September 29, 2011
Satellites Predict City Hot Spots
Satellites are helping to forecast the location of urban areas most affected during heat waves, helping planners to design cooler, more comfortable cities.
The temperature in densely urbanized areas can be several degrees higher than in nearby rural areas — a phenomenon known as the ℠urban heat island´ effect.
These ℠heat islands´ are particularly noticeable at night. During the day, cities accumulate solar radiation and release the energy after the Sun sets.
The negative effects of this increase in urban temperatures are multiple: health problems, higher energy demand, air pollution and water shortages.
At their final review held at ESA´s ESRIN site Frascati, Italy, the Urban Heat Islands and Urban Thermography team presented its findings on how remote sensing allows the continuous monitoring of thermal radiation emitted by urban surfaces.
Monitoring thermal radiation can help city planners to design more ℠liveable´ cities, assist civil protection authorities in taking adequate measures during heat waves and create maps of energy efficiency.
The project analyzed trends in heat distribution over 10 European cities — Athens, Bari, Brussels, Budapest, Lisbon, London, Madrid, Paris, Seville and Thessaloniki — over the last 10 years, using multiple sensors.
Satellite sensors played a large role in collecting data, providing thermal-infrared measurements that scientists then used to improve urban climate and weather prediction models that can forecast heat waves. Two airborne campaigns and multiple ground sensors also contributed.
In mid-August 2010, two strong heat islands were correctly forecast in Thessaloniki, Greece a day in advance. These heat islands lead to elevated temperatures and reduce thermal comfort.
At night, the most vulnerable areas of city retained high temperatures, above 31°C.
According to the forecast, there was a small area within the urban center where both temperature and risk were expected to be low — corresponding to an open space with abundant vegetation cover.
Thermal radiation maps of Madrid compared to soil surface maps showed that the night air temperature in parks or areas of vegetation is significantly cooler than other areas. This demonstrates the important role that green areas play in the overall thermal radiation and circulation of urban areas.
The new urban climate models show a muggy outlook for the future. During the summer of 2003, large portions of Europe were struck by a major heat wave. Paris was affected severely as the urban heat island effect prevented the city from cooling during the night, leading to thousands of heat-related deaths.
Modelling results suggest that, in the future, heat waves of this intensity and duration might occur every 3—4 years.
Image 1: Mean air temperature in Paris, France at 22:00 CESTin summer 2003. During that summer, large portions of Europe were struck by a major heat wave. Paris was affected severely because the urban heat island effect prevented the city from cooling during the night, leading to thousands of heat-related deaths. Modelling results suggest that in the future, heat waves of this intensity and duration might occur every 3—4 years. Thermal-infrared measurements from satellites continue to help us understand the dynamics of urban heat islands and their patterns within cities. Credits: VITO, Planetek
Image 2: On the night of 16—17 August 2010, two strong heat islands were forecast in the center of Thessaloniki, Greece. These islands led to elevated temperatures in the center of the city which, in turn, reduced the expected thermal comfort conditions. According to the forecasts, there was a small area within the urban center where both temperature and risk were expected to be low: an open space area with abundant vegetation cover. This map shows the difference in air temperature (+/—°C) between the areas of the city. Credits: Laboratory of Atmospheric Physics Aristotle University Thessaloniki, National Observatory of Athens
Image 3: The left image shows the air temperature for Madrid on 25 June 2008 at 22:18 UTC. The difference between the minimum and maximum temperatures in the color legend is 6°C. The right image shows the sealed soil surfaces percentage (provided by the European Environmental Agency). The position of the Retiro Park is at the center of the small rectangle, and shows an almost non-existent heat island at this time of the day. This demonstrates the important role that parks play in cooling city centers at night. Credits: VITO, Indra, Planetek, European Environmental Agency
On the Net: