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Numerical Validation of a Diurnal Streamflow-Pattern-Based Evapotranspiration Estimation Method

Gribovszki, Zoltán and Kalicz, Péter and Szilágyi, József (2011) Numerical Validation of a Diurnal Streamflow-Pattern-Based Evapotranspiration Estimation Method. ACTA SILVATICA ET LIGNARIA HUNGARICA, 7. pp. 63-74. ISSN 1786-691X

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Abstract

The evapotranspiration (ET) estimation method by Gr ibovszki et al. (2010b) has so far been validated only at one catchment because good q uality discharge time series with the required high enough temporal resolution can probably be fou nd at only a handful of watersheds worldwide. To fill in the gap of measured data, synthetic groundw ater discharge values were produced by a 2D finite element model representing a small catchment. Geome trical and soil physical parameters of the numerical model were changed systematically and it was checked how well the model reproduced the prescribed ET time series. The tests corroborated t hat the ET-estimation method is applicable for catchments underlain by a shallow aquifer. The slop e of the riparian zone has a strong impact on the accuracy of the ET results when the slope is steep, however, the method proved to be reliable for gentle or horizontal riparian zone surfaces, which are more typical in reality. Likewise, errors sligh tly increase with the decrease of riparian zone width, and unless this width is comparable to the width of the stream (the case of a narrow riparian zone), th e ET estimates stay fairly accurate. The steepness of the valley slope had no significant effect on the r esults but the increase of the stream width (over 4 m) strongly influences the ET estimation results, so t his method can only be used for small headwater catchments. Finally, even a magnitude change in the prescribed ET rates had only a small effect on the estimation accuracy. The soil physical parameters, however, strongly influence the accuracy of the method. The model-prescribed ET values are recovere d exactly only for the sandy-loam aquifer, because only in this case was the model groundwater flow system similar to the assumed, theoretical one. For a low hydraulic conductivity aquifer (e.g. clay, silt), root water uptake creates a considera bly depressed water table under the riparian zone, ther efore the method underestimates the ET. In a sandy, coarser aquifer the flow lines never become vertica l even bellow the root zone, so the method overestimates the ET rate, thus the estimated ET va lues need to be corrected. Luckily the prescribed and estimated ET rates express a very high linear c orrelation, so the correction can be obtained by th e application of a constant, the value of which solel y depends on soil type.

Item Type: Article
Subjects: Q Science / természettudomány > QE Geology / földtudományok > QE08 Hydrosphere. Hydrology / hidroszféra, hidrológia
SWORD Depositor: MTMT SWORD
Depositing User: MTMT SWORD
Date Deposited: 09 Oct 2014 13:48
Last Modified: 11 Dec 2015 14:18
URI: http://real.mtak.hu/id/eprint/17633

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