NASA scientists have discovered that satellite-tracked plant fluorescence can predict sudden droughts months in advance, helping to limit the effects of drought and better understand the effects of the carbon cycle. Credit: NASA’s Scientific Visualization Studio
An unusual increase in plant productivity may indicate an impending serious groundwater loss. NASA satellites track this subtle glow and provide early warnings of possible sudden droughts in various landscapes.
The drought that gripped much of the United States in the summer of 2012, flaring quickly and without warning, was one of the most extensive the country had seen since the years-long Dust Bowl of the 1930s. The “sudden drought,” fueled by extreme heat that evaporated moisture from soils and plants, led to widespread crop failures and economic losses costing more than $30 billion.
Although archetypal droughts can develop over seasons, flash droughts are characterized by rapid desiccation. They can take hold within weeks and are difficult to predict. In a recent study, a team led by scientists at NASA’s Jet Propulsion Laboratory in Southern California was able to detect signs of flash droughts up to three months before they begin. In the future, such advance notice could support mitigation efforts.
How did they do it? By following the glow.
In a field in western Kentucky, a machine sprays cover crops in preparation for the planting season. NASA scientists are looking to space-based tools to help predict rapid, creeping droughts responsible for severe agricultural losses in recent years. Credit: U.S. Department of Agriculture/Justin Pius
A signal seen from space
During the day photosynthesisWhen a plant absorbs sunlight to convert carbon dioxide and water into food, the chlorophyll will ‘leak’ some unused photons. This faint glow is called solar-induced fluorescence, or SIF. The stronger the fluorescence, the more carbon dioxide a plant takes from the atmosphere to stimulate its growth.
Although the glow is invisible to the naked eye, it can be detected by instruments aboard satellites such as NASA’s Orbiting Carbon Obsevatory-2 (OCO-2). Launched in 2014, OCO-2 has seen the US Midwest on fire during the growing season.
Growing plants emit a form of light that is detectable by NASA satellites orbiting hundreds of miles above the Earth. Parts of North America seem to glitter in this visualization, which depicts an average year. Gray indicates areas of little or no fluorescence; red, pink and white indicate high fluorescence. Credit: NASA’s Scientific Visualization Studio
The researchers compared years of fluorescence data with an inventory of flash droughts that hit the US between May and July from 2015 to 2020. They discovered a domino effect: In the weeks and months leading up to a sudden drought, vegetation initially flourished as conditions changed. warm and dry. The flowering plants emitted an unusually strong fluorescent signal for the time of year.
But by gradually reducing the water supply in the soil, the plants posed a risk. When extreme temperatures hit, already low moisture levels plummeted and a sudden drought developed within days.
The team correlated the fluorescence measurements with moisture data from NASA’s SMAP satellite. SMAP, short for Soil Moisture Active Passive, monitors changes in groundwater by measuring the intensity of natural microwave emissions from the Earth’s surface.
The scientists found that the unusual fluorescent pattern correlated extremely well with soil moisture loss in the six to 12 weeks before a sudden drought. A consistent pattern emerged across diverse landscapes, from the temperate forests of the eastern US to the Great Plains and western scrublands.
For this reason, plant fluorescence “shows great promise as a reliable early warning indicator of sudden drought, with sufficient lead time to take action,” says Nicholas Parazoo, an earth scientist at JPL and lead author of the recent study.
Jordan Gerth, a scientist with the National Weather Service Office of Observations who was not involved in the study, said he was pleased with the work on flash droughts given our changing climate. He noted that agriculture benefits from predictability wherever possible.
Although early warning cannot eliminate the effects of sudden droughts, farmers and ranchers with advanced operations can better use water for irrigation to reduce the impact on crops, avoid crops that are likely to fail, or plant a different type of crop. to achieve the most ideal yield when they have weeks to months of lead time.”
Tracking carbon emissions
In addition to trying to predict sudden droughts, the scientists wanted to understand how they affect CO2 emissions.
By converting carbon dioxide into food during photosynthesis, plants and trees are carbon sinks, absorbing more CO2 from the atmosphere than they release. Many types of ecosystems, including agricultural lands, play a role in the carbon cycle: the constant exchange of carbon atoms between the land, the atmosphere and the ocean.
The scientists used carbon dioxide measurements from the OCO-2 satellite, along with advanced computer models, to monitor carbon uptake by vegetation before and after flash droughts. Heat-stressed plants absorb less CO2 from the atmosphere, so the researchers expected to find more free carbon. What they discovered instead was a balancing act.
Warm temperatures prior to the onset of the sudden drought tempted plants to increase their carbon uptake compared to normal conditions. This abnormal uptake was, on average, sufficient to fully offset the decrease in carbon uptake caused by the warm conditions that followed. The surprising finding could help improve the carbon cycle model’s predictions.
Celebrating its tenth year in orbit this summer, the OCO-2 satellite will map natural and man-made carbon dioxide concentrations and vegetation fluorescence using three camera-like spectrometers tuned to detect CO2’s unique light signature. to detect. They measure the gas indirectly by tracking how much reflected sunlight it absorbs in a given column of air.