# G files of the global or regional data set on cd the

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‘copy and paste’ of data in other Excel files (e.g. files of the Global or Regional Data Set on the CD). The Dates are entered in column A, starting with cell A2, and streamflow values in column B, starting with cell B2 (Figure 1). There are no restrictions for the units of the streamflow – the calculated base flow values will have the same units as the input data and the BFIs are relative measures without unit. Figure 1 Data input. The sample data can be loaded directly by pressing the button. 4 Calculation When column A and B contain the necessary input data, the calculation can be started by pressing the button. The calculated base flow values are displayed in column C and a window shows up for the selection of season (Figure 2). Figure 2 Selection of season. In this window, the start and end day of the hydrological year or season for which the BFI will be calculated, can be specified. The full calendar year is given as default dates. The season may contain a year shift if the hydrological year does not equal the calendar year.
3 After pressing the ‘Run’ button in the ‘Seasonal BFI’ window, the base-flow-index calculations are performed and the results are displayed as described in the next section. 5 Output 5.1 Graph A graph of the base flow separation, showing the total streamflow (input data) and the calculated base flow values, is displayed in the middle part of the ‘Calculation’ sheet. The displayed interval corresponds to the season selected for the calculation. To view the graphs of different years, use the arrow buttons below the graph or chose the year from the year-selection field (Figure 3). Figure 3 Year selection. The year-selection field also shows the year of the displayed graph. If the hydrological year or season chosen contains a year shift, the displayed year number is the year of the end day of the year or season. If a more detailed view of part of the hydrograph and the separation line is wanted, the user can choose to estimate the BFI for a shorter period (similar to seasonal calculation). 5.2 Results: Annual values BFIs for individual years are displayed below the graph. These are based on full year or seasonal calculations. If a hydrological year or season contains a year shift, the displayed year number is the year where the end day of the year or season belongs (analogue to the years of the graph). Under ‘Lost days’ the number of days which are missing in the first and last season of the data series, are displayed. Days are lost as the base flow separation cannot start on the first day of the record nor end on the last day. Further, when the chosen season starts earlier or ends later than the time series, these days before or after the series increase the number of lost days. However, when the season start is chosen later that the start of the time series or the season end earlier than the end of the time series, the number of lost days may be reduced to zero.

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