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Regional climate modeling in Morocco within the project IMPETUS
Westafrica
K. Born, H. Paeth, K. Piecha, and A. H. Fink
Institute for Geophysics and Meteorology, University Cologne, Kerpener Str. 13, 50937 Cologne, Germany.
1. Introduction
In IMPETUS Westafrica (http://www.impetus.uni-koeln.de),
consequences of possible future climate change impacts on
local economic and social conditions in two river
catchments were investigated: the Drâa in Morocco and the
Ouémé in Benin. Climate changes were assessed using a
model hierarchy from global down to local scales. Different
techniques of dynamical, statistical and statistical-dynamical
downscaling had to be applied in order to fulfill demands of
hydrological and socio-economic models.
strength of dry periods, whereas the nature of wet periods
seems to be unchanged (Born et al., 2008). Besides
changes in rainfall variability, the most important change
is the rise of the snowline due to the greenhouse gas
induced warming.
2. The Hierachy of Climate Models
In Morocco, climate ranges from High Mountain climates to
steppe and deserts. Due to this strong spatial heterogeneity,
different techniques had to be applied in order to assess
future climate change patterns. An overview of the
downscaling techniques is shown in Figure 1.
Figure 1. IMPETUS hierarchy of climate models and
according downscaling techniques.
Climate model applications started on the global scale using
results from the consortium runs of ECHAM5 performed by
the Max-Planck Institute for Meteorology in Hamburg,
accompanied by ECHAM5 climate simulations using a
vegetation model adapted to the peculiarities of West
African climate, which were performed at the University of
Cologne. The first downscaling step was a dynamical
downscaling from ECHAM5 to synoptic scales using the
regional climate model REMO with 0.5° Lon/Lat resolution.
The ECHAM5 simulations covered the 20 th century climate
and the future climate using greenhouse gas emissions
defined by the SRRES A1B and B1 scenarios up to 2100,
the REMO simulations covered the period 1960-2050.
Details about the REMO climate simulations may be found
in Paeth et al. (2005) and Paeth et al. (2009).
For Morocco, climate simulations for the 21 st century reveal
a continuation of the drying trend, which can already be seen
for the 20th century observations. A classification of the
Koeppen climate zones is presented in Fig. 2. The climate
model data show a considerable dry bias compared to CRU
TS2.1. An analysis of wet and dry periods for Morocco
suggest that this is due to an increase of the number and
Figure 2. Koeppen climate classification for CRU
TS2.1 data and for REMO regional climate
simulations.
For smaller scale regional climate scenarios, statisticaldynamical
and statistical techniques were applied in order
to circumvent the large computational effort. In this step,
first the COSMO-LM – embedded in REMO model output
and into analysis data – has been applied for single years
under present day and future climate conditions. The grid
spacing was 0.25°, 0.1° and 0.0625° on a rotated grid,
corresponding to about 27 km, 11 km and 7 km,
respectively. From these simulations, shorter episodes
have been simulated with 3km and 1km resolution using
FOOT3DK, which was nested into the COSMO-LM. The
episodes were chosen to be representative for typical,
climate relevant weather situations and could be
“recombined” using weights depending on frequencies of
occurrence in order to estimate patterns of small-scale
climatic scale.
Alternatively, the dynamic and statistical-dynamical
approaches have been supplemented by a statistical
regionalization method. This had to be applied because (1)
climate model data and observations have – especially
with the focus on hydrological modeling – dramatically