Less frequent but more intense rainfall events drive major shifts in global vegetation

Authors: FELDMAN, A.F. - National Aeronautics And Space Administration (NASA); KONINGS, A.G. - Stanford University; GENTINE, P. - Columbia University; ASADOLLAHI, M. - Columbia University; WANG, L. - Purdue University; SMITH, W.K. - University Of Arizona; Biederman, Joel; CHATTERJEE, A. - California Institute Of Technology; JOINER, J. - National Aeronautics And Space Administration (NASA) - Johnson Space Center; POULTER, B. - National Aeronautics Space Administration (NASA) - Jet Propulsion Laboratory

Submitted to: Nature
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: In many parts of the world, rain storms are delivering greater rainfall amounts, but there are longer dry periods in between storms. It is unknown how this temporal repackaging of precipitation affects plant growth. Here we used several different data sources including satellite data and ground-based measurements to evaluate how plant growth is being affected rainfall temporal repackaging into fewer, larger storms. We find that about half of Earth’s surface is showing changes in plant growth due to rainfall repackaging. The differences in annual growth can be as much as 20-50% of the long-term average. Fewer, larger precipitation events tend to increase plant growth in arid regions, likely due to infiltration of water to greater depths, where it can be stored for longer in the root zone. We found negative impacts on plant growth in humid regions, where plants are adapted to frequent rainfall. Our results imply that as the hydrologic cycle intensifies under climate change, dryland regions may experience improved plant growth, while humid regions may see some inhibition.

Technical Abstract: Rain events are globally becoming less frequent but more intense under a changing climate, shifting climatic conditions for terrestrial vegetation independent of annual rainfall amount changes. While these changes in daily precipitation timing and amount have been well established, relatively little research has focused on how these changes are impacting global photosynthesis, despite potentially major consequences for the global carbon cycle. Using global photosynthesis observations from multiple independent satellite proxies and field measurements, we find that variations in wet day frequency and intensity impact photosynthesis across 47% of Earth’s vegetated land surfaces and with nearly the same magnitude as variations in annual rainfall amount. Specifically, a one standard deviation shift in rainfall frequency and intensity toward fewer, larger wet days can change annual mean photosynthesis by 20% to 50% across various climatic conditions. Under fewer, larger wet days, photosynthesis generally responds positively in drier ecosystems and negatively in wetter ecosystems, found here to be due primarily to differences in soil texture, plant sensitivity to individual wet days, and atmospheric aridity. Importantly, wet day frequency and intensity are changing as rapidly as and more commonly across the globe than changes in annual rainfall amounts, resulting in a more dominant role of wet day alterations than annual rainfall amounts in driving changes in global photosynthesis. Our findings thus provide strong evidence that the trend toward fewer, larger wet days is having substantial impacts on global vegetation and will continue to do so with further climatic changes.