MADRID - Spain's third heatwave of the summer was set to reach its peak on Wednesday, with temperatures reaching as high as 44 degrees Celsius (111 degrees Fahrenheit) in central and southern Spain and authorities warning of the risk of wildfires.

The mercury could also rise to 40 C in the Basque Country in northeastern Spain, an area less accustomed to such high temperatures, the state weather agency AEMET said.

It warned of so-called dry storms - thunder and lightning without rainfall - in many parts of the country.

Southern European countries have been grappling with record-breaking temperatures this summer, prompting authorities to warn of health risks, particularly for the elderly and those with medical conditions.

Temperatures in some areas in the southern half of Spain remained above 27 C on Tuesday night and Wednesday morning, AEMET spokesperson Ruben del Campo said.

"Wednesday will be the most intense day in terms of extension and temperatures," Del Campo said, adding that the heatwave will continue until the weekend.

With the tourist season also hitting its peak, sightseers in Madrid were getting more sun than they bargained for. Visitors waiting in line at the Prado museum were sprayed with water by employees. Tourists said they were keeping to the shade, drinking lots of water and eating ice cream to stay cool.

The heatwaves recorded in Spain and wider Europe this summer have worsened a prolonged drought, lowering reservoir levels as water evaporation and consumption increase and prompting authorities in Catalonia to impose new water usage restrictions.

As Spain suffocates under high temperatures, ice on its mountains is melting.

The Cryosphere, a scientific journal focused on frozen water and ground, published a peer-reviewed paper on Tuesday showing how the Aneto Glacier, the largest in the Pyrenees, is melting and could disappear altogether.

The paper shows the glacier lost about two-thirds of its surface area between 1981 and 2022 and has been reduced to just half a square km. The glacier's mean ice thickness was reduced by about 30 meters in the same period.

The melting sped up in 2021 and 2022, which were particularly warm years in Spain.

(Reporting by Charlie Devereux and Inti Landauro, Editing by Angus MacSwan)