Monitoring urban forest change in a metropolitan region in the Pacific Northwest, U.S.A.

Keywords: urban canopy, tree mapping, land cover classification, high spatial resolution imagery, change detection, Google Earth Engine
Session Type: Virtual Paper Abstract
Day: Friday
Session Start / End Time: 2/25/2022 08:00 AM (Eastern Time (US & Canada)) - 2/25/2022 09:20 AM (Eastern Time (US & Canada))
Room: Virtual 1

Abstract

Urban trees are at the core of city-wide climate change adaptation strategies for providing numerous benefits to society, including air purification and cooling. Thus, having a clear understanding of urban tree distribution, their ecosystem services, and how they have changed over time is an essential part of these efforts.
In this study, we assessed changes in tree cover distribution in the Portland metropolitan region (Oregon, USA) between 2014 and 2020 using publicly available orthoimagery from the U.S. Department of Agriculture’s National Agriculture Imagery Program (NAIP). This assessment allowed us to address the following research questions: (a) what are the spatial patterns of tree canopy change across the study area? (b) how do tree canopy changes correlate with sociodemographic trends, focusing on income and community diversity? And (c) to what extent do these changes in tree canopy cover correlate with land surface temperatures across the study region?
We mapped urban tree cover in Google Earth Engine following an object-based, post-classification approach. Our findings revealed that while changes in tree canopy and land surface temperature vary by neighborhood, there was a substantial increase in tree cover and cooling in areas where trees are historically present, but a continuous decline in tree cover and rise in temperature in areas where tree cover is historically limited. These findings support a call for policies that center historically marginalized communities in greening efforts, since the distributional effects of climate change are largely felt by those with limited access to cooling resources.