Operational correction of daily precipitation measurements in Finland

An operational method for daily precipitation observation correction of aerodynamic, wetting and evaporation errors is presented. The aerodynamic correction method used has been developed for Finnish conditions when wind observations at the gauge are not available but the data from the nearest synoptic station can be used. Daily precipitation observations in Finland and its cross-boundary watersheds from the period 1961–2011 were corrected. It was discovered that the mean annual total sum of all gauges increased by 13.6% from 590.3 mm to 670.6 mm. The average overall proportions were 8.6%, 22.8% and 68.6% for evaporation, wetting and aerodynamic corrections, respectively. On a daily basis, the correction factor varied remarkably according to the form and intensity of precipitation, the median value being 1.21. Positive linear trends were identified in observed, corrected total and liquid precipitation, whereas a negative linear trend was obtained in corrected solid precipitation. The preliminary assessment using a watershed model indicated that the amount of correction is approximately correct for liquid precipitation but might slightly be too large for solid precipitation. Using corrected precipitation as a hydrological model input is recommended but a more comprehensive research is needed.