for elderly persons refresh their feet in a swimming pool on a hot summer day on Thursday. The United Nations warned the day before of the dangers posed by hot weather, especially to children and the elderly. (Yves Herman/Reuters) At that time, "people were really caught unawares by the combination of rising risk and changing structure of society", van Aalst said.

Traditionally, extended families have looked after the elderly in places like France, he said. But social changes now mean many more older people live alone in cities, with no one to ensure they do basic things like drink enough water in the heat.

Cities facing heat waves are having to adjust the way they deal with the threat, including through simple measures such as sending out social media messages urging people to "give a call to your grandmother", van Aalst said.

In the Netherlands, television weather presenters now remind viewers when the country's "heat wave plan" — put together after a 2006 heat wave there — has been activated, and give them tips on how to stay cool, he said.

Across Europe, "there's been a massive investment in such plans", he said, alongside a range of efforts to deal with more frequent heat waves, such as adding green spaces in cities.