Exposure to Severe Weather Events: Exposure to Severe Weather Events: A review of recent experience in the A review of recent experience in the

Western CapeWestern Cape

Disaster Mitigation for Sustainable Livelihoods ProgrammeUniversity of Cape Town

September, 2009

Ailsa Holloway, Gillian Fortune,Ailsa Holloway, Gillian Fortune,

Presentation FocusPresentation Focus

Knysna 2007Knysna 2007

Southern Cape 2006Southern Cape 2006

Port Shepstone 2008Port Shepstone 2008

• 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

Managing Risk – Role of Ex Post AnalysisManaging Risk – Role of Ex Post Analysis

• Risk is a Risk is a probalisticprobalistic concept – about a concept – about a future negative future negative outcome (it has yet to outcome (it has yet to happen)happen)

• ‘‘Ex postEx post’ disaster ’ disaster event research event research analyses actual analyses actual events that events that have have happened.happened.

It provides useful insights about:It provides useful insights about:– What/who resists and what failsWhat/who resists and what fails in a in a

severe weather event. The severe weather event. The ‘what’,‘what’, the the ‘where’ ‘where’ and theand the ‘when’ ‘when’ and theand the ‘who’‘who’

– How much How much this coststhis costs

– The The causal chaincausal chain that leads to the that leads to the loss (ie the mix of risk factors) the loss (ie the mix of risk factors) the ‘why’ and the ‘how’

– Ex post research studies actual Ex post research studies actual disaster events to guidedisaster events to guide risk averse risk averse developmentdevelopment

20032003

20042004

20052005

20062006

2007 - June2007 - June

241 mm241 mm

228mm228mm

218mm218mm

324mm324mm

2007 - Nov2007 - Nov

150 mm150 mm

206 mm206 mm

Severe Weather Events for 2003, Severe Weather Events for 2003, 2004, 2005, 2006, 2007 and 20082004, 2005, 2006, 2007 and 2008

2008 - July2008 - July

2008 - Nov2008 - Nov

93 mm93 mm

150 mm150 mm

DateDate Area most affectedArea most affected Loss (R. Mil)*Loss (R. Mil)*Mar 2003Mar 2003 EdenEden 212.4212.4

Dec 2004Dec 2004 EdenEden > 60.0> 60.0Apr 2005Apr 2005 OverbergOverberg 5.05.0Aug 2006Aug 2006 Eden & OverbergEden & Overberg 510.5510.5Jun 2007Jun 2007 West CoastWest Coast 128.3128.3Nov 2007Nov 2007 Eden & OverbergEden & Overberg 1.2 bn1.2 bnJul 2008Jul 2008 West CoastWest Coast 74.174.1Nov 2008Nov 2008 Overberg & Cape Overberg & Cape

WinelandsWinelands943.0943.0

TotalTotal Four districtsFour districtsR 3 bn R 3 bn in 6 yrsin 6 yrs

Severe weather events - costly for W. CapeSevere weather events - costly for W. Cape

* Not adjusted for inflation

Focus on Cut-off Lows Affecting Eden Focus on Cut-off Lows Affecting Eden ie Prov. Depts and Municipal Impactsie Prov. Depts and Municipal Impacts

20032003MarMar

20062006AugAug

20072007NovNov

20082008NovNov

TotalTotal(R. m)(R. m)

Prov Prov DeptsDepts 172.7172.7 248.6248.6 784.4784.4 865.3865.3 2.1 bn2.1 bn

Municips Municips in Edenin Eden

4.54.5 98.298.2 348.3348.3 1.91.9 452.9452.9

Severe weather losses 2003 - 2008Severe weather losses 2003 - 2008

Prov. Dept 2003 2006 2007 Total HousingHousing 0.0 28.9 187.5 216.4

AgricultureAgriculture 89.689.6 109.9109.9 178.9178.9 378.4378.4Cape Nat. 1.1 3.4 8.0 12.5

Education 1.7 2.6 4.3

Prov RoadsProv Roads 78.678.6 90.890.8 408.2408.2 577.6577.6Public Wks 0.0 13.0 13.0

