New crop reaps climate rewards
The impact of climate change and the potential for more days of extreme heat are concerns for airports around the world but Adelaide Airport is investigating ways to use water to lower ambient temperatures.
A trial involving SA Water and Adelaide Airport to assess the use of stormwater to irrigate big buffers around the airport has produced promising early results, demonstrating the cooling effect of lucerne hay.
The trial compared lucerne against some other types of grasses and was able to demonstrate it produced a 2-3C average fall in ambient temperature – with a bigger impact on extreme heat days.
Air temperatures above the plots of lucerne were significantly cooler that those above plots of other grasses such as tall fescue, couch or kikuyu.
“What we found with the lucerne is it delivers good cooling compared to some of the other grass types that we looked at,’’ says Adelaide Airport Sustainability Manager Leigh Gapp.
“It’s a crop with commercial value, so it can be farmed, and we didn’t see any negative impact on wildlife hazard management in the trial space.”
The worry for Adelaide and other airports in hot regions is that increasing temperatures could lead to operational problems.
The impact on aircraft of extreme temperatures was demonstrated in the US city of Phoenix in 2017 when 48.3C (119F) temperatures saw airlines cancel and retime flights because of difficulties taking off.
Adelaide got close to this last summer when temperatures hit a sizzling 46.2C and broke a record set in 1939.
There’s also no denying that South Australia is hot a state: the Bureau of Meteorology says Oodnadatta Airport still lays claim to the nation’s highest recorded temperature of 50.7C on January 2, 1960.
Gapp notes that it’s not just the possibility of cancellations or delays on extreme heat days that have an operational impact, but also the incremental effect of temperature on aircraft efficiency.
This will be one of the areas investigated in the next phase of the trial which will see the amount of lucerne planted increased to 7ha.
He notes this is a difficult area to get a handle on because the airport does not get data from airlines on passengers or freight offloaded due to heat.
“The standard performance models for aircraft start at 15C and then performance deteriorates from that point,’’ he says.
“Even at 30C compared to 32C, there’s potentially an incremental benefit for fuel use and freight and more at the higher end of the temperature scale.”
This phase will seek to understand the extent of cooling required to impact aircraft performance and demonstrate if this can be achieved with the larger trial area.
Gapp indicated that the larger size of lucerne leaves compared to turf grasses could be one factor responsible for the plant’s superior cooling ability and notes it has other advantages.
“It’s perennial so you don’t have to keep planting it, you can keep the same plant in there for up to seven years before you need to re-sow,’’ he says.
“And I think there are even demonstrations in other places where it can be left much longer than that.”
The fact that it can be cropped means that the cost of sowing and maintaining it can be offset and SA Water says economists using conservative and very conservative scenarios put the payback period at seven to 12 years.
“These results gave us confidence that using airport buffers for cropping could be viable, compared with current maintenance,’’ says SA Water environmental opportunities manager Greg Ingleton. “And best of all, the cooling component is free.”
Wildlife management will remain under the spotlight, with the bigger lucerne plot to be monitored for increased bird activity to confirm the preliminary findings that it did not result in an increase in high-risk species such as galahs, corellas and pigeons.
The grass can be cut before flowering while insects can be managed, and Gapp says it grow to a height in line with “long grass policy”.
A detailed survey of plant species on the airport’s site found about 16 per cent is bare earth, which can be as hot as bitumen, and uncovered a high percentage of undesirable vegetation it is moving to eradicate.
The study identified couch, which covers about 20 per cent of the site, as a the most appropriate grass species to promote because of characteristics such as drought tolerance and small seeds.
What Gapp suspects could ultimately happen is a crop such as lucerne would be sown in the outer areas and couch would be grown in the inner areas closer to runways, taxiways and aprons.
He says it will probably take 12 to 24 months to examine the relationship between the cooling benefits of lucerne and aircraft performance, starting with desktop studies and then moving to planting the bigger area this summer.
“We’ll have a fairly good understanding as soon as we do the desktop studies and assess the impact of aircraft performance,’’ he says.
“Then it will be process of really demonstrating that through the trial.”
Adelaide is also looking at other ways of reducing its impact as an urban “heat island”.
It has replaced the usually black fuel resistant membrane in pavement with a lighter colour.
“A lighter colour can change the surface temperature by up to 30 degrees and that can translate again into another ambient temperature reduction of about three degrees,’’ he says.
“That can have a couple of impacts, obviously on the ambient temperature but also on the longevity of pavement.”
By Steve Creedy
About Steve Creedy
An award-winning journalist, Steve began covering aviation in the United States in the early nineties before returning to Australia later that decade and editing The Australian’s aviation section for 17 years. He is editor of Airline Ratings and has co-authored books on industry initiatives aimed at reducing greenhouse emissions.
Steve has joined the AAA to write interesting and informative editorial on the aviation industry.
