InfruTreeCity: Understanding Infrared radiative performance of urban trees for better future city

Lead Research Organisation: University of Reading
Department Name: Construction Management and Engineering


Urban green spaces and trees have substantial beneficial effects on people's health, thermal comfort, pollution and noise reduction, sustainable urban drainage and carbon sequestration. The proposed research focuses on the radiative thermal performance of urban trees in the context of summer thermal comfort and cooling energy consumption in towns and cities that are subject to increasing heat stress under projected climate change.

Trees and green spaces offer significant cooling benefits, thereby helping to create comfortable micro-climates in towns and cities. They are also effective, though to a lesser extent, in ameliorating the urban heat island (UHI) effect. Buildings shaded by trees experience 25-50% reduction of cooling load, often removing the need for energy intensive mechanical cooling.

The effective use of trees and green spaces in urban environments by building designers and urban planners has been impeded by the lack of fundamental insights and quantitative information. It has been found that tree species differ by up to 9C in their canopy surface temperatures. Choosing the right tree species for urban planting schemes is critical for maximizing their cooling effects, but systematic information is currently not available. A further obstacle is the lack of an integrated multidisciplinary approach to the investigation of thermal performance of urban trees, where a tree or a group of trees were treated as a 'black box' , i.e., without consideration of the fundamental physical and (plant) physiological processes, nor the influence of the urban environment on these processes. The results thus have limited applicability to other urban settings. Crucially, the consideration of infrared radiation, which accounts for over 50% of the solar radiation reaching the Earth, is largely missing in previous investigations.

The proposed study aims to overcome these obstacles by investigating urban tree - built environment interactions, focusing on infrared radiative energy exchange, and in the context of prevention of summer overheating in cities. Specific objectives include:
- quantify, for the first time, radiative and other cooling mechanisms of selected common urban trees based on a multidisciplinary approach that integrates building and climate physics with plant physiology, addressing radiative energy exchange, tree physiological processes, urban built forms and materials and the influences of tree forms and species;
- provide guidance to building / landscape designers and urban planners for effective integration of trees in towns and cities including tree species selection and appropriate urban form and building materials;
- develop an online presentation tool to allow rapid access to and effective utilisation of the results and guidance generated from the work.

Planned Impact

The main categories of beneficiaries and the way they will benefit from the proposed research are outlined below

Building Environment and Architecture design practices
These consultancies and practices are engaged in the building design in new build and retrofit projects. The knowledge and guidance resulting from the research would allow these companies to better utilise passive cooling benefits of urban trees to minimise or prevent the substantial energy consumption associated with mechanical cooling. This ability would enable the companies to be more successful technically and commercially in the rapidly evolving and expanding eco-building sector.

Urban planning authorities
Urban planning policy makers /local authorities would benefit from the knowledge and guidance to produce new and improved policies that encourage the best practice in tree species selection and mix as well as tree-building integration. These policies will in turn result in future cities that are more energy efficient and facilitate the creation of urban environments that promote healthy outdoor life styles and well-being of residents.

Urban design consultancy
Theprofessional practices specialising in urban design would gain greater expertise and knowledge which will allow them to design more comfortable and healthy outdoor living spaces, and to better integrate green infrastructure with the urban built environment. As a result, the companies will become more successful, technically and economically, in sustainable urban design.

Arboriculture and horticulture companies
These companies will gain greater understanding of the building-tree and climate-tree interactions. As a result, they will be better able to develop the mix and range of tree species that would both thrive in the built environment and provide good cooling benefit to users of buildings and urban spaces. These companies will be more skilled in tree management in our cities too.

Construction material company
Results and guidance from the project could allow these companies to develop and manufacture new building materials that interact with trees in optimal ways resulting in buildings and outdoor urban spaces that are both energy efficient and comfortable to users. The new products would enhance the competitiveness of the companies.
Description • Established the first known method for tree crown-level solar radiation spectroscopy. This method differs from leaf or forest canopy level methods in that it allows tests of solar NIR spatial distribution all around a crown.
• Introduced new concepts needed for crown level spectroscopy. For example, transflection = transmission + reflection from a patch of crown contour; contribution volume, single reference plane for multiple patches of a tree crown etc
• Solar NIR performance of 10 common tree species in the UK quantified
• Transflectance of tree crown is dominated by NIR and influenced by crown morphology and foliage structure (crown patch contour shape, large gaps in crown, foliage size, density); for example, trees with larger leaf sizes tend to have stronger performance though oak is an exception
• Effects of environmental factors (e.g. solar altitude and radiation, air T) on tree radiative performance quantified
• Preliminary results indicating built environment impact on trees' biological and radiative performances.
- Tree planting design, e.g. proximity of a group of trees, impact on the extent they are stressed by environmental factors and on their radiative performances.
Exploitation Route The development enables other researchers to carry out whole-tree solar interaction study over the full solar radiative spectrum using spectrometers.

