from”Who is thunkit?” Department and NASA Goddard completed the obvious science, complete with a picture that proudly proclaimed that “the desert is hot and dry.” Government “science” at its best.
go through Madeleine Gregory
NASA Goddard Space Flight Center, Greenbelt, Maryland
Any city dweller who has experienced a heat wave knows that a shade tree can make all the difference. But what happens if there is no shade?
a recent study nature communications Satellite data from the National Aeronautics and Space Administration (NASA) found that there is a major gap in the global ability to cope with climate change: Southern cities have far less green space than northern cities and therefore have lower cooling capabilities. The study uses the terms “global North” and “global South” to distinguish between developed countries (mainly in the Northern Hemisphere) and developing countries (mainly in the Southern Hemisphere).
Cities tend to be hotter than nearby rural areas due to the urban heat island effect. Heat-trapping dark surfaces such as sidewalks, buildings and roads absorb heat from the sun's rays, raising temperatures in cities. Extreme heat poses serious health risks to urban residents, including dehydration, heat stroke, and even death. While greenery is not a panacea, it can provide shade and release moisture into the air, cooling the surrounding environment.
“Cities can strategically prioritize the development of new green space in areas with less green space,” said Christian Braneon, a climate scientist at NASA’s Goddard Institute for Space Studies in New York who was not involved in the effort. research. “Satellite data is very helpful with this.”
An international research team led by Nanjing University doctoral student Li Yuxiang analyzed the world's 500 largest cities and compared their cooling capabilities. They used data from the Landsat 8 satellite, which is co-managed by NASA and the U.S. Geological Survey, to determine how effective green space is in cooling each city.
First, they calculated the average surface temperature for each city in the hottest month of 2018, as well as the average of the hottest months from 2017 to 2019. Next, the researchers used a metric called the Normalized Difference Vegetation Index (NDVI) to calculate and map how much green space each city has. NDVI relies on the fact that healthy vegetation absorbs red light and reflects infrared light: the ratio of these wavelengths shows the density of healthy vegetation in a given satellite image.
The researchers found that the greening-related freezing capacity of cities in the Southern Hemisphere is only 70% of that of cities in the Northern Hemisphere. On average, green space in cities across the Global South lowers temperatures by about 4.5 degrees Fahrenheit (2.5 degrees Celsius). The average amount of air conditioning in cities in the Global North is 6.5 F (3.6 C). This exacerbates an existing problem: Southern cities, which tend to be at lower latitudes (i.e. closer to the equator), are expected to experience more extreme heat in the coming years.
“It is clear that countries in the Southern Hemisphere will be more vulnerable to heat waves, rising temperatures and extreme weather conditions than countries in the Northern Hemisphere,” said Xu Chi, a co-author of the study and a professor of ecology at Nanjing University. Southern countries are less able to adapt to the heat because of air conditioning Less common, power outages are more frequent.
Why are cities in the Southern Hemisphere struggling to stay cool? Cities in the Southern Hemisphere tend to have less green space than cities in the Northern Hemisphere. This reflects research on differences within cities, sometimes called the “luxury effect”: Wealthier neighborhoods tend to have more green space than poorer neighborhoods. “Wealthier cities also have more urban green space than the poorest cities,” Chi said.
Urban planners are unlikely to close the gap between the worst-performing city in the study (Mogadishu, Somalia) and the best-performing city (Charlotte, North Carolina).
Mogadishu is a densely populated city with a dry climate that limits vegetation growth. Still, each city can learn a lot from its neighbors. Within a given region, the researchers identified the cities with the greatest cooling capabilities and targeted them. They calculated the difference between the region's top-performing city and every nearby city for potential additional cooling capacity. They found that by systematically increasing the quantity and quality of green space, a city's average cooling capacity could be significantly increased, by as much as 18 degrees Fahrenheit (10 degrees Celsius).
“How you use green space actually differs depending on the climate and urban environment you're looking at,” said Brannion, whose research at NASA focuses on climate change and urban planning.
Green cities in the United States and Canada have lower population densities. However, fewer people per square mile is not necessarily good for the environment: residents of low-density cities are more dependent on cars, and their homes tend to be larger but less efficient. Branion noted that there is a whole range of solutions beyond planting trees or designating parks: Cities can increase cooling capacity by creating bodies of water, seeding green roofs and painting roofs or pavements lighter colors to reflect more light.
Through global studies like this, urban planners can compare strategies in cities in the same region or with similar densities. “There is still a lot of room for design changes in emerging urban areas that are not yet fully built out,” Brannion said.
Journal – Nature Communications
Paper: DOI 10.1038/s41467-024-51355-0
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