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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hessd-11-12765-2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
17 Nov 2014
Review status
This discussion paper has been under review for the journal Hydrology and Earth System Sciences (HESS). The manuscript was not accepted for further review after discussion.
Investigation of variable threshold level approaches for hydrological drought identification
B. S. Beyene1,*, A. F. Van Loon1,**, H. A. J. Van Lanen1, and P. J. J. F. Torfs1 1Hydrology and Quantitative Water Management Group, Wageningen University, Wageningen, the Netherlands
*now at: both Blue Nile Water Institute and College of Science, Bahir Dar University, Bahir Dar, Ethiopia
**now at: School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
Abstract. Threshold level approaches are widely used to identify drought events in time series of hydrometeorological variables. However, the method used for calculating the threshold level can influence the quantification of drought events or even introduce artefact drought events. In this study, four methods of variable threshold calculation have been tested on catchment scale, namely (1) moving average of monthly quantile (M_MA), (2) moving average of daily quantile (D_MA), (3) thirty days moving window quantile (30D) and (4) fast Fourier transform of daily quantile (D_FF). The levels obtained by these methods were applied to hydrometeorological variables that were simulated with a semi-distributed conceptual rainfall-runoff model (HBV) for five European catchments with contrasting catchment properties and climate conditions. There are no physical arguments to prefer one method over the other for drought identification. The only way to investigate this is by applying the methods and visually inspecting the results. Therefore, drought statistics (i.e. number of droughts, mean duration, mean deficit) and time series plots were studied to compare drought propagation patterns determined by different threshold calculation methods. We found that all four approaches are sufficiently suitable to quantify drought propagation in contrasting catchments. Only the D_FF approach showed lower performance in two catchments. The 30D approach seems to be optimal in snow-dominated catchments, because it follows fast changes in discharge caused by snow melt more accurately. The proposed approaches can be successfully applied by water managers in regions where drought quantification and prediction are essential.

Citation: Beyene, B. S., Van Loon, A. F., Van Lanen, H. A. J., and Torfs, P. J. J. F.: Investigation of variable threshold level approaches for hydrological drought identification, Hydrol. Earth Syst. Sci. Discuss., 11, 12765-12797, doi:10.5194/hessd-11-12765-2014, 2014.
B. S. Beyene et al.
B. S. Beyene et al.

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This paper explores possible threshold level calculation methods for hydrological drought analysis. We proposed four threshold methods applied to time series of hydrometeorological variables and inter-compared the drought propagation patterns. Our results have shown that these methods can influence the magnitude and severity of droughts differently and even may introduce artefact drought events. Therefore, we suggest the use and checking of these threshold approaches for drought analysis.
This paper explores possible threshold level calculation methods for hydrological drought...
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