Assessment of snowfall accumulation underestimation by tipping bucket gauges in the Spanish operational network

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 1.5ms(-1) the tipping bucket recorded only 70% of the reference precipitation. At 3ms(-1), the amount of measured precipitation decreased to 50% of the reference, was even lower for temperatures colder than -2 degrees 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.