When wind blows over a city, buildings interact with the moving air mass, generating turbulence, much like sticking your fingertips into a stream forms visible vortices on the water surface. This turbulence spreads up into the atmosphere and down into the streets. As a result, more heat, humidity, and pollutants are transported upwards from the ground. At the same time, more of the wind's turbulent energy dissipates between streets, in gardens, or in other open spaces.