Proceedings zur 6. Fachtagung BIOMET - Deutsche ...

The Influence of Climate Change and Land-use on the
Water Budget of a Forested Catchment
Christian Bernhofer, Uwe Eichelmann, Johannes Franke, Valeri Goldberg,
Thomas Grünwald, Janet Häntzschel, Barbara Köstner, Heiko Prasse, Ronald Queck,
Andreas Schreiber, Jörg Seegert und Uwe Spank
Institute of Hydrology and Meteorology, Technische Universität Dresden
Abstract
Almost 40 yrs of water budget measurements of a forested watershed in Central Europe are
utilised to investigate (i) effects of observed climate trends since the 1960ies, and (ii) effects
of land-use changes due to a change in forest management since the 1990ies. Main focus is on
evapotranspiration (ET) as it is expected to show the most pronounced response. Potential ET
did increase due to changes in saturation deficit and radiation, though no changes are detectable
in actual ET until mid of the 1990ies. Since then a clear trend of observed watershed ET
exists. This can be attributed to a reduced amount of clear cuts and an increased proportion of
under storey beech or a change in the reference meteorological or hydrological data used to
construct watershed ET. Modelling with the lumped parameter model BROOK90 showed no
change in modelled ET in the same period indicating that either parameters have to be adjusted
or data need additional homogenisation.
1 Introduction
The interannual variation and trends in forest water budgets reflect both, land use change and
change in climate. Today, with an already observed climate trend in Central Europe (e.g., of
about 1K in the last 50 yrs in Germany; FRANKE et al., 2004) we investigate whether the climate
signal in the observed long-term water budget can be separated from the “noise” originating
from interannual variability and land-use change. Basis are flux measurements in a
forested area near Tharandt (Tharandter Wald), about 25 km SW of Dresden/Saxony (GOLD-
BERG & BERNHOFER, 2006). This forest has a size of approximately 60 km², and a long history
of forestry documentation (about 180 yrs.) as well as meteorological and hydrological
measurements: (i) climate data since mid of the 19th century, (ii) continuous hydrological
data of the Wernersbach catchment since 1968 (covering 4.6 km²), and (iii) continuous flux
measurements by Eddy Covariance (EC) within EUROFLUX, Carbo-Euroflux, and Carbo-
Europe since 1996 (representative for approximately 0.5 km²).
2 Material and Methods
Altitude of the Wernersbach catchment ranges from 323 to 424 m a.s.l., slopes are moderate
(40 percent of slopes