If the city feels hotter to you in the summer, you're right.
The Japan Meteorological Agency has proved that all the asphalt and tall buildings and exhaust heat are indeed to blame.
"Urban heat islands" raised the daily August temperatures by 1 to 2 degrees in Japan's three biggest megalopolises of Tokyo, Osaka and Nagoya, the JMA said July 9.
This is the first time the JMA has analyzed the effects of urban heat islands, where asphalt, buildings and heat from the exhaust of automobiles and air conditioners and other factors contribute to a rise in temperatures.
The JMA used data from last August to simulate air temperatures on the assumption that all ground surface was covered by grassland and that there was no exhaust heat from human activities in the three megalopolises, and compared the numerical outcomes with what was actually recorded.
The urban heat islands accounted for rises of about 2 degrees in the cities' central areas and about 1 degree on their outskirts, JMA officials said.
It is believed that air temperatures have risen about 3 degrees in the three big cities during the last 100 years due to both global warming and urban heat islands, but the JMA has never evaluated to what extent the urban heat islands are responsible.
"Urbanization accounted for as much part of the temperature rises as global warming," a JMA representative said. "The situation is thought to be similar in other regions of advanced urbanization."
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