Precipitation

Precipitation can optionally be given as a series of pulses, with regular frequency and specified pulse height, as determined by the switch PrecInput, (see viewing function Precepitation generator). Normally, however, it is given as a measured timeseries. Measured precipitation, P_m, is almost always less than the ”true” value, P, primarily because of wind losses. These losses are more pronounced for snowfall than for rain. An acceptable long term, average, correction can be given by multiplying the measured value by a constant fraction, different for rain and snowfall:

                                                    (8.6)

For Swedish conditions, the Swedish Meteorological and Hydrological Institute (SMHI) recommends a rain correction of 7% and a snow correction of 15%, meaning that c_rain = 1.07 and c_snow = 0.08.