How Climate Change Is Making Evaporation Worse in Australia

Australia has always been a hot, dry continent. As climate change pushes temperatures higher and brings more extreme heat, evaporation from farm dams during hot spells is becoming a bigger risk to water security for farmers, property owners and water managers.

How does climate change affect evaporation?

Evaporation is driven mainly by energy. The more heat reaching a water surface, the faster water turns to vapour and leaves. Higher air and water temperatures raise evaporative demand, which is the atmosphere’s capacity to draw moisture from land and water.

Australia has warmed by an average of 1.51 ± 0.23°C since national records began in 1910, with an increase in extreme heat events, according to the Bureau of Meteorology’s State of the Climate 2024.

Several climate factors push evaporation up:

• Higher average temperatures: more energy at the water surface.
• More frequent heatwaves: runs of extreme heat drive rapid losses over days or weeks.
• Drier air during drought: low humidity lets the air absorb more vapour.
• Hot, dry winds: wind clears moist air from above the water and speeds evaporation.

Is evaporation actually increasing in Australia?

The answer is more nuanced than it first appears. Evaporative demand rises with temperature, but measured pan evaporation does not always follow.

Pan evaporation in south-eastern Australia generally declined over recent decades, largely because average wind speeds fell, according to a review of pan evaporation trends by Roderick and colleagues at ANU.

For a dam owner, the long-term average is less important than the bad years. Warming makes extreme heat more common, and evaporation peaks in hot, dry and windy spells, often when rain is not arriving to refill the dam. Average annual pan evaporation already exceeds 2,000 mm across much of inland Australia, as the Bureau of Meteorology evaporation maps show, which is far more than the rainfall in those regions.

The real impact on Australian farm dams

The consequences are practical. In a long hot spell, a dam that normally carries stock through summer can fall to critical levels. Stock water, irrigation and fire reserves all depend on what is left.

Up to 40% of storage volume can be lost to evaporation each year in the irrigation areas of northern NSW and Queensland, according to University of Southern Queensland research. To estimate your own dam’s loss, see how much water your dam is losing to evaporation.

The same pressure applies at a larger scale to council water supplies, irrigation network storages and mine process water dams.

Which parts of Australia are most at risk?

• The Murray-Darling Basin: already under heavy pressure over allocations, so every megalitre lost from storage matters.
• Inland Queensland and NSW: among the highest evaporation rates in the country.
• The WA wheatbelt: declining autumn rainfall and hot summers put farm storages under stress.
• Northern Australia: wet season rain is plentiful, but holding it through a hot dry season is hard.

What can property owners do now?

You cannot control the climate, but you can control how much water your dam gives up to it.

Install a floating cover or shade balls

Continuous floating covers cut evaporation by 70 to over 90% and suit smaller dams kept near full. Shade balls save roughly in proportion to the share of the surface they cover and handle changing levels and larger dams. Our shade balls vs floating covers guide compares the two, and the shade ball cost calculator prices a cover for your dam.

Design the dam for a hotter climate

Deep, narrow dams lose a smaller share of their water than shallow, wide ones. If you are building or enlarging a dam, maximising depth relative to surface area is one of the most effective long-term measures, and it is a core part of how Lindsey Hughson and the Big Ditch team design farm dams.

Use evaporation suppressants

Monolayer suppressants are fatty alcohol compounds that spread into a film one molecule thick on the water surface to slow evaporation. They suit dams where a full cover is not practical, but wind and wave action break the film up, so they need regular reapplication.

Plant windbreaks

Trees or wind barriers on the prevailing wind side reduce the wind-driven part of evaporation. Keep tree roots well clear of the dam wall to avoid creating leak paths.

A long-term challenge

Evaporation is not a new problem for Australian farms, but a hotter climate with more extreme heat makes it a bigger one. Investing in evaporation control is a resilience decision that protects stock, production and fire safety in the years when water is tightest.

Frequently Asked Questions

How does climate change affect evaporation rates in Australia?

Warming raises evaporative demand, and Australia has warmed by about 1.51°C since 1910 with more extreme heat. Measured pan evaporation has not risen everywhere, because falling wind speeds offset some of the effect, but heatwaves still drive sharp losses from open dams.

How much water can a dam lose to evaporation in a hot Australian summer?

Inland pan evaporation can reach 10 mm or more a day in summer, and open water loses roughly 70% of the pan figure. On a 1 hectare dam, every 7 mm of lost depth is about 70,000 litres.

What can farmers do to protect their dams from increased evaporation?

Cover the surface with a floating cover or shade balls, design new dams deeper and narrower, plant windbreaks clear of the wall and, where covers are impractical, use monolayer suppressants.

Worried your dam will not last the next heatwave? Book a site inspection with Big Ditch to plan cover or design upgrades before summer.