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Model calibration is done separately for each site using site specific upper boundary conditions for partitioned evapotranspiration (Fig. 3) and interception (Fig. 4), as well as the different model approaches (Fig. 5). Evapotranspiration (ET) in average decreases with increasing grazing intensity. For the grazed sites we observe higher E/ET ratios than for the ungrazed sites indicating the strong influence of the plant canopy on the upper boundary. Diurnal variations in E/ET ratios show that great differences between Tp and E occur in the midday and vapor is condensated during the night. Water interception decreases with increasing grazing intensity with significantly lower values at the heavily grazed site (Fig. 4) due to lower canopy and residue coverage. Note that the SHAW model calculates intercepted evaporation as a function of LAI, plant biomass, amount of residue, precipitation, and previously intercepted water and therefore accounts for temporal dynamics of intercepted water. Evapotranspiration rate (mm h -1 ) 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 WG 0.5 UG 79 UG 99 0.4 ETa E Ep 21-Aug 22-Aug 22-Aug 22-Aug 23-Aug 24-Aug 21-Aug 21-Aug 21-Aug 22-Aug 23-Aug 24-Aug Time (day/hour) 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 HG 21-Aug 21-Aug 22-Aug 22-Aug 23-Aug 24-Aug 21-Aug 22-Aug 22-Aug 22-Aug 23-Aug 23-Aug 23-Aug 24-Aug Time (day/hour) Fig 5.4. Curve of partitioning evapotranspiration (ET) into transpiration (Tp) and evaporation (E) in August 2006 determined by weighing lysimeter experiments for four sites (error bar represents standard deviation of three replicates). 98
Chapter 5 Modeling Grazing Effects on Coupled Water and Heat Fluxes in Inner Mongolia Grassland Accumulative interception (mm) Accumulative rainfall (mm) 20 16 12 8 4 0 240 200 160 120 80 40 0 UG 79 UG 99 WG HG 20-May 9-Jun 29-Jun 19-Jul 8-Aug 28-Aug 17-Sep 20-May 9-Jun 29-Jun 19-Jul 8-Aug 28-Aug 17-Sep Time (days) Fig. 5.4. Cumulative canopy and residue interception calculated by SHAW model for the four sites during the growing period in 2006 (accumulative rainfall as a reference). Model parameterization was conducted from 1 Aug. to 31 Aug. 2004. The general trend in terms of model approaches is the same in different sites, this is exemplarily demonstrated for the treatment UG 79 at 5, 20, and 40 cm depths (Fig. 5). Except for the inverse model, all model approaches underestimate soil moisture at 40 cm depth, which might be associated with a high unsaturated hydraulic conductivity in this layer. Model accuracy among the five model approaches is compared in terms of RMSE (Table 4). The RMSE is the lowest for inverse model exhibiting the best goodness-of-fit, followed by LDP and then NN. This proofs that the calibrated and measured parameters are more accurate than the statistical estimations based on pedotransfer functions (PTFs). The weakest predictions are found for LDP-NN and LDP+NN, i.e., the approaches which measured and statistical parameters were mixed. However, the prediction by LDP-NN is closer to that by LDP, indicating that parameters θr, θs, α, and n are more sensitive than Ks, which is also supported by the fact that the estimation by LDP+NN is almost identical to that by NN. 99
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SCHRIFTENREIHE Institut für Pflanz
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Aus dem Institut für Pflanzenernä
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I Table of contents I Table of cont
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controlling soil moisture are of pa
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Zusammenfassung Überweidung wird a
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Die Beweidung beieinflusst besonder
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II List of figures Fig. 2.1. Locati
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measured soil moisture in time stab
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III List of tables Table 2.1. Descr
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1.1 Background Chapter 1 Introducti
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Chapter 1 Introduction is also unce
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Chapter 1 Introduction water in spr
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Chapter 1 Introduction requires the
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Chapter 1 Introduction Krümmelbein
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Chapter 2 Spatial variability of so
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Chapter 3 Spatio-temporal variabili
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Page 93 and 94: MRD(%) MRD(%) 100 80 60 40 20 0 -20
Page 101 and 102: Soil water content (%) 40 30 20 10
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Page 167 and 168: References Chapter 7 General discus
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Chapter 7 General discussion and co
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8. ACKNOWLEDGMENTS Firstly I would
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Curriculum Vitae M.Sc. Ying Zhao Of
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Schriftenreihe des Instituts Neuere
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