i-Tree: heat adaptation in the city

It is known that trees can be an important means of mitigating high temperatures in the city during a heatwave. The canopy captures sunlight and, in that way, prevents the ground or pavement beneath from heating up. Planting trees or - even better - creating green spaces in a city is not only a great Nature-Based Solution but also a cost-effective climate adaptation measure.

However, the role of urban trees in climate adaptation remains limited. One of the reasons is the lack of data and robust scientific tools to quantify the performance of trees in the urban heat cycle. The absence of practical methods for managers, policymakers, and designers to integrate urban trees into their practice forms a second obstacle. And last, there is an absence of correlated strategies to utilize green infrastructure for greater urban and citizen resilience effectively.

i-Tree NL
In recent years, a start has been made with implementing a useful modeling tool for green managers, policymakers, and designers with i-Tree NL. i-Tree is a software package developed by American scientists for the benefit analysis of the urban forest and has been made available for general use. Initial results from trials with the tool in the Netherlands are positive, but the effectiveness of modeling tree performance in heat stress still needs further development.

i-Tree 2.0-NL
In the three-year research project i-Tree 2.0-NL, a consortium of 29 involved partners is developing accurate measurement data about Dutch urban trees for heat adaptation. These measurement data are translated into databases, application software, and 'orgware'.

1. The development of indicators through which the effect of different tree species (categorized into tree architecture types) on ground temperature, air temperature, and perceived temperature in cities can be accurately calculated;
2. The development of species-specific growth curves for individual urban trees that enable predictions to be based on the growth cycle of trees; and
3. The creation of applications and tool implementations in various urban cases for optimal utilization by users and stakeholders.

Capturing Cooling Performance
A tree's architecture is central to understanding tree species' cooling performance. Physical characteristics such as crown morphology, wood anatomy, and leaf traits determine how and to what extent a tree cools its environment and promotes thermal comfort. Data on this will be collected and compared with measurements of transpiration rates of different tree species, as leaf transpiration further enhances the cooling capacity of a tree. Finally, a connection is made with the (subsurface) water and soil characteristics of the growth site, which in turn can strongly influence the performance of tree species - especially during water shortages during a heatwave.

Changes During Growth
Whether a tree is small or large, still growing or no longer, it is important to estimate what trees can contribute over a period of twenty to fifty years to achieve the climate goals of many cities. However, there is still very little systematic knowledge about the growth of urban trees in the Netherlands and how it differs between tree species or between trees from different urban areas. The second aim of this project is, therefore, to focus on the growth curves of urban trees in our climatic zone.

Practical Applications
The collection of this data and its integration into i-Tree ensures that urban planners, designers, and green professionals will be better equipped to design urban green spaces for climate adaptation effectively. However, the success of a comprehensive modeling tool relies not only on the data and software but also on its usability and applicability. We therefore also focus on the 'orgware': we aim to develop i-Tree applications so that users can make optimal use of them, and for that reason, we do so in close collaboration with all users.

Objective Contribution to Public Input
The results of this project enable a more objective input that hopefully contributes to well-informed decisions and quicker decision-making in the creation and implementation of plans for existing and future urban green spaces. New insights into the performance of the urban forest are expected to contribute to new perspectives on the future of cities. Lastly, the acquired insights enable tree nurseries to timely adjust their assortment to emerging changes in the purchasing policies of green asset managers in cities.

Consortium partners:

• Institutional Research team: TU Delft Fac. Architecture and the Built Environment, TU Delft, Fac. Industrial Design, WUR Plant Research, WUR Environmental Research
• Industry Researchers/contributors: Terra Nostra, Cobra Groeninzicht, Plantkundig, Davey Institute, USDA Forest Service, Arcadis, MVRDV, Tree Ground Solutions
• City administrations: Amsterdam, Rotterdam, Den Haag, Utrecht, Groningen, Dordrecht, Heerhugowaard, Hendrik-Ido-Ambacht
• Consultancies and firms: Idverde, Bomenwacht, Pius Floris
• Nurseries: Anthos, Udenhout, M. van den Oever, Van den Berk, Ebben
• Other: Stadswerk, VHG, AMS Institute