D. Pascual1*, M. Johansson1, A.
Pongracz1, & J. Tang1,2
1Department of Physical Geography and Ecosystem
Science, Lund University, Lund Sweden
2Section of Terrestrial Ecology, Department of
Biology, University of Copenhagen. Copenhagen, Denmark
* Corresponding author. E-mail:
Didac.pascual@nateko.lu.se - Affiliation address: Sölvegatan 12, 223 62
Lund, Sweden - Telephone dir 0046 720324595
Key Points:
- Winter warming events (WWEs) have increased in the Arctic and are
expected to increase further, but their impacts are not thoroughly
evaluated in large-scale ecosystem models.
- We applied different scenarios of enhanced WWEs in a widely used
ecosystem model, LPJ-GUESS, and found that their impacts on ecosystem
processes could be substantial and of magnitudes comparable to those
of altered winter climatologies.
- The direction of the modeled WWE impacts on ground temperatures
differed from what the observation-based literature suggests, and we
identified essential processes lacking in LPJ-GUESS that may cause
this mismatch.
Abstract
Winter warming events (WWEs) are short-lasting events of unusually warm
weather, occasionally combined with rainfall, which can cause severe
ecosystem impacts by altering ground temperatures and water fluxes.
These impacts are generally overlooked in large-scale ecosystem models.
The frequency and intensity of WWEs will likely increase further in the
future. We used an ecosystem model, LPJ-GUESS, to investigate the
responses of four subarctic ecosystems to different levels of predicted
WWEs, and identify model gaps hindering accurate estimates of these
responses. In response to WWEs, the model simulated substantial ground
cooling (up to 2 °C in winter) in contrast to the observed warming,
leading to changes in biogeochemical fluxes often comparable in
magnitude to those from altered winter climatologies. The mismatch
between the modelled and the observed ground temperature changes may be
due to the 1) lacking surface energy balance, 2) daily timestep, and 3)
simplistic water retention scheme in LPJ-GUESS.