Exposure to Severe Weather Events:
A review of recent experience in the
Western Cape
Ailsa Holloway, Gillian Fortune,
Disaster Mitigation for Sustainable
Livelihoods Programme
University of Cape Town
September, 2009
Presentation Focus
Southern Cape 2006
• Role of ex post analysis in
managing climate risk
• Overview of recent severe
weather in Western Cape
• Reflection on severe
weather & consequences for
flood risk management.
• Unpacking ‘ causal chain’’
between ‘development’ and
severe weather impacts
Knysna 2007
Port Shepstone 2008
Managing Risk – Role of Ex Post Analysis
• Risk is a probalistic
concept – about a
future negative
outcome (it has yet to
happen)
• ‘Ex post’ disaster
event research
analyses actual
events that have
happened.
It provides useful insights about:
– What/who resists and what fails in a
severe weather event. The ‘what’,
the ‘where’ and the ‘when’ and the
‘who’
– How much this costs
– The causal chain that leads to the
loss (ie the mix of risk factors) the
‘why’ and the ‘how’
– Ex post research studies actual
disaster events to guide risk averse
development
Severe Weather Events for 2003,
2004, 2005, 2006, 2007 and 2008
2003
241 mm
2004
218mm
2005
228mm
2006
324mm
2007 - June
150 mm
2007 - Nov
206 mm
2008 - July
93 mm
2008 - Nov
150 mm
Severe weather events - costly for W. Cape
Date
Mar 2003
Area most affected
Eden
Dec 2004
Apr 2005
Aug 2006
Eden
Overberg
Eden & Overberg
> 60.0
5.0
510.5
Jun 2007
Nov 2007
Jul 2008
West Coast
Eden & Overberg
West Coast
128.3
1.2 bn
74.1
Nov 2008
Overberg & Cape
Winelands
943.0
Total
Four districts
Loss (R. Mil)*
212.4
R 3 bn
in 6 yrs
Focus on Cut-off Lows Affecting Eden
ie Prov. Depts and Municipal Impacts
Prov
Depts
Municips
in Eden
2003
Mar
2006
Aug
2007
Nov
2008 Total
Nov (R. m)
172.7
248.6
784.4
865.3 2.1 bn
4.5
98.2
348.3
1.9
Severe weather losses 2003 - 2008
452.9
Provincial losses are substantial (2003, 2006 &
2007 weather events total R 1.2 bn)
Prov. Dept
Housing
Agriculture
Cape Nat.
Education
Prov Roads
Public Wks
Social Dev.
Total
2003
2006
2007
Total
0.0
28.9
187.5
216.4
89.6
109.9
178.9
378.4
1.1
3.4
8.0
12.5
1.7
2.6
78.6
90.8
0.0
13.0
1.6
0.00
1.4
3.0
172.6
248.6
784
1.2 bn
4.3
408.2
577.6
13.0
A Review of Ten Damage-Bearing Severe
Weather Events Since 2003
Cape Town
August 2004 and 2008
W. Coast
June 2007, July 2008
Winelands/
Overberg
March 2003, April 2005,
November 2008
Eden
December 2004, August 2006
November 2007
Cape Town – August 2004 and 2008
A little history…
Image from 23
June, 1904
62.5 mm fell in
one hour
100 years later…
5-9 August 2004 (2 large cold fronts)
• Resulted in flooding in
Maitland, Woodstock,
Pinelands, Athlone,
Bonteheuvel, Nyanga,
Guguletu and
Somerset West
(Mainly Salt Water
Catchment)
• Peak rainfall
intensities over 3 hr
durations exceeded
100 year storm
Athlone (67mm) &
Pinelands
Source:
CoCT in 2004 (62
Stormmm)
Report on www.egs.uct.ac.za
Cape Town Superstorm, 30-31 August 2008
100mm
24 hour rainfall, 30 August
2008 (46% August
monthly rainfall – 24 hrs)
Source: Thea Beckman, UCT
Storm surge > 5 m and wave heights > 7
metres; Images www.news24.com
West Coast June 2007
6-11 June (Cut-off low), 25-26 June (Frontal system)
• First event … rainfall over
Bergriver Municipality > 130
mm (but total rain 280318mm); Swartland (120mm)
Saldhana Bay (110 mm)
• Second event … Rainfall over
Witzenberg Municipality > 50
mm
• Combined totals for June
2007 … 200 mm greater than
mean historical average
Roode Els Berg 289 mm
Assegaibos
328 mm
Ceres
394 mm
Hawequas
219 mm
Jonkershoek
198 mm
West Coast and Western Winelands
4 – 9 July 2008 (Cut off low)
• Most striking feature – long
duration of heavy
precipitation.
