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The simulated and observed soil moisture at 10, 50, and 100 cm depths in the A. capillaris and P. australis communities for both calibration and validation periods are shown in Figure 5. The simulated soil moisture displayed similar variation tendencies as the observed data by visual comparison. The differences between simulated and observed values were partly due to model uncertainty, soil spatial heterogeneity, and observation errors, which are inevitable in field conditions and model setup. The observed soil moisture remained low from January 1 to June 30, 2012 while the simulated soil water content increased with rainfall. The reason for this discrepancy was presumably due to the influences of initial field observation and the model warm-up period, which were more or less non-existent after a certain period of time when the system operated stably. Overall, the HYDRUS-1D model was capable of simulating the seasonal variations of field soil water content. For the A. capillaris community, the RMSE of soil moisture ranged from 0.03 to 0.07 cm3 cm−3 in both calibration and validation periods, the RE values varied from −0.00 to 0.16, and the R values were within 0.85–0.96 (Table 3). For the P. australis community, the RMSE ranged from 0.03 to 0.04 cm3 cm−3, the RE varied from −0.02 to 0.03, and the R values were within 0.81–0.92. The simulations were in good agreement with the measurements.
Table 3

Assessment of the observed and simulated soil moisture and evapotranspiration in calibration and validation periods

VegetationItemsSoil depthCalibration
Validation
RMSERERRMSERER
A. capillaris community  10 cm 0.04 0.10 0.91 0.03 0.16 0.85 
50 cm 0.05 −0.00 0.88 0.03 −0.00 0.88 
100 cm 0.07 0.02 0.87 0.04 0.08 0.96 
ETa – 0.50 −0.10 0.89 1.01 −0.08 0.73 
P. australis community  10 cm 0.03 −0.00 0.82 0.02 0.00 0.90 
50 cm 0.03 −0.02 0.84 0.02 0.03 0.91 
100 cm 0.04 −0.02 0.92 0.02 0.03 0.81 
VegetationItemsSoil depthCalibration
Validation
RMSERERRMSERER
A. capillaris community  10 cm 0.04 0.10 0.91 0.03 0.16 0.85 
50 cm 0.05 −0.00 0.88 0.03 −0.00 0.88 
100 cm 0.07 0.02 0.87 0.04 0.08 0.96 
ETa – 0.50 −0.10 0.89 1.01 −0.08 0.73 
P. australis community  10 cm 0.03 −0.00 0.82 0.02 0.00 0.90 
50 cm 0.03 −0.02 0.84 0.02 0.03 0.91 
100 cm 0.04 −0.02 0.92 0.02 0.03 0.81 

Note: The unit for RMSE for is cm3 cm−3 and for ETa is mm d−1.

Figure 5

Comparison of observed and simulated soil moisture at three depths for calibration (January 1, 2012–May 31, 2013) and validation (June 1, 2013–July 30, 2014) periods in the A. capillaris (a) and P. australis (b) communities.

Figure 5

Comparison of observed and simulated soil moisture at three depths for calibration (January 1, 2012–May 31, 2013) and validation (June 1, 2013–July 30, 2014) periods in the A. capillaris (a) and P. australis (b) communities.

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