climate system analysis group simulating the characteristics of extreme rainfall events in southern...
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Climate System Analysis Group
Simulating the Characteristics of Extreme Rainfall Events in Southern
Africa using Regional Climate Models
Babatunde J. Abiodun
Sabina Abbar Omar and Arlindo Meque
Climate System Analysis Group (CSAG)Department Environmental and Geographical Science
University of Cape Town (South Africa)
Presented by: Kamoru A. Lawal
Climate System Analysis Group
Study Domain: Southern Africa
Cape Town Western Cape
Mozambique
Climate System Analysis Group
City of Cape Town
Climate System Analysis Group
Impacts of Extreme Rainfall Events in Cape Town
Climate System Analysis Group
Impacts of Extreme Rainfall Events in the Western Cape
• Displacement of communities
• Damages to infrastructure
• Loss of lives
Damaging extreme rainfall event remains a big threat in the Western Cape.
Climate System Analysis Group
Causes of Extreme Rainfall in the Western Cape
•Kalahari trough
•Mid-latitude cyclone
•Cut-off low
•Tropical Temperate Trough
•Agulhas Current
Climate System Analysis Group
Aim and Objectives
• Examine the capability of regional climate models (RCMs) in simulating the characteristics of widespread extreme rainfall events (WERE) over the Western Cape
• Examine how GCM boundary forcing may alter the characteristics of the simulated WERE.
Climate System Analysis Group
Simulation and observation Datasets
SMHI-RCA
PRECISREMO
CRCM5
RACMO
CCLM
ARPEGE
ERAINT
CCMA
NCC
ICHEC
MIROC
MPI
CNRM
REGCM3WRF
CORDEX RCMs
SMHI-RCA
TRMM
GPCP
ERA-Interim
Climate System Analysis Group
• Extreme rainfall event: defined at each grid point as rainfall above the 95th percentile of daily rainfall at the grid point
• Widespread extreme rainfall event (WERE): defined as a simultaneous occurrence of extreme rainfall events over at least 60% of the Western Cape area (i.e. about 60 grid points).
Methods
Climate System Analysis Group
Simulated and observed threshold of extreme rainfall over Southern Africa (mm/day)
•There are notable differences between GPCP and TRMM results
•Only four RCMs (CRCM5, RCA3,WRF and REMO) perform better than ERAINT in simulating the observed threshold pattern
Climate System Analysis Group
Frequency distribution of rainfall over the Western Cape
Climate System Analysis Group
Seasonal distribution of widespread extreme rainfall over the Western Cape
•GPCP and ERAINT report different total number of WERE.
•Among the RCMs, PRECIS reports the highest number the WERE, while CCLM reports the lowest number.
Climate System Analysis Group
The classification of the observed and simulated WERE, using the Self Organizing Map (SOM), shows four main groups of WERE over the Western Cape
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Climate System Analysis Group
The frequency of WERE in each SOM node as observed (GPCP and TRMM) and simulated (ERAINT and RCMs).
Climate System Analysis Group
The sensitivity of RCA-simulated WERE over the Western Cape to GCM forcing
All the WEREs are link to mid-latitude rainfall activities
Climate System Analysis Group
Conclusion• Only four RCMs perform better than ERAINT in
simulating the threshold of extreme rainfall over Southern Africa
• All RCMs underestimate the extreme rainfall threshold over the Western Cape
• The RCMs perform very well in simulating the seasonal variation of WERE over the Western Cape, but perform poorly in simulating the inter-annual variability.
• When forced with ERINT, all RCMs reproduce the four main pattern of WERE in the Western Cape, but when forced GCM, RCA model reproduces only one pattern.
