Fourth Study Conference on BALTEX Scala Cinema Gudhjem

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Extreme Precipitation on a Sub-Daily Scale Simulated with an RCM:
Present Day and Future Climate
O.B. Christensen 2 , A. Guldberg 2 , A.T. Jørgensen 1 , R.M. Johansen 1 , M. Grum 1 , J.J. Linde 1 and J.H.
Christensen 2
1 Technical University of Denmark
2 Danish Meteorological Institute (obc@dmi.dk)
An analysis has been performed on hourly precipitation
output from the regional climate model (RCM) HIRHAM.
As part of the EU 5th FP project PRUDENCE, this model
has been run in 25 km resolution over an area covering
Europe and the eastern Atlantic with boundary conditions
from the atmospheric high-resolution global model
HadAM3H using sea-surface temperatures (SSTs) from
observations for present day conditions. A second
experiment uses SST observations plus anomalies based on
a climate change simulation with the coupled global model
HadCM3.
Two time slices corresponding to 1961-90 and 2071-2100
have been simulated. Hourly precipitation for the whole year
over Denmark has been analyzed. A comparison is made
between simulated grid point values and observation-based
values aggregated over a comparable area. The model
somewhat underestimates the very extreme precipitation.
But appropriate scaling indicates that the model reproduces
the observed shape near the tail of the precipitation intensity
distribution function reasonably well.
The modeled climate change exhibits an increase of 30-40%
for precipitation for return periods of less than about 4 years.
For larger return periods there is a higher increase of up to
80%.
In the paper we also assess the role of model resolution, as
the same experimental setup has been applied at 50 km
resolution, while preliminary analyses of a 12 km simulation
also will be presented.