For EFAS v4.0, LISFLOOD model calibration was performed on 1137 stations from 215 different catchments on the Pan-European EFAS domain. Multiple calibration points are generally available in one catchment, often with a mix of 6-hourly and daily data. LISFLOOD simulations are performed with 6-hourly steps for all calibration catchments, for calibration points with daily observations, 6-hourly LISFLOOD time series are aggregated at daily steps to allow comparison with daily observed discharge data. Each calibration station uses a different calibration period, depending on length of available discharge observations, but a minimum of 4 years is always used for calibration. If a longer record was available, the discharge record was split in two for calibration and validation purposes. If the record was shorter than eight years, four years were used for calibration and the remaining days were used for validation. If the record was equal to or longer than eight years, half was used for calibration and half for validation. The most recent period was used for the calibration because the earlier forcing data and discharge observations have greater uncertainty. An additional spin up period of three year is added to each model run to ensure that model's variable are correctly initialised.

Figure 1 - EFAS v4.0 - Sub-division of EFAS domain into LISFLOOD calibration inter-catchments.

The modified Kling-Gupta efficiency KGE' (Gupta et al., 2009Kling et al., 2012) was selected as the objective function for the calibration. A combination of improvement based criteria (i.e., improvements in the objective functions) and exhaustion-based criteria (fixed number of generations) was employed for stopping the calibration algorithm. 


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