Forecasting for Urban Water Demand Management

The water supplies for major cities of the Pacific Northwest depend on surface runoff stored in reservoirs. The reservoir operation goal is to refill during the spring melt so that supplies will be available during the summer when precipitation is usually small and water demands are high. The possibility of water shortages during the late summer and fall is always a concern. The probability of water shortages depends on the probability distribution of inflows to the reservoirs, and the probability distribution of water consumption. In general, these distributions are not independent, nor are they highly correlated. Together they define the joint probability distribution function which is required to determine the reliability of the water supply system. The consumption can be managed through appeals to the customers as part of a water shortage response plan. This paper describes the methodology used in developing the water consumption forecast for the summer season in Vancouver and Victoria and the economic risk analysis used in the Seattle water supply expansion planning study.