Three perceptions of the evapotranspiration landscape: comparing spatial patterns from a distributed hydrological model, remotely sensed surface temperatures, and sub-basin water balances

T Conradt,A Bronstert,F Wechsung

doi:10.5194/hess-17-2947-2013

Abstract

Abstract. A problem encountered by many distributed hydrological modelling studies is high simulation errors at interior gauges when the model is only globally calibrated at the outlet. We simulated river runoff in the Elbe River basin in central Europe (148 268 km2) with the semi-distributed eco-hydrological model SWIM (Soil and Water Integrated Model). While global parameter optimisation led to Nash–Sutcliffe efficiencies of 0.9 at the main outlet gauge, comparisons with measured runoff series at interior points revealed large deviations. Therefore, we compared three different strategies for deriving sub-basin evapotranspiration: (1) modelled by SWIM without any spatial calibration, (2) derived from remotely sensed surface temperatures, and (3) calculated from long-term precipitation and discharge data. The results show certain consistencies between the modelled and the remote sensing based evapotranspiration rates, but there seems to be no correlation between remote sensing and water balance based estimations. Subsequent analyses for single sub-basins identify amongst others input weather data and systematic error amplification in inter-gauge discharge calculations as sources of uncertainty. The results encourage careful utilisation of different data sources for enhancements in distributed hydrological modelling.

Highlights

IntroductionA distributed hydrological model which accurately simulates discharges at the basin outlet while producing poor results at interior points seems to be a paradox
1.1 Improving spatial representativeness of distributed modelsA distributed hydrological model which accurately simulates discharges at the basin outlet while producing poor results at interior points seems to be a paradox
Respective results obtained from numerous models in the first phase of the Distributed Model Intercomparison Project (Reed et al, 2004) gave rise to adding more stream gauges at interior points for the second project phase (Smith et al, 2012a) which confirmed the observed trend of model fidelity increasing with basin size (Smith et al, 2012b)

Summary

Introduction

A distributed hydrological model which accurately simulates discharges at the basin outlet while producing poor results at interior points seems to be a paradox. This feature has been shown by many studies on distributed modelling where inner point discharges were evaluated. Respective results obtained from numerous models in the first phase of the Distributed Model Intercomparison Project (Reed et al, 2004) gave rise to adding more stream gauges at interior points for the second project phase (Smith et al, 2012a) which confirmed the observed trend of model fidelity increasing with basin size (Smith et al, 2012b)

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Methods

Discussion

Conclusion