SPICE – Improving snowfall measurements

SPICE (Solid Precipitation Intercomparison Experiment) is a WMO/CIMO multi-sites intercomparison of instruments and systems of observation for the measurement of solid precipitation. One of the main objectives is the assessment of a wide range of instruments under various climates. For that purpose, around 20 sites worldwide are equipped and configured according to standards defined within the project, in order to allow comparison between the sites. The experiment started in October 2013 and is meant to last over two winter seasons.


The Solid Precipitation Intercomparison Experiment (SPICE), launched by the Commission for Instruments and Methods of Observations (CIMO) on 20 sites in 15 countries, will carry out a full suite of experiments in the winter of 2013/14. Solid precipitation quantity is a key factor for water and risk management, therefore, accurate and continuous measurements of this parameter are needed. Led by Environment Canada, SPICE will contribute to improvements in automatic point measurements of snowfall and snow depth at high time resolutions. The project is scheduled to last two winters and to deliver a report on the Field Reference System in 2014 and a Final Report in 2016.

Snowfall measurements are confounded by many technical and environmental factors, therefore, measuring snowfall is not similar to measuring rainfall as illustrated by the results from two distinct events – rain and snow – observed at Environment Canada facilities. While different types of instrument (tipping buckets and weighting gauges) perform equally well for the rain event, it shows dramatic differences between the two measuring principles for the snow event. The SPICE challenge will be to assess, understand and quantify these differences, and to provide recommendations to stakeholders.

The 20 SPICE sites are in both the Northern and Southern hemispheres, they range in latitude from 100 to 5 000 metres above sea level. Over 20 manufacturers have provided some 400 measuring instruments for the experiments. These cover 30 different models – weighing gauges, tipping buckets, optical sensors, particle disdrometers, hot plates, GPS based snow depth sensors, acoustic and laser snow depth sensors, snow water equivalent sensors, and more – using various type of shields.


SPICE will investigate in situ measurement and reporting of precipitation amount over various time periods as a function of precipitation phase – liquid, solid, mixed – and snow on the ground (snow depth), including linkages with snowfall. Its main objectives are to define field references using automatic instruments, to characterize operational and emerging automatic instruments for measuring for snow, to derive the adjustments to be applied to measurements as functions of wind, temperature and precipitation type, to assess the minimum practicable temporal resolution for reporting valid snow measurements, and to configure a comprehensive intercomparison dataset for further data mining (e.g. radar- and satellite-based snowfall estimation).

SPICE will recommend well characterized automated field reference systems for the unattended measurement of solid precipitation. Currently, the only well characterized field reference for the measurement of solid precipitation, worldwide, is the Double Fence International Reference (DFIR), recommended at the end of the previous intercomparison for the measurement of solid precipitation, organized by WMO, between 1987-1993. With this configuration in mind, the International Organizing Committee has defined the reference R2 for the SPICE project : an automatic shielded gauge inside the double wood fence, together with a precipitation detector. For those sites that can’t afford a DFIR, an R3 reference has been defined with two identical automated gauges, one shielded and one unshielded. The sites comprising an R2 reference have to include R3 reference as well. These field references will give the opportunity to compare one site with another in support of the intercomparison of the SPICE project and lead to a recommendation of the best configuration for an automated field reference system.


The Final Report will provide recommendations for automatic field reference systems, performance characterization of existing and emerging technologies measuring solid precipitation and a comprehensive data set for legacy use. In addition, the Report will update relevant chapters of the Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8), providing a guide for WMO Members in transition to automation and recommendations made to manufacturers.

The international organizing committee and project team will meet in Sodankylä, Finland, from 19–23 May to follow-up on the project objectives.


Contact: Rodica Nitu, Environment Canada , Project Leader, rodica.nitu@ec.gc.ca

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