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Application of regional-scale climate modelling to account for climate
change in hydrological design for dam safety in Sweden
Sten Bergström, Johan Andréasson and L. Phil Graham
Swedish Meteorological and Hydrological Institute, SE 601 76 Norrköping Sweden, sten.bergstrom@smhi.se
1. Background
Accounting for the impact of climate change on dam safety
is not a trivial task in the Nordic climate where, a mix of
snowmelt and extreme rainfall determines the most extreme
hydrological conditions. Nevertheless, this is required in the
new edition of the Swedish guidelines for the determination
of design floods for dams (Svenska Kraftnät, Svensk energi
and SveMin, 2007). Therefore a study has been initiated to
assess the impact of climate change on the national
guidelines for design floods. The basic question is how to
best use regional-scale climate scenarios to account for
climate change in hydrological design studies.
For dams where the consequences in case of failure are
less serious, Design Flood Category II, the 100 year flood
is prescribed as criteria for design. The development of
100-year floods in a changing climate is therefore studied
in a larger sample of 65 basins in Sweden. The location of
these basins is shown in Fig. 2.
Design floods are calculated both according to present day
climate conditions and with available climate scenarios.
Focus for the design studies in a changing climate is on
the first half of the century, but simulations will also be
made up to the year 2100.
2. Methods
The work relies on climate scenarios from the Rossby
Centre and the European Ensembles project, the HBV
hydrological model and the simulation scheme for design of
dams as prescribed in the Swedish guidelines for dam
design. Development of the interface between the climate
model output and the hydrological simulations is a major
effort. It is treated by two methods, delta change, where the
climate change signal is superimposed upon an observed
climate record, and scaling were the output from the climate
models is used directly after bias-correction (Yang et al.,
2008).
A number of drainage basins and dams relevant to the power
industry have been selected for the studies of dams
according to Design Flood Category I (Fig.1).This category
represents dams with the greatest consequences in case of a
failure.
Figure 2. Location of the 65 test basins used for
analysis of the development of the 100-year flood in
a climate change perspective.
Figure 1. Basins where climate impact studies for
dams according to Design Flood Category I of the
Swedish guidelines are carried out.
3. Preliminary results.
A lot of effort has been spent on the scaling interface. It is
a complex process to go from a climate model to an offline
hydrological simulation without loosing statistical
information. At present the regional climate scenarios
from the Ensembles project are being processed and
analysed as they appear. Fig. 3 shows an example of the
development of 100-year floods according to a number of
climate scenarios for River Byskeälven in northern
Sweden. It is based on a running frequency analysis with a
window width of 30 years.