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Urban heat island (UHI) is one major anthropogenic modification to the Earth system that transcends its physical boundary. Using MODIS data from 2003 to 2012, we showed that the UHI effect decayed exponentially toward rural areas for majority of the 32 Chinese cities. We found an obvious urban/rural temperature “cliff”, and estimated that the footprint of UHI effect (FP, including urban area) was 2.3 and 3.9 times of urban size for the day and night, respectively, with large spatiotemporal heterogeneities. We further revealed that ignoring the FP may underestimate the UHI intensity in most cases and even alter the direction of UHI estimates for few cities. Our results provide new insights to the characteristics of UHI effect and emphasize the necessity of considering city- and time-specific FP when assessing the urbanization effects on local climate.

18Urbanization-induced phenological shifts may provide evidence on how vegetation 19 will respond to global warming. However, the effects of urbanization on vegetation 20 phenology are poorly understood in urban environments. Using MODIS data between 21 2007 and 2013, we investigated the trends of the phenological metrics (i.e., start, end, 22 and length of growing season: SOS, EOS and GSL) of individual cities and across 23 cities relative to rural areas for China's 32 major cities. We found that the effects of 24 urbanization on phenology decayed exponentially toward rural areas, and were 25 closely related to the land surface temperature (LST) for more than half of the cities. 26The phenological sensitivity to temperature were 9-11 days SOS advance and 6-10 27 days EOS delay per 1 o C increase of LST. On average across all cities, the growing 28 season started 11.9 days earlier and ended 5.4 days later in urban zones compared to 29 rural counterparts. The urbanization effects increased with increasing latitudes, 30 following the pattern of urban heat island effects in general. Our study suggests the 31 value of urban environments in studying the phenological responses to future global 32 change. However, the urbanization impacts are complex and need more direct 33 observations, experimental manipulations, and cross-boundary inter-comparison 34 studies. 35Keywords: start of growing season; end of growing season; urban heat island; 36 vegetation phenology; global warming; urbanization 37 3 / 35

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