Effectiveness of the proposed soil parameter estimation method was assessed based on performance of SWAT hydrological simulation in the target basin. Table 3 lists the SWAT parameters considered. The first ten parameters have been regularly calibrated in studies from the literature (e.g., Yang et al. 2008; Li et al. 2010; Shen et al. 2012). The last three parameters in Table 3 describe soil hydraulic characteristics. As three soil types were involved in SWAT simulation, a total of nine soil parameters (three soil types × three soil parameters) were addressed. Two model calibrations were executed. In the first calibration, all the aforementioned 19 parameters (i.e., first ten parameters in Table 3 and the nine soil parameters) were obtained by calibration against streamflow data using an automatic optimization scheme. In the second calibration, the nine soil parameters were attained via the pedotransfer functions, whereas the other ten parameters were derived by model calibration using the above scheme. The aforementioned two calibrations are hereafter referred to as CAL_19 and CAL_10, respectively. The model simulation corresponding to CAL_19 was treated as a benchmark. The differences in model simulation results corresponding to the two calibrations are considered to be caused by the way of deriving soil parameters (i.e., through calibration or pedotransfer functions).

Table 3

SWAT model parameters

NameDescriptionInitial range
CN2 SCS runoff curve number 20–90
ALPHA_BF Baseflow recession coefficient 0–1
GW_DELAY Groundwater delay time (days) 30–450
GWQMN Threshold water level in shallow aquifer for base flow 0–2
GW_REVAP Groundwater evaporation coefficient 0–0.2
ESCO Soil evaporation compensation coefficient 0.8–1
CH_N2 Manning coefficient for the mail channel 0–0.3
CH_K2 Hydraulic conductivity in main channel (mm/hr) 5–130
ALPHA_BNK Bank flow recession coefficient 0–1
SFTMP Snowfall temperature (°C) −5–5
SOL_AWC Available soil water capacity (mm H2O/mm soil) 0–1
SOL_BD Soil moist bulk density (g/cm31.1–2.5
SOL_K Soil Saturated hydraulic conductivity (mm/hr) 0–2,000
NameDescriptionInitial range
CN2 SCS runoff curve number 20–90
ALPHA_BF Baseflow recession coefficient 0–1
GW_DELAY Groundwater delay time (days) 30–450
GWQMN Threshold water level in shallow aquifer for base flow 0–2
GW_REVAP Groundwater evaporation coefficient 0–0.2
ESCO Soil evaporation compensation coefficient 0.8–1
CH_N2 Manning coefficient for the mail channel 0–0.3
CH_K2 Hydraulic conductivity in main channel (mm/hr) 5–130
ALPHA_BNK Bank flow recession coefficient 0–1
SFTMP Snowfall temperature (°C) −5–5
SOL_AWC Available soil water capacity (mm H2O/mm soil) 0–1
SOL_BD Soil moist bulk density (g/cm31.1–2.5
SOL_K Soil Saturated hydraulic conductivity (mm/hr) 0–2,000

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