Looking down, not up, to predict drought

ANU scientists are working with space technology to predict droughts months in advance. Will Wright reports.

What is drought? This seems like a straightforward question, but it is surprisingly tricky to answer.

Droughts are unlike most other natural disasters, because they are not a single extreme weather event. Instead, they form from the absence of something that is essential for all life to survive – water.

Drought reveals itself through dried-up riverbeds, dams, forests, grasslands and farms. Each of these impacts is affected by more than just a particular amount of rain over some months. That makes the task of defining drought difficult.

The risk of a drought developing is considered in practical decisions every day. How many firefighters should be on call? Should we prepare for water restrictions? Should we budget for drought assistance?

ANU scientists have been investigating ways to measure the impacts of drought to help answer these kinds of questions. They have used space technology to predict the varied impacts of droughts up to five months in advance.

Siyuan Tian, one of the scientists who is a Postdoctoral Fellow from the ANU Research School of Earth Sciences, says the team realised they needed to move into space to get closer to understanding the complex nature of drought.

They used satellites to detect variations in water availability that affect the growth and condition of grazing land, dryland crops and forests, and that can lead to increased fire risk and farming problems several months down the track.  

“We used data from multiple satellites to measure water below the Earth’s surface with unprecedented precision and we were able to relate this to drought impacts on vegetation several months later,” she says.

“The way these satellites measure the presence of water on Earth is mind-boggling. We discovered this detailed information allowed us to predict for how much longer there was enough moisture for vegetation to survive.”

Co-researcher Professor Albert van Dijk from the ANU Fenner School of Environment and Society says combining this data with a computer model simulating the water cycle and plant growth enabled the team to build a detailed picture of the water’s distribution below the surface and likely impacts on vegetation months later.

“We have always looked up at the sky to predict droughts – but not with too much success,” Dijk says.

“This new approach – looking down from space and underground – opens up possibilities to prepare for drought with greater certainty. It will increase the amount of time available to manage the dire impacts of drought, such as bushfires and livestock losses.”

The team used data from the Gravity Recovery and Climate Experiment (GRACE) satellites, which were decommissioned in October 2017. In future, researchers will be able to use data from the GRACE Follow-On satellites, which were launched in May 2018. The new satellites were developed by American, German and Australian scientists and ANU Professor Daniel Shaddock led the Australian team.

Dr Paul Tregoning from the ANU Research School of Earth Sciences said the GRACE space gravity mission provided a measurement of changes in total water storage anywhere on Earth for the first time.

“Combined with measurements of surface water and top soil moisture from other satellites, this provides the ability to know how much water is available at different depths below the soil,” he says.

“What is innovative and exciting about our work is that we have been able to quantify the available water more accurately than ever before. This leads to more accurate forecasts of vegetation state, as much as five months in advance.”

The drought forecasts will be combined with the latest satellite maps of vegetation flammability from the Australian Flammability Monitoring System at ANU to predict how the risk of uncontrollable bushfires will change over the coming months.

Tregoning says the team’s work is another reminder that space technology and research is not just about new astronomical discoveries.

“Space research offers great solutions for the big challenges we’re facing here on Earth, by helping to observe and predict the ever-changing environment,” he says.

This research profile originally appeared in ANU Reporter