Sydney, May 28 (The Conversation) Imagine walking into a double-brick house on a scorching 40 degrees Celsius summer day – it feels cool almost straight away. Now imagine stepping into a corrugated tin
shed – it feels like an oven. The difference is simple: some materials slow heat down, while others let it rush through.
Soil works in a similar way. Soil in fully functioning condition can act as a thermal buffer: a giant shock absorber for temperature. It holds water and organic matter such as leaf litter, and slows sharp changes in temperature.
But when soil becomes dry, bare or damaged, that protection weakens. During heatwaves, the roots of crop plants may be sitting in rapidly heating soil.
Our new research shows Australia has “thermal gaps” in large areas. A thermal gap is the difference between a soil’s natural ability to absorb heat and keep temperatures steady, and what it is actually doing now after years of farming, land use change and a warming climate.
In some areas, especially across southeastern and central Australia, soils are no longer protecting plants from heat as well as they could.
This matters because soil is not just dirt under our feet. It is a buffer against climate change. Soil controls how heat and moisture move between the land and the atmosphere. When soil loses its buffering power, ground temperatures can rise more quickly.
This can reduce plant growth, lower crop and pasture production, and even affect local weather and climate over large areas.
What we did and what we found
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To understand where this is happening, we created the first continent-wide map of Australia’s soil thermal buffering capacity.
In other words, we mapped how well different soils can slow heat and keep ground temperatures stable.
We compared each soil’s natural potential with its current condition. This helps show where soil buffering is strong, where it has weakened, and where it may have changed for better or worse.
The results show a clear contrast between soil types.
Clay-rich soils can hold more water and behave more like the double-brick house. They warm and cool slowly, which helps keep roots in a steadier environment.
Iron-rich red and yellow soils in parts of northern Australia, known as Kandosols, also showed good natural capacity and good current condition in our study. These landscapes are still working well as soil heat buffers.
But this does not mean every Kandosol is the same. Soil condition, ground cover, moisture and management still matter.
Sandy soils tell a different story. They naturally hold far less water. When ground cover is low, they lose water faster. Under a hot sun, they behave more like the tin shed. They heat quickly and offer plants much less protection.
That’s why the difference between “just dry” and “hot and dry” is so important. Once dry or degraded soils lose moisture, the sun’s energy heats the ground directly. Roots can become stressed, soil life slows down and crops may decline before the problem is obvious above ground.
This is one reason flash droughts are so dangerous. A flash drought can develop in days or weeks when high temperatures, dry winds and low soil moisture arrive together.
One 2025 global study found flash droughts linked with extreme heat are more severe and take longer to recover from than flash droughts without extreme heat.
For farmers, trouble may already be building below the surface before normal weather warnings capture the full risk.
The good news
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The good news is that soil can regain some of its lost heat protection. We can help “re-insulate” the ground with practical farming methods.
One is called “stubble retention”, which means leaving old crop stalks and leaves on the field after harvest rather than burning or removing them.
This layer shades the soil and slows water loss.
Another method, called “cover cropping”, involved growing plants mainly to protect and feed the soil (not necessarily to harvest them). Cover crops keep living roots in the ground, reduce bare soil and add organic matter.
Studies overseas show why this matters. In the US state of Missouri, fields kept covered with plants held more moisture than bare fields. In North Dakota, bare soil was much hotter near the surface than soil protected by barley residue or cover crops.
These methods do not make heatwaves disappear, but they can reduce the stress heat places on soils and crops. Cooler, moister soils may also help surrounding vegetation dry out more slowly, although this is only one part of reducing bushfire risk.
The next step
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Our national map is a starting point. It shows where soils may be losing their ability to buffer heat. The next step is to test that risk on real farms.
That means pairing the map with local sensors, such as soil-temperature and soil-moisture probes buried near plant roots. These sensors can show when the soil is drying and how quickly it is heating, and when roots may be coming under stress.
Farm trials can then test which actions work best in different soil types, such as keeping stubble, planting cover crops, adjusting irrigation or reducing grazing pressure.
The results could be turned into simple tools for farmers, such as paddock maps, heat-risk alerts or irrigation guides.
Asking “how dry is the soil?” is no longer enough. We must go further by asking “how fast will this soil heat up once it dries?”
That question matters for irrigation, grazing, crop planning and drought warnings.
If farmers can see heat stress building below the surface, they may be able to act earlier. They can protect ground cover, adjust irrigation, reduce grazing pressure or harvest sooner before the damage becomes obvious above ground.
Soil is one of Australia’s hidden climate defences. Healthy soil stores water, slows heat and protects roots. Damaged soil loses that shield.
By understanding and closing the thermal gap, we can give farms, landscapes and rural communities a better chance in a hotter, drier future. (The Conversation) PY
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