Comparative analysis of neural network techniques for predicting water consumption time series
Introduction
Water demand forecasting is essential for the planning and management of water resources. There are several factors affecting the demand for water. These factors include population, rainfall, humidity, temperature, industrial and commercial conditions. A reliable forecast is expected to include the effects of such socio-economic and climatic factors. The conventional approaches such as regression techniques and time series models have been used to forecast future water demand. Lahlou and Colyer (2000) used multiple regression demand models to forecast water demand incorporating water conservation activities. Froukh (2001) used mathematical and heuristic approaches for long-term water demand forecasts in a decision-support system framework integrating demand management into demand forecasting. Wong and Mui (2007) constructed a mathematical model to determine flushing water demands for high-rise residential buildings in Hong Kong. Babel et al. (2007) developed a multiple coefficient water demand forecast and management model for the domestic sector considering various socio-economic, climatic and policy-related factors. Jain et al. (2001) used autoregressive models to forecast peak weekly water demand. Zhou et al. (2000) proposed time series models to forecast daily water consumptions based on trend, seasonality, and climatic correlation and autocorrelation components.
Artificial Intelligence techniques including Artificial Neural Networks (ANN) and Fuzzy Inference Systems (FIS) have been in use for some time as an alternative tools for predicting complicated water systems. Some specific ANN applications to water resources systems include rainfall-runoff modeling (Kumar et al., 2005), hydrologic time series modeling (Jain and Kumar 2007), runoff and sediment yield modeling (Turan and Yurdusev, 2009, Agarwal et al., 2006), water demand forecasting in irrigation delivery system (Pulido-Calvo et al., 2007). Unlike many hydrological applications, it is observed that there are limited applications of ANN to water consumption modeling. Liu et al., 2003, Griñó, 1992 applied ANN techniques to forecasting water demand in urban areas. Bougadis et al. (2005) investigated the relative performance of regression, time series analysis and ANN models for short-term peak water demand forecasting. Firat et al. (2009a) used several ANN techniques to model monthly water consumptions based on several socio-economic and climatic factors. The same data is also used by Yurdusev and Firat (2009) to develop an Adaptive Neuro Fuzzy Inference System. There appeared to be a need to model the monthly water consumption values used in Firat et al. (2009a) as time series. Firat et al. (2009b) performed a comparative modeling exercise using two Fuzzy Inference Systems. There left to be an obvious need to compare the ANN techniques for modeling monthly water consumption time series based on how well they perform. This study attempts to perform this task. The ANN techniques considered includes Generalized Regression Neural Network (GRNN), Cascade Correlation Neural Network (CCNN) and Feed Forward Neural Network (FFNN). The models based on the combinations of the antecedent water consumption records are constructed and the best fit input structure is investigated. The performance of ANN models in training and testing sets are compared with the observations and the best fit model forecasting model is identified.
Section snippets
Artificial Neural Networks (ANN)
ANN inspired by using studies of biological neural system is composed of processing elements called neurons or nodes. In literature, different types of ANN methods are used for forecasting and modeling of engineering problems. Three ANN techniques are considered in this study, for which brief descriptions are provided as follows.
A FFNN consists of at least three layers, input, output and hidden layers. The input signals presented to the system in input layer are processed in forward through to
Study area
The values of the metropolitan area of Izmir, Turkey are used for modeling monthly water consumptions. Based on her population and industrial development, Izmir is the third largest city of Turkey. Her population is rapidly growing due to the domestic population movement to the city from the disadvantageous parts of the country. The water resources of the city are scarce as it is located in the west coast of the country where the average temperature is significantly high whereas the rainfall is
Data set
For the development of the prediction models, the total 108 monthly data records of water consumption were collected in the period 1997–2005 for the city of Izmir, Turkey (Fig. 2). The data set was divided into two subsets, training and testing sets. The statistical parameters such as minimum value (xmin), maximum value (xmax), mean (), standard deviation (sx) and skewness coefficient (csx) for training and testing data sets are calculated and given in Table 1 to provide a comparison of the
Results and discussion
The models given in Table 2 were trained and tested using associated data sets by three different ANN methods, GRNN, CCNN and FFNN. The performances of models are shown in Fig. 4.
Comparing the results of models, it is seen that performances of M5 models consisting of the combination of five antecedent values of water consumption records are better than other models. The NRMSE and AARE values of M5 GRNN, CCNN and FFNN models are higher than those of other models. According to these criteria, M5
Conclusions
The capability of Artificial Neural Networks to model water consumption time series is tested in this study. The ANN techniques considered include Generalized Regression Neural Networks (GRNN), Cascade Correlation Neural Networks (CCNN) and Feed Forward Neural Network (FFNN). For this purpose, six models based on several combinations of previous monthly water consumption values are constructed. Comparison of model results have shown that the performance of the M5 model consisting of five
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