Abstract
Abstract. In this paper, a method combining graphical and statistical techniques is proposed for surface resistance calibration in a distributed hydrological model, WaSiM-ETH, by comparing daily evapotranspiration simulated by model WaSiM-ETH with corresponding daily evapotranspiration retrieved from remote sensing images. The study area locates in Nahe catchment (Rhineland-Palatinate, Germany, 4065 km2) forest regions. The remote sensing based observations are available for a very limited number of days but representative for most soil moisture conditions. By setting canopy resistance (rc) at 150 s/m, soil surface resistance (rse) at 250 s/m or at 300 s/m for deciduous forest and setting rc at 300 s/m, rse at 600 s/m or at 650 s/m for pine forest, the model exhibits its best overall performance in space and time. It is also found that with sufficient soil moisture, the model exhibits its best performance in space scale.
Highlights
The Penman-Monteith (PM) equation is widely used for evapotranspiration estimation
This study proposes a method for surface resistance calibration of the WaSiM-ETH model based on a limited number of observations in time series retrieved from remote sensing images
Model performance For deciduous forest, five day’s Mean absolute error (MAE) between ET 150_250 and LE and five day’s MAE between ET 150_300 and LE indicate relatively better overall model performance – the MAE of five days are all in relatively small ranges (below the horizontal reference line, Fig. 3(a))
Summary
Surface resistance (rs) is a critical parameter, to which the evapotranspiration is highly sensitive, especially in dry canopy (no-rainfall) cases in forest (Beven, 1979). It is described as the bulk resistance of all transmission mediums such as crop, soil and others (Li et al, 2013). For no-rainfall conditions in forest regions, the canopy resistance (rc) and soil surface resistance (rse) are further defined, since actual evapotranspiration mainly comes from transpiration from plant leaves and evaporation of bare soil between plants. Interception evaporation is not taken into account due to its negligible contribution with a dry canopy
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