Trials at the South Australian capital’s airport in conjunction with state-owned utility SA Water have been ongoing for the past three years and have shown the cooling effects of lucerne can drop air temperatures by more than 3C on warm days.
A business case is being finalised to extend the project from its current 4ha trial plot to up to 200ha of airport land. The lucerne is being irrigated by stormwater captured as part of SA Water’s aquifer storage program but will also include recycled water from SA Water if the project is extended.
The 4-hectare trial site is 600 metres south of the airport’s main runway. A number of grass species were initially tried including tall fescue, couch and kikuyu but lucerne, which can be cut into hay and sold as a premium stock feed, had the greatest impact on ambient temperatures.
During the study, between 12 and 15 millimetres of recycled suburban stormwater was applied to the area up to three evenings a week, with more than 40 temperature and humidity sensors monitoring conditions in the irrigation area, and the persistence of cool air outside of the test zone.
This has led to a reduction in average ambient air temperatures in and around the irrigation area of more than 3C on warm days.
In warmer, less dense air, planes must travel faster down the runway to produce the lift needed for take-off. When a runway lacks the distance required to reach these speeds, a plane’s weight must be lowered by removing passengers, luggage and cargo. This reduces profit for the airline.
There is also a threshold temperature above which some smaller domestic aircraft simply cannot take-off.
SA Water Environmental Opportunities Manager Greg Ingleton, who developed the world-first Adelaide Airport concept, said there may be opportunities to extend the cropping concept to other airports in Australia and internationally.
“No other airport in the world has looked at it from a reducing air temperature perspective,” Ingleton said.
“We’re getting a lot more momentum now, there’s a lot more airport interest and we’ve been contacted by some interstate and international airports.”
Adelaide Airport is the fifth-largest domestic airport and sixth-largest international airport in Australia and processes more than 8 million passengers annually.
It has the potential for up to 200ha of lucerne and a further 50-100ha of irrigated turf around the main runway and other infrastructure.
SA Water and Adelaide Airport recently engaged economists to determine if lucerne could be used to recoup some of the irrigation and maintenance costs.
The economists extrapolated the costs and benefits of lucerne hay from the trial site to the wider 200ha area at Adelaide Airport, using a conservative and a very conservative scenario. The results showed a payback period of 7–12 years.
A decision on the business case is expected later this year.
“These results gave us confidence that using airport buffers for cropping could be viable, compared with current maintenance. And best of all, the cooling component is free,” Ingleton said.
“It’s one of those projects where everybody benefits: SA Water will benefit from the sale of the recycled water, the airport will benefit from the sale of the lucerne and a reduction in energy usage, the airlines benefit because of the savings that can be achieved in fuel and maintaining payload on warm days.”
Ingleton said the next stage of the trial would be the installation of a permanent centre pivot irrigation system that would expand the watered area from 4ha to 7ha and allow more lucerne planting to take place.
Adelaide is known for its hot, dry summers. The city has experienced 12 days where daytime temperatures exceeded 37C since January 1 including a maximum temperature of 46.6C on January 24.
Ingleton said the time it would take to increase the irrigation and planting area to the full 200ha would depend on investment.
“If it was based on the economics of each step such as using the sale of lucerne to fund the next stage then that would be a long process,” he said.
“But if it was something the airlines latched onto because they see the benefit from it then it could get to that 200-300ha quite quickly.
“One of the other things we are interested in looking at is the ability to get carbon credits for it to make it a carbon farming initiative and that could be a really attractive component for the airlines.”
According to AgriFutures Australia, a well-managed irrigated lucerne stand can produce 15-25 tonnes of lucerne hay per hectare per year from 5-7 cuts, which typically occur between October and April.
The lucerne has been cut regularly throughout the trial but it has not been harvested. It is also yet to be tested to for quality and the potential presence of airport or general urban pollution.
“I was cutting it about six times a year so it is a fairly high volume lucerne crop,” Ingleton said.
“There are no obvious fumes in the air when you are down at the airport – you can’t smell anything – so we’re assuming the lucerne wouldn’t be affected.
“At the moment it’s a fair distance from the runway, about 500m-600m, so there’s probably more pollution coming from traffic on the surrounding roads than from the airport itself but we need to do some tissue testing to confirm that.”
Adelaide Airport’s Sustainability Manager Leigh Gapp said the potential benefits of the project were numerous.
“There is an exciting opportunity to demonstrate the ability to reduce costs associated with terminal cooling and to maintain and improve aircraft performance on hot and extreme heat days, including reduced fuel use and maintenance of payloads if the cooling persists sufficiently,” he said.Jump to next article