Stochastic forecasting of monthly behavior of unit hydrograph, Shiraz aquifer, Iran

Industrial and agricultural developments cause decreasing groundwater level in the world and Iran also. This tends to drying of water wells, decrease in river flow, lowering of water quality, increase of pumping costs, ground settlements and aquifer death. Shiraz aquifer ,area of 270 square kilometer, located in south of Iran. Monthly unit hydrograph data was measured in 16 years 1993 – 2008, calculated with average weighting method. ITSM software is used for all calculations in this research. For achieving a stationary series, trend and seasonal components removed from original data by differencing operator (first with 2 lags and then with 12 lags). Then the autoregressive (order 24) fitted to the series with AIC=165.117 . Coefficient of the fitted model finalized by the residual tests. All test of randomness (6 tests) confirmed the selected model. For 5 years in the future, forecast data evaluated by 95% confidence interval. In period of 1993-2008 and 2009-2013, no tremendous reduction in the mean groundwater level recorded or will be seen.

Keywords:

ARMA , Autoregressive , Stochastic model , Forecasting , Time series , Unit hydrograph , Test of randomness