Abstract
Abstract. Evapotranspiration (ET) plays a key role in hydrological impact studies and operational flood forecasting models as ET represents a loss of water from a catchment. Although ET is a major component of the catchment water balance, the evapotranspiration input for rainfall–runoff models is often simplified in contrast to the detailed estimates of catchment averaged precipitation. In this study, an existing conceptual rainfall–runoff model calibrated for and operational in the Bellebeek catchment in Belgium firstly has been validated and its sensitivity to different available potential ET input has been studied. It has been shown that when applying a calibrated rainfall–runoff model, the model input should be consistent with the input used for the calibration process, not only on the volume of ET, but also on the seasonal pattern. Secondly, estimates of the actual evapotranspiration based on measurements of a large aperture scintillometer (LAS) have been used as model forcing in the rainfall–runoff model. From this analysis, it has been shown that the actual evapotranspiration is a crucial factor in simulating the catchment water balance and the resulting stream flow. Regarding the actual evapotranspiration estimates from the LAS, it has been concluded that they can be considered realistic in summer months. In the months where stable conditions prevail (autumn, winter and (early) spring), an underestimation of the actual evapotranspiration is made, which has an important impact on the catchment's water balance.
Highlights
Floods are among the most common natural disasters in the world
In order to evaluate the effect of the temporal resolution of the evapotranspiration input, daily, monthly and annual averages of potential evapotranspiration calculated with the Penman (Ep,P) and Penman–Monteith (ETp,PM) equations are calculated and distributed hourly so that they can be used as evapotranspiration input for the Bellebeek probability distributed model (PDM), which is run with a time step of 1 h
From the comparison of the model performance based on potential evapotranspiration on the one hand and based on actual evapotranspiration input on the other hand, it is clear that using actual evapotranspiration as input for PDM affects the simulated stream flow
Summary
Among other infrastructure protecting measures, one indispensable tool to manage floods is the use of operational rainfall–runoff models to predict the arrival of discharge peaks These rainfall–runoff models are usually forced with continuous time series of the catchment averaged precipitation and evapotranspiration rates. Oudin et al (2005b) studied the impact of different potential ET inputs on the model performance of four different rainfall–runoff models over a large and climatically varied catchment sample of 308 catchments located in France, Australia and the United States. They concluded that looking for daily observed ETp data as input for rainfall–runoff models is not necessary and that a long-term average regime curve of ETp resulted in an equal stream flow simulation efficiency.
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