• Wettest July in recent
history for Ceres, Roode
Els Berg
• July 2008 totals were
300% (Roode Els Berg),
145% (Assegaibos) and
200% (Ceres) of July mean
rainfall
2003 and 2005 Winelands and Overberg
Cut-off Lows
• 22-25 March 2003
‘Montagu floods’
241 mm in Montagu,
(Kingna River – mainly
responsible for
flooding)
160 mm in
Swellendam
• 10-12 April 2005,
‘Bredasdorp flood’
228 mm rain
11-13 November 2008 Cut off Low –
Overberg and Winelands
• Meterologically, less significant than 2007
cut-off low during the same month.
• However, still significant losses – and
research now ongoing
Korinte-vetdam
281 mm
Hawequas Forest 250 mm
Eden - December 2004, Jul/August 2006,
November 2007 Cut-off lows
21 – 23 December
2004 (Heidelberg 168
mm, Knysna 219 mm)
Flood line inside a house on
the Duiwenhoks River
Jul/August 2006
George Rainfall
31 Jul – 4 Aug 2006 328 mm
PLUS
21 – 24 Aug 2006
118 mm
Total
446 mm
2006 Cut-off low profiled exposures
generated by non-perennial floodways that
flash-flood in a severe weather event
Source: Xavier Middleton
It also indicated the role of increasing
urbanisation in George Municipality from 1957
to 2004…
1957
1957 to 1985
1985 to 2004
Increased by 728.28
hectares from 1957 to 1985
Source: Xavier Middleton
Increased by 7,488.4
21-22 November 2007 Cut-off Low
This 3-day event
created new rainfall
records for areas it
affected:
Contributed over 70%
to highest November
total rainfall in the last
30 years
Assegaibos – 500%
and George 530%,
respectively of the
November mean.
Wolwedansdam 316 mm
George
333 mm
Institutional risk factors (ie
under- investment in municipal
maintenance)
Planned Per
Capita
Expenditure
S
Municip.
Bitou
2006-2007
Pop.
Gross Econ
Loss
[Million
ZAR]
Econ. Loss
[ per cap]
Maintenance
& Repair
[per cap]
34 859
0.88
25.16
447.61
George
154 828
16.7
107.81
284.58
Knysna
55 057
33.0
599.35
164.44
Mossel Bay
80 999
15.5
190.85
246.55
Oudtshoorn
93 917
7.0
74.26
419 660
73.4
174.86
Total
Investments in municipal
maintenance are
protective and reduce
losses
700
600
500
400
300
200
100
0
Bitou
George
Knysna
Mossel Bay
Oudtshoorn
700
600
500
400
300
200
100
0
500
400
300
200
100
0
Bitou
George
Knysna
Mossel Bay
Per Capita Maintenance/
Repair
Per Capita Economic Loss
Per Capita Economic Loss
Per Capita Maintenance/ Repair
Oudtshoorn
Per Capita Economic Loss
Per Capita Maintenance/ Repair
To conclude:
• Severe weather is a reality for us in the
Western Cape – no region can be
complacent.
• There has been impressive improvement
in managing severe weather since 2003 …
especially in mobilising following warnings.
• However… still a long way to reducing
climate risk developmentally..