Urban Trees and Flood Resilience: Monitor, Evaluate and Optimise.

Climate change is leading to rainfall events increasing in intensity and frequency. However, traditional drainage infrastructure, such as drains and pipes, struggle to cope with this change resulting in urban areas experiencing increased surface water flooding intensity and occurrences. As a result of this, Newcastle City Council launched Blue Green Newcastle (BGN), a scheme designed to help prevent flooding while also providing wider benefits to support communities by using nature.

Trees are commonly introduced to urban areas as one form of blue-green infrastructure. To explore the interaction between trees and water, a rain garden containing a Alnus glutinosa Imperialis (Cut Leaf Alder) has been instrumented. Sensors include a sap-flow-meter, which allows water uptake to be established. The tree currently being monitored is located in a rain garden which has soil-water content sensors and water potential sensors (to understand plant water availability). These additional sensors help map the flow of water while also allowing the impact of the rain garden to be factored into the evaluation of the tree contribution to managing water through-flow. All sensors on site and the monitored weather conditions, including rainfall and temperature, help reveal the relationship between the tree, soil and atmosphere. Monitoring was setup on 19/08/25 and will run for 3 years to provide empirical evidence of how the tree-rain garden system responds to a range of seasonal (natural) and augmented rainfall conditions. Furthermore, the impact the tree has on surface water flooding during different conditions can be understood more through further modelling.

To best capture the characteristics of trees within an urban space and to support the further introduction of trees through projects like BGN, more sites will be monitored. These sites will explore trees of various ages, species and at different site types aiming to explore the impact these changes have on performance. The performance of the different monitored sites including within open spaces and tree pits can be compared against each other. Since projects that will most benefit from this evidence, including BGN, have many stakeholders, including water companies, local government and those who live, work and visit the area, exploring a wider range of site types is beneficial. Therefore, extrapolating this knowledge and evidence by using models and using the collected data to verify them is beneficial. Evidence-based guidance will ensure findings based on the data collected is accessible and supports stakeholders to deliver effective city-scale green infrastructure schemes, helping to reduce surface water flooding and the impact of rainfall events while improving the built environments for communities. Overall, this research provides a pathway for projects like BGN to lead in climate-resilient urban design where every tree planted becomes an active part of the city’s drainage network.