TRANSFER-FUNCTION MODELS OF DAILY URBAN WATER-USE

A time series model of daily municipal use as a function of rainfall and air temperature is developed. Total water use is separated into base use and seasonal use. The seasonal use series is detrended, then a nonlinear heat function relating water use to air temperature during rainless periods is employed to deseasonalize the series. The residuals are modeled using Box-Jenkins transfer functions with transformed rainfall and air temperature as independent variables. The model is applied to daily data from Austin, Texas from 1975 to 1981 and accounts for 97% of the variance of daily municipal water use over that period. Forecasts of daily usage are made for a two-week lead time.