An unusual increase in plant productivity could be a sign of serious moisture loss in the soil, and NASA satellites are looking for clues. The drought that struck quickly and without warning across much of the United States in the summer of 2012 was one of the nation’s worst droughts since the permanent Dust Bowl of the 1930s. The “flash drought,” caused by intense heat that parched moisture in soil and plants, led to massive crop failures and economic losses of more than $30 billion.
While typical droughts can develop over seasons, flash droughts are characterized by rapid drying. It can take weeks to create and is difficult to predict. In a recently published study Geophysical Research Letters A team led by scientists at NASA’s Jet Propulsion Laboratory in Southern California was able to detect signs of a flash drought three months in advance. In the future, such early notifications may aid mitigation efforts.
How did the team achieve this? By adhering to the light.
A signal visible from space
During photosynthesis, when a plant absorbs sunlight to convert carbon dioxide and water into food, chlorophyll “leaks” some unused photons. This faint glow is called solar fluorescence, or SIF. The stronger the fluorescence, the more carbon dioxide the plant takes from the atmosphere for its growth.
Although the glow is not visible to the naked eye, it can be detected by instruments on satellites such as NASA’s Orbiting Carbon Observatory-2 (OCO-2). Launched in 2014, OCO-2 observed the glow of the US Midwest throughout the growing season.play
The researchers compared multi-year fluorescence data to a list of flash droughts that hit the United States between May and July from 2015 to 2020. They discovered a domino effect: In the weeks and months before the sudden drought, vegetation initially flourished when conditions changed. hot and dry. Flowering plants emitted an unusually strong fluorescence signal for this time of year.
However, the gradual decrease in the amount of water in the soil posed a risk to plants. When extreme temperatures hit, already low humidity levels dropped rapidly and a sudden drought began within a few days.
The team correlated the fluorescence measurements with humidity data from NASA’s SMAP satellite. SMAP, short for Soil Moisture Active Passive, monitors soil water changes by measuring the intensity of natural microwave radiation coming from the Earth’s surface.
The scientists found that the unusual fluorescence pattern correlated well with soil moisture loss 6-12 weeks before a flash drought. A consistent pattern has emerged across diverse landscapes, from temperate forests in the eastern United States to the Great Plains and western chaparral.
Plant fluorescence therefore “holds promise as a reliable early warning indicator of flash drought and sufficient time to take action,” said Nicolas Parazu, a JPL geoscientist and lead author of the latest study.
Jordan Gerth, a scientist with the National Weather Service who was not involved in the research, said he was happy to see studies on flash droughts in light of climate change. He noted that agriculture benefits from as much predictability as possible.
While early warning cannot eliminate the effects of flash droughts, Gert said: “Farmers and ranchers with improved management practices can make better use of irrigation water to reduce crop impacts, avoid planting crops that are likely to fail, or plant another type of culture. If weeks to months are “To achieve the most ideal efficiency.”
Tracking carbon emissions
In addition to trying to predict flash droughts, scientists also wanted to understand how they affect carbon emissions. Plants and trees that convert carbon dioxide into food during photosynthesis become carbon “sinks” by absorbing more CO2 from the atmosphere rather than releasing it. Many types of ecosystems, including farmland, play a role in the carbon cycle (the continuous exchange of carbon atoms between land, atmosphere and ocean).
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. Plants suffering from heat stress absorb less CO2 with Therefore, the researchers expected to find more free carbon. Instead, they discovered a balancing act.
High temperatures before the onset of the flash drought prompted plants to increase their carbon uptake compared to normal conditions. This abnormal uptake was, on average, sufficient to completely offset the reduction in carbon uptake due to the ensuing warm conditions. The surprising discovery could help improve carbon cycle model predictions.
The OCO-2 satellite, celebrating its 10th anniversary in orbit this summer, maps natural and man-made carbon dioxide concentrations and vegetation fluorescence using three camera-like spectrometers tuned to detect CO’s unique light signature.2. They measure the gas indirectly by tracking how much reflected sunlight it absorbs in a given column of air.
Source: Port Altele
