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SnowMIP Project
(Last modified: 9/12/01)

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Introduction

The IAHS/ICSI working group on Snow and Climate, which gathers scientists from different backgrounds, thought that there was a need for an intercomparison of existing snow models.  In March 1998, participants in an EISMINT workshop expressed interest in this initiative.  In the end of 2000, Météo-France, Centre national de researches météorologiques initiated the SnowMIP project.

The originality of SNOWMIP was to gather several types of models: general circulation models parametrization (simplified models because of computer constraints), snow melt models (used in hydrology) and detailed snow models (used for avalanche forecasts or research in snow physics). The aim of the project was not to select the
"best" model, but to identify processes important for each application (climate simulation, snow physics ...). It is anticipated that the comparison of detailed and simple models will be of great interest for the design of future GCM snow parametrizations and simple snow melt models. Moreover, the intercomparison of detailed models is also of great interest for further research in snow physics.

Input data and requested outputs

Four validation sites were selected for this experiment, see Table 1.

Table 1.  The validation sites characteristics and the corresponding seasons

Name	Acronym	Lat/Lon	Elevation (m)	Air Pressure (hPa)	Selected Seasons
Col de Porte (France)	CDP	45.30N 05.77E	1340	840	10/06/96-06/10/97 10/08/97-06/20/98
Goose Bay (Canada)	GSB	53.32N 60.42W	46	1005	08/01/69-07/31/84
Sleepers River (USA)	SLR	44.50N 72.17w	552	948	11/01/96-05/10/97
Weissfluhjoch (Switzerland)	WFJ	46.83N 09.81E	2540	748	08/01/92-07/31/93

Hourly short- and long-wave solar radiation, air temperature, precipitation, precipitation phase, wind speed, and relative humidity were provided for each site for selected seasons (see Table).   Each participant should produce simulation results including snow water equivalent, snow depth, and other variables (e.g. surface temperature, albedo, liquid water content, etc.) depending on a model complexity.  Observed snow water equivalent and snow depth data were not released before simulation outputs were submitted.  It did not allow any calibration of model parameters. Some additional information on SnowMIP project can be found in http://www.cnrm.meteo.fr/*.
 

OHD/HL participation

More than 20 snow models from 10 countries including 7 from USA, 4 from France, 3 from Japan, etc. were submitted to the project, see participants list in Appendix I.  Participating models represented a wide range of snow physics complexities including 1) simple  temperature index-based models, 2) one layer energy-based models, and 3) most sophisticated multilayer energy-based models.

HL submitted results from two models of different complexity: 1) SNOW-17, which is a temperature index-based model with a simplified treatment of an energy balance transfer; 2) NOAH snow-frozen ground parameterization that is a one layer energy-based model.  SNOW-17 requires only air temperature, precipitation, and precipitation phase (if available) while NOAH uses solar radiation, wind speed, humidity, air pressure in addition.  Because there was no calibration, most SNOW-17 model parameters were assigned values recommended by the NWSRFS User's manual.  A parameter UADJ (rain-on-snow melt events) was estimated as a ratio of 6hr wind travel during snowmelt for each site. Calibrated early parameter MFMAX for the Sleeper River was slightly adjusted based on the snowmelt period for each site (it was increased/decreased by ratio of increase/decrease of daylight time for different site).

The project provides an opportunity to compare non-calibrated index-based parameterization to more sophisticated energy-based models, and to define most common causes of index-based model deficiencies.  At this stage, observed data are still not available to make a comprehensive analysis of simulation results.   However, during the IAMAS Conference in Innsbruck, Austria in July 10-13, 2001, the organize committee presented preliminary results from all participated models.  A range of simulated snow depth and water equivalent was unexpectedly very wide from close to zeros for most of cold season to unrealistically high values.  Figures 1 through 5 display observed and simulated from all participated models snow water equivalent, and Figures 6 through 10 display snow depth simulation results.  Most important finding was that there was no dependency of simulation accuracy on the model complexity. Some simple index-based models reproduced snow cover dynamics better than some of the most complex models.  Results from HL submitted index-based and energy-based models agreed with this general conclusion.  Both models reproduced snow water equivalent and depth reasonably close.  However, these results suggest that under some weather conditions the energy-based model works better if radiation data are high quality.
 

Our plan is to perform more comprehensive analysis of SNOW-17 and NOAH simulations after data will be released.  Effects of weather conditions on SNOW-17 simulation results will be investigated.

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