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.
Citation
ID:
198175
Ref Key:
rydsaa2017biogeoscienceseffects