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As average temperatures continue to rise, and the number of extreme heat days each year increases, keeping cool is more important than ever. In Australia and worldwide, our cities are particularly affected by hot weather, with severe public health, liveability, environmental and economic consequences. Adopting innovative smart irrigation can significantly and cost-effectively cool urban spaces, mitigating the effects of heatwaves while also saving water.

According to data from the Bureau of Meteorology, 2020 was Australia’s fourth hottest year on record, despite La Nina conditions which usually result in lower daytime temperatures.

As a result of climate change, temperatures are expected to rise even further over years to come, even with strong climate mitigation action.

Projections suggest that temperatures in cities worldwide could rise by up to 4°C or more by 2100, depending on emissions scenarios.

Australia is already a land prone to heat and drought, with our human population, wildlife and economy feeling the effects of heatwaves each year. These include an estimated 36,000 deaths between 2006 and 2017, flora and fauna die-offs, and an annual cost of $7.92 billion.

Undeniably, we have an urgent and growing need to find effective methods to keep spaces cool, especially in cities, where temperatures can be significantly higher than in less urbanised areas.

Inner-city hot spots: the urban heat island effect

Cities are particularly vulnerable to high temperatures due to a phenomenon known as the urban heat island effect. The urban heat island effect refers to the tendency for built-up urban areas to retain more heat than their non-urban counterparts.

In Australia, average temperatures in major cities can be 2-10°C higher than in surrounding regions. Urban heat islands result from a combination of contributing factors including an abundance of dark, heat-retaining surfaces (like roads and buildings); fewer trees to provide shade and evapotranspiration to cool the air; closely spaced structures limiting air movement; impermeable surfaces reducing the moisture available for evaporative cooling; pollution; waste heat from cars, buildings and industrial activities; and more.

As a result, the urban heat island effect exacerbates the negative consequences of high temperatures, making it harder for people to cool down.

This particularly impacts those most vulnerable to heat-related health risks, such as young children, the elderly and the poor. The higher temperatures also cause increased air pollution, greenhouse gas emissions and costs associated with cooling.

Smart irrigation combats urban heat islands

Evidence suggests that adopting smarter irrigation practices within cities, especially for irrigating urban green spaces, can markedly reduce ambient temperatures in these spaces and their surrounds, helping Australian city-dwellers cope with hot summers while optimising water efficiency.

Living urban green spaces, such as city parks and nature reserves, are well-established as one of the most cost-effective ways to combat urban heat islands.

The urban green space cooling effect occurs due to shade, alteration of wind movement and evapotranspiration (the process by which water is transferred into the atmosphere via evaporation from surfaces such as soil or wet vegetation, and the transpiration of plants).

This passive cooling means that urban parks can create a precinctscale microclimate that reduces temperatures by up to 1-1.5°C. Thus, they can be critical in assisting people, as well as urban flora and fauna, cope during heatwaves.

The greatest cooling effects usually occur if the green space is effectively irrigated. While large, irrigated urban parks and reserves generally have the greatest impact on ambient temperatures, any other city vegetation and green infrastructure also contributes.

Examples include street trees and hedges, lawns, community gardens, as well as green rooftops, walls and facades. Every 1°C temperature reduction achieved through this kind of innovation equates to a five per cent saving in energy costs that would otherwise be expended on cooling.

These reduced cooling loads bring with them substantial social, economic and environmental benefits, contributing to the long-term sustainability of Australian cities.

However, many of our green spaces are not currently being watered as efficiently as they could be. For instance, many public green open spaces are thought to be overwatered by around 20 per cent, because traditional irrigation systems don’t respond to weather conditions, soil moisture levels and other variable factors.

Smart irrigation uses real-time data to optimise green-space watering, maximising the cooling potential of urban green spaces, and increasing water efficiency.

Unlike traditional irrigation systems operating on pre-set timers, smart irrigation delivers the right amount of water, at the right time, to maintain lush green spaces and facilitate cooling.

Urban green spaces are subject to variations in rainfall, temperature, winds, humidity, public traffic and other external factors, all of which can affect irrigation requirements and efficiency.

Smart irrigation systems employ cloud computing and the Internet of  Things to collect and collate relevant data from multiple sources, such as weather forecasts and GIS data, as well as input from real-time sensors, monitoring parameters including air or soil temperature, humidity, light levels and soil moisture content.

The smart-irrigation platform combines the real-time data with information on the properties of the soil and characteristics of the plants in a green space to determine optimum irrigation volumes and schedules.

Smart irrigation saves water through increased water efficiency, safeguarding water security as a result. It can also be combined with the use of alternative water sources, such as recycled or rainwater, for appropriate applications.

Doing so further reduces the amount of potable water required to keep urban spaces green and cool, and our cities liveable despite the summer heat.

An efficient solution with demonstrated benefits

An expanding number of smart irrigation projects across Australia are already demonstrating its urban cooling potential. These include a smart irrigation initiative by SA Water, which saw smart systems installed in 25 council-operated public green spaces in Adelaide.

The project involved effective, site-specific use of water in the spaces, using real-time data from an integrated system of soil moisture probes, daily weather forecasts and smart water meters, with information provided to water users through a weekly irrigation schedule to optimise water efficiency.

Due to the project’s success, SA Water intends to expand the program in the future. SA Water also undertook a threeyear world-first heat mitigation trial at Adelaide Airport, using smart irrigation to maintain soil moisture and cultivate green space. Recycled water from SA Water’s nearby reuse scheme was used to irrigate four hectares of lucerne crops near the airport’s runway, cooling average ambient temperatures by more than 3°C.

Temperature reductions of this magnitude can have a measurable effect on jet-engine performance during take-off, reducing the required fuel burn, and, in turn, the associated emissions.

Expanding on the concepts of this project, in future we could see airport land transformed to green spaces growing profitable crops that sequester carbon and cool the airport and surrounding suburbs, protecting travellers from heat and saving on fuel and air-conditioning costs.

In Victoria, South East Water’s urban cooling and development project, a collaboration with the University of Melbourne and the Cooperative Research Centre for Water Sensitive Cities, is investigating the effectiveness of smart irrigation and misting to cool the urban landscape, mitigating innercity warming and heat islands.

Data is fed into a specialised controller, called OneBox®+, and SEW’s SCADA system, from the project’s lowcost prototype environmental sensors. This smart irrigation system uses the data from the sensors and the Bureau of Meteorology to determine when to water for maximum cooling effects and utilises rainwater backed up by recycled water supply for irrigation and misting.

Innovations in smart irrigation, combined with a proliferation of urban green spaces, offer data-driven, cost-effective solutions to help cool our cities, and enhance water efficiency and security.

As such, these technologies and systems will be vital tools in the ongoing battle against urban heat islands exacerbated by increasing temperatures caused by climate change.

The widespread rollout of intelligent irrigation in our urban green spaces could unlock better public health, environmental and economic outcomes, and improve the long-term liveability of Australian cities in a warming climate. All things considered; smart irrigation is a smart investment in our future.

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