JWSS - Journal of Water and Soil Science

Temporal and spatial distribution of water components in watersheds, estimation of water quality, and uncertainties

associated with these estimations are important issues in freshwater studies. In this study, Soil and Water Assessment

Tool (SWAT) model was used to estimate components of freshwater availability: blue water (surface runoff plus deep

aquifer recharge), green water flow (actual evapotranspiration) and green water storage (soil water), in Hamadan-Bahar

watershed. Also, the Sequential Uncertainty Fitting program (SUFI2) was used to calibrate and validate the SWAT

model and do the uncertainty analysis. Degree of uncertainty is calculated by R-factor and P-factor parameters. In this

paper, results of calibration and validation are given for the river monthly discharge. In most stations, especially in

outlet of the watershed (Koshkabad station), simulation of river discharge was satisfactory. Values of R-factor in

calibration of monthly runoff were 0.4-0.8. These small values show good calibration of runoff in this watershed.

Values of P-factor were 20-60%. These small values show high uncertainty in estimations. For most stations of the

watershed, lack of data on river-water withdrawal caused poor simulation of base-flow and therefore the P-factor values

were low. Nash-Sutcliff (NS) coefficient was 0.3-0.8 after calibration, which shows good model calibration of outlet.

This study provided good information on the components of freshwater availability at spatial (sub-basin) and temporal

(monthly) scales with 95% prediction uncertainty ranges. The results of uncertainty analysis of components of

freshwater availability show that uncertainty ranges of average monthly blue water are larger than the other

components, because of its sensitivity to more parameters.