Phenology, the timing of recurring events in a plant’s life cycle, exerts strong influences on seasonal fluxes of carbon, water, and energy. In this dissertation, I investigated the responses of phenology to a variety of changes in environments and improved phenological modeling. I focus on four primary questions: (1) How does spring phenology respond to urban warming? (2) How does spring phenology respond to asymmetric diurnal warming? (3) How does photoperiod affect spring phenology? (4) Does nighttime light have a significant effect on phenology?

First, I investigated the changes in spring phenology and its covariation with temperature in 85 large U.S. cities. Results demonstrated that spring phenology came significantly earlier in most cities, and the magnitude of the covariation between phenology and temperature decreased in urban compared to surrounding rural areas. The magnitude of phenological changes primarily correlated with the intensity of urban heat island. Second, I used satellite images to characterize the response of spring phenology to daily minimum and maximum temperatures across the Appalachian Trail regions in the Eastern United States. Results showed that warming in daytime and nighttime played distinct or even contrasting roles in phenological changes, and such effects showed large regional variations. Spring phenology predicted by considering the divergent responses to asymmetric warming advances less than that without such consideration. Third, I investigated the photoperiod effect on spring leaf-out for six deciduous tree species during 1980-2016 using the European observational phenology and gridded climate datasets. I found a stabilizing effect of photoperiod on spring leaf-out and it interacted with temperature. It suggests that while a warming climate will continue to move spring phenology earlier with an increased risk of frost damage, photoperiod will play a bigger role in securing spring phenology to a safe time zone. Fourth, I examined the impacts of nighttime light on phenology in the conterminous United States using the Visible Infrared Imaging Radiometer Suite (VIIRS) Day/Night Band Nighttime Lights and USA National Phenology Network observation. I found that nighttime light significantly advanced spring phenophases (i.e., breaking leaf buds, leaves, and flowers) and delayed autumn phenophases (i.e., colored leaves, and falling leaves). The findings suggest that light pollution may exacerbate the advance of spring phenology and delay of autumn phenology, extending the growing season in cities. Taken together, these results quantify the phenological responses to a changing environment and improve the prediction of phenological response under a warming climate, thus contributing to accurate risk assessment of frost events and development of adaptation strategies of climate change.