Social Dev. 1.6 0.00 1.4 3.0

Total 172.6 248.6 784 1.2 bn

Provincial losses are substantial (2003, 2006 & Provincial losses are substantial (2003, 2006 & 2007 weather events total R 1.2 bn)2007 weather events total R 1.2 bn)

2007 losses up by more than five times March 20032007 losses up by more than five times March 2003

A Review of Ten Damage-Bearing Severe A Review of Ten Damage-Bearing Severe Weather Events Since 2003Weather Events Since 2003

Cape Town Cape Town August 2004 and 2008August 2004 and 2008

W. CoastW. Coast June 2007, July 2008June 2007, July 2008

Winelands/ Winelands/ March 2003, April 2005,March 2003, April 2005,Overberg Overberg November 2008November 2008

EdenEden December 2004, August 2006December 2004, August 2006November 2007November 2007

Cape Town – August 2004 and 2008Cape Town – August 2004 and 2008

A little history…

Image from 23 June, 1904

62.5 mm fell in one hour

100 years later…100 years later…5-9 August 2004 (2 large cold fronts)5-9 August 2004 (2 large cold fronts)

• Resulted in flooding in Resulted in flooding in Maitland, Woodstock, Maitland, Woodstock, Pinelands, Athlone, Pinelands, Athlone, Bonteheuvel, Nyanga, Bonteheuvel, Nyanga, Guguletu and Guguletu and Somerset West Somerset West (Mainly Salt Water (Mainly Salt Water Catchment)Catchment)

• Peak rainfall Peak rainfall intensities over 3 hr intensities over 3 hr durations exceeded durations exceeded 100 year storm 100 year storm Athlone (67mm) & Athlone (67mm) & Pinelands (62 mm)Pinelands (62 mm)Source: CoCT in 2004 Storm Report on www.egs.uct.ac.za

Cape Town Superstorm, 30-31 August 2008Cape Town Superstorm, 30-31 August 2008

Storm surge > 5 m and wave heights > 7 metres; Images www.news24.com

24 hour rainfall, 30 August 24 hour rainfall, 30 August 2008 (46% August 2008 (46% August monthly rainfall – 24 hrs)monthly rainfall – 24 hrs)Source: Thea Beckman, UCTSource: Thea Beckman, UCT

100mm100mm

West Coast June 2007West Coast June 20076-11 June (Cut-off low), 25-26 June (Frontal system)6-11 June (Cut-off low), 25-26 June (Frontal system)

• First event … rainfall over First event … rainfall over Bergriver Municipality > 130 Bergriver Municipality > 130 mm (but mm (but total rain 280-total rain 280-318mm318mm); Swartland (120mm) ); Swartland (120mm) Saldhana Bay (110 mm)Saldhana Bay (110 mm)

• Second event … Rainfall over Second event … Rainfall over Witzenberg Municipality > 50 Witzenberg Municipality > 50 mmmm

• Combined totals for June Combined totals for June 2007 … 200 mm greater than 2007 … 200 mm greater than mean historical averagemean historical average

Roode Els Berg 289 mmRoode Els Berg 289 mm

AssegaibosAssegaibos 328 mm 328 mm

Ceres Ceres 394 mm 394 mm

HawequasHawequas 219 mm 219 mm

Jonkershoek 198 mmJonkershoek 198 mm

West Coast and Western Winelands West Coast and Western Winelands 4 – 9 July 2008 (Cut off low)4 – 9 July 2008 (Cut off low)

• Most striking feature – long Most striking feature – long duration of heavy duration of heavy precipitation.precipitation.

• Wettest July in recent Wettest July in recent history for Ceres, Roode history for Ceres, Roode Els BergEls Berg

• July 2008 totals were July 2008 totals were 300% (Roode Els Berg), 300% (Roode Els Berg), 145% (Assegaibos) and 145% (Assegaibos) and 200% (Ceres) of July mean 200% (Ceres) of July mean rainfallrainfall

2003 and 2005 Winelands and Overberg2003 and 2005 Winelands and OverbergCut-off LowsCut-off Lows

• 22-25 March 2003 22-25 March 2003 ‘Montagu floods’‘Montagu floods’

