For early warning of drought, look at the plants


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Among the extreme weather impacts resulting from climate change, drought is a growing problem worldwide, leading to frequent forest fires, threats to water resources, and greater food insecurity.

Drought is being observed around the world — including Connecticut — with warnings issued when conditions become dry enough to warrant a notice. By then, however, it is often too late to respond. UConn researchers have found a way to predict drought conditions weeks or even months before they happen, not by looking at weather data, but rather at plants. The study is published this week in the journal PNAS.

The study focuses on a type of drought called flash drought, which is characterized by a rapid onset that can quickly intensify and lead to devastating results. Flash droughts typically last one to two months, but sometimes they continue as a conventional drought for longer, explains UConn environmental engineering professor and American Meteorological Society fellow Guiling Wang.

The U.S. witnessed major flash droughts in 2012 and 2017. Wang cited how the 2012 drought led to record high food prices in the United States. Existing monitoring technology is unable to predict these rapidly occurring droughts, so to better understand them, the researchers focused on data from 2012 and 2017.

“We looked at vapor, temperature, soil moisture, vapor pressure deficit and remotely sensed vegetation data to see how drought is progressing and how plants are responding. One signal really stood out,” says Wang.

When photosynthesis takes place, the pigment chlorophyll emits a small amount of light. This fluorescence, called solar-induced chlorophyll fluorescence (SIF), is observed by satellite and serves as a useful proxy for measuring the level of ongoing photosynthesis. SIF is a more accurate reflection of photosynthesis than others satellite signals such as the Normalized Difference Vegetation Index (NDVI), Wang says. Photosynthetic output varies with seasons and other conditions, and the researchers noticed interesting trends in SIF ranging from two weeks to two months before the onset of a sudden drought.

“We could see a strong signal that preceded droughts, indicating a slower than usual increase in SIF at a time when plant photosynthesis is expected to increase rapidly.” We expected to see a response that lagged behind the drought. Instead, we saw the signal weeks to months before the drought signal was picked up by the US Drought Monitor (USDM). Then we realized that it’s no longer just the drought response, but more importantly how we predict it,” says Wang.

One of the next steps in the team’s research is to identify exactly what is behind these changes in the SIF trajectory.

“The signal could be due to depletion of soil moisture, low humidity in the air, high temperature that makes the air relatively dry, or any combination of these factors that progressively affect the state of growth,” says Wang.

For the 2012 and 2017 droughts, Wang explains, the signal started in the spring at the beginning of the growing season, when the drought was preceded by a slower-than-usual increase in photosynthesis. For droughts in other seasons, the drought precursor may instead be a faster than usual decline in photosynthesis.

Environmental Engineering Ph.D. student and first author of the report Kushan Mohammadi says, “Existing drought warning systems require high-quality hydrometeorological data, which are unavailable or scarce in many regions of the developing world. Our approach can support the development of a global early warning system to help protect people’s food security. I plan to expand our research to develop regimes where rainfed agriculture is the mainstay and is extremely vulnerable sudden drought.”

With time, stakeholders may be able to implement proactive measures to better withstand the drought and potentially mitigate some of the negative effects.

The SIF signal is promising, and the team plans to further investigate its utility – “these are very good results, but we need to understand them better to ultimately develop reliable models for subseasonal to seasonal predictions, whether it’s drought or other conditions.”

‘Sudden droughts’ are coming faster, global study shows

More info:
Koushan Mohammadi et al, Early warning of sudden drought based on the trajectory of solar induced chlorophyll fluorescence, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2202767119

Quote: For an advance drought warning, see Plants (2022, August 5), retrieved August 6, 2022, from

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