A STUDY OF FORECASTING ERROR WITH FORECASTING METHOD CONCERNING WATER DEMAND

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Forecasting the water demands is very important for pure-water reservoirs. Because the value of water supply to the water supply stations cannot be changed frequently according to the variation of water demands. The goal of this study is to propose forecasting method of water demands applying all over the country in Japan. In previous studies, we proposed three kinds of forecasting method and one kind of correcting method for water demand using data of four prefectures in Japan. The points of these forecasting methods are following three matters. 1) Based multivariate regression analysis. 2) Using multiple years’ data of the value of water supply per day. 3) Correcting the obtained multivariate regression formula by single regression analysis. As the results, forecasting precision is leaded approximately 2% by proposed forecasting methods. However, forecasting precision cannot be improved beyond it. Then, correcting method and forecasting error are focused in this paper. In the previous studies, correcting method is proposed by single regression analysis. The concept of correcting method is consisted of following three steps. In step 1, temporary forecasting values are calculated by multiple regression formula using data of water supply per day near forecasting day. In step 2, correcting coefficient are estimated by single regression analysis using relation between temporary forecasting values and actual values. In step 3, multiple regression formula is corrected by obtained correcting coefficient. Thus, proposed correcting method is very simply in the previous studies. In this paper, factors of forecasting error are estimated by relation between forecasting values and actual values. New correcting method is examined by obtained these factors.