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ENSEMBLES regional climate model simulations for Western Africa (the
“AMMA” region)
Markku Rummukainen 1 , Filippo Giorgi 2 and the ENSEMBLES RT3 participants
1 SMHI, SE-601 76 Norrköping, Sweden. Markku.Rummukainen@smhi.se
2 ICTP, Strada Costiera 11, IT- 34014 Trieste, Italy
1. Introduction
This presentation introduces and discusses common aspects
and lessons learnt in a co-ordinated regional climate
modeling experiment for Western Africa, performed within
the EU Integrated Project ENSEMBLES, see e.g. Hewitt and
Griggs (2004), and collaborating with the AMMA project
(Redelsperger et al. 2006).
2. Regional climate and Africa
While the threat of climate change to Europe is real, the
threat to other regions of the world is far greater both from a
climate change perspective and due to vulnerability. This is
especially true for Africa, as is emphasized in Boko et al
(2007). At the same time, there is a deep lack of climate data
on regional and local scales both on the recent past and on
possible future conditions (cf. Christensen et al. 2007).
Whereas information on the recent past conditions is
important in characterizations of climate variability
including extremes, as well as in development and
evaluation of seasonal forecasting and impact models, future
projections in turn are needed for weather and water related
risk assessments and adaptation efforts. Estimates of
regional/local climate change are therefore an important
question for Africa.
3. ENSEMBLES regional climate modelling
One research theme of the EU Integrated Project
ENSEMBLES is on regional climate models (RCM). In
particular, there is co-ordinated experimentation with a
number of European and one Canadian RCM. These
simulations are made in two patches. One is for a recent past
period (not least for assessing RCM performance), using
global reanalysis (ERA40, Uppala et al. (2006)) data as
boundary conditions, in runs performed for Europe,
followed with climate change projections, with
ENSEMBLES global model projections providing the
boundary conditions, run mostly with the SRES A1B
emissions. Similar set-up is now made for Western Africa.
The ENSEMBLES regional climate model study covers the
so-called AMMA region. Again, there are two simulation
streams. The first one covers 1989-2007, relying on ERA-
Interim reanalysis data for boundary conditions (see
www.ecmwf.int). As for Europe, a second stream consists of
climate change projections, for the 1990-2050 period and
run at 50 km resolution, relying on few GCMs for boundary
conditions and again the A1B emission scenario
(Nakićenović et al. 2000).
The RCM runs for western Africa are performed by 11
regional climate modeling groups, with almost as many
RCMs (HIRHAM (in two versions), RCA3 (by two groups9,
RACMO2, RegCM, HadRM, REMO, PROMES, ALADIN
CY28T3, CCLM). Whenever possible, the models are run
with the same (minimum) domain with perfectly
overlapping grids (so as to provide for easier comparisons).
As some the RCMs have different co-ordinate systems,
some of the models have slightly different grids compared to
the body of the contributing models.
Figure 1. ENSEMBLES general Western Africa
minimum RCM domain.
4. ENSEMBLES – AMMA collaboration
The RCM simulations have been set up and are evaluated
in dialogue with the EU/AMMA project. Herein focus is
on one hand on relevant climate aspects for significant
impact applications, and on the other hand, the capture of
important climate phenomena in the region. Indeed,
whereas ENSEMBLES benefits from the experience of
applying the RCMs in another region, thus putting them to
test under a different climate regime (cf. Rockel et al.
2005), EU/AMMA gains a database covering the past two
decades and extending to the middle 21 st Century.
Compared to earlier, rather sporadic regional climate
model simulations for the region, this constitutes a major
resource for impact research.
5. Models and data
The RCM runs have been underway in 2008-2009.
Various evaluation data are collected. Especially the
databases collected by AMMA are valuable for this
purpose. The first analyses concerned temperature,
precipitation and surface energy fluxes. Some of the
comparisons were made for specific regions, such as river
catchments. Continued evaluation efforts are to extend to
look at the course and character of such meteorological
phenomena as the timing of the monsoon season, diurnal
cycles and variability on different scales.
In many respects, the RCMs exhibit skill in reproducing
the regional climate, but also deficiencies can be found.
These provide information for model development efforts
and also for identifying data needs.
6. Next steps
The ENSEMBLES RCM efforts will include joint
analyses and RCM intercomparisons for both the
simulations over the recent climate period (see above) and
the future scenario period. The model data will be
available for other researchers’ efforts, thus facilitating