The Science

Researchers investigated changes in the start of season (SOS) and the covariation between SOS and temperature () investigated using remote-sensing SOS observations and process-based phenology models for 85 large cities and adjacent rural areas across the conterminous United States between 2001–2014.

The Impact

Researchers provided the first observational evidence of a reduction in the response of urban phenology to temperature in major U. S. cities. The research team discovered these urban-rural phenology differences are mainly associated with the changes of background climate and urban heat island (UHI) effect intensity.

Summary

Urbanization causes environmental changes, such as urban heat islands, which affect terrestrial ecosystems. However, how and to what extent urbanization affects plant phenology remains relatively unexplored. Researchers investigated the changes in the satellite-derived and the  in 85 large cities across the conterminous United States between 2001–2014. They found that (1) the SOS came significantly earlier (6.1 ± 6.3 days) in 74 cities, and  was significantly weaker (0.03 ± 0.07) in 43 cities when compared with their surrounding rural areas (P < 0.05); (2) the decreased magnitude in  mainly occurred in cities in relatively cold regions with an annual mean temperature of <17.3°C (e.g., Minnesota, Michigan, and Pennsylvania); and (3) the magnitude of urban-rural difference in both SOS and  was primarily correlated with the intensity of UHI. Simulations of two phenology models further suggested that more and faster heat accumulation contributed to the earlier SOS, while a decrease in required chilling led to a decline in  magnitude in urban areas. These findings provide the of reduced covariation between temperature and SOS in major US cities, implying the response of spring phenology to warming conditions in non-urban environments may decline in the future.

Principal Investigator

Jiafu Mao
Oak Ridge National Laboratory
mao@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This work is supported by DOE Office of Science, Biological and Environmental Research, including support from the following programs:

• Terrestrial Ecosystem Science Program (ORNL TES SFA)
• Regional and Global Climate Modeling Program (RUBISCO SFA)
• Earth System Modeling Program (the Energy Exascale Earth System Model (E3SM) project)

References