Urban warming advances spring phenology but reduces the response of phenology to temperature in the conterminous United States

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 8; pp. 4228 - 4233
• Main Authors: Meng, Lin, Mao, Jiafu, Zhou, Yuyu, Richardson, Andrew D., Lee, Xuhui, Thornton, Peter E., Ricciuto, Daniel M., Li, Xuecao, Dai, Yongjiu, Shi, Xiaoying, Jia, Gensuo, 贾根锁
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25-02-2020
• Subjects: Biological Sciences; Cities; Cold regions; Computer simulation; Environmental changes; ENVIRONMENTAL SCIENCES; island; Phenology; Rural areas; Spring (season); Temperature; temperature response; Terrestrial ecosystems; Terrestrial environments; Urban areas; urban heat; Urban heat islands; Urbanization; United States > US; temperature response; urban heat island; urbanization; phenology
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1911117117

Urbanization has caused environmental changes, such as urban heat islands (UHIs), that affect terrestrial ecosystems. However, how and to what extent urbanization affects plant phenology remains relatively unexplored. Here, we investigated the changes in the satellite-derived start of season (SOS) and the covariation between SOS and temperature (RT
) in 85 large cities across the conterminous United States for the period 2001–2014. We found that 1) the SOS came significantly earlier (6.1 ± 6.3 d) in 74 cities and RT
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 RT
mainly occurred in cities in relatively cold regions with an annual mean temperature <17.3 °C (e.g., Minnesota, Michigan, and Pennsylvania); and 3) the magnitude of urban−rural difference in both SOS and RT
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 RT
magnitude in urban areas. These findings provide observational evidence of a reduced covariation between temperature and SOS in major US cities, implying the response of spring phenology to warming conditions in nonurban environments may decline in the warming future.