Julia Poska | February 27, 2020

Vegetation starts turning green earlier in cities than surrounding rural areas, but urban plants are less sensitive to unseasonable warmth, new Iowa State University-led research found. The authors attribute the difference to the urban “heat island” effect.

Cities typically have somewhat higher temperatures than surrounding rural areas because materials like asphalt and brick absorb heat more readily than natural landscapes. For example, New York City is about 7 degrees Fahrenheit warmer than surrounding areas in summer, according to NASA’s Climate Kids site.

Researchers found this “heat island” phenomenon causes urban vegetation to perceive the start of spring and begin greening an average of six days earlier than surrounding rural plants.

As climate change progresses, however, plants in both rural and urban areas are responding to unseasonably warm temperatures by beginning growth earlier and earlier over time. Pollinators and last frosts have failed to keep up, which has damaged the early bloomers’ ability to survive and reproduce.

The study found that rural vegetation is more sensitive to early spring weather than urban vegetation, perhaps due to the urban heat island effect as well.

ISU Ph.D. student Ling Meng led the research team, which included CGRER member Yuyu Zhou, an ISU geological and atmospheric scientist, among others. The study, published this month in Proceedings of the National Academy of Sciences, was based on satellite images from 85 large U.S. cities from 2001 to 2014.

Zhou told the Iowa State News Service that this sort of research can help predict how plants will respond to climate change and urbanization.