Urban Heat Islands

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Urban heat islands are places in the world that have higher temperatures than the locations around them. These urban heat islands can be created by natural factors like mountains, plains, or deserts, or by man-made factors like cities, industrial areas and intentional landscaping. Scientists have been studying the effects of urban heat islands since the 1800s when observers began noticing and documenting the temperature changes between the cities and surrounding rural areas, which was particularly obvious in the summer months.

Many of the materials that are used in the construction of cities and urban areas have impervious surfaces and have a dense mass which results in a high absorption of solar radiation during the day.  That solar radiation is then released at night in the form of heat. This affects the temperature around them greatly. Materials like concrete and asphalt absorb much of this solar radiation and can influence the temperature of the areas around them by many degrees.

Another major influencing factor when it comes to urban heat islands is how much of the city and areas around it are covered by greenery, trees, and other vegetation. Green spaces and forests absorb solar radiation but to lesser degrees than impervious surfaces, making the temperature differential between urban and rural areas greater.

Measuring Urban Heat

Scientists have a very specific system for accurately measuring the air temperature of areas. The thermometer must be 1.2 to 2 meters off the ground and not located in direct sunlight, although it can also not be placed in the shade of a building, mountain or tree. This, according to the World Meteorological Organization, is the most accurate way to read air temperature. Scientists have also begun to rely on satellite imagery in order to determine air temperature on Earth, using a variety of wavelengths and heat sensors to accurately depict temperatures where there is no way to measure air temperature on the ground.

Mean air temperature in Paris, France at 22:00 CESTin summer 2003. Credits: VITO, Planetek.
Mean air temperature in Paris, France at 22:00 CEST in summer 2003. Credits: VITO, Planetek.

Urban centers are warmer than surrounding areas because of the impervious surfaces used in construction; urban areas are unable to use the cooling effects of water on the land to cool down the surrounding air temperature, unlike forests or green spaces which can minimize the effects of solar radiation on the earth through moisture absorption.

Scientists are searching for answers to the question of whether urban heat islands have an effect on the overall temperature of Earth’s surface; basically, whether or not the collective heat increase of cities and other heat islands has contributed to global warming, and whether or not the continued urbanization of the globe will have a permanent effect on the Earth’s temperature. The local temperature changes that occur in urban heat islands could have a very big effect when combined together, and scientists continue to search for ways to mitigate the urban heat island effect as well as the overall issue of global warming.

Urban Heat Island Profile.  Source: NASA.
Urban Heat Island Profile. Source: NASA.

How Understanding the Hottest Places on Earth Helps Scientists Learn More About Urban Heat Islands

The hottest places on earth aren’t located in urban centers; scientists and weather aficionados the world over have been searching for the hottest place on earth for many years and only recently have been able to adequately give an answer to that burning question. China’s Taklimakan Desert and Tian Shan mountain range has had a record temperature of 50-80 degrees Celsius (122-175 degrees Fahrenheit) and is the hottest location in China, if not the world. But scientists do not consider a few record temperatures to be an indication of the true location of the hottest point on earth; rather, they are looking for the hottest consistent temperatures in a particular location. Other hot locations of notability include Death Valley, California’s Furnace Creek (56.7 degrees Celsius, or 134 degrees Fahrenheit), and El Azizia, Libya at 58 degrees Celsius (136.4 degrees Fahrenheit). Scientists continue to try and record the temperatures of remote locations like the Gobi Desert, the Sahara Desert, and more, despite the lack of on the ground equipment.

Dark surfaces like dark stones and fertile soil absorb solar radiation and can create an environment where the air temperature is less than the temperature taken just a few inches below the surface of the ground. Lut’s Desert in Iran is one example of this; the dark ground surface creates a heated atmosphere in the desert giving it the most consistent hot temperatures on Earth. While air temperature can be mitigated by wind and surrounding features that block the sun the surface of the Earth absorbs solar radiation and retains it.

Studying the hottest places on Earth, both urban and rural, are essential for continuing to know and understand the effects urban heat islands have on the rest of the globe’s temperatures. Knowing how urban heat islands are formed and what factors can influence them is important for city planning, water management, and much more.


Earth Observatory. Where is the Hottest Place on Earth? 5 April 2012. http://earthobservatory.nasa.gov/Features/HottestSpot/

Nasa. Ecosystem, Vegetation Affect Intensity of Urban Heat Island Effect. 15 December 2009. http://www.nasa.gov/mission_pages/terra/news/heat-islands.html

Urban Heat Island Analysis. GIS Lounge, September 29, 2011. http://www.gislounge.com/urban-heat-island-analysis/


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