Abstract
Abstract. Medium-resolution satellite observations show great potential for characterizing seasonal and annual dynamics of vegetation phenology in urban domains from local to regional and global scales. However, most previous studies were conducted using coarse-resolution data, which are inadequate for characterizing the spatiotemporal dynamics of vegetation phenology in urban domains. In this study, we produced an annual vegetation phenology dataset in urban ecosystems for the conterminous United States (US), using all available Landsat images on the Google Earth Engine (GEE) platform. First, we characterized the long-term mean seasonal pattern of phenology indicators of the start of season (SOS) and the end of season (EOS), using a double logistic model. Then, we identified the annual variability of these two phenology indicators by measuring the difference of dates when the vegetation index in a specific year reaches the same magnitude as its long-term mean. The derived phenology indicators agree well with in situ observations from the PhenoCam network and Harvard Forest. Comparing with results derived from the moderate-resolution imaging spectroradiometer (MODIS) data, our Landsat-derived phenology indicators can provide more spatial details. Also, we found the temporal trends of phenology indicators (e.g., SOS) derived from Landsat and MODIS are consistent overall, but the Landsat-derived results from 1985 offer a longer temporal span compared to MODIS from 2001 to present. In general, there is a spatially explicit pattern of phenology indicators from the north to the south in cities in the conterminous US, with an overall advanced SOS in the past 3 decades. The derived phenology product in the US urban domains at the national level is of great use for urban ecology studies for its medium spatial resolution (30 m) and long temporal span (30 years). The data are available at https://doi.org/10.6084/m9.figshare.7685645.v5.
Highlights
Dynamics of vegetation phenology in urban ecosystems play an important role in influencing human activities, such as energy use and public health
We derived the annual variability of phenology indicators in urban and surrounding rural areas (Fig. 1b), by measuring the difference of dates when the enhanced vegetation index (EVI) in a specific year reaches the same magnitude as its long-term mean (Li et al, 2017b)
The definition of start of season (SOS) and end of season (EOS) we used in the PhenoCam data is consistent with our result derived from Landsat data
Summary
Dynamics of vegetation phenology in urban ecosystems play an important role in influencing human activities, such as energy use and public health. The change of vegetation greening and dormancy affects various ecological and environmental processes, such as carbon storage, energy use, water cycle, and climate change (Zhou et al, 2016; Keenan et al, 2014; Peng et al, 2013; Tang et al, 2016). These influences are amplified in urban ecosystems due to the urban environment being notably altered by anthropogenic activities. The change of vegetation phenology affects the start and duration of the pollen season in urban domains, which has become a major concern for public health authorities due to the potential risks of polleninduced respiratory allergies (e.g., asthma) (Aas et al, 1997; Anenberg et al, 2017; Gong et al, 2012; Li et al, 2019b).
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