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Effects of Land Use Changes on Water Balance __________________________________ 1165 Table 3. Mean monthly discharge values during the calibration and validation periods at Galinak and Joestan Stations. Station Period Observed (m3 s-1) Predicted (m3 s-1) Deviation (%) Joestan Calibration 7.5 8.7 16.1 Validation 8.1 10.4 27.3 Galinak Calibration 11.5 11.7 1.2 Validation 12.1 11.4 -5.3 Table 4. Results of the statistical evaluation of model performance on the monthly discharge in the calibration and validation periods at Joestan and Galinak Stream Gauging Stations. Gauging station Period MARE R2ENSResults Joestan Calibration 0.43 0.76 0.75 Acceptable Validation 0.61 0.83 0.73 Acceptable Galinak Calibration 0.33 0.84 0.84 Good Validation 0.34 0.90 0.89 Good calibrated by SWAT during the model calibration period for Galinak Station were in good agreement. The observed discharge was equal to 11.5 m3 s-1 compared with the calibrated discharge of 11.7 m3 s-1. Similarly, for the validation period, the above values were 12.1 and 11.4 m3 s-1, respectively. Notably, the comparative evaluation of the average monthly discharge values at Joestan Station showed relatively good fit between the estimates during the calibration and validation periods. As far as the calibration period is concerned, the average monthly observed and predicted discharges assumed the values of 7.5 and 8.7 m3 s-1, respectively. Similarly for the validation period, the observed average monthly discharge was 8.1 m3 s-1, whereas the predicted value was equal to 10.4 m3 s-1. Meanwhile, the average deviation of the predicted discharges at Joestan Station from the observed ones were 16.1 and 27.3% in the calibration and validation stages, respectively (Table 3). The values of MARE calculated for the two stations are generally low and close to zero (Table 4). The R2 and ENS coefficient are two important statistical indicators for evaluation of the results. In the case of Joestan Station, the R2values corresponding to the relationships between the observed and predicted average monthly discharges were found to be 0.76 and 0.83 during the calibration and validation periods, respectively. However, the corresponding values for Galinak Station were 0.84 and 0.90. Therefore, all of results in both stations and both periods (calibration and validation) for mean monthly flow showed the goodness fit of the simulation in the study area. Therefore, in general, SWAT model was reasonably capable to reproduce mean monthly discharge in Taleghan area. Consequently, based on statistical analysis, the results show: (i) the model can predicate the runoff accurately; (ii) the model is suitable and recommended for the study area. Runoff Components The runoff components encompass surface runoff, lateral flow, and groundwater flow. According to Linsley et al. (1949); Linsley et al. (1982), and Klemes (1986), drawing distinction between the components of runoff is arbitrary and the source(s) of the water passing a gauging station cannot be identified, therefore, comparing the predicted fluxes against any observation at the two gauging stations within the Taleghan basin is not possible. Figures 3 and 4 show the monthly surface runoff, lateral flow, and
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