| Qualified knowledge about the impacts of climate change
on hydrology is needed for the derivation of adaptation measures in the water
sector. As temperature and precipitation time series in Thuringia, Germany
of the last 50 years reveal that the climate is becoming warmer and drier in
summer and wetter in winter, the question of changes in runoff time series
arises. In the presented study, simple robust analysis approaches to detect
changes in runoff characteristics are applied. A selection of 19
anthropogenically undisturbed Thuringian catchments with daily runoff time
series of up to 78 years without gaps, covering different landscapes and
climatic conditions in Thuringia, is made. Indicators of mean, high, and low
runoff in the hydrological year, winter and summer are derived and tested
for trends, using the non-parametric Mann-Kendall trend test. To analyze the
impact of significant lag-1 autocorrelation (AR) in the series, a prior
removal of AR from the series before testing for trend
(trend-free-pre-whitening) is performed. Results show that removal of AR has
only minor influence on test results and is therefore considered as not
necessary. Mean flow and high flow indicators in annual and winter time
frame show increasing trends, escpecially in catchments in the higher
regions of Thuringia like the Thuringian forest. In summer, all indicators
show decreasing trends, especially in the drier central and northern
Thuringian basin area. In order to assess changes in floods, 8 gauges,
covering the 50-year time period 1949–1999, are selected. Annual maximum
flow series are derived for the hydrological year, winter and summer. After
fitting of 8 theoretical distributions to the samples by the method of
L-moments, 3 goodness-of-fit tests are applied. Flood quantiles for the
return periods 2, 5, 10, 20, 50 and 100 years are calculated from means of
well fitted distributions for all gauges. To analyze change in flood values,
the relative difference of flood quantiles in 2 time periods, 1949–1979 (TP 1)
and 1969–1999 (TP 2), with respect to the whole time period 1949–1999 are
calculated. Results show that flood values have increased in the later time
period in annual and winter time frame and have decreased in summer. |