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Comparing Performance and Parameterization of a One-Dimensional Unsaturated Zone Model across Scales

^a Erosion and Soil & Water Conservation Group, Wageningen Univ., Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlands, and Gorgan Univ. of Agricultural Sciences & Natural Resources, Gorgan, Iran
^b Inst. for Biodiversity and Ecosystem Dynamics, Univ. of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands

View larger version (20K): [in this window] [in a new window]   FIG. 1. Geographical position of study area and location of the measurements (Gr = grass, WW = winter wheat, CST = conservation tillage, CVT = conventional tillage, YM = yellow mustard, NO = 2-yr-old orchard, and OO = 5-yr-old orchard).

View larger version (77K): [in this window] [in a new window]   FIG. 2. Land use in the Catsop catchment during the winter season of 2003–2004.

View larger version (15K): [in this window] [in a new window]   FIG. 3. Communication between SWAP and PEST during parameter calibration.

View larger version (21K): [in this window] [in a new window]   FIG. 4. Comparison of observed and predicted soil moisture in the top layer (0–20 cm) for tubes within orchards for unaggregated observations and predictions (Aggregation Level 0). The graphs in the left column show time series of observations (symbols) and predictions (lines). The vertical line in each time series separates calibration (left side) and validation (right side) period. The graphs in the right column are scatter graphs of observation vs. predictions. Similar graphs can be made for the second and third layer of the model; the overall pattern in (dis)agreement between observation and prediction is the same for all three layers. The labels NO up, NO down, OO up, and OO down refer to the tubes depicted in Fig. 1.

View larger version (14K): [in this window] [in a new window]   FIG. 5. Comparison of observed and predicted soil moisture in the top layer (0–20 cm) for the new orchard (NO) and old orchard (OO). Observations are unaggregated (so the observations for, e.g., OO up and OO down are the same as those in Fig. 4) and predictions are for Aggregation Level 1. The graphs in the right column are scatter graphs of unaggregated observations vs. aggregated predictions.

View larger version (11K): [in this window] [in a new window]   FIG. 6. Comparison of observed and predicted soil moisture in the top layer (0–20 cm). Observations are unaggregated (so these are the same as those in Fig. 4 and 5) and predictions are for Aggregation Level 2 (here, orchard). The graph at the right shows unaggregated observations vs. aggregated predictions.

View larger version (11K): [in this window] [in a new window]   FIG. 7. Comparison of observed and predicted soil moisture in the top layer (0–20 cm). Observations are unaggregated (so these are the same as those in Fig. 4–6) and predictions are for Aggregation Level 3 (catchment average). The graph at the right shows unaggregated observations vs. aggregated predictions.

View larger version (12K): [in this window] [in a new window]   FIG. 8. The values of Mualem–van Genuchten parameters and n per layer for different aggregation levels. Each dot is a parameter value for a particular land unit, each + represents the mean of the parameter values per aggregation level. The dots are jittered per aggregation level to distinguish the individual parameter values. The parameter values for Aggregation Level 0 correspond with the values in Table 2.

View larger version (17K): [in this window] [in a new window]   FIG. 9. Discharge as predicted by the SWAP models for the different aggregation levels (AggL0, AggL1, AggL2, and AggL3) against the observed daily discharge. SWAP does slightly overpredict discharge for low observed discharge and underpredicts severely for high observed discharge.