CALCULATING SNOWMELT BACKWARDS – USING THE DATE OF SNOWPACK DISAPPEARANCE TO DETERMINE HOW MUCH SNOW FELL OVER A SEASON

Total solid precipitation can be determined at a location with knowledge of seasonal snow water equivalent (SWE) accumulation. One way of estimating the seasonal accumulation of SWE is by summing estimated snowmelt from the start of the ablation season to the date when snowpack disappears (determined by remote sensing or surface measurements). This method has been applied in several previous studies, but no study has thoroughly tested the method at control sites to identify its accuracy in estimating seasonal snowfall accumulation. In this study, this SWE reconstruction method is tested at 180 weather stations with snow pillows in the maritime mountain ranges of Washington, Oregon, and California across 13 water years. Snowmelt is calculated using the Snow-17 temperature-index snow model, the temperature-index Snowmelt Runoff Model with a net radiation component, and the full energy balance Utah Energy Balance model. A baseline collection of model simulations is produced by assuming precipitation data are accurate and do not require correction. The reconstruction method is then applied at each study site with each snow model by iteratively running the model and adjusting a precipitation correction factor until the snowpack disappears as close to the observed date as possible. The performances of the SWE reconstruction method and the baseline simulations are compared to determine its efficacy in reproducing maximum SWE, and thus total winter snowfall accumulation.