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Green Coverage

Variable Definitions:

All Green Coverage: the share of land surface green coverage including tree canopies, public greenspaces, sidewalk plantings, green roofs, and residential gardens in a given area by using NDVI* analysis. 

Public Access Green Coverage: the share of public park land covered by vegetation such as grass, meadows, and tree canopies in a given area by using NDVI* analysis.

*NDVI is the Normalized Difference Vegetation Index, which quantifies the presence and health of vegetation on the land surface.  It is calculated using the reflectance values of near-infrared (NIR) and red light (RED) from satellite or aerial imagery.

Source: 

The National Agriculture Imagery Program (NAIP) in Google Earth Engine Datasets

Years Available:
2009, 2012, 2014, 2016, 2018, 2020, 2022 

Methodology Note:

The original data comes in raster images with a 0.6m resolution for the years 2016-2022 and with a 1m resolution for the years 2009-2014. Our team calculated the Normalized Difference Vegetation Index (NDVI) and determined the share of the area covered by vegetation (NDVI value above 0.2) in a given area. 

Why are these variables important to measure?

Due to urbanization, concerns over environmental and public health issues are growing. Urban greenery has gained significant attention for its numerous benefits, including air purification, heat mitigation, energy consumption reduction, stormwater management, and the promotion of physical and mental health (Zupancicm, Westmacott, & Bulthuis, 2017; Environmental Protection Agency, 2021). However in Los Angeles County, in addition to income disparity, the unequal distribution of vegetation cover causes more intense heat waves in low-income neighborhoods (Yin, He, Wennberg, & Frankenberg, 2023). 

Land surface green coverage is a crucial metric in landscape ecology, quantified using the Percentage of Landscape (PLAND) (Herold, Couclelis, & Clarke, 2005). This measure calculates the proportion of a landscape occupied by a specific type of land cover,  such as vegetation. By employing high-resolution NDVI, green coverage includes various forms of greenery, such as tree canopies, public greenspaces, sidewalk plantings, green roofs, and residential gardens (Esri, 2024). This metric not only reflects urban design but also indicates the maintenance and quality of the greenery (Pettorelli et al., 2005). Consequently, green coverage serves as a comprehensive measure of the presence and health of greenery in urban environments. 

Written by Jiyoon Kim

Citations:

Connolly, R., Lipsitt, J., Aboelata, M., Yañez, E., Bains, J., & Jerrett, M. (2023). The association of green space, tree canopy and parks with life expectancy in neighborhoods of Los Angeles. Environment International, 173, 107785. doi:10.1016/j.envint.2023.107785

Environmental Protection Agency. (2021). Using trees and vegetation to reduce heat islands. United States Environmental Protection Agency. Link

Esri. (2024). NDVI function. NDVI function—ArcGIS Pro | Documentation 

Herold, M., Couclelis, H., & Clarke, K. C. (2005). The role of spatial metrics in the analysis and modeling of urban land use change. Computers, Environment and Urban Systems, 29(4), 369-399. doi:10.1016/j.compenvurbsys.2003.12.001

Kim, D., & Ahn, Y. (2021). The contribution of neighborhood tree and greenspace to asthma emergency room visits: An application of advanced spatial data in Los Angeles County. International Journal of Environmental Research and Public Health, 18(7), 3487. doi:10.3390/ijerph18073487

Yin, Y., He, L., Wennberg, P. O., & Frankenberg, C. (2023). Unequal exposure to heatwaves in Los Angeles: Impact of uneven green spaces. Science Advances, 9(17), eade8501. doi:10.1126/SCIADV.ADE8501

Zupancicm, T., Westmacott, C., Bulthuis, M. (2017). The impact of green space on heat and air pollution in urban communities: A meta-narrative systematic review. David Suzuki Foundation. Link

 

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