The Shade Availability Index: a new quantitative scale to support the design of shaded sidewalks and walking paths

Shade as an urban asset depends entirely on planning and design decisions. To optimise the allocation of shading resources and achieve effective shading, such decisions must follow quantitative methods, which currently hardly exist, for assessing shade quality according to a uniform normative scale. The Shade Availability Index, which quantifies shading conditions on sidewalks and walking paths, was developed with this goal in mind.

The Shade Availability Index is calculated by shading conditions at ten hourly intervals between 08:00 and 17:00 on a typical Northern Hemisphere summer day in early August, which is also indicative of spring shading conditions. At each hour, a walking strip is considered sufficiently shaded if shade covers more than half of its area. This allows for an index that considers time as the main normative criterion for quantifying shade: when the sidewalk is sufficiently shaded for at least 50% of the reference time, we describe the shading level as acceptable; 70% or above of the time means that shading is very good; and 90% and above indicates excellent shading. The Shade Availability Index does not assign different weights to shading at different times since, under hot sunny conditions, the need for shading is continuous throughout the daytime hours.

The applicability of the normative scale of the Shade Availability Index was examined through comprehensive parametric modelling of thousands of design scenarios to assess the difficulty of achieving any of the three shading thresholds. This examination revealed that it is possible to reach the index’s upper threshold in almost any reasonable planning scenario of urban streets. However, to achieve this, it would be necessary to plant shade trees along the walking strips. This is true regardless of a street's orientation, although, in certain directions, the upper shading threshold can be met through clever building massing.