Abstract
Abstract It is increasingly recognised that urban trees can contribute to reducing stormwater runoff by intercepting and retaining a fraction of rainfall received. What is less studied is the translation of this to reduced pollutant loads being transferred to receiving streams, rivers, and water bodies. In this paper, we assess interception of two tree species (Eucalyptus microcorys and Ulmus procera) in an urban park. These data are used in simple water balance modelling to predict the environmental and economic benefit of reducing nitrogen loads to receiving waterways as a function of reduced runoff volume resulting from rainfall interception by urban trees on public land (21% of the catchment area). We use a highly urbanized catchment in Melbourne, Australia to demonstrate the impact of an urban forest dominated by deciduous trees, evergreen trees or a mixed tree canopy cover. We found that doubling the urban canopy cover in the catchment, while keeping the current mix ratio of deciduous and evergreen trees, could reduce annual runoff volume by 30 mm (92 MLyr−1). Using the prescribed values that developers must pay the local water authority for nitrogen treatment as a condition of new development, we calculate that this would deliver a nitrogen load removal benefit of AUD$ 200/tree. If only deciduous trees are planted, the annual runoff reduction would decrease to 24 mm (73 MLyr−1) and increases to 37 mm (112 MLyr−1) if only evergreen trees are planted. This study highlights both the additional benefits of public street trees and the differences in deciduous and evergreen trees which should be accounted for by policy makers.
Highlights
IntroductionSince the 1990s decision-makers in cities around the world have come to realise the benefits of green infrastructure; all green spaces, plants and designed vegetation systems within the urban landscape
One of the most detailed and complex urban tree hydrology models was developed by Xiao et al (2000), including stemflow, and throughfall, and input data relating to leaf angle, leaf area index, stem/branch area index, and leaf surface water storage capacity
Our study suggests that this figure could be augmented by a ‘blue-green’ flat-rate of N-load reduction per tree of ∼AUD$170 in the Elizabeth Street catchment for many years until a replacement tree can be grown in the same place, based on the current number of street trees in the catchment (∼3,500) and calculated economic benefit on N-load reduction (∼$AUD 600,000)
Summary
Since the 1990s decision-makers in cities around the world have come to realise the benefits of green infrastructure; all green spaces, plants and designed vegetation systems within the urban landscape. It is well known that trees can have multiple benefits when looked at holistically as part of a bluegreen system Trees have benefits such as buffering extreme rainfall events by intercepting water and holding it on their leaf and branch surfaces. In Melbourne, Australia, the regional water authority (Melbourne Water) has budgeted more than AUD$700 M on projects to reduce flood risk and manage storm water quality and quantity over five years (Melbourne Water 2016)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
