Assessing the performance of CORDEX regional
climate models over Eastern Africa: Simulating
seasonal variability of rainfall associated with
ENSO and IOD
Hussen Seid
Supervisors: Bruce Hewitson, Chris Lennard & Frode Stordal
Department of Environmental and Geographical Science
University of Cape Town
19 Mar 2013
Outline
• Introduction
• Objectives of the study
• Data and methodology
• Results and discussion
Climatology
Interannual variability
Teleconnections
• Conclusion
Introduction
• Eastern Africa is characterized by complex topographical
features: High mountains, large inland lakes, coastal lines,
forests ....
• These features and their interactions with large-scale forcing
mechanisms significantly contribute for the diverse patterns of
rainfall over the region.
• The interannual variability of seasonal rainfall anomaly has
been shown to be teleconnected to SST (Ogallo et al., 1988;
Indeje et al., 2000; Omondi et al., 2012 & others.)
• Knowledge of these teleconnections is increasingly used to
provide better predictions of such rainfall anomalies.
Cont’d
• GCMs can satisfactorily simulate the atmospheric general
circulation at the continental scale, but not regional/local
detailed processes.
• RCMs are presently one of the fundamental tools used to
downscale global (large-scale) climate information to regional
scales.
• ...... they have the potential to provide insights into regional
scale responses to large scale climate dynamics such as ENSO.
• Therefore, for improving seasonal predictions, it’s critical to
evaluate and understand the limitations of RCMs in
representing the teleconnection signals.
Objectives of the study
• Main objective
To examine the ability of the RCMs to accurately reflect the
teleconnection signals originating from outside the regional
model domain.
• Specific objectives
To assess the performance of CORDEX RCMs based their
ability to simulate rainfall climatology.
To evaluate their ability to capture the interannual variability
of rainfall.
To examine their ability in capturing the responses between
two different phases of ENSO and IOD, and to assess the
relative influence of these events (ENSO and IOD) over the
region.
Model domain and study region
• Model Domain
24.64o W to 60.28o E
45.76o S to 42.24o N
• Study region (shaded):
22o E to 52o E
16o S to 18o N
• Boxes 4, 5 and 9 are area
of analysis (Favre et al.,
2011).
Data and methodology
• Model output
10 CORDEX RCMs
1989-2008 period
50 km resolution
forced by ERA-INTERIM
• Observed data
GPCC-Reference field
ERA-INTERIM
• Methodology
Time series analysis
(temporal & spatial
correlations are computed)
Composite analysis
Rainfall climatology during JJAS
Rainfall climatology during OND
Spatial correlation
•
Over R4 during JJAS CRCM5,
RACMO, RegCM3, RCA35 &
ensemble mean have high and
consistent correlation with GPCC.
CCLM & HIRHAM are weakly
correlated.
•
Over R5 during OND RACMO,
RegCM3 & the ensemble average have
relatively good and consistent rainfall
representation. CCLM, HIRHAM &
REMO have relatively low correlation.
•
Over R9 during OND all RCMs and
ERA-INTERIM had nearly same level
of consistency in representing spatial
distribution of rainfall.
Interannual variability
Model
R4
R5
R9
CCLM
0.46*
0.93*
0.69*
ARPEGE
0.56*
0.88*
0.91*
HIRHAM
0.71*
0.88*
0.68*
RegCM3
0.32
0.86*
0.39*
RACMO
0.69*
0.92*
0.77*
REMO
0.68*
0.77*
0.70*
RCA35
0.38*
0.86*
0.75*
PRECIS
0.68*
0.92*
0.79*
WRF
0.54*
0.90*
0.73*
CRCM5
0.58*
0.91*
0.88*
INTERIM
0.51*
0.91*
0.82*
ENSEMBLE
0.85*
0.95*
0.82*
Composite analysis
• Classification of ENSO and IOD events from 1989 to 2008 period (by
Meyers et al., 2007; Ummenhofer et al., 2009)
Pure NIOD
Pure La Niña
Pure PIOD
Pure El Niño
Co-El Niño
Co-La Niña
& PIOD
& NIOD
1989
1998
1994
-
1991
-
1992
1999
2004
-
1997
-
-
2007
-
-
-
-
• Composite analysis:
NiñoAno = Niño - Clim
Niño = El Niño composite value of rainfall for a given season
Climatology = the climatological average of rainfall for the same season
...........................
JJAS rainfall anomaly during pure La Niña
JJAS rainfall anomaly during the co-occurrence of El Niño
and positive IOD
OND rainfall anomaly during pure La Niña
OND rainfall anomaly during the co-ocuurence of El Niño
and positive IOD
JJAS rainfall anomaly during positive IOD
OND rainfall anomaly during positive IOD
Conclusion
• Most RCMs fairly simulate the rainfall climatology, and also
reproduce the majority of documented regional responses to
ENSO and IOD forcing.
• IOD has relatively weak and localized effect compared to
ENSO influence. The effect of IOD is relatively higher during
OND over equatorial and southern part of the region.
• Some regional climate models used outperformed the
ERA-INTERIM rainfall.
• The multi-model ensemble mean generally has better
agreement with GPCC than the individual models.