bangladesh presentations flooding nabiul islam

8/3/2019 Bangladesh Presentations Flooding Nabiul Islam

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Urban and Non-agriculturalImpacts of Flooding Methods ofAssessments and VulnerabilityAnalysisK. M. Nabiul Islam

Senior Research FellowBangladesh Institute ofDevelopment Studies (BIDS)


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2

Urban and Non-agriculturalImpacts of Flooding Methods ofAssessments and Vulnerability Analysis

STRUCTURE OF DISCUSSION

I. Impacts of urban Floods

II. Flood Loss Assessment Methods

III. Vulnerability Analysis

IV. Urban Floods : Related Issues(e.g. poverty, adpatations)


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Paper highlights urban flood impacts at

micro- & macro level. It discusses econ.linkages & multiplier effects, interface offloods with poverty.

Briefly discusses impact assessmentmethods suitable for Bangladesh. Inprocess, it identifies various econ. sectorsthat are more vulnerable, drawing onexperience from recent vulnerability studyconducted in India.


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Fig 1: Rising trend of economic losses in Bangladesh

Economic Losses (US $ Million: current values)

936 1167 14242201 2067

0100020003000

1974 1987 1988 1998 2004

Flood years

Million

Fig 2 : Trend in urbanization, Bangladesh

0

20

40

60

80

100120

140

160

1951 1961 1974 1981 1991 2001 2007

0

5

10

15

20

25

30

Population Urban Population Urban population (%)

Population(million)

Urbanpopulation

(%)


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IMPACTS OF CC & SLR on FLOODING

CC will lead to uncertainity in rainfalls

- So, floodings will also be uncertain. Recurrence for 1998 flood (90 Yr Flood) is likelyto be reduced to 30 years in 2020s, and 15 yearsin 2050s.

Drainage congestion likely to be aggravated bySLR

Inundated areas will increase Frequency will increase.

So, increase in flood severity, on one hand,and faster urbanization due to in-migration,on the other, are great concern forcountries e.g., Bangladesh


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Confronting CC risks for fast changing urbansettings is a challenging task

- however, we cannot reverse the situation.

- what can be done is to respond/adjust to situation.

Most important way of confronting the alarming situationis to obtain

- a better understanding of climate change & its

dynamics, which is linked to water/flood management.- to improve on knowledge of how natural hazardsmagnified by urbanisation & climate change can causehavoc to lives & property

this is crucial for taking calculated action, especially inthe context of

- land use planning, resilience-building, emergency

planning & management & reducing vulnerability


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1. FLOOD LOSS TO

NON-AGRICULTURAL SECTOR

Flood loss to non-agri. sectors areenormous

In 2004 flood, non-

agri. sectorssuffered lossaccounting for74%, with 26%

suffered to agri.sector (crop + non-crop).

Similarly, 2007 Sidr :

- Non-agri = 72%

1998 Flood 2004 Flood

Sector % oftotal

damage

% of

total

damage

Infrastructure 51 74

Agricultural 49 26

Total 100.0 100.0

Flood damage to selected sectors


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Fig 3: % of agri. & urban flood loss

Potential urban flood loss gettingincreasingly important, especially inwake of CC & SLR.


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2 . Flood Loss Assessment Methods Flood research - advanced-countries oriented

As in other developing countries, flood research inBdesh limited to appraisals - focusing on agri.

Bangladesh has serious lack of damage data& methodology for flood loss assessment.

As a result, loss assessment have been basedon arbitrary methods, e.g., in 2004 Flood,Estimate ranging from 10,000 crore to 42,000crore Taka.

Important to build knowledge & data networksTo enhance economic and social resilienceSo, it explores applicability of advanced countries-oriented methods for Bdesh


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3. Flood Impacts Methods in UrbanBangladesh at Micro Level

2 Modelling Flood Impacts

Basic structure of modelling: Employs combinationof (1) unit-loss method (2) Cobb-Douglas model(3) multiple regression (4) input-output model (Fig4-6) for

1) direct loss 2) primary indirect loss & 3) multipliereffects.

