Hot cities Seville's ancient fix to tackle worsening problem

Beneath the streets of Seville - where summer temperatures regularly top 40C -a €5m (about £4m) cooling strategy is taking the city back in time.

- Chris Michael

The millennia-old Persian technique of "qanat" features underground channels filled with water and shafts that bring the cooler underground air to the surface. Seville is doing the same, adapting a 1992 experimental qanat to use renewable power and - in a new twist - pumping the water to the tops of buildings, where it will trickle down inside the walls to cool them. Even the benches will be chilled.

It sounds like a luxury, but it is nothing of the sort. Heat has become a leading health threat to cities, and not just in Seville. Last year 645 people died from overheating in Phoenix.

Counterintuitively, the fire trucks in Phoenix now carry ice, packed into body bags. Its first responders have learned through the experiences of the past few years that you can save lives by packing overheated people into ice - a coldwater immersion therapy used in extreme endurance tests, such as military training and marathon running-in order to bring their temperature down rapidly while whisking them to hospital.

Nor is Phoenix an outlier. On this year's hajj, the Muslim pilgrimage to Mecca, an estimated 1,300 people died in heat that surpassed 51C more than halfway to the boiling point of water, a toxic level that cooks human cells, thickens blood and cuts off oxygen to the brain. Extreme heat in New Delhi has killed more than 100 people in the last three months alone, probably a vast undercount. It is now considered unsafe to work outside at all in Doha, a factor behind the deaths of an estimated 6,500 migrant workers in the 10 years after Qatar won the right to host the World Cup.