On a summer afternoon, the centre of a large city can be several degrees hotter than the around it. Scientists call this the urban effect. , and glass absorb the sun's energy during the day and release it slowly at night, while cars and air conditioners pump out even more heat.
For cities in the Gulf, where temperatures regularly 45°C, the issue is . Extreme heat puts pressure on electricity networks, discourages walking and can be dangerous for vulnerable groups such as the and outdoor workers.
Urban planners are now looking to both modern technology and traditional architecture for solutions. Planting trees is one of the most effective approaches: a single tree can cool the air around it as much as several air conditioners. Riyadh, for example, has launched a project to plant millions of trees across the city. Other ideas include painting roofs white to sunlight and designing streets that are narrower and shaded.
Interestingly, many of these ideas are not new. Old towns across the region were built with narrow , thick mud walls and wind towers — known as barjeel — that captured and pushed cool air into houses. As one architect put it, "Our grandparents already knew how to live with the heat. We just forgot."