Direct loss model

Direct loss model uses multiple regression by

dam. components (e.g. struct. Inventory, m/c &stock to estimate at disaggregated levels ofdepths/durations.

Model can use either absolute or proportional

damages.


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Indirect Loss Model

Indirect loss model has 2 components:

(1) through Cobb-Douglas production function(2) Linkage Effects or Multiplier Effects through Input-output model.

Cobb-Douglas model is based on Cobb-Douglas prod.

function, which is of form: Qt = At Kt

Lt

Once function is estimated for before-flood situation,primary losses to output due to flood can be estimatedthrough imputing reduced capital & labour

This way STANDARD DEPTH DAMAGE DATA SETSARE CONSTRUCTED- Data sets used to carry outnational flood loss assessments in 1998, 2004


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Fig 4: Flood Loss Model : Model 1


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Fig 5: Flood loss model 2


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Fig 6: Flood Loss Model: Model 3


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4.Vulnerability Analysis of Urban Sectors

Unit-loss Models

Unit-loss model, as widely used in USA/UK,involves, first, identify flood prone propertiesaccording to land uses, & estimate property floorheights. Through an interactive computer model(used in UK/USA; SPSS used in Bdesh/India)the model then employs standard potentialdepth-damage data & frequency analysis offlood levels, to estimate flood damage potentials

in an area under study for floods of variousmagnitudes


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Fig 7: Unit-loss Model (Modified from Parker et al.1987)

SELECTION OFOPTIMUM SCHEME

SPECIFYBENEFIT AREA

SITE SURVEY

INTERVIEW HYDROLOGICAL SURVEY AREA SURVEY

- HOUSE HOLD

-INDUSTRIES

- BUSINESS

- OFFICE/ROAD

AVERAGE

DAMAGE DATA

FLOOD LEVELRECORDS

FREQUENCYANALYSIS

LAND USE CODE

L USE SURVEY

LEVEL SURVEY

PROPERTIES

FLOOR HEIGHTUNIT BY UNITDAMAGE ESTIMATES RANGE OF

SCHEMES

EXPECTED ANNUALVALUE OFBENEFITS*DISCOUNT

COSTOF

SCHEMES DISCOUNT

PRESENT VALUE

OF BENEFITS

PRESENT VALUEOF COSTS

COMPARE BENEFIT& COST FOR

DIFFERENT SCHEMES

COST BENEFIT

ITERATIONS

*Tangible benefitsPRINCIPAL CONCERN OF LOSS/BENEFIT ASSESSMENT


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Thus, for any econ. orvulnerability analysis of anyfloodplain management, the

single most essential figure is theestimate of Expected AnnualDamage (EAD), which is theultimate output of the unit-lossmodel.


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Unit-loss model is proved to be suitable invulnerability analysis in Bdesh/India

modeling regional impacts and therebyappraise urban protection schemes, throughuse of SPSS. Only recently, the model has

been applied to Indian state of Gujarat in 4cities (Ahmedabad, Surat, Rajkot &Vadodara)to 3.3 million urban properties to assessvulnerability analysis of various urban sectors(to prepare cities disaster plan, sponsored byWBank). The Model also going to be used forHo Chi Minh City soon.


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Land use and height survey

The land use survey classifies properties intomajor sectors (e.g., residential, business,industry, office and roads), ideally, each havinga geo-reference as to the location of the

properties. Land use survey is followed by afloor height survey of individual properties, whichis of key importance to the precision of flooddamage assessments.


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Area approach and valuation approach

Both area (carpet area) & valuation (value of

properties) approach can be adopted,depending on the data availability but the lateris ideal

Calculation of flood damages by return period

Empirical relationships (Damage data sets)are combined with the flood conditions, &with land use information & hazard intensityto arrive at vulnerability for each area or foreach broad sector for each of selected floods

(with different return periods).


