An urban heat island (UHI) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The main causes of the UHI effect are the modification of land surfaces (e.g. buildings, asphalt, etc.) and the waste heat generated by energy usage in buildings, transports and industry. The volume and shape of buildings themselves plays an important role in the creation of an UHI. As a matter of fact, tall buildings provide multiple surfaces for the reflection and absorption of sunlight, increasing the heating of urban areas. Another possible effect of tall buildings is the blocking of wind, which inhibits the cooling of outdoor spaces by convection.