Multidecadal Changes in Urban Greenness, Temperature, and Vegetative Cooling at the Continental Scale
Abstract
Urban vegetation, through transpiration and shading, partially mitigates the urban heat island. While we have a good understanding of the spatial distribution of urban greenness and heat, climate change, as well as an increase in global greenness, necessitate understanding how urban climates have changed over time. To determine temporal change in the inter-urban cooling ability of plants we used satellite remote sensing to assess how urban greenness, temperature, and the cooling provided by urban plants changed from 2000-2020 in 36 cities across the United States. We hypothesize that differences in vegetative cooling among cities is driven by climate, where increasing temperature, or vapor pressure deficit (VPD) increases transpiration and cooling. We derived urban greenness (NDVI) and land surface temperature (LST) from the Landsat suite of satellites. Of our 36 cities, nearly all demonstrated significant urban greening since 2000; two cities, Raleigh, North Carolina, and Spokane, Washington browned. We detected an increase in LST in only four cities. Trends in urban NDVI and LST are best explained by climate. Cities with the highest VPD warmed more slowly, and those with intermediate VPD had the highest rate of NDVI increase. Finally, cooling provided by urban plants changed in 15 out of our 36 cities, increasing on average 0.1226 °C/NDVI year1 in seven cities. In two of these cities, Boise and Los Angeles, vegetative cooling increased despite no long-term change in greenness, suggesting urban plants here have become more effective at cooling. In the remaining eight cities, urban plants have become less effective at cooling by 0.1853 °C/NDVI year-1 despite an increase in urban greenness. This study shows that urban vegetation, and microclimates, are primarily controlled by the macroclimate at the continental scale. Further, these results highlight challenges to building urban resilience to global change; urban climates have not changed uniformly, further, in some cities, urban plants have decreased their ability to cool.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMGC35L0834K