Abstract
Abstract. Derived flood frequency analysis allows the estimation of design floods with hydrological modeling for poorly observed basins considering change and taking into account flood protection measures. There are several possible choices regarding precipitation input, discharge output and consequently the calibration of the model. The objective of this study is to compare different calibration strategies for a hydrological model considering various types of rainfall input and runoff output data sets and to propose the most suitable approach. Event based and continuous, observed hourly rainfall data as well as disaggregated daily rainfall and stochastically generated hourly rainfall data are used as input for the model. As output, short hourly and longer daily continuous flow time series as well as probability distributions of annual maximum peak flow series are employed. The performance of the strategies is evaluated using the obtained different model parameter sets for continuous simulation of discharge in an independent validation period and by comparing the model derived flood frequency distributions with the observed one. The investigations are carried out for three mesoscale catchments in northern Germany with the hydrological model HEC-HMS (Hydrologic Engineering Center's Hydrologic Modeling System). The results show that (I) the same type of precipitation input data should be used for calibration and application of the hydrological model, (II) a model calibrated using a small sample of extreme values works quite well for the simulation of continuous time series with moderate length but not vice versa, and (III) the best performance with small uncertainty is obtained when stochastic precipitation data and the observed probability distribution of peak flows are used for model calibration. This outcome suggests to calibrate a hydrological model directly on probability distributions of observed peak flows using stochastic rainfall as input if its purpose is the application for derived flood frequency analysis.
Highlights
For reliable flood risk assessment and the development of effective flood protection measures a good knowledge of flood frequencies at different points in a catchment is required
– first, when using hydrological modeling for design it is possible to consider planned alterations in land use and management, future changes in climate or the introduction of new flood protection measures, whose effect is not contained in observed historical flood records;
The classical approach for the estimation of design floods based on rainfall–runoff modeling uses statistical storms derived from rainfall intensity-duration-frequency (IDF) curves
Summary
For reliable flood risk assessment and the development of effective flood protection measures a good knowledge of flood frequencies at different points in a catchment is required. An alternative is to apply derived flood frequency analysis, where design floods are estimated based on simulation results from a hydrological model, which is driven by observed or synthetic rainfall data. This approach is indispensable if no historical flood peak records are available for statistical analysis or regionalization. It is hypothesized that calibrating the hydrological model directly on the observed flood frequency distributions would provide the best results This approach would have two advantages: statistical peak flow data have usually much longer records of registration than continuous high resolution flow data and they permit the direct use of stochastic rainfall data for calibration of the hydrological model.
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