Abstract
The urban heat island effect is commonly defined as the thermal differences between cooler rural and warmer urban areas, but it also refers to microclimatic differences within an urban area that arises from varied combinations of land cover related to different land uses. Microclimatic variations should also produce intra-urban differences in vegetation phenophases, although few studies have investigated urban phenology. Most phenological studies are usually regional to continental in scale, predominantly tracking changes in start of season related to climate change. This study reports results of an exploratory analysis using TIMESAT (Lund University, Lund, Sweden) software and MODIS NDVI 250-m resolution data (Goddard Space Flight Center, Greenbelt, MD, USA) to identify intra-urban differences in start of season for the City of Roanoke, Virginia. We compare these results to our in-situ temperature collection campaign. Additionally, we completed an in-situ start of season data collection by observing select tree species. Our results demonstrate that MODIS, processed by TIMESAT software, identified intra-urban start of season variations, and these variations are consistent with differing intra-urban microclimates and our in-situ start of season observations. Furthermore, results from such analyses can aid plans for increasing the urban tree canopy or in cultivating locations for urban agriculture—i.e., warmer areas with a longer growing season could accommodate warmer weather trees and crops.
Highlights
Phenology is the recurring seasonal activity of plants and animals, i.e., mating, birth, and death in animals; and germination, leaf bud burst, flowering, and fruit production in plants [1,2]
Our study evaluates differences in start of season within an urban area—the City of Roanoke, Virginia—but we go beyond methods used in other intra-urban studies
For 2010, TIMESAT identified an earlier start of season across the entire image as compared to 2013
Summary
Phenology is the recurring seasonal activity of plants and animals, i.e., mating, birth, and death in animals; and germination, leaf bud burst, flowering, and fruit production in plants [1,2]. Most involving temporal analyses of remotely sensed images, documenting advancing start of season on broad regional or continental scales—an effect possibly related to climate change [3,4]. Urban heat island studies analyze remotely sensed images for phenological comparisons between urban and rural areas and along the urban-rural gradient (e.g., [8,9,10,11]). These studies have documented an earlier start of season within urban areas as compared to surroundings rural areas
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