Seite - 254 - in Book of Full Papers - Symposium Hydro Engineering

5°C threshold. This method (GDD) by Ernst and Loeper is widely used in German agriculture. The commencement of the growing season is set at a daily mean temperature sum of GDD=200°K and the annual temperature sum is a proxy for duration and intensity of the growing season. Vegetative development was analysed at Herrmannsacker phenological station, where the day of year (DOY) of the onset of the pine sprouting is being recorded since 1965 (data: DWD). Flow data is being recorded at the dams inflow gauging station Neustadt 1/Krebsbach (AE = 2.96 km2, records 1912 - 2016, 1 gap year). Furthermore, the state-run stream gauging stations at Ilfeld/Bere (AE = 62.5 km2, 1952 - 2015) and Ellrich/Zorge (AE = 42.1 km2, 1970 - 2015) were also analysed (data: TLUG). All data series were analysed for long-term trends using the package „Trend“, implemented in the R software [1]. Since several studies have indicated that climate and phenological changes might occur suddenly rather than as a long-term gradual trend [2], [3], such a test was also carried out with all long-term data, using the package „Kendall“ in R. 3. RESULTS AND DISCUSSION 3.1. AIR TEMPERATURE AND GROWING SEASON Recorded annual temperature sums above the 5°C-threshold ( GDD5°C) at both Braunlage and Artern meteorological stations showed no clear trend in the first half of the data series, but a steady and significant increase from the late 1980ies onwards (Figure 2). A highly significant breakpoint (p< 0.0001) was Fig. 2 Annual temperature sum > 5°C at Artern und Braunlage met stations identified in 1987/88, which is in line with earlier studies in Europe [4]. The day of year (DOY) at which the sum of mean daily temperature had reached the 200°K y = 0.56x + 821.47 R² = 0.00 y = 8.04x - 13,917.40 R² = 0.30 y = -0.55x + 2,359.12 R² = 0.00 y = 7.51x - 13,597.73 R² = 0.27 1000 1200 1400 1600 1800 2000 2200 2400 2600 Artern (1961-1987) Artern (1988-2016) Braunlage (1961-1987) Braunlage (1988-2016) Data source:DWD 254