Neighborhood (block group) tree canopy goals estimate the percent tree canopy required to deliver a minimum standard of tree cover to a block group. Goals are canopy targets based on natural biome baselines then adjusted based on building density, as buildings limit plantable space.

Baseline canopy targets were adjusted according to the slope of the trend line between building density and tree canopy in each biome. Adjustment factors are in increments of 0.25 and were applied as follows:

• The forest and Mediterranean biomes had the steepest trend lines and thus three adjustment points.
• The grassland biome had a more moderate slope and two adjustment points. Building densities below 20% were assigned a single adjustment factor.
• The desert biome, which has a nearly flat slope and no clear relationship between the two variables, was not adjusted by building density.

Tree canopy cover, AREA_trees, is derived from pre-aggregated Google high-resolution tree canopy sourced from Google Environmental Insights Explorer. This is substituted by local high-resolution tree canopy in cities that have Tree Equity Score Analyzers. Tree canopy cover percent is calculated as follows, where:

• AREA_land is the land area of the block group, not including water area. AREA_land is the land area of the block group, not including water area.

TREE CANOPY COVER % = AREA_trees / AREA_land * 100

Compute the percent area of a block group that could be planted to reach the neighborhood tree canopy goal.

The neighborhood tree canopy gap, GAP, is calculated by subtracting the percent existing neighborhood canopy, EC, from the density adjusted Tree Canopy Goal, GOAL (%):

GAP = GOAL - EC

Surface temperature is a good estimate of where excess heat is generated in urban areas.

All Landsat 8 Collection 2 Level 2 Surface Temperature scenes from the summer of 2022 that intersect urban areas were compiled (may include summers from earlier years for locations with less data).

All scenes that fell within the same path and row in the Worldwide Reference System were merged and the maximum temperature value for each pixel selected. Maximum pixel values were extracted to represent the highest extremities of surface heat for all urban areas in the United States.

Block group and urban area averages were calculated from the heat extremity dataset, excluding water area. If not enough data were available for a block group, the block group was set to the urban area average.

For each block group, the difference from the urban area average measures how much each block group fell above and below the urban area mean. This produces a measure of heat disparity, TEMP_diff, where:

• TEMP_bg,ave is the block group average of all maximum pixel values for summer surface temperature
• TEMP_ua,ave is the urban area average of all maximum pixel values for summer surface temperature

TEMP_diff = TEMP_bg,ave - TEMP_ua,ave

• Positive values indicate hotter than average block groups, and negative values indicate cooler than average block groups. Block groups set to the urban area average due to lack of data result in a heat disparity value of zero.

The Priority Index helps prioritize the need for planting to achieve Tree Equity based on climate, health and socio-economic variables.

The index comprises seven equally-weighted indicators:

• Age: Dependency ratio of seniors (65+) and children (0 - 17) to working-age adults.
• Employment: Unemployment rate.
• Health burden: Prevalence of poor mental, physical, respiratory and cardiac health.
• Income: Percentage of population below 200% of the poverty line.
• Linguistic isolation: Percentage of households where no person age 14+ speaks only English, or no person age 14+ who speaks a language other than English speaks English "very well."
• Race: Percentage of people that are Black or African American, American Indian or Alaska Native, Asian, Native Hawaiian or Other Pacific Islander, and includes all people classified as Hispanic by the Census Bureau.
• Heat extremity: A measure of urban heat severity, based on the highest extremities of 2022 summer surface temperatures averaged by block group.

The indices, N, are normalized as follows, where, for each indicator, N_i:

• x_i is the value for that neighborhood for that indicator, i;
• x_i,max is the maximum value for that indicator across each urban area*, i; and
• x_i,min is the minimum value for that indicator across each urban area*, i.

N_i = (x_i - x_i,min ) / (x_i,max - x_i,min)

*All urban areas <10,000 were grouped within each state and treated as a single urban area. Any urban areas crossing state lines were split and treated as separate urban areas in each state.

The indices are then combined to create a simple priority index from 0.1 to 1, where 1 indicates greater priority. The Priority Index, E, is calculated as follows, where N_i refers to each indicator value:

E = 0.1 + (1 - 0.1) * (N₁ + N₂ + N₃ + N₄ + N₅ + N₆ + N₇) / 7

Tree Equity Scores range from 0 to 100. A lower Tree Equity Score indicates a greater priority for tree planting and protection. A score of 100 means the block group meets or surpasses the canopy goal for that block group.

The canopy gap is normalized to a score from 0-100 for each urban area as follows, where:

• GAP_max is the maximum GAP value for that indicator across each urban area*
• If the GAP is negative (i.e., existing canopy is greater than the neighborhood goal), it is adjusted to 0 before normalizing to calculate Gap_score.
• If Gap_max = 0, then Gap_score is set to 0 as well.

GAP_score = GAP / GAP_max

*All urban areas <10,000 were grouped within each state and treated as a single urban area. Any urban areas crossing state lines were split and treated as separate urban areas in each state.

Tree Equity Score, TES, is calculated by multiplying the Gap_score by the Priority Index, E:

TES = 100 (1 - GAP_score * E)