Increased precipitation in the Norwegian Arctic: True or false?

Results from the WMO Solid Precipitation Measurement Intercomparison and parallel precipitation measurements from Svalbard are used to evaluate and adjust models for estimating true precipitation under Arctic conditions. The conclusion is that true precipitation in the Arctic may be estimated reasonably well when the wind speed at gauge height is less than 7 m/s. It is possible to give good estimates of true annual and seasonal precipitation at Svalbard, as only a small part of the precipitation is falling at wind speeds above 7 m/s. For rough calculations, the correction factors for liquid precipitation is estimated to be 1.15 and for solid precipitation 1.85. The developed correction models are used to estimate amounts and trends of true precipitation for two sites in the Norwegian Arctic. In Ny-Angstrom lesund the true annual precipitation is more than 50% higher than the measured amount. As the aerodynamic effects leading to precipitation undercatch are dependent on precipitation type and temperature, the observed and projected increase in the air temperature in the Arctic would also affect the measured precipitation, even if the true precipitation was unchanged. Since the mid 1960s the temperature at Svalbard Airport has increased by 0.5 degrees C per decade, resulting in a reduced fraction of annual precipitation falling as snow. In the same period, the measured precipitation has increased by 2.9% per decade and the 'true' by 1.7% per decade. Estimates are made of the fictitious precipitation increase that would result from a general temperature increase of 2, 4 and 6 degrees C. The increase in the measured annual precipitation would be 6, 10 and 13%, respectively. The expected fictitious precipitation increase is thus of the same magnitude as the real precipitation increase which according to recent GCM projections may be expected in Northern Europe as a result of a doubling of the atmospheric CO2 content.