Changing rainfall intensity has a major impact on the world’s forests, with new research revealing that the water flow is just as important as total volumes. That is according to a NASA study, Large Global-scale Vegetation to Daily Rainfall Variability, revealing that broadleaf forests (oak, maple, and beech) are highly vulnerable to changing climates.
Led by Andrew Feildman, a hydrologist and ecosystem scientist from the NASA Goddard Space Center, scientists found that in years of similar rainfall totals, plants, trees, and forests fared differently when the water came in fewer, bigger bursts—with pines and crops growing faster in areas like the American South, home to the country’s food and fibre basket than in rainforests within the lower and middle latitudes (e.g., Indonesia and the Philippines).
“You can think of it like this: if you have a house plant, what happens if you give it a full pitcher of water on Sunday versus a third of a pitcher on Monday, Wednesday, and Friday?” according to Feldman, who said that the research has major implications for timber plantations, crop yields and ultimately, how much carbon dioxide plants remove from the atmosphere.
The team, which included researchers from the U.S. Department of Agriculture and multiple American universities – including Stanford, Columbia, Indiana, and the University of Arizona, analysed more than two decades of field and satellite observations spanning millions of square kilometres from Siberia to Patagonia. They found that plants across 42% of Earth’s vegetated land surface were sensitive to daily rainfall variability. Of that, a little over half fared better—often showing increased growth—in years with fewer but more intense wet days, including pines, croplands, and drier landscapes like grasslands and deserts.
Wood Central understands the study relied on a suite of NASA missions and datasets, including the Integrated Multi-satellitE Retrievals for GPM (IMERG) algorithm, which provides rain and snowfall rates for most of the planet every 30 minutes using a network of international satellites. To gauge plant response day to day, the researchers calculated how green an area appeared in satellite imagery.
“Greenness,” known as the Normalised Difference Vegetation Index, is commonly used to estimate vegetation density and health. Researchers also tracked a faint reddish light that plants emit during photosynthesis. When a plant absorbs sunlight to convert carbon dioxide and water into food, its chlorophyll “leaks” unused photons. This faint light is called solar-induced fluorescence, a telltale sign of flourishing vegetation.
According to Feldman, the findings highlight plants’ vital role in moving carbon around Earth—a process called the carbon cycle. Vegetation, including crops, forests, and grasslands, forms a vast carbon “sink,” absorbing excess carbon dioxide from the atmosphere: “A finer understanding of how plants thrive or decline day to day, storm by storm, could help us understand their role in that cycle.”
For more information: Andrew Feldman et al., Large global scale vegetation sensitivity to daily rainfall variability, Nature (2024). DOI: 10.1038/s41586-024-08232-z. www.nature.com/articles/s41586-024-08232-z. www.nature.com/articles/s41586-024-08232-z
