A quantitative framework for the evaluation and enhancement of urban shade and urban forestry

2022-2024

Funding agency: Yad Hanadiv

Research leaders: Or Aleksandrowicz and David Pearlmutter

Researchers: Naama Shapira, Michelle Clark Levenson, Shachar Zur

Shading in the urban environment is closely related to the planning and design of built-up spaces. In certain street orientations, the design of buildings can result in good shading conditions along the sidewalks. However, in many cases, it is necessary to use additional elements such as pergolas, shading fabrics, and especially street trees to secure even reasonable levels of shade.

Shade promotion using trees, as a central part of Israel’s policy towards adaptation to global warming, also lies at the centre of the Israeli Government’s Resolution 1022 of 23 January 2022. Yet, the national strategic plan for shading and cooling of urban spaces published at the end of 2022 included an implicit acknowledgement of the methodological difficulties inherent in the implementation of the government’s decision from the beginning of that year. The plan recognized that there is still a lack of an established scientific methodology for determining urban shading and forestry goals and for defining the mapping needs arising from these goals. In the absence of such a methodology, all the factors involved in promoting the decision will have difficulty in efficiently and effectively implementing the planting of shade trees in Israeli cities, monitoring the progress of operations in this area, and directing resources to places where they are mostly needed.

The purpose of this project was to present a systematic methodology for promoting strategic shading programs in urban spaces and to provide planning bodies and planners with indicators for quantitative and qualitative assessment of existing and future shading levels according to various planning scenarios. We suggested starting strategic planning with comprehensive shade mapping using a method we had developed in previous projects and prioritising intervention according to the mapping results. Detailed intervention should follow a new grading system according to a new quantitative index, the Shade Availability Index (SAI), which emphasizes the conditions of shading on sidewalks. We proposed to establish three ascending levels of SAI (reasonable, very good, and excellent) that should serve for setting municipal shading goals in different streets. In addition to the description of the index and the goals derived from it, the work also contained systematic demonstrations of the application of the index in different planning scenarios and an analysis of the applicability of meeting these goals in real-life design of streets in Israel.

Shade Maps and their application for shade conservation and intensification in Tel Aviv-Yafo

2017-2021

Funding agency: Tel Aviv-Yafo Municipality

Research leader: Or Aleksandrowicz

Researchers: Shachar Zur, Yonatan Lebendiger, Yoav Lerman

The project attempted to apply state-of-the-art mapping technologies and calculation algorithms for high-resolution city-scale analysis of urban shade. This was done by developing several indices that can be used for comparing the microclimatic characteristics of streets and neighbourhoods across a city. 

To calculate spatial shade indices, we first had to perform a calculation of solar insolation at street level using the Area Solar Radiation function in ArcMap, based on 2.5D mapping of all the buildings and trees in Tel Aviv-Yafo. Using the results of this calculation, we were able to calculate a Shade Index (SI) value for each pixel in the provided mapping, which describes, on a scale of 0 to 1, the ratio between the blocked insolation at a certain location and the maximal insolation of an unobstructed horizontal surface at the same time and location. The lower the exposure to direct solar radiation, the higher the SI value. 

One of the city-scale maps we produced using the SI calculation procedure was a map showing average SI values for every street segment in the city during summer (specifically, in the month of August). The map highlighted the climatic advantages of north-south oriented streets over east-west oriented streets in terms of summer shade. This is a result of the local characteristics of the sun path: in east-west oriented streets, buildings’ effect on street shading is minor (since the summer southern sun appears high in the sky), and therefore reasonable SI values cannot be achieved without the application of a substantial and continuous layer of wide tree canopies.

Following the analysis of shade conditions at street and neighbourhood levels, we proposed a method for prioritizing municipal action towards urban shade management based not only on street-level microclimatic conditions but also on walkability potentials within the urban street network.

For more information on the way shade maps are calculated and used, click here.

A comprehensive set of shade maps and tree maps developed for the Tel Aviv-Yafo Municipality can be accessed here.