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Abstract. Although precipitation has been measured for many centuries, precipitation measurements are still beset with significant inaccuracies. Solid precipitation is particularly difficult to measure accurately, and wintertime precipitation measurement biases between different observing networks or different regions can exceed 100 %. Using precipitation gauge results from the World Meteorological Organization Solid Precipitation Intercomparison Experiment (WMO-SPICE), errors in precipitation measurement caused by gauge uncertainty, spatial variability in precipitation, hydrometeor type, crystal habit, and wind were quantified. The methods used to calculate gauge catch efficiency and correct known biases are described. Adjustments, in the form of "transfer functions" that describe catch efficiency as a function of air temperature and wind speed, were derived using measurements from eight separate WMO-SPICE sites for both unshielded and single-Alter-shielded precipitationweighing gauges. For the unshielded gauges, the average undercatch for all eight sites was 0.50 mm h −1 (34 %), and for the single-Alter-shielded gauges it was 0.35 mm h −1 (24 %). After adjustment, the mean bias for both the unshielded and single-Alter measurements was within 0.03 mm h −1 (2 %) of zero. The use of multiple sites to derive such adjustments makes these results unique and more broadly applicable to other sites with various climatic conditions. In addition, errors associated with the use of a single transfer function to correct gauge undercatch at multiple sites were estimated.

Abstract. Within the framework of the World Meteorological Organization Solid Precipitation Intercomparison Experiment (WMO-SPICE), the Thies tipping bucket precipitation gauge was assessed against the SPICE reference configuration at the Formigal-Sarrios test site located in the Pyrenees mountain range of Spain. The Thies gauge is the most widely used precipitation gauge by the Spanish Meteorological State Agency (AEMET) for the measurement of all precipitation types including snow. It is therefore critical that its performance is characterized. The first objective of this study is to derive transfer functions based on the relationships between catch ratio and wind speed and temperature. Multiple linear regression was applied to 1 and 3 h accumulation periods, confirming that wind is the most dominant environmental variable affecting the gauge catch efficiency, especially during snowfall events. At wind speeds of 1.5 m s −1 the tipping bucket recorded only 70 % of the reference precipitation. At 3 m s −1 , the amount of measured precipitation decreased to 50 % of the reference, was even lower for temperatures colder than −2 • C and decreased to 20 % or less for higher wind speeds.The implications of precipitation underestimation for areas in northern Spain are discussed within the context of the present analysis, by applying the transfer function developed at the Formigal-Sarrios and using results from previous studies.Copyright statement. The works published in this journal are distributed under the Creative Commons Attribution 3.0 License. This license does not affect the Crown copyright work, which is re-usable under the Open Government Licence (OGL). The Creative Commons Attribution 3.0 License and the OGL are interoperable and do not conflict with, reduce or limit each other.

Snow cover is spatially heterogeneous at the local scale because of microclimatic, topographic and vegetative effects on snow accumulation, redistribution and ablation-processes which vary between different environments. Automated, fixed point snow depth measurements are the norm at research as well as operational sites, and the ability of these single point measurements to characterize snow depth for the surrounding area is an important issue. In this study, data for three winter seasons (2002-03, 2003-04, 2004-05) from ten Boreal Ecosystem Research and Monitoring Sites (BERMS) in northern Saskatchewan were used to assess the relationships between local scale snow depth variability, ascertained from snow survey transects, and single point measurements made with sonic depth sensors. Analysis of the snow surveys showed a wide range of depths at each site, with increased variability as winter progressed. Single, fixed-point measures of snow depth did not statistically represent the average snow depth at a site, even for relatively uniform snow covers. Consistent over-or under-representation of the landscape mean allowed the development of a "scaling equation" for each point measurement, improving confidence in the use of these data for modelling and climate variability studies. Where manual snow surveys may not be practical, the use of multiple automated point depth measurements may be adopted, and for the BERMS sites it was found that the minimum number of point measurements required to represent the landscape mean within 25% ranged from 1 to 44, depending on the degree of variability in snow depth associated with the landscape type, and the magnitude of the site mean depth. The relationships between point snow depth measurements and mean areal snow depth are important to consider both when utilising historical point observations for climatological and hydrological analysis, and for decision-making with regards to snow depth observing networks.

Weighing precipitation gauges are used widely for the measurement of all forms of precipitation, and are typically more accurate than tipping-bucket precipitation gauges. This is especially true for the measurement of solid precipitation; however, weighing precipitation gauge measurements must still be adjusted for undercatch in snowy, windy conditions. In WMO-SPICE (World Meteorological Organization Solid Precipitation InterComparison Experiment), different types of weighing precipitation gauges and shields were compared, and adjustments were determined for the undercatch of solid precipitation caused by wind. For the various combinations of gauges and shields, adjustments using both new and previously existing transfer functions were evaluated. For most of the gauge and shield combinations, previously derived transfer functions were found to perform as well as those more recently derived. This indicates that wind shield type (or lack thereof) is more important in determining the magnitude of wind-induced undercatch than the type of weighing precipitation gauge. It also demonstrates the potential for widespread use of the previously developed transfer functions. Another overarching result was that, in general, the more effective shields, which were associated with smaller unadjusted errors, also produced more accurate measurements after adjustment. This indicates that although transfer functions can effectively reduce measurement biases, effective wind shielding is still required for the most accurate measurement of solid precipitation.