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Drivers of shortwave radiation fluxes in Arctic tundra across scales


Juszak, Inge; Iturrate-Garcia, Maitane; Gastellu-Etchegorry, Jean-Philippe; Schaepman, Michael E; Maximov, Trofim C; Schaepman-Strub, Gabriela (2017). Drivers of shortwave radiation fluxes in Arctic tundra across scales. Remote Sensing of Environment, 193:86-102.

Abstract

Vegetation composition and water surface area are changing in many tundra regions due to climate warming,
which is twice as strong in the Arctic as compared to the global mean. Such land cover changes feed back
to climate and permafrost thaw through altering the surface energy budget. We quantified the influence of
vegetation type, canopy characteristics, and patchiness on the tundra shortwave radiation components. We
used in situ measurements and vegetation mapping to parametrise a 3D radiative transfer model (DART)
for summer conditions at the Kytalyk test site in northeast Siberia. We analysed model results assessing
the most important drivers of canopy albedo, transmittance, and absorptance of photosynthetically active
radiation (PAR). Tundra albedo was strongly influenced by the fractional cover of water surfaces. Albedo
decreased with increasing shrub cover. However, plant area index effects on albedo were not statistically
significant. Canopy transmittance and PAR absorptance (fAPAR) were almost entirely controlled by plant area
index at the landscape scale. Only about one half of the total plant area index consisted of green leaves, while
wood and standing dead leaves contributed equally to the other half.While spatial patterns and patch sizes
of vegetation types and open water did not significantly influence the radiation budget at the landscape
scale, it contributed to the large variability at the local scale. Such local variability of shortwave radiation
may impact evapotranspiration and primary productivity at a range of scales. Therefore, the variation of
radiation fluxes within single vegetation types potentially affects larger scale energy, water, and carbon
fluxes.

Abstract

Vegetation composition and water surface area are changing in many tundra regions due to climate warming,
which is twice as strong in the Arctic as compared to the global mean. Such land cover changes feed back
to climate and permafrost thaw through altering the surface energy budget. We quantified the influence of
vegetation type, canopy characteristics, and patchiness on the tundra shortwave radiation components. We
used in situ measurements and vegetation mapping to parametrise a 3D radiative transfer model (DART)
for summer conditions at the Kytalyk test site in northeast Siberia. We analysed model results assessing
the most important drivers of canopy albedo, transmittance, and absorptance of photosynthetically active
radiation (PAR). Tundra albedo was strongly influenced by the fractional cover of water surfaces. Albedo
decreased with increasing shrub cover. However, plant area index effects on albedo were not statistically
significant. Canopy transmittance and PAR absorptance (fAPAR) were almost entirely controlled by plant area
index at the landscape scale. Only about one half of the total plant area index consisted of green leaves, while
wood and standing dead leaves contributed equally to the other half.While spatial patterns and patch sizes
of vegetation types and open water did not significantly influence the radiation budget at the landscape
scale, it contributed to the large variability at the local scale. Such local variability of shortwave radiation
may impact evapotranspiration and primary productivity at a range of scales. Therefore, the variation of
radiation fluxes within single vegetation types potentially affects larger scale energy, water, and carbon
fluxes.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Date:2017
Deposited On:04 Aug 2017 16:06
Last Modified:04 Aug 2017 16:06
Publisher:Elsevier
ISSN:0034-4257
Publisher DOI:https://doi.org/10.1016/j.rse.2017.02.017

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