30 May 2024

NASA follows the light and anticipates flash droughts


Space Agency researchers have found a correlation between flash drought and the intensity of induced fluorescence. A phenomenon related to photosynthesis and observable from space

by Matteo Cavallito


Detecting flash drought, or the phenomenon of sudden water shortage that produces rapid drying of the soil, up to three months before it begins. That is what a team of scientists at NASA’s Jet Propulsion Laboratory in Southern California reportedly did. Their result is significant news in mitigation efforts for a highly insidious and, more importantly, difficult-to-forecast event.

Induced fluorescence

Everything is about a phenomenon known “solar-induced fluorescence” (or SIF) that occurs during photosynthesis. When a plant absorbs sunlight to convert CO2 and water into energy, NASA explains, its chlorophyll loses some unused photons. This mechanism produces an extremely weak glow, fluorescence precisely, whose intensity is proportional to the amount of carbon dioxide sequestered by the plant.

Such a glow, the space agency reminds us, is invisible to the naked eye. But it can be detected by the instruments with which some satellites are equipped.

These include NASA’s Orbiting Carbon Observatory-2 (OCO-2), which was launched into orbit 10 years ago and has been engaged in observing the phenomenon ever since. But what does fluorescence have to do with flash drought? How are the two events connected? Explaining this is a study conducted by the same U.S. agency, which, thanks to the satellite instrumentation, were able to study data on glows and sudden water shortages detected between 2015 and 2020.

An indicator of drought

Researchers, NASA explains, reported that in the weeks and months before a sudden drought, vegetation initially thrived by taking advantage of the warm, dry weather. At the same time, the plants emitted an unusually strong fluorescence signal. The subsequent reduction in soil water supplies, however, worsened with the onset of extreme temperatures, creating the conditions for a sudden drought.

“The scientists found that the unusual fluorescence pattern correlated extremely well with soil moisture losses in the six to 12 weeks before a flash drought,” NASA explains.

An obvious pattern, in particular, “emerged across diverse landscapes, from the temperate forests of the Eastern U.S. to the Great Plains and Western shrublands.” The study’s experience, in short, shows how plant fluorescence can be “a reliable early warning indicator of flash drought with enough lead time to take action.”

The importance of observation from space

Researchers’ hope is that by predicting drought in advance, farmers and ranchers can better plan water management. The one dedicated to fluorescence, in any case, is not the only such monitoring action carried out by NASA satellites. Orbiting Carbon Observatory-2 itself, for example, can track carbon uptake by vegetation before and after flash droughts. And that’s not all.

In March, the U.S. Space Agency launched two remote monitoring missions of the ground and atmosphere. One receiver, called Signals of Opportunity P-Band Investigation (SNoOPI), specifically aims to measure soil moisture in the root zone by exploiting radio signals produced by commercial satellites. Another instrument, the Hyperspectral Thermal Imager (HyTI), on the other hand, measures trace gases related to the Planet’s volcanic activities.