Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 14, issue 18
Biogeosciences, 14, 4209–4227, 2017
https://doi.org/10.5194/bg-14-4209-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 14, 4209–4227, 2017
https://doi.org/10.5194/bg-14-4209-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 21 Sep 2017

Research article | 21 Sep 2017

Effects of shrub and tree cover increase on the near-surface atmosphere in northern Fennoscandia

Johanne H. Rydsaa1, Frode Stordal1, Anders Bryn2, and Lena M. Tallaksen1 Johanne H. Rydsaa et al.
  • 1Department of Geosciences, University of Oslo, Oslo, Norway
  • 2Natural History Museum, University of Oslo, Oslo, Norway

Abstract. Increased shrub and tree cover in high latitudes is a widely observed response to climate change that can lead to positive feedbacks to the regional climate. In this study we evaluate the sensitivity of the near-surface atmosphere to a potential increase in shrub and tree cover in the northern Fennoscandia region. We have applied the Weather Research and Forecasting (WRF) model with the Noah-UA land surface module in evaluating biophysical effects of increased shrub cover on the near-surface atmosphere at a fine resolution (5.4 km  ×  5.4 km). Perturbation experiments are performed in which we prescribe a gradual increase in taller vegetation in the alpine shrub and tree cover according to empirically established bioclimatic zones within the study region. We focus on the spring and summer atmospheric response. To evaluate the sensitivity of the atmospheric response to inter-annual variability in climate, simulations were conducted for two contrasting years, one warm and one cold. We find that shrub and tree cover increase leads to a general increase in near-surface temperatures, with the highest influence seen during the snowmelt season and a more moderate effect during summer. We find that the warming effect is stronger in taller vegetation types, with more complex canopies leading to decreases in the surface albedo. Counteracting effects include increased evapotranspiration, which can lead to increased cloud cover, precipitation, and snow cover. We find that the strength of the atmospheric feedback is sensitive to snow cover variations and to a lesser extent to summer temperatures. Our results show that the positive feedback to high-latitude warming induced by increased shrub and tree cover is a robust feature across inter-annual differences in meteorological conditions and will likely play an important role in land–atmosphere feedback processes in the future.

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We investigate the atmospheric sensitivity to an expansion in shrub and tree cover in the northern Fennoscandia region. We applied a regional weather and climate model in evaluating biophysical effects of increased shrub cover at a fine resolution. We find that shrub cover increase causes a warming that is sensitive to the shrub and tree heights. Cooling effects include increased snow cover, cloud cover, and precipitation. We show that the net warming will likely increase in the future.
We investigate the atmospheric sensitivity to an expansion in shrub and tree cover in the...
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