Page - 255 - in Book of Full Papers - Symposium Hydro Engineering

mark has moved forward by 17 and 12 days at Artern and Braunlage, respectively, when comparing the 1988-2016 with the 1961-1987 sub-periods. At Herrmannsacker, beginning of pine tree sprouting has been advancing at a rate of 6 days per decade, or with a sudden shift of two and a half weeks starting in the late 1980ies (Figure 3). These results can be directly transferred to the catchment area of Neustadt dam, which has a forest cover of 96 %. Fig. 3 Trend and breakpoint of the observed commencement of pine tree sprouting (Picea abies) at Herrmannsacker 3.2. PRECIPITATION Precipitation is a key determinant of catchment runoff. At Harztor-Ilfeld- Hufhaus gauging station seasonal long-term trends (1916 - 2016) were weak and statistically not significant, showing small increases in the winter (Nov-Apr) and small decreases during the summer (May-Oct), as shown in Figure 4. Monthly trends for the entire record and sub-periods thereof are given in Table 1 for three precipitation gauging stations in the Southern Harz region. Two of the three stations showed significant linear increases in winter precipitation over the 101 year record length. Comparing annual precipitation for the 1961-1987 and 1988- 2016 period revealed s small but significant increase during the latter period for two out of the three stations. A comparison of individual months prior to and after the 1987/88 breakpoint revealed significant decreases in April and June at all stations and, while July, September and October and to some extent also January and February stood out with particularly large increases. y = -0.59x + 1301.6 R² = 0.47 90 100 110 120 130 140 150 Observations 1967 - 1987 Observations 1992 - 2012 Average 1967 - 1987 Average 1992 - 2012 Data source: DWD 255