One of the challenges facing urban environments is the heat island effect. The annual mean air temperature of a city with 1 million people or more can be 1–3 degrees Celsius warmer than its surroundings.1 Heat islands impact communities in many ways including increasing summertime peak energy demand, heat-related illness and mortality, and water quality. For the aviation sector, extreme heat impacts on productivity. Airplanes take off due to lift, the force from the movement of air underneath a plane’s wings.2 Hotter air is thinner, meaning there are less molecules to support an aircraft’s weight. As temperatures rise airplanes therefore need more thrust. To manage extreme heat airplanes may reduce cargo or passengers, or as was demonstrated in June 2017 at Phoenix Sky Harbor International Airport cancel flights.3 With Adelaide experiencing higher average temperatures the stewardship challenge is to find a way to reduce heat at the airport to ensure continued efficient operations.4
SA Water is a government owned statutory corporation providing water and sewerage services to 1.6 million people in South Australia. Adelaide Airport Ltd is the fifth-largest domestic airport in Australia serving around 8 million passengers annually.5
SA Water and Adelaide Airport have conducted a three year trial to study the possible temperature reductions that can be achieved through irrigation of open space at Adelaide Airport.
As part of the regulations to operate an airport, areas adjacent to runways are required to be open space. Airports must actively manage open spaces in order to manage risks including birds that can be hazardous to aircraft. Management activity in many cases simply involves mowing the grass.
SA Water and Adelaide Airport wanted to investigate whether, through irrigation and use of particular crops, it was possible to cool the airport precinct. From SA Water’s perspective a trial aimed to demonstrate a new use for recycled water from a nearby wastewater treatment plant and provided an opportunity to gather data on the extent of cooling that can be achieved. This information could be used to demonstrate the benefits of irrigation, particularly for custodians of large open public spaces and not only increase revenue from recycled water use, but also improve liveability in urban areas. The trial participants identified a number of potential aviation benefits that could apply including reduced air temperature on and above the runway on take- off and reduced energy consumption by cooling towers at the terminal building.
Adelaide Airport set aside 3.5 hectares for irrigation south of the runway away from aircraft activities. The original aim of the trial was to quantify the air temperature reductions that could be achieved through irrigation and to identify and trial potential low bird density ground covers that would be suitable for irrigation across the airside area. Once the trial was implemented it became clear that there may be other benefits from irrigating open space including, potential fuel savings from aircraft take off, maintenance of aircraft payloads during high and extreme high temperatures and reduction in erosion from both jet engines and from summer storms.
Originally only one of the 3.5 hectares was sown to Lucerne, however due to the quantification of the larger temperature reduction in the Lucerne crop compared to the irrigated grassed areas and observation that Lucerne had not proved more attractive to wildlife in the small plots in which it was planted, the entire 3 hectare area was sown with Lucerne in January 2018. The area was irrigated on average three times per week between the start of December to the end of April for the first year of the trial, and twice per week during the second year of the trial. The irrigation occurred at night, initially during the airport curfew hours of 11pm to 5am, but then extended to the night-time hours of 9pm to 5am. The rate of water application per irrigation event was in the order of 12 to 15 millimetres.
Lucerne is a high water use crop, with high evapotranspiration rates so it has a higher potential to contribute to temperature reduction compared to other crops or ground cover. Importantly there is also an established market for hay which creates an economic opportunity from actively managing of open space.
The water used for irrigation was sourced from a nearby stormwater Managed Aquifer Recharge (MAR) scheme that is owned by SA Water. If the trial is to be expanded in the future, recycled water from the Glenelg Wastewater Treatment Plant would be used as the quality and quantity are more suitable for the site.
The results of the trial reveal that the average temperature difference on irrigated land was 2.4 degrees Celsius below that of unirrigated areas, with most warm days having a difference of more than three degrees Celsius. The trial then used this information to undertake financial and economic assessment based on expansion of the irrigation area to a 200 hectare plot.
The introduction of Lucerne production was shown to provide a financial advantage over the current management practice (base case). Extrapolated the costs and benefits of Lucerne hay from the trial site to a wider 200 hectare area at Adelaide Airport, using a conservative and a very conservative scenario. The results showed a payback period of 7–12 years. The net present value (NPV) over a 25 year period shows a significant financial advantage relative to the NPV of the base case. Whilst there is a significant upfront expenditure due the installation of irrigation infrastructure analysis suggests that this cost is expected to be neutral after 9 years compared to the on-going cost associated with current management but could vary between 7 and 12 years, depending on yield outcomes.6
SA Water and Adelaide Airport’s Heat Reduction Trial demonstrates the opportunity that comes from infrastructure operators coming together with their unique skills and assets to solve problems. There is the potential that if the trial is successfully expanded that airlines would benefit from ability to maintain payloads on days of extreme heat, less stress on engines resulting in maintenance costs and fuel savings. Extreme temperatures impact on the ability of aircraft to achieve thrust, requiring more fuel and potentially less cargo and passengers. The risk of flight cancellations, when temperatures rise above the safe operating limits of aircraft, is also likely to reduce.7
Finding a viable funding and financing model to support this pilot is an important next frontier to focus on.