SoCoCa Workshop: Oslo, Norway, March
19th – 20th , 2013
Simulation of extreme rainfall
events over Southern Africa using
RegCM4
Ismaila Diallo and Filippo Giorgi
Earth System Physic section, The Abdus Salam ICTP, Trieste, Italy
idiallo@ictp.it
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Introduction
South Africa receives about 60% of its total rainfall during the austral
summer season (December-January-February, DJF) except for
southwestern region and along the south coast and has large spatiotemporal variability.
Performance of summer rainfall is much important for the population of
this region due to the agriculture dependence economy.
Due to its subtropical location, South Africa comes under the influence of
both tropical and mid-latitudes dynamics. This region comes also under
the influence of both Atlantic and Indian ocean.
This complexity makes difficult for a reliable simulation of summer
rainfall and temperature as well as the related circulation features.
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Recently RCM model has been increasingly used for downscaling studies
over southern Africa (eg. Ratnam et al. 2011; Cretat and Pohl, 2012; Sylla
et al. 2012).
These studies used a lower resolution and none of them downscaled a GCM
Ability of RegCM4 to capture and predict the daily extreme events
during the austral summer season (DJF)
(1) How well this indices are
captured over SA
(2) How they are projected to
change during the early future
Model set up…
 RegCM4: Giorgi et al. 2012
 A countunious simulation of 40 years : 1990-2029
Grell /Fritsch and Chapell
 CAM4 0.9x1.25 deg.
25km and 18 vertical levels
 Present day and future under RCP4.5
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 Validation data
GPCP (2.5 x 2.5°) 1990-2009 period
 Monthly data
UDEL (0.5 x 0.5°) 1990-2009 period
ERA-Interim reanalysis (1.5 x 1.5°)
 Daily rainfall: TRMM (0.25 x 0.25°) and GPCP1DD (1 x 1°)
 Indexes
CDD: days
R< 1mm/day
R20mm: days
R>=20 mm/day
CWD: days
R>=1 mm/day
Frequency
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 Temperature climatology: CAM4 vs RegCM4
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 Rainfall climatology: CAM4 vs RegCM4
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 Wind and mixing ratio climatology: CAM4 vs RegCM4
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 Mean Annual Cycle over Homogeneous Climate Sub-regions:
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 Mean
intensity and Heavy rainfall (R20):
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 CWD and CDD: CAM4 vs RegCM4
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 Temperature Change: CAM4 vs RegCM4
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Rainfall change: CAM4 vs RegCM4
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 Change in CWD and CDD: CAM4 vs RegCM4
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Conclusions
 RegCM4: captures fairly well the mean spatial and annual cycle as well as the
associated circulation.
 RegCM4 outperforms CAM4 over SA.
 RegCM4 is a valuable tools for downscaling CAM4 over SA
 The projected change shows a warming up to 2 °C for the period 2011-2029
compared to the present day (1991-2009) almost everywhere over Southern Africa.
 Precipitation is also predicted to increase in regions such us northward Malawi
and South DRC.
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