A Method for Estimating Monthly Freshwater Discharge Affecting British Columbia Coastal Waters

River runoff is an important influence for many coastal oceanographic processes, but in many places of the world much of the flow is in ungauged rivers. The model developed here uses the historical relationship between precipitation and runoff and applies it to the ungauged areas to produce an estimate of ungauged flow. The combination of gauged and ungauged flow is then used to estimate the total freshwater discharge affecting the coastal waters of British Columbia. A distinction is made between pluvial and nival-glacial watersheds to accommodate their widely different precipitation regimes within the study area. Calendar Year and Water Year variants of the model are tested with the Water Year version proving to be superior for short time-span evaluations. Hindcasts are computed for the period 1970 to 2009, and the average annual runoff for the study area is found to be 998 km(3). No statistically significant trend is found for the forty-year time series. Runoff estimates from a subset of the study area are shown to match an earlier study that used area scaling, rather than precipitation scaling. The freshwater flux estimated by this method is twice the flux predicted for this region by a global runoff model but that global model reported a suspected under-representation of precipitation.