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Estimation of Expected Annual Damage (EAD)

Relationships bet. return period/flooddamages are converted into prob.

density functions & latter is integratedbetween various return periods. Ofcourse, one has to incorporate, as well,the future vulnerability, fragility andexposure into the assessment.


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Fig 8 : Estimation of Expected Annual DamageTrapezoid Rule : Divide curve into series of trapezoids, each with area =(average

height)(width) EAD = Area under curve = Sum the areas of the strips.

=(B6+B5)/2*(A6-A5)

=SUM(C5:C10)

Area under curveTrapezoid Rule, Method 1

x y trapezoid

1 0 32 6 11

5 16 23

10 30 39

25 48 59

50 70 83

100 96

area 218 0

20

40

60

80

100

120

1 2 5 10 25 50 100

Flood Years

Exceedance probability

.50 .50 .10 .05 .02 .01.1

Hypothetical

Damage


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5. Interface of Flooding with Poverty

Empirical evidence shows that low-income occupants

are relatively more vulnerable to floods. Lower level of income higher percentage of damages to

their total asset values (Table 1). On average, poorest-type house suffers (in proportional

terms) 4, 5 & 3 times as much, compared to that suffered

by a richest-type house, in river, flash & tidal flood. Floods not only deepen poverty levels but also may help

widen income gap between rich & poor.

Another analysis shows that land poor HH (also lower

income categories) suffer higher inundation levels & arehence more exposed to flood risks.

An analysis on WFP data for 92 UZs shows a closepositive relationship between percentage of floodedareas & percentage of ultra people (r=0.33, p < 0.001).


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Table 1: FLOOD AND POVERTY

House type/ Socio-econ.Groups

Damage as % of property

value

River

flood

Flash

flood

Tidal

flood

BB (High-income )

7.3 6.2 22.5BC (Middle-income) 10.7 NA 32.1MC (Lower -income) 11.2 11.6 55.0

MT (Lowest-income) 26.2 30.7 64.1ALL 10.2 11.4 33.6


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6. Selected Adaptation Options Flood loss potentialsto roads & highwaysinfrastructure have

been huge.

- Protecting nearly 21,000 km of R & H is of primeimportance for national economy.- An analysis (DFID) shows that flood proofing of R & Hwould Pro Poor & economically efficient.- Best estimate of B-C ratio is found to be 1.7 (at12%)

- The option will also bring other socialbenefits (intangible),in terms of (1) saving human lives/livestock (2) use as refuge(3) damage saving of inventory (4) employment generation &poverty reduction, & (5) facilitation of movement of reliefgoods during flood emergencies.

Thesecond optionrelates to flood proofing of individualhomesteadsby means of constructing raised platforms- Again best estimate of B-C ratio is 1.9 (at 12%)- Besides, the option will crate additional employment,thereby contributing to poverty reduction (Fig 9).


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Fig 9: Women involved in homestead raising


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7. Concluding Remarks It is high time to act now to avoid the very worst

impacts of climate change.

Important link exists between spatial planning/urbanplanning and Flood Risk, via land use, zoning violations,illegal economic activities, urbanization, loss of infiltration

capacity, reduced storage for flood waters, worsened by CC A comprehensive prior knowledge of the

dimension/magnitude of urban flood damage is crucial fortaking calculated action

Some floods in agricultural sector can be adjusted while

urban & non-agricultural flood losses are enormous. Hence,greater attention has to be given on urban flood hazard.


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Floods not only deepen poverty levels but alsohelp widen income gap between rich & poor.

Distributional effects are important as, these arerelated to equity, which, in turn, is associatedwith sustainability of economic development.

Primary & long run indirect effects of floods onpoor need careful consideration whenformulating mitigation plans.


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Many problems still to come Avoid multiplying the problems Avoid problems with new developments- Coordinated efforts in urban infrastructure devlpment,- Proper spatial planning, Zoning- Enforcement of land development regulations,

land conservation- No Space for Water, no space for people- Integrate Spatial planning with Water/Flood Mngement

IT IS TIME TO ACT BEFORE IT IS LATE


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bangladesh presentations flooding nabiul islam

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