Nearly 3000 river gauging stations with discharge data available from EFAS Hydrological Data Collection Centre database in July 2018 where considered for calibration of EFAS v4.0. Following a first screening of stations on the LISFLOOD 5 km drainage network, available discharge data were quality checked to exclude stations where discharge data showed issues with instrumentation, rating curves or extremely large regulations. 

Calibration stations were selected based on the following criteria (with some exceptions):

• Drainage area from data provider larger than 500 km² . For stations where information on the drained area was not provided, a model drainage area larger than 350 km² was considered.
• A minimum of 4 years with 6-hourly or daily discharge data within the calibration period (1990-2017). Preference was given to 6-hourly data according to this order: 6-hourly historic data, 6-hourly near real-time data, daily historic data and daily near real-time data. Exceptions were made for stations with nearly 4 years of data.
• Stations improving the spatial coverage of calibrated catchments in the Pan-European domain were included with some tolerance on data quality and availability.
• Stations located very close to another station (i.e. a small difference in drained area) with the same data quality were excluded. Between two stations, the one with 6-hourly data, the longer time series or the larger catchment was selected.
• Few stations that did not fulfil one or more of the previous criteria were selected for calibration when no better alternative was available in the nearby area.

Daily and 6-hourly stream flow observations from 1137 stations in 215 different catchments in the Pan-European EFAS domain were selected for the LISFLOOD model calibration and evaluation, 406 with 6-hourly data and 731 with daily data. In total 44.49% of EFAS domain area belongs to a calibrated catchment, corresponding to 4'081'475 km² over 9'174'725 km², with the catchments area of the stations varying from 468 km² (Ishem catchment, AL) to 807'000 km² (Danube catchment, RO) and a median area of 3000 km². 

Figure 1 - EFAS v4.0 - Location of calibration stations in EFAS domain. Stations with 6-hourly discharge data in blue. Stations with daily observed discharge data in red.

Figure 2 - EFAS v4.0 - Area of EFAS Pan-European domain included in the calibration (in red).

Compared to the previous operational system, EFAS v3.5, the number of calibration points increased by 416 stations, up from 711. Note that 144 stations used to calibrate EFAS3.5 had to be excluded after quality assurance.

Figure 3 - Location of calibration stations in EFAS domain for EFAS v4.0 (black dots) and EFAS v3.5 (blue circles).