The ShadeScape of Cambridge

Massachusetts experienced the third hottest year on record in 2024. The rest of New England suffered the warmest year since historical records began 130 years ago. Not only are we witnessing an overall hotter climate, we are also experiencing more intense and more frequent heat waves, locally. Needless to say, we are in a new climate era, one that puts an increasing amount of heat stress on residents of Cambridge —both daytime and nighttime— affecting our thermal comfort and health.

Shade plays a crucial role in cities for mitigating heat and creating a more comfortable environment on summer days, particularly in the context of increasing urban heat islands and rising temperatures. Shade from trees and buildings significantly reduces surface temperatures and lowers the ambient air temperature, which in turn enhances comfort for anyone outdoors, including pedestrians and cyclists. Mapping shade from these sources is essential as it helps us identify areas where shade is lacking and where interventions are needed to improve thermal comfort. The novelty of this work is accurately mapping shade for each hour of the afternoon. By understanding both the spatial and temporal distribution of shade, urban planners and designers can make informed decisions, ensuring that future investments prioritize shade creation to fill these gaps, thereby contributing to a more resilient and livable Cambridge. This project also draws a roadmap for shade creation.

We used the 2021 Light Detection and Ranging (Lidar) data from  MassGIS  Data. We separated the LiDAR points that represent trees and buildings using the vegetation class and other 2D layers. For both buildings and trees, we created 3D multipatch forms that were used for mapping shade using ArcGIS Pro tools.

We calculated the shade of buildings and trees separately for 6 afternoon hours (12 PM to 5 PM) of a typical summer day in July. We created a separate shade layer for buildings and trees every hour. For many purposes, the type of shade may not matter; However, the city may want to investigate each type for more sophisticated analysis and planning. Eventually, we aggregated the shade layers of buildings and trees for each of the six hours.

The following figure shows the overall shade for each hour and each type (buildings and trees).

In the following slides, you can use the arrow buttons to see how the shade of the trees changes in one-hour increments (between 12 PM and 5 PM).

In the following slides, you can use the arrow buttons to see how the shade of the buildings changes in one-hour increments (between 12 PM and 5 PM).

You may want to know the status of shade in your neighborhood. Well, here you go! This interactive 3D visualization allows you to explore the distribution of shade (both buildings and trees) across the city. The shade is represented by a color gradient, ranging from light gray to dark gray. Darker shades indicate areas that experience more hours of shade. For instance, if a location is covered by shade for the entire time between 12 PM and 5 PM, it will be represented by the darkest gray color.

The following map shows the distribution of shaded and non-shaded sidewalk segments in Cambridge, focusing on the crucial period from 12 to 3 PM, the hottest hours of the day when the sun's intensity is strongest. During this time, shade is key in mitigating urban heat and providing cooler, more comfortable walking conditions.

The following map shows the shaded parts (blue color) and unshaded (red color) parts of the sidewalks in Cambridge.

Shade is spatially and temporally variable. We calculated the shade of trees and buildings on sidewalks every hour between 12 PM and 5 PM. The following maps show how the shade progresses at each hour. For each block, these maps represent the percentage of shade coverage (either from trees or buildings) on the sidewalks. At 12 PM, the average shade coverage on sidewalks is about 40%. The shade grows in the afternoon hours. At 5 PM, the average shade coverage on sidewalks grows to 62%.

While it is interesting to see the percentage of shade on the sidewalks of each block, it is also useful to know how much of the main corridors are covered by shade. Therefore, we measured the percentage of shade coverage for several major corridors. The following interactive maps represent the percentage of shade coverage (from both trees and buildings) on corridors at each hour. Notice how different sides of the street have different shade coverage.

Similar to sidewalk corridors, we measured the shade coverage of both buildings and trees in major bike lane corridors. The following maps show how the shade expands from 12 PM to 5 PM. The average shade at 12 PM is about 20% in the bike lane corridors, while the average shade at 5 PM is about 40%.

How much does each neighborhood benefit from the shade of trees and buildings on their sidewalks?

There are multiple ways to combat extreme heat during summer months — staying in air-conditioned spaces, hydrating, and relegating outdoor time to the morning and evening—but ultimately, in summertime, heat is unavoidable. With that in mind, this research on shade in the city allows city staff and decision makers to be more precise in determining where gaps in shade exist during summer months and, thus, where we should focus our attention to cool public spaces. Shaded spaces, whether tree canopy or structural shading, significantly improve one's thermal comfort, making time outdoors more tolerable. Our hope is that this critical information will be a valuable resource for all staff that work in the public realm, including urban design and public space planning, urban forestry and park design, and public health planning and emergency response, among others. As Cambridge warms, we have to adapt, and data like this helps us do just that, making a cooler, safer, and more hospitable city.