Adjusting snow runoff correlation curves by use of autumn precipitation

Stream runoff from snow is affected by the moisture content of the soil beneath the snow cover. Soil moisture condition is largely determined by precipitation during the autumn, months before the snowpack accumulates. Records of precipitation for August, September and October for 7 years at the Birchbank area of the Columbia River Basin were averaged and the departure from average was obtained for each year. Departure from average was multiplied by 1.5 and these corrections were added to or subtracted from the snow water content of the basin on each April 1. A graph of corrected snow water content against total streamflow showed closer correlation than when using uncorrected water content. Similar corrections for streamflow in other areas using factors of 0.5 and 3.0 show similar improvements in correlation.