Shade maps, theory and practice: the basis of efficient and effective heat adaptation actions in cities

Outdoor shade, as a vital environmental asset of heat stress reduction, has long been evading systematic treatment in theory and practice. Yet, to become an effective climatic tool to address urban heat, outdoor shade has to be systematically quantified, mapped, and managed. The spatial Shade Index (SI) we have developed in the past allows us to describe on a simple scale from 0 to 1 the extent to which the cumulative effect of solar radiation at ground level is blocked during a typical spring or summer day. By calculating an average SI for each street segment, open space, or any other spatial unit of interest in a city, it is possible to produce maps that present the shade hierarchy of the city’s main pedestrian spaces, allowing for a quick and easy comparison of their shading quality.

 

Recently, we have managed to develop a computationally efficient method for producing high-resolution urban shade maps in a relatively short time by processing digital surface models, tree canopy contour maps, and official spatial land use layers. With experience gained from generating shade maps for 15 cities, it is now possible to conclude that shade mapping can only be the first step in a more complex procedure of prioritising shading actions across a city. In each of the mapped cities, the high number of street segments or open spaces with poor shading conditions made it impossible to allocate enough municipal resources to bring each and every one of them to a reasonable level of spatial shading. A shade map and the SI it assigns to each spatial unit thus become only the starting point of evidence-based policy negotiations that bring to the table other climate-related considerations, including public health, social equity, promotion of public transport travel, and increasing the appeal of commercial streets.

 

The presentation will provide examples of the application of shade maps in real-life planning tasks in different cities, including as the basis for developing strategic urban forestry plans. It will also expand on the underlying differences and discrepancies in historical urban planning concepts and resource allocation preferences that shade maps expose, given that outdoor shade in its entirety is always, even inadvertently, the product of urban planning and design decisions.