Effects of urban climate on land surface phenology
SUMMARY: Researchers are studying urban climate drivers and their effects on land surface phenology variation to determine if a higher urban index (level of “urbanness”) affects specific aspects of forest vegetation timing and development. Impacts of increasing urbanization and land cover fragmentation include regional climate change, changes in forest health, increased risk of invasive species, and shifts in phenological ecoregions (areas with similar climates and timing of biological events). Phenological metrics, such as start of season and end of season, are sensitive to change, thus are excellent indicators of changes in climate, forest health, and net primary production at the phenological ecoregion level. Results of this study may yield urban index thresholds which could be used by urban planners to avoid altering the development of urban forest vegetation.
EFETAC's ROLE: The project is being led by EFETAC scientists and supported with EFETAC funding.
PROGRESS: Researchers are combining fine-scaled population data modeled from the U.S. Census with the density of impervious surfaces to develop a continuous Ubanness Index. This Urbanness Index conceptually treats cities as a continuous gradient, from the heart of the downtown of the largest city to the most rural place that is farthest from any road. The Urbanness Index quantitatively assigns a relative index value to all cities, towns, and rural areas in the conterminous United States. These Urbanness Index values can be used to rank all U.S. cities and towns in an even-handed way across the country. Researchers have created a series of maps (below) that can be used as urban "masks" within a Geographic Information System (GIS) to help examine the effects of increasing urbanness levels on several aspects of forest phenology, including start of spring and fall, end of spring and fall, and duration of the growing season.
The Urbanness Index value is quantitatively divided into 9 levels of Urbanness (left - continental U.S.; right - North Carolina). Cities are shown as irregularly shaped "bulls-eyes", in which the city center has a higher Urbanness Index ranking, decreasing as one travels away from the city center toward the suburbs and exurbs. (Click to enlarge.)
Greater detail can be seen in the maps of Level 8 (left) and Level 7 (right) cities within North Carolina. North Carolina contains no Level 9 cities. Interestingly, the Raleigh/Durham/Chapel Hill urban complex is not included in these maps. The heart of this urban complex has an Urbanness Index value that reaches only Level 6, making it insufficient to be included in Level 7 cities, even though its total population would otherwise make it comparable to this group. Presumably, this indicates more urban "sprawl" in this area, diluting the population and imperviousness density sufficiently to result in a lower Urbanness intensity ranking. Thus, the relationship between the total population of a city and its Urbanness Index could be a quantitative way to identify cities having urban "sprawl". (Click to enlarge.)
LINKS: National Phenology dataset