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GIS-Based Urban Tree Canopy Mapping for Heat Mitigation

Solution Overview

Fort Lauderdale will use GIS mapping and other tools to evaluate shade and cooling available at pedestrian, transit (train and bus) and bicycle facilities, and assess whether the urban tree canopy is sufficient to protect people from heat and pollution.[5] This approach builds on Broward County's broader initiative to map and monitor the percentage of tree canopy county-wide, establishing a baseline that enables urban foresters to evaluate the present extent of tree canopy and monitor changes over time.[4] The methodology provides critical data for addressing urban heat islands, which increase maximum temperatures by as much as 5°F above the local baseline in Broward County.[6]

Technical Components

Broward County created a series of maps using GIS software that showed the 32 cities within Broward County and their percentage of tree canopy, amount of green space and other indicators of a healthy urban environment to identify the areas with the lowest tree canopy.[1] The County completed the latest survey of the urban tree canopy coverage in 2018, using Geographical Information Systems (GIS).[3] The imagery used for the tree canopy project were color infrared scanned photographs taken in January 1996, and it was decided that the 1996 imagery would be mapped and classified as a baseline for tree canopy in Broward County.[4] In a pilot test, digital image processing techniques took 4 hours to create a coverage for a one-mile section, compared to approximately 4 weeks for one staff member to digitize tree polygons manually in the same area.[4]

Implementation Details

The Broward County Board of Commissioners established the Broward Urban Forest Initiative in 1999 to stem the loss of tree canopy from Broward's urban landscape.[4] The tree canopy survey provides the technical basis for the County's Urban Forest Management Plan.[3] Broward County will perform a tree canopy study every five years as part of efforts to reduce urban heat island effect.[2] The County will work with community and governmental partners to identify needs and involve community members in the policy and planning process for urban tree canopy enhancement.[2] The survey will be used to develop targets for future tree canopy by the various municipalities who are trying to develop achievable goals, and to evaluate achievable canopy coverage for various zoning and land use categories.[3] The County will establish support for tree maintenance to encourage long-term canopy growth and tree retention as part of the urban tree canopy enhancement initiative.[2]

Benefits and Impacts

The analysis found that certain communities in central, inland Broward County had less tree canopy than the rest of Broward County, and these cities also had some of the lowest income per capita in the region.[1] Urban vegetation offers shade and evapotranspiration, which can lower peak summer temperatures 2-9°F.[6] In Broward County, 90,000 people live in neighborhoods where the urban heat islands increase temperatures by 2°F or more and where average per capita incomes are less than 200% the federal poverty level.[6] Additionally, 33,000 people live in areas that meet the above criteria and have a high percentage of population in high risk age groups (under age 14 or over age 65).[6] One-third of the 90,000 Broward County residents living in higher-temperature neighborhoods are at higher risk to heat health impacts due to their age.[2] The County aims to increase the urban tree canopy to at least 40% county-wide as part of Action 30 to reduce urban heat island effect.[2] The initiative will enhance the tree canopy equitably countywide.[2]

Climate Adaptation Relevance

Broward County experiences 74 days above 88°F per year, on average.[6] The number of days above 88°F has increased 36% since 2000, to 90 days per year, with projections suggesting 144 days per year by 2050.[2] In the County's most severe urban heat islands, all-cause mortality rates are estimated to increase by 4.7% (2.4% - 7%) when baseline temperatures exceed 90°.[6] The urban heat model estimated that 13 to 44 lives are lost in the County annually due to excessive heat.[2] On the current trajectory, Broward County will experience 144 days above the temperature threshold by 2050, and 223 days above the threshold by 2100.[6]

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