On frictional and orographic effects on precipitation in coastal areas

Methods have been designed to calculate orographic and frictional influences on precipitation in coastal regions. A model computes the vertical fluxes of water vapor at the top of the planetary boundary layer due to these two effects. The horizontal downwind displacement of falling precipitation is also allowed for. The procedures are applied over southwestern British Columbia to monthly amounts and maximum 24-h rainfalls for return periods of 2–50 yr. Correlation coefficients between observed and computed precipitation vary from 0.65 to 0.97, the average being 0.84.