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Richard Essery
,
Nick Rutter
,
John Pomeroy
,
Robert Baxter
,
Manfred Stähli
,
David Gustafsson
,
Alan Barr
,
Paul Bartlett
, and
Kelly Elder

The Northern Hemisphere has large areas that are forested and seasonally snow covered. Compared with open areas, forest canopies strongly influence interactions between the atmosphere and snow on the ground by sheltering the snow from wind and solar radiation and by intercepting falling snow; these influences have important consequences for the meteorology, hydrology, and ecology of forests. Many of the land surface models used in meteorological and hydrological forecasting now include representations of canopy snow processes, but these have not been widely tested in comparison with observations. Phase 2 of the Snow Model Intercomparison Project (SnowMIP2) was therefore designed as an intercomparison of surface mass and energy balance simulations for snow in forested areas. Model forcing and calibration data for sites with paired forested and open plots were supplied to modeling groups. Participants in 11 countries contributed output from 33 models, and the results are published here for sites in Canada, the United States, and Switzerland. On average, the models perform fairly well in simulating snow accumulation and ablation, although there is a wide intermodal spread and a tendency to underestimate differences in snow mass between open and forested areas. Most models capture the large differences in surface albedos and temperatures between forest canopies and open snow well. There is, however, a strong tendency for models to underestimate soil temperature under snow, particularly for forest sites, and this would have large consequences for simulations of runoff and biological processes in the soil.

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Cecile B. Menard
,
Richard Essery
,
Gerhard Krinner
,
Gabriele Arduini
,
Paul Bartlett
,
Aaron Boone
,
Claire Brutel-Vuilmet
,
Eleanor Burke
,
Matthias Cuntz
,
Yongjiu Dai
,
Bertrand Decharme
,
Emanuel Dutra
,
Xing Fang
,
Charles Fierz
,
Yeugeniy Gusev
,
Stefan Hagemann
,
Vanessa Haverd
,
Hyungjun Kim
,
Matthieu Lafaysse
,
Thomas Marke
,
Olga Nasonova
,
Tomoko Nitta
,
Masashi Niwano
,
John Pomeroy
,
Gerd Schädler
,
Vladimir A. Semenov
,
Tatiana Smirnova
,
Ulrich Strasser
,
Sean Swenson
,
Dmitry Turkov
,
Nander Wever
, and
Hua Yuan

Abstract

Twenty-seven models participated in the Earth System Model–Snow Model Intercomparison Project (ESM-SnowMIP), the most data-rich MIP dedicated to snow modeling. Our findings do not support the hypothesis advanced by previous snow MIPs: evaluating models against more variables and providing evaluation datasets extended temporally and spatially does not facilitate identification of key new processes requiring improvement to model snow mass and energy budgets, even at point scales. In fact, the same modeling issues identified by previous snow MIPs arose: albedo is a major source of uncertainty, surface exchange parameterizations are problematic, and individual model performance is inconsistent. This lack of progress is attributed partly to the large number of human errors that led to anomalous model behavior and to numerous resubmissions. It is unclear how widespread such errors are in our field and others; dedicated time and resources will be needed to tackle this issue to prevent highly sophisticated models and their research outputs from being vulnerable because of avoidable human mistakes. The design of and the data available to successive snow MIPs were also questioned. Evaluation of models against bulk snow properties was found to be sufficient for some but inappropriate for more complex snow models whose skills at simulating internal snow properties remained untested. Discussions between the authors of this paper on the purpose of MIPs revealed varied, and sometimes contradictory, motivations behind their participation. These findings started a collaborative effort to adapt future snow MIPs to respond to the diverse needs of the community.

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