Satellite data predicts drought months in advance

Scientists from the Australian National University (ANU) are using satellites to measure the presence of water on Earth, in a breakthrough that enables them to predict droughts and increased bushfire risk up to five months in advance. Their work has been published in the journal Nature Communications.

Knowing they needed to move into space in order to better understand the complex nature of drought, ANU researcher Siyuan Tian and her colleagues used data from multiple satellites to measure water below the Earth’s surface with apparently unprecedented precision. They were then able to relate this to drought impacts on the vegetation several months later.

“The way these satellites measure the presence of water on Earth is mind-boggling,” said Tian, from the ANU Research School of Earth Sciences.

“We’ve been able to use them 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.”

Professor Albert van Dijk, a co-researcher on the study, said combining these 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 the vegetation months later.

“We have always looked up at the sky to predict droughts — but not with too much success,” said Professor van Dijk, from the ANU Fenner School of Environment and Society.

“This new approach — by 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 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.

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

“The thing that’s really important about GRACE is it measures the change in the Earth’s gravity from one month to the next, and that tells you how mass moves around the Earth — and the only thing that really moves around from one month to the next is water,” explained Prof Shaddock. “And so it can tell us things like changes in sea level rises, it can give us a complete map of the melting of ice in Greenland or Antarctica, but it can also tell us how the groundwater changes in the Murray–Darling Basin, for example, from one month to the next.

“What GRACE does is, it puts up two satellites which are 200 km apart, and they’re basically following each other around in this orbit. And when one of them passes over an area of higher mass concentration, it speeds up and then slows down. The satellites are 200 km apart, and they move closer together and further apart by about the diameter of a red blood cell. If the groundwater level changes by only a few millimetres, that’s enough that the spacecraft 500 km away can sense that motion, and then we can use that to inform policymakers, or farmers who are relying irrigation, about where things are headed and what we need to do to change.”

According to Dr Paul Tregoning, from the ANU Research School of Earth Sciences, the GRACE mission provides 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 said.

“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.”

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