Afternoon Jolt

Friday Jolt: Green Group Says Canopy Has Decreased

Satellite data shows tree canopy decreases sharply for vulnerable populations.

By Josh Feit February 13, 2015

Afternoon Jolt

And now for the latest in the great tree canopy debate—a proxy for the ongoing Seattle civil war about development. Of course, shrinking tree canopy = development is bad; increased tree canopy = development is good. 

Futurewise, the pro-transit, smart growth group (so, a member of the pro-urban development crowd, obviously) has been working on a report that overlays a batch of livability metrics—transportation, education, health, housing, and the environment (that's where the tree canopy metric comes in)—with data about income and race to suss out how equity has changed in Seattle.

They've given me a sneak peek at the tree canopy data. And by tree canopy, they actually mean Seattle's NDVI—Normalized Difference Vegetative Index—rating. NDVI uses satellite photos to calculate the ratio of land which is covered by vegetation like grass, crops or trees. And it gives a range of zero to one, with zero being no vegetation and one being dark green. Using King County data, Futurewise found that Seattle's NDVI score decreased between 2000 and 2010 from .36 to .35, a 2.7 percent drop.

The data also showed that the NDVI decreased more sharply for non-white and lower income populations, For example, while the citywide average in NDVI decrease was 2.7, it was 8.5 percent in the lowest-income neighborhoods. Meanwhile, it was 2.3 percent in higher income sections.

And the higher income populations started out with more cover to begin with—going from .43 to .42 for the top income and white populations and from .35 to .32 for the poorest and most non-white populations.

Interestingly, former city council member Peter Steinbrueck did a study of Seattle neighborhoods for the city late last month and found that canopy had increased.

Meanwhile, using different metrics, city data shows that canopy has ultimately increased over the years.


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