241 mm in Montagu,241 mm in Montagu, (Kingna River – mainly (Kingna River – mainly

responsible for responsible for flooding)flooding)160 mm in 160 mm in SwellendamSwellendam

• 10-12 April 2005, 10-12 April 2005, ‘Bredasdorp flood’ ‘Bredasdorp flood’ 228 mm rain228 mm rain

11-13 November 2008 Cut off Low – 11-13 November 2008 Cut off Low – Overberg and WinelandsOverberg and Winelands

Korinte-vetdam 281 mmKorinte-vetdam 281 mm

Hawequas Forest 250 mmHawequas Forest 250 mm

• Meterologically, less significant than 2007 cut-off low during the same month.

• However, still significant losses – and research now ongoing

Eden - December 2004, Jul/August 2006, Eden - December 2004, Jul/August 2006, November 2007 Cut-off lowsNovember 2007 Cut-off lows

21 – 23 December 21 – 23 December 2004 (Heidelberg 168 2004 (Heidelberg 168 mm, Knysna 219 mm)mm, Knysna 219 mm)

Flood line inside a house on the Duiwenhoks River

Heidelberg Municipal Chalets 22 Dec, 2004

Jul/August 2006Jul/August 2006 George RainfallGeorge Rainfall31 Jul – 4 Aug 2006 328 mm31 Jul – 4 Aug 2006 328 mm PLUSPLUS21 – 24 Aug 2006 118 mm21 – 24 Aug 2006 118 mm

Total 446 mm

2006 Cut-off low profiled exposures 2006 Cut-off low profiled exposures generated by non-perennial floodways that generated by non-perennial floodways that

flash-flood in a severe weather eventflash-flood in a severe weather event

Source: Xavier MiddletonSource: Xavier Middleton

1957 to 1985 1957

1985 to 2004

It also indicated the role of increasing It also indicated the role of increasing urbanisation in George Municipality from 1957 urbanisation in George Municipality from 1957

to 2004…to 2004…

Increased by Increased by 728.28 728.28 hectareshectares from 1957 to 1985 from 1957 to 1985

Increased by Increased by 7,488.4 7,488.4 hectareshectares from 1985 to 2004 from 1985 to 2004

Source: Xavier Middleton

21-22 November 2007 Cut-off Low21-22 November 2007 Cut-off Low

Wolwedansdam 316 mmWolwedansdam 316 mm

George 333 mmGeorge 333 mm

This 3-day event This 3-day event created new rainfall created new rainfall records for areas it records for areas it affected:affected:

Contributed over 70% Contributed over 70% to highest November to highest November total rainfall in the last total rainfall in the last 30 years 30 years

Assegaibos – 500% Assegaibos – 500% and George 530%, and George 530%, respectively of the respectively of the November mean.November mean.

Institutional risk factors (ie Institutional risk factors (ie under- investment in municipal under- investment in municipal

maintenance)maintenance)

S

Planned Per Capita

Expenditure

2006-2007

Municip. Pop.

Gross Econ Loss

[Million ZAR]

Maintenance & Repair [per cap]

Econ. Loss [ per cap]

Bitou 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  

Total 419 660 73.4 174.86

Investments in municipal Investments in municipal maintenance are maintenance are protective and reduce protective and reduce losseslosses

0100200300400500600700

Bitou George Knysna Mossel Bay Oudtshoorn

Per C

apita

Eco

nom

ic L

oss

0

100

200

300

400

500

Per C

apita

Mai

nten

ance

/ Re

pair

Per Capita Economic LossPer Capita Maintenance/ Repair

0

100200

300

400

500600

700

Bitou George Knysna Mossel Bay Oudtshoorn

Per Capita Economic LossPer Capita Maintenance/ Repair

To conclude:To conclude:

• Severe weather is a reality for us in the Severe weather is a reality for us in the Western Cape – no region can be Western Cape – no region can be complacent.complacent.

• There has been impressive improvement There has been impressive improvement in managing severe weather since 2003 … in managing severe weather since 2003 … especially in mobilising following warnings.especially in mobilising following warnings.

• However… still a long way to reducing However… still a long way to reducing climate risk developmentally..climate risk developmentally..