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City Trees Benefit from Stormwater Harvesting

Local governments are facing increased pressure to enhance the health of urban street trees as reports suggest that tree canopy coverage is dwindling throughout city suburbs.

City Trees Benefit from Stormwater Harvesting.
Associate Professor Huade Guan and Xanthia Gleeson use a handheld camera to monitor tree growth. Image Credit: Flinders University

The study performed at Flinders University has discovered that stormwater interception and infiltration enabling water to soak into tree root zones is proving efficient for a shady tree canopy in concrete urban surroundings where extreme heat regularly occurs.

The new study analyzes how water use, growth, leaf-level gas exchange and productivity of white cedar (Melia azedarach) trees have benefitted from a well-known stormwater harvesting device, called the TREENET Inlet.

This checks stormwater runoff from roads and soaks it into the soil via a porous well near street trees. The study has been published in the journal Frontiers of Climate.

Increased land surface sealing due to urbanization and building homes and infrastructure has decreased rainfall infiltration to the soil, decreased vegetation cover and increased demand on mains water resources.

Xanthia Gleeson, Study Lead Researcher, Environmental Science Graduate and PhD Candidate, Flinders University

Gleeson stated, “As a result, city water management projects using stormwater harvesting and infiltration are increasingly combined with urban greening to support adaptation and resilience to the changing climate.”

The study displays that stormwater harvesting and infiltration by TREENET Inlets offers considerable benefit to white cedar trees growing in a suburban street in the City of Mitcham. It consists of mature trees transpiring 17% more amount of water on average for more than a year, and 21% more during dry seasons.

White cedar saplings were able to grow 60% more in diameter at breast height and 65% more in height with stormwater harvesting over three years compared to saplings without stormwater harvesting.

This is consistent with noted 106% greater stomatal conductance and up to 169% greater photosynthesis rate in dry seasons for saplings that are aided by harvested stormwater.

When moisture update accounts for nearly 25% of complete daily tree water use, the stormwater inlets not only offer 20% more water for cedar tree transpiration in summer but help root zone moisture at night.

Over the last five years, to comprehend the advantages of water-sensitive urban designs (WSUD) for enhancing the surrounding, scientists from Flinders University are examining how several WSUD implementations may have helped ease tree water stress in the City of Mitcham.

It’s clear this passive irrigation directly into street tree root zones greatly benefits mature trees. It makes sense because increased stormwater discharge presents risks to marine and other ecosystems, and infiltration in-situ is a low-cost and sustainable alternative.

Huade Guan, Study Lead Author, Researcher and Associate Professor, National Centre for Groundwater Research and Training, Flinders University

Guan added, “Quick urban drainage exacerbates the heat island effects which is raising the stakes on the health and lifestyle risks of extreme climate events under climate change. We need to do more to mitigate the problems as we face more extreme climate events, with summer maximum temperatures likely to reach 50C by 2050.”

Journal Reference:

Gleeson, X., et al. (2022) Enhanced Passive Stormwater Infiltration Improves Urban Melia Azedarach Functioning in Dry Season. Frontiers in Climate.


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