Impact Reports

Soil carbon

Urban soils are hotspots for carbon sequestration but the mechanisms and patterns remain largely unknown and undescribed. Total carbon in urban soils is 1.5-3 times higher than non-urban soils and carbon accumulation occurs at deeper profiles, which results in urban soils having 3-5 times larger total carbon stocks. Soil organic carbon is significantly lower under impervious surfaces.

A typical Depave project removes pavement from and re-greens 3,600 square feet (SF) with trees, landscaping, and restored soils, sequestering an estimated 0.05-0.10 metric tons of soil carbon per year. For Depave’s whole portfolio (80 sites, 366,535 SF) we estimate that between 5.10 and 10.21 metric tons of carbon per year are sequestered in restored soils. Additional carbon sequestration benefits accrue from trees planted in depaved areas.

Urban runoff

Portland’s annual rainfall is 37 inches, so the removal of 1,000 square feet (sf) of pavement eliminates 22,000 gallons of stormwater runoff per year, redirecting it to the soil. A typical depave project footprint is 3,600 SF, but runoff from adjacent impervious areas may multiply the stormwater mitigation benefits of the project. The area of adjacent impervious surfaces from rooftops and surrounding pavement that run off to Depave project footprints varies widely and ranges from 0-203,000 SF per project, with a median of 4,200 SF.

Altogether a typical project (3,600 SF of pavement removal and 4,200 SF of runoff redirected from adjacent impervious surfaces) reclaims and re-purposes 208,872 gallons of stormwater runoff per year. Across the whole of Depave’s project portfolio (80 projects over the period 2008-2023, 8.4 acres of pavement removed plus 12.6 acres of adjacent impervious areas running off to our project areas), we estimate that 24.4 million gallons of stormwater runoff is redirected each year into on-site soils.

Urban heat

Recent NASA studies demonstrated the significance of Depave’s efforts in mitigating urban heat on a local scale. Their recent case study revealed that Depave’s impact on urban heat is observable and quantifiable using remote-sensing data and geospatial tools. Across six sites, NASA measured decreases of up to 7.7-degree Fahrenheit in reflected heat from Depave’s urban greening treatments. As these greenspaces grow out and mature, NASA hypothesized that the cooling effects of vegetation will increase. The NASA analysis provides quantitative measures for the site-specific urban heat mitigation benefits of Depave’s work.