Plants are crucial in influencing the weather and climate of the planet because they act as a physical link between the earth and the sky. Researchers from Stanford University have now shown how a closer look at the inside of a plant could help predict some very bad things that could happen around the world. Changes in evapotranspiration, the mechanism by which plants move moisture from their roots to the air, are linked to flash droughts, which rapidly develop and reduce water supply in a couple of weeks. Understanding the effects on water supplies and ecosystems depends on accurate estimations of the water that is lost by evapotranspiration. This water is commonly referred to as “lost” to the atmosphere.
Researchers determined variations in evapotranspiration during droughts that occurred globally from 2003 to 2020 by evaluating satellite data of both precipitation and below-ground moisture. The study, which came out on October 27 in Nature Climate Change, adds to what we know about how evapotranspiration affects these kinds of disasters.
Meng Zhao, a postdoctoral researcher in Earth system science at Stanford Doerr School of Sustainability and the study’s primary author, said that when water is already scarce, evapotranspiration will continue to accelerate water loss. This will cause the drought to worsen much more quickly. The underestimate of water loss “may be a huge hurdle in that projection,” which is a very large task for us.
Fast-onset and escalating flash droughts can harm vulnerable communities and destroy food production, as was the case with the Central Great Plains flash droughts in 2012, which caused more than $30 billion in losses. The researchers say that to improve models, it is important to take into account a hidden part of evapotranspiration: how plants change the structure and paths in the soil around their roots.
According to senior study author Alexandra Konings, an assistant professor of Earth System Science, “we found that the model inaccuracy seems to be explained by the way plants affect how particles are distributed in the soil.” These changes to the soil change how water moves through it, which changes where and how much water is available for plants to soak up and release as water vapor.
Juggling act
Similar to how individuals can adapt their diets, exercise routines, and sleep schedules based on the resources at their disposal, plants too react to droughts in a variety of ways. Not all plants close their stomata equally or at the same rate, but they can close. Stomata are small pores in leaves that release water. During a drought, evapotranspiration is more likely to take water from the ground because the air is drier. However, if the stomata close enough, evapotranspiration will be less than when there is no drought.
According to Konings, “plants behave in such a diversity of ways that it can be exceedingly difficult to fully comprehend, forecast, and quantify in the models.” And it’s too bad that if this increase in evapotranspiration happens more often than we think, it will make the drought worse because more water is being lost to the air than we think.
Increasing evapotranspiration, in which stomata are more open, happens around 25% of the time during droughts, according to current Earth system models. However, a new estimate by the researchers indicates that it happens roughly 45% of the time. The study’s authors say that “this underestimation is especially big in places with drier climates and less biomass.”
Global evapotranspiration measurements were calculated using data on precipitation collected by the Global Precipitation Climatology Project and observations of water storage made by the Gravity Recovery and Climate Experiment (GRACE) satellites. A number of variables determine whether a particular drought in a certain area causes significant evapotranspiration and has the potential to turn into a flash droughts. According to the authors, dry soils constitute a significant control. They also discovered that the impact of roots on how water moves through soil is not taken into account by current models. As a result, there were errors in the models of evapotranspiration and soil dryness.
We were aware that the models had issues, but Konings admitted that he was shocked by how inaccurate they were. I’d like to see the lessons from our paper used by other people in the community who are making different models.
A practical strategy
The results highlight the need for improved model representations of plant characteristics, soil structure, and water transport effects on evapotranspiration, soil moisture, and evapotranspiration. The findings should be easily transferrable to other models, the researchers claim, even though they did not compute how these new evapotranspiration measures may alter future climate scenarios, which are anticipated to bring more frequent and severe droughts. Additionally, since it is based on satellite data, no resources from the ground are needed for the project.
For arid and semi-arid locations, “you can plainly see that the models underestimate the rise in evapotranspiration during droughts,” Zhao added. “I hope our work can assist in increasing the knowledge of these regions that are already water-stressed.” “This means that we don’t know much about this phenomenon in places that already have problems with environmental injustice.”
The Ohio State University and the University of California, Irvine are co-authors of the study. The study was paid for by both a NASA MAP program award and a NASA Terrestrial Ecology program award through the New Investigator Program.
