Are from Pacific Northwest National Laboratory (PNNL), more confirming the nighttime warming trend in the climate record due to increased infrastructure.
RICHLAND, Wash. — City life has its perks: Live music, museums, trendy cafes and more.
But urban life is not so cool when it comes to summer weather.
According to a study, living in a city leads to unpleasant weather two to six hours a day in the summer for people in the eastern and central United States. published December 9 in Geophysical Research Letters. The scientists presented this and related work this week at the annual meeting of the American Geophysical Union.
Additional hours of discomfort occur mainly at night. Cities bask in the summer sun, with concrete, dark pavement and structures soaking in heat during the day and radiating out at night, increasing the heat index at night.
Living in a city increases the urban heat stress index at night by 1.9 to 4.9 degrees Celsius (about 3.5 to 9 degrees Fahrenheit) compared to nearby rural areas. The effect during the day is much less. During the day, some cities actually become a bit more pleasant due to the lower humidity.
Researchers at the Department of Energy of Pacific Northwest National Laboratory also found that when a heatwave hits, the heat penalty of living in the city increases even more. Although everyone in the area is experiencing warmer temperatures, the amount of heat felt by city dwellers compared to their rural neighbors is even greater. The hotter, the bigger the penalty – a concern especially in the context of future global warming.
Because more than four out of five Americans live in urban areas, the scope of punishment can be very broad. Extreme heat is now regularly listed as the leading cause of weather-related deaths in the United States, often before floods, wildfires, and hurricanes.
“People have known about the urban heat island effect for over 180 years, but the fact is that the differences between night and day and between different cities are startling,” says atmospheric scientist Dr. PNNL Yun Qian, the corresponding author of the paper said.
Qian added: “Our findings suggest that urban life makes nighttime in all of the US cities studied more uncomfortable.
Distance between city and countryside
The researchers found that in the US cities studied, a 1 degree Celsius increase in temperature (about 2 degrees Fahrenheit) resulted in an extra 30 minutes of unpleasant weather a day for city dwellers. That means a heatwave, or future warming, that raises the base temperature by 6 degrees Celsius — about 11 degrees Fahrenheit — could lead to more than three hours of nasty weather in a day.
It is more than the discomfort experienced by other residents living in less urban areas in the same area.
To conduct the study, the scientists designed and ran an urban-climate model and analyzed the results over six summers, from 2008 to 2013. The study included major cities such as New York, Boston, Philadelphia, Washington, Atlanta, Miami, Chicago, Detroit, Houston and Dallas. The scientists looked at the heat stress index, which describes how temperature feels when humidity is taken into account.
The team then calculated “heat warning hours,” which they define as the hours when the heat index reaches over 27 degrees Celsius or around 80 degrees Fahrenheit – the dividing line they used between comfortable and uncomfortable. roof.
The team observed a competitive dynamic between temperature and humidity in cities. When it comes to comfort, cities have the edge when it comes to humidity. There is usually less moisture in urban areas because there are not many plants, trees and other vegetation to escape moisture. But uncomfortably higher temperatures in cities are a stronger factor, with five times the impact of humidity.
In all the cities studied, the air became more uncomfortable at night as temperatures increased, regardless of humidity. In addition, the effects of urban living vary slightly between regions.
Regional difference
At night, metropolitan areas in the Northeast, such as New York and Philadelphia, experienced the greatest nighttime fines, with the heat index rising to around 4.5 degrees Celsius.
But in terms of overtime hours of nasty weather, the effect was most pronounced in the southeastern United States. For example, Atlanta residents experience an average of four to five hours a day during the summer of nasty weather. People living in the Northeast are more likely to have two or three such hours.
In many cities, urban living also makes daylight hours less comfortable. Philadelphia, Washington, New York and Chicago all experience higher heat index and heat stress during the day, compared to neighboring rural areas. But as lower humidity is accompanied by higher temperatures in the cities, daytime comfort has been slightly enhanced in the southern and eastern US, including Dallas, Houston, Atlanta and Miami.
“It is important to note the differences between cities,” said co-author TC Chakraborty. “What is useful for heat mitigation in Chicago, for example, may be different from what is useful in Miami. Even within a city, different neighborhoods can be very different — for example, a riverside area versus an area with no grass or water nearby. ”
Together with Qian, former PNNL postdoctoral fellow Chandan Sarangi, now working at the Indian Institute of Technology in India, is the lead author of the paper. Other PNNL authors are Jianfeng Li, Ruby Leung and Ying Liu.
The study was funded by the DOE Office of Science.
# # #
The link for the published article is here.
Related
