Page - 258 - in Book of Full Papers - Symposium Hydro Engineering

sub-period ending in 1987, hinting at an earlier and smaller snowpack-melt, which is well in line with the temperature records presented above. However, the statistically significant decrease in March runoff during the most recent period (1988-2016) at two out the three gauging stations seems to indicate that the run- off shift towards the start of the year is still ongoing (Table 2). Fig. 5 Changes in mean monthly runoff at Neustadt 1 streamflow gauging station after the 1988 breakpoint 3.4. IMPLICATIONS FOR RESERVOIR MANAGEMENT AND POSSIBLE REMEDIES With climate projections for the coming decades all pointing towards a strengthening of the trends observed in the last three decades, the dam operators working hypothesis at this point is, that the current changes in runoff regimes are likely to continue into the foreseeable future. This hypothesis must be verified periodically by rigid statistical analyses of measured data. However, there is a residual risk that sudden shifts and breakpoints will only be recognizable in hindsight, when the subsequent time period is long enough, i.e. at least 10 years. The seasonal partitioning of reservoir inflow flow (winter/summer), as a percentage of mean annual inflow, shifted from a 26/74 ratio during 1912-1987 to a 19/81 ratio after the 1987/88 breakpoint. This increased seasonality and variability has a diminishing effect on safe raw water withdrawals from the reservoir, as has been shown in [7]. Keeping with the current raw water withdrawal RWW365 of 3650 m3 d-1 would in turn mean decreasing reliabilities of supply RoS once mean inflow decreases and becomes more variable. Hence it is 0.0 0.1 0.2 0.3 Mean 1912 - 1987 Mean 1988 - 2016 258