NASA finds plants essential for limiting urban warming.
Plants reduce temperatures as much as 4 degrees according to a new NASA study that for the first time assess the impacts of cities and urbanization for the entire continental United States. Their conclusion: the presence of vegetation is an essential factor in limiting urban heating.
Cities are literally covered—in pavement, roads, and buildings. All those impervious surfaces heat up, causing a difference in surface temperature between urban areas and surrounding vegetated areas. NASA researchers modeled observations from multiple satellites to find out exactly how much cities heat up. What they found was that averaged over the continental United States, areas covered in part by impervious surfaces, be they downtowns, suburbs, or interstate roads, had a summer temperature about 4F (1.9C) higher than surrounding rural areas. In winter, the temperature difference was 3F (1.5 °C) higher in urban areas.
“Everybody thinks, ‘urban heat island, things heat up.’ But it’s not as simple as that. The amount and type of vegetation plays a big role in how much the urbanization changes the temperature,” said research scientist and study co-author Kurtis Thome of NASA Goddard.
Trees with broad leaves, like those found in many deciduous forests on the East coast, have more pores to exchange water than trees with needles, and so they have more of a cooling effect, he said.
The northeast I-95 corridor (Baltimore-Washington), Atlanta and the I-85 corridor in the Southeast, and the major Midwest and West Coast cities and roads show the highest urban temperatures relative to their surrounding rural areas.
NewTerrain newsletter September 4, 2015.