Operating the Seattle water system during the 1987 drought

The Seattle Water Department receives its supply from reservoirs on the Cedar and Tolt rivers, which drain the western slopes of the Cascade Mountains. Most droughts in the Northwest are the result of deficient winter snowfall. The 1987 drought was unusual in that the previous winter's precipitation was close to normal, but the summer dry period extended into the late fall, causing a severe water shortage. For this reason, a medium-term forecast model was developed to assist in the evaluation of management alternatives during a critical 16-week period from late summer to late fall 1987. A key feature of the model was that it predicted a best forecast at each of four inflow points, as well as the probability distribution of the forecasts.