Urban heat island (UHI) is a climatological phenomenon representing the difference in air temperature between urban areas and its surrounding suburbs and undeveloped areas. Urban structures absorb and re‐radiate solar radiation and from anthropogenic heat sources, causing UHI. In the rapidly urbanizing Arab region, the intensifying UHI leads to thermal discomfort of urban dwellers.

 

As urban areas develop, changes occur in their landscape. Buildings, roads, and other infrastructure replace open land and vegetation. These urban changes, along with waste heat generated by energy usage cause urban regions to become warmer than their rural and undeveloped surroundings, forming an "island" of higher temperatures in the landscape.  The annual mean air temperature of a city with one million or more people can be 1 to 3C warmer than its surroundings, and on a clear, calm night, this temperature difference can be as much as 12C .  

 

60% of world population is expected to live in cities by the year 2030. This poses unique challenges to city planners. Elevated temperatures from urban heat islands, particularly during the summer results in increased energy consumption, emissions of air pollutants and greenhouse gases, seasonal health problems like respiratory difficulties, heat cramps and exhaustion, stroke, high consumption of water and impaired water quality, increase in global warming etc.

 

Heat Islands are mainly of 2 types: surface and atmospheric. Surface UHI tends to be strongest during the day while atmospheric urban heat island is elevated after sunset due to the slow release of heat from urban structures and surfaces. Atmospheric heat islands can be Canopy layer urban heat islands- the layer of air where people live from the ground to below the tops of trees and roofs, or Boundary layer urban heat islands which start from the rooftop and treetop level and extend up to the point where urban landscapes no longer influence the atmosphere.

 

UHI can be reduced by controllable factors like design and planning of cities. The direct solar heating will affect both urban and rural areas simultaneously and equally, the indirect solar heating is a main cause of UHI. It depends on building geometry and surface thermal properties. In hot arid regions like the Middle Eastern countries, these two factors play a bigger role due to intense solar radiation.  

 

Good reduction in UHI effect cab be achieved by orienting street canyons to north‐south, creating cold corridors through wind directions, adopting proper ratios in constructions, creating a connected oasis of courtyards and open spaces to moderate temperature and enhance airflow and cross ventilation, creating smaller self-sustained clusters, transit oriented with mixed land uses to discourage car‐based designs and plans, applying cool roofs, pavements and walls, plantation wherever possible etc. Using materials certified for green buildings like the LEED which is increasingly being adopted helps reduce UHI. Leadership in Energy and Environmental Design (LEED) is a rating system devised by the United States Green Building Council (USGBC) to evaluate the environmental performance of a building and encourage market transformation towards sustainable design

An example is UAE's Masdar City which is successfully pioneering a green-print for how cities can accommodate rapid urbanization and dramatically reduce energy, water and waste. The city is a combination of ancient Arabic architectural techniques with modern technology and captures prevailing winds. It is naturally cooler and more comfortable during the high summer temperatures. Masdar uses clean energy generated on site from rooftop solar technology and has one of the largest photovoltaic installations in the Middle East.