2.2 SIMULATION RESULTS OF THE REGIONAL CLIMATE MODEL ...

2.2 SIMULATION RESULTS OF THE REGIONAL CLIMATE MODEL STAR
F.-W. GERSTENGARBE, P.C. WERNER
Potsdam Institute for Climate Impact Research, P.O.Box 601203, 14412 Potsdam
gerstengarbe@pik-potsdam.de
Keywords: Future scenario, precipitation, temperature, relative humidity, vapour
pressure, sunshine duration, cloud cover, global radiation, wind
Summary
The chosen global scenario of 1.4 K rise in temperature up to 2055 represents for the
Elbe basin a moderate scenario in the sense of the IPCC definition. Analysis of the
most probable realization shows that the area under investigation will on the whole
become drier (except for high altitude, mountain locations), that the decline in
precipitation will be more moderate in winter than in summer, and that the radiation
conditions in summer will change considerably (longer sunshine length with less
cloud cover and thus increased global radiation). Winters are characterized by an
increase in mean wind speed, which results from intensification of the westerly wind
patterns. The origins of all the described development tendencies can be found in the
observation data (1951/2000).
Results:
The scenario calculations are based on a given temperature trend of 1.4 K for the
period 2001 – 2055. This trend was determined by the climate model run ECHAM4-
OPYC3 of the Max Planck Institute for Meteorology, Hamburg. This run is based on
the A1-CO 2 emissions scenario, which causes a relatively moderate increase in
temperature. In order to obtain a sufficiently large sample, 100 simulation runs were
performed both for the observation period and for the simulation period. Of the range
of precipitation trends obtained, the most probable realisation was selected for
interpretation.
Precipitation
Looking at the development of precipitation in the scenario period, it can be seen that
the area with an annual precipitation sum < 500 mm is considerably enlarged. There
are even regions within this area where the precipitation sum sinks to under 400 mm
per year, such as in the lee of the Harz mountains. On the other hand, an increase in
precipitation of up to 300 mm can be observed in the westerly mountain regions
(Harz mountains and Thuringian Forest). Precipitation is very differentiated according
to season. While in summer a decline in precipitation for the whole region can be
observed, in winter precipitation declines for some subregions only, while in
mountainous regions it increases markedly. In summary it can be said that under the
given development, there is a high probability that large parts of the Elbe basin will
face a significant decline in precipitation.
- 1 -

Temperature
Since the changes for temperature are predetermined by the underlying model
philosophy, temperature need not be discussed here. We mention only that the
spatial structures of the temperature distribution are unchanged in the simulation.
Relative humidity
The spatial structures of the annual mean of relative humidity shows approximately
the same structure for both investigation periods, although at a different level. The
mean level for the period 2046/55 is 3% lower than for the reference period
1951/2000. But the relative humidity in the mountains and the northern part of the
investigation area is greater than for the other parts of the Elbe basin. In the drier
areas, particularly, there is a tendency that this situation is further intensified. The
spatial structures are retained both in summer and in winter. However, a much
greater decrease can be seen in summer than in winter.
Water vapour pressure
The spatial structures of the annual mean values of vapour pressure mirror the
geographic and orthographic features of the investigation area both for the reference
and the scenario periods (higher values in the NW, lower values in the mountains).
The vapour pressure increases slightly for the whole investigation area in the
scenario period, in summer more than in winter.
Sunshine duration
A significant increase in sunshine duration can be seen for the summer in the
scenario period. There are regions where it increases by 1.5 hours per day. In winter
there are negligible changes only.
Cloud cover
Similarly to sunshine duration, the amount of cloud cover is spatially only weakly.
Inversely to sunshine duration, the annual mean cloud amount decreases for the
scenario period, with a considerably stronger decrease in summer than in winter, but
with some regions even showing a slight increase.
Global radiation
For global radiation, the scenario period shows greater spatial differentiation than the
reference period. Overall global radiation increases, with the trend being much
stronger in summer than in winter.
Wind velocity
Wind velocity declines in summer for almost the whole investigation area. In winter,
however, an increase can be observed.
- 2 -