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Beyond cloud cover : Low- and high-altitude clouds have distinct impacts on tree sap flow and transpiration

Talvinen, Sini ; Salmon, Yann ; Lopez, Jose Gutierrez ; Linderson, Maj Lena Finnander LU ; Řehořková, Štěpánka ; Šigut, Ladislav ; Devasthale, Abhay ; Ylivinkka, Ilona ; Greiser, Caroline and Ezhova, Ekaterina , et al. (2026) In Agricultural and Forest Meteorology 384.
Abstract

Transpiration drives up to 40 % of terrestrial precipitation, with forests playing a critical role. This study combines long-term sap flow measurements and surface-based cloud observations to examine how different clouds affect tree transpiration across boreal and temperate European forests. Under specific cloudy conditions, sap flow can exceed clear-sky levels, reflecting distinct radiation effects of various cloud types. However, overall cloudiness reduces maximum sap flow by up to 40 %. A key finding is the contrasting influence of low- and high-altitude clouds: low-altitude clouds suppress transpiration by limiting incoming radiation, while high-altitude clouds have negligible impact even when overcast. Structural equation modelling... (More)

Transpiration drives up to 40 % of terrestrial precipitation, with forests playing a critical role. This study combines long-term sap flow measurements and surface-based cloud observations to examine how different clouds affect tree transpiration across boreal and temperate European forests. Under specific cloudy conditions, sap flow can exceed clear-sky levels, reflecting distinct radiation effects of various cloud types. However, overall cloudiness reduces maximum sap flow by up to 40 %. A key finding is the contrasting influence of low- and high-altitude clouds: low-altitude clouds suppress transpiration by limiting incoming radiation, while high-altitude clouds have negligible impact even when overcast. Structural equation modelling further indicates a pathway linking transpiration to cloudiness when other meteorological and site factors are accounted for. Satellite data show a decline in low‑altitude cloud fraction over boreal forests, and a highly simplified model-based order‑of‑magnitude estimate suggests a potential associated increase in transpiration equivalent to ∼0.6–1.2 mm of precipitation annually. These results emphasize how climate change driven changes in cloud cover and type may alter the moisture flux to the atmosphere, impacting regional and global water cycles.

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type
Contribution to journal
publication status
published
subject
keywords
Atmosphere-biosphere interactions, Atmospheric dryness, Boreal forests, Cloud height and cover, Sap flow, Soil moisture
in
Agricultural and Forest Meteorology
volume
384
article number
111182
publisher
Elsevier
external identifiers
  • scopus:105035244822
ISSN
0168-1923
DOI
10.1016/j.agrformet.2026.111182
language
English
LU publication?
yes
additional info
Publisher Copyright: © 2026 The Authors
id
9192f9e5-cddd-44e0-87f5-aac0d4b26175
date added to LUP
2026-04-17 12:31:33
date last changed
2026-04-17 14:50:37
@article{9192f9e5-cddd-44e0-87f5-aac0d4b26175,
  abstract     = {{<p>Transpiration drives up to 40 % of terrestrial precipitation, with forests playing a critical role. This study combines long-term sap flow measurements and surface-based cloud observations to examine how different clouds affect tree transpiration across boreal and temperate European forests. Under specific cloudy conditions, sap flow can exceed clear-sky levels, reflecting distinct radiation effects of various cloud types. However, overall cloudiness reduces maximum sap flow by up to 40 %. A key finding is the contrasting influence of low- and high-altitude clouds: low-altitude clouds suppress transpiration by limiting incoming radiation, while high-altitude clouds have negligible impact even when overcast. Structural equation modelling further indicates a pathway linking transpiration to cloudiness when other meteorological and site factors are accounted for. Satellite data show a decline in low‑altitude cloud fraction over boreal forests, and a highly simplified model-based order‑of‑magnitude estimate suggests a potential associated increase in transpiration equivalent to ∼0.6–1.2 mm of precipitation annually. These results emphasize how climate change driven changes in cloud cover and type may alter the moisture flux to the atmosphere, impacting regional and global water cycles.</p>}},
  author       = {{Talvinen, Sini and Salmon, Yann and Lopez, Jose Gutierrez and Linderson, Maj Lena Finnander and Řehořková, Štěpánka and Šigut, Ladislav and Devasthale, Abhay and Ylivinkka, Ilona and Greiser, Caroline and Ezhova, Ekaterina and Quaas, Johannes and Kowalska, Natalia and Pavelka, Marian and Juráň, Stanislav and Larmanou, Eric and Paljakka, Teemu and Mohr, Claudia and Riipinen, Ilona and Krejci, Radovan}},
  issn         = {{0168-1923}},
  keywords     = {{Atmosphere-biosphere interactions; Atmospheric dryness; Boreal forests; Cloud height and cover; Sap flow; Soil moisture}},
  language     = {{eng}},
  month        = {{06}},
  publisher    = {{Elsevier}},
  series       = {{Agricultural and Forest Meteorology}},
  title        = {{Beyond cloud cover : Low- and high-altitude clouds have distinct impacts on tree sap flow and transpiration}},
  url          = {{http://dx.doi.org/10.1016/j.agrformet.2026.111182}},
  doi          = {{10.1016/j.agrformet.2026.111182}},
  volume       = {{384}},
  year         = {{2026}},
}