A plant’s ‘glow’ can predict some droughts weeks in advance: UConn

Our planet is heating up. One needs only to look at the summer of 2022 as proof.

A group of wildfires burned hundreds of parched acres in the normally lush forests of the Shawangunk Mountains in New York’s Hudson Valley in August. The fires were a rarity in this part of the country, as drought baked the tri-state region for weeks.

Elsewhere in the U.S., wildfires raged amid unprecedented heatwaves in the Pacific Northwest and the Colorado River, a source of drinking water for 40 million people, continued to dwindle. Overseas, countries like France, Spain, and China were scorched by wildfires, while similar and ongoing drought conditions in East Africa pushed populations to the brink of survival.

Droughts and their subsequent disasters often take communities by surprise — displacing people from their homes, destroying crops and leaving governments to scramble for resources. But researchers at the University of Connecticut have stumbled upon a curious, new method to predict flash droughts weeks before they begin.

They’re using radiation coming from plants. As grade school taught us, plants make chlorophyll — a green pigment in their leaves that absorbs the sun’s energy and turns it into sugars, carbohydrates and starch. But that’s not all chlorophyll does.

“Plants that photosynthesize absorb solar radiation and a small part of that is re-emitted by the plants in the form of fluorescence,” said Dr. Guiling Wang, a professor of environmental engineering at UConn.

In other words, plants glow. This radiation isn’t harmful to humans, but plants produce enough of it en masse to be seen from space. “That glow can be captured by satellite,” Wang said.

In a new study out of UConn’s Center for Environmental Sciences and Engineering, Wang and her colleagues monitored this electromagnetic radiation — known as solar-induced chlorophyll fluorescence (SIF) — over time using data from the European Space Agency’s GOME-2 satellite instrument.

They found that if SIF levels either increased slower than normal or decreased faster than normal, then a flash drought was more likely to occur. Flash droughts come on at a rapid pace, said Dennis Todey, director of the USDA Midwest Climate Hub, based in Ames, Iowa. “We're talking drought conditions developing on the order of weeks,” he said.

Wang and her team were able to predict flash droughts two weeks to two months before onset, compared to forecasts from the U.S. Drought Monitor. This prediction tool could provide several weeks of lead time for preparation and recovery, they said. Their report was published last month in the Proceedings of the National Academy of Sciences.

“Indeed, we were surprised because we thought plants responded to drought. Therefore, we expected to see a lagged response around the plants, instead of the plants leading the drought signal by so much,” Wang said.

Previous studies have measured SIF levels as a way to monitor arid conditions, as well as how drought impacts plant health.

“The problem is by the time SIF is lower than normal, the plants are already very stressed,” Wang said. “And by that time it's too late to forecast the drought.” Her team, instead, is checking the progress of the trend over time.

Wang and her team used two flash droughts as case examples: the flash drought in the Northern Plains in 2017, and another in the Central Great Plains in summer 2012, which led to $30 billion in agricultural losses.

Todey from the USDA referred to the 2012 flash drought as the worst in recent memory. “We had a fairly rapid-onset drought in May, into June, that affected much of the Great Plains and much of the Midwest,” he said. “We saw widespread corn and soybean losses.”

In the U.S., flash droughts are most common in the Midwest and areas of the Southeast, said Andrew Hoell, a research meteorologist at the NOAA Physical Sciences Laboratory and co-lead of the NOAA Drought Task Force.

Agricultural loss and wildfires are too often the outcomes of flash droughts, he said. “In this country, they tend to happen during the warm season, and because of that, what we see is reduced agriculture,” said Hoell, along with crop shortages that drive up prices. “So, economically they can be very costly,” he said.

Hoell agreed that SIF could serve as a useful method to predict flash droughts in the future. “I think it's another tool in our toolbox,” he said.

Scientists typically use hydrometeorological data such as temperature and soil moisture to forecast drought. And the NOAA Climate Prediction Center’s drought outlooks are the leading sources for drought prediction in the U.S., said Hoell.

But Wang noted that meteorological data isn’t always available in some parts of the world where drought happens often and with increasing intensity. Wang points to Africa and Southeast Asia as examples.

Solar-induced fluorescence, on the other hand, can be recorded around the globe, Wang said. “Because it comes from the satellite, which can capture information globally, it doesn't really have the limitation (of) ground-based data,” she said.

Wang hopes the team’s research can help inform climate agencies and lessen the agricultural damage caused by flash droughts – which are expected to intensify in the coming years.

“Early warning will not prevent the drought, but it provides lead time so that farmers can prepare better,” Wang said.

Editor's note: This story has been updated to correct the spelling of Guiling Wang's first name and a detail surrounding the levels of solar-induced chlorophyll fluorescence (SIF).