It’s a symptom of the way cities trap heat, a phenomenon known as the “heat island effect,” said the authors of a recently published study in the academic journal Proceedings of the National Academy of Sciences. The study has ramifications for anyone interested in the ecological impact of climate change or who suffers from allergies, said Yuyu Zhou, an associate professor of geological and atmospheric sciences at Iowa State University and a co-author of the study.
The study examined satellite images of 85 large cities in the United States from 2001 to 2014. The satellite images allowed the researchers to detect the changes in greenness of plants and thus determine the timing when plants start to grow in spring. The data show the start of the season arrived on average six days earlier in the studied cities than surrounding rural areas due to the heat island effect.
Zhou said little research has investigated the connection between the heat island effect and phenology, or the study of cyclical and seasonal natural phenomena. Zhou said this kind of information will become increasingly important as scientists attempt to predict how plants will respond to changing environmental conditions, including climate change and urbanization.
“In the future, we want to have more accuracy in our earth system models to predict changes in our environment. Taking into account the interactions between temperature and phenological change in vegetation will mean those model predictions will improve,” Zhou said.
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