The results, e.g. those on various tree species and planting design will be valuable to professional urban and built environment designers, tree companies and specialists, and policy makers.
Sectors Construction,Energy,Environment,Leisure Activities, including Sports, Recreation and Tourism

Description Research findings have been disseminated to users including tree and urban design specialist at Reading Borough Council, who have expressed a wish to implement the recommendations about tree planting arrangement in the future.
First Year Of Impact 2019
Sector Environment,Leisure Activities, including Sports, Recreation and Tourism,Government, Democracy and Justice,Culture, Heritage, Museums and Collections
Impact Types Cultural,Societal,Policy & public services

Description Optimising tree planting design
Geographic Reach Local/Municipal/Regional 
Policy Influence Type Influenced training of practitioners or researchers
Impact The research results led to recommendation of optimal urban tree planting design which helps to ensure optimal thermal performance / urban stress tolerance of urban trees
Title A new methodology for quantifying solar spectral performance of whole tree crowns using in-situ spectroscopy. 
Description Established a new methodology for quantifying solar spectral performance of whole tree crowns (vs leaf in lab or remote sensing, both measuring a flat surface) using in-situ spectroscopy. The methodology was developed to understand trees interaction with solar infrared radiation in the context of preventing summer urban and building overheating for now and for future warmer climates. 
Type Of Material Physiological assessment or outcome measure 
Year Produced 2019 
Provided To Others? Yes  
Impact This new method for quantifying solar spectral performance of whole tree crowns bridges the the current gap where tree spectroscopy is either performed in the lab on individual leaves or via remote sensing on top of the tree crowns often in a forest scenario. In either of the previous cases, the method treats the measurement target as a flat surface. The new method treats the crown as the full 3D objects and the measurement is performed on the ground in situ around a tree. This information is need for urban thermal comfort design, especially in creating comfortable and low energy micro climate and buildings. 
Title Data for 'Infrared radiative performance of urban trees: spatial distribution and interspecific comparison among ten species in the UK by in-situ spectroscopy' 
Description The datasets include 1) Leaf reflectance spectra of 9 common tree species (carpinus betulus, acer campestre, quercus robur, platanus x acerifolia, tilia platyphyllos, acer x freemanii, betula pendula, acer platanoides, aesculus hippocastanum) in the UK over the full wavelength range of 400 - 2500 nm. The leaf reflectance spectrum of each species was sampled from 5 to 10 individual trees with 10 leaves randomly collected from each tree. The collected leaves were measured promptly in the laboratory. Statistical mean leaf reflectance spectra and the spectral standard errors of the 9 tree species were estimated by the measuring samples within species. 2) Tree crown transflectance spectra samples of 10 tree species (sequoiadendron giganteum, carpinus betulus, acer campestre, quercus robur, platanus x acerifolia, tilia platyphyllos, acer x freemanii, betula pendula, acer platanoides, aesculus hippocastanum) in the frontal sunlit area of the trees, with a wavelength range of 350 - 1000 nm. The tree crown transflectance spectra were sampled in the sunlit side of trees by in-situ spectroscopy measurements using a vertical reference plane perpendicular to the transient solar azimuth direction. For each tree species, at least 5 trees were sampled at the crown level with visibly dense foliage (no obvious gaps in foliage and no concave crown contours). Statistical mean transflectance spectra of multiple tree species were determined in terms of intraspecific transflectance spectra in the frontal sunlit area, by converting transflectance spectra samples to the equivalent spectra at a solar altitude of 45° (benchmark condition). 3) Interspecific comparison of radiative performance levels across 10 species on sunny days determined in the benchmark conditions of 45° solar altitude. The statistical mean transflectance spectra and the standard mean errors of the 10 tree species implied interspecific difference of the radiative performance levels. 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Description Bartlett Trees 
Organisation Barcham Trees Plc
Country United Kingdom 
Sector Private 
PI Contribution Testing the radiative performance of trees from the Company
Collaborator Contribution Technical advise about tree selection for testing, tree care, site management as well as attending Advisory Panel meetings and provide technical advice about project direction and methodology
Impact The two papers reported in 2019
Start Year 2018
Description Reading Borough Council (RBC) 
Organisation Reading Borough Council
Country United Kingdom 
Sector Public 
PI Contribution The research team have provided RBC with updates about project research findings with recommendation e.g. re tree planting arrangement for best urban thermal performances.
Collaborator Contribution RBC provided technical advice through attending the Advisory Panel meetings and access to urban tree testing sites with power and water supply.
Impact The RBC tree and urban design specialists are interested in putting the project findings and recommendations into practice in future.
Start Year 2018
Description Engagement with local authorities 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Professional Practitioners
Results and Impact Professor Shao was invited by Reading Borough Council to give a presentation/workshop about thermal performance of urban trees to a group of about 20 professional practitioner and policy makers within/associated with Reading borough Council. Professor Shao's work cover both the research within the EPSRC/NERC Infrutreecity project and also broader urban tree thermal performances and related issues. The workshop was based on a presentation by Professor Shao but it was highly interactive with warm discussion and contributions in both ways including best planting and designing guidance and other professional practice issues. A MSc student supervised by Professor Shao, Wesley Tang, who carried out dissertation work using iTree gave presentation to the same group and it was also well received.
Year(s) Of Engagement Activity 2019