EVALUATING INVESTMENT IN FLOOD PROTECTIONAT RIVER BASIN SCALE

TRANSDISCIPLINARY APPROACH, DISASTER RISK REDUCTION,RECOVERY/ RECONSTRUCTIONSENDAI, MARCH 10, 2023

Mikio Ishiwatari

The University of Tokyo / JICA

Masashi Sakamoto, and Daisuke
Sasaki,
IRIDeS Tohoku Univ.

This research is a part of the project “Research on Demand Estimate
on Infrastructure in Asia” by the JICA Ogata Research Institute.

CONTENTS
1. Introduction
2. Economic benefits of flood protection in Sendai City
3. How to share benefits and costs among multistakeholders

I. INTRODUCTION

1. INTRODUCTION
 Disaster risk reduction (DRR) Investment
 crucial for decreasing damage
 Information is essential for formulating investment policies and financial
arrangement

However, Scale and effect of DRR investment are not clear
1. how much are countries investing?
2. how much do countries need in future?
3. how much return can be expected from investment

INTERNATIONAL ARENAS
 Sendai Framework for DRR, adopted at 3rd UN World
Conference on DRR in Sendai in 2015: investment as a priority
action Copenhagen Accord, COP in 2009: set a target of $100 billion
per year by 2020 to support mitigation and adaptation measuresin developing countries
 Kumamoto Declaration, adopted at 4th Asia-Pacific Water
Summit in 2022 by the participating leaders, double investment tosolve water issues.

PURPOSE This study aims at proposing methodologies for estimating thebenefits for flood protection infrastructure in river basin scale
 Case study in Sendai City, Natorigawa River BasinII. ECONOMIC BENEFITS OF FLOOD
PROTECTION IN SENDAI CITY8CASE OF NATORI RIVER, SENDAI CITY

Natorigawa
River basin• river basin: 939 km2
including Sendai City• main channel: 55 km.
• 76% mountain forests,
12% agricultural land
12% urban areas.
• Population; 1.1 million

Concept of economic analysis for long-termand large-scale investment
Past

Benefit

Evaluation time

Reducing damage costs caused
by major flood disasters
Construction period

Cost

Dam and dike
construction

FutureReducing damage costs causedby expected floods according toprobability
Depression period of facilities
50 years
Operation and maintenancePast cost

To collectconstruction
costs

FuturecostPast benefits

Socio-economic, hydrological, & geographical data
To simulate
inundation by
TyH withoutstructure

To assessO&M costs

Flood volume

Deflatorsocialdiscountratio

CostTOTAL
COST

To simulate inundation by 1/150
scale flood without structure
To estimate
damage by
1/150 scale flood

To estimate
damage by TyH

decided byratios with TyH

Cost

Future benefits

Urbanization
ratio

Costbenefit ratio

To estimate
damage foreach majorflood

To estimate
damage for 1/20
-1/100 floods

Benefits

EAD reductionTOTAL
BENEFIT

Damage ratio
against target
safely scaleunderstructure
constructedSocialdiscount ratio

1. Benefits
floodprotection
projectstockeffectdirectdamagebenefit:effect ofdamagereductionfloweffecteffect of
upgradingland use

reducing property
damagereducing death andinjury
reducing businessinterruption

indirectdamagereducing
secondary damage
reducing mental
damagereducing otherdamage

2019 TYPHOON HAGIBISWITHOUT INVESTMENT

岡田小Estimated damage
350billion JPY
郡山小(2.5 billion USD)
one-third budget of Sendai
Inundated houses 150,000

中田中

六郷小

四郎丸小

Flood depthTagajo City

Tagajo City
Aoba ku

Inundation simulation
Typhoon No. 19 in 2019

1/150 scale flood

Aoba ku

Miyagino ku

Miyagino ku

L-1

L-1
Wakabayashi ku

Wakabayashi ku

L-2

L-2

Taihaku ku

Taihaku ku

R-1

R-1

LegendInundation Depth

Natori City

~ 0.5m

Iwanuma
City1

Inundation Depth~ 0.5m

0.5~2.9m

0.5~2.9m

3.0~4.9m

3.0~4.9m

5.0m ~0Natori City

Legend2

34km

Iwanuma
City5.0m ~01

2

34km

Total past Benefit: 3.7 trillion JPY (26.4 billion USD)
Flow
Ratio ofRatio ofBenefit(With urbanization )volume volume toresidential(m3/s) Typ. Hagibis land to 2019 (present value)
August 1986
August 1989
September 1994
July 2002
September 2011
September 2007
October 2019
Base case
Total

2,690
3,280
2,270
2,920
2,180
2,740
3,300

0.82
0.99
0.69
0.88
0.66
0.83
1.00

0.76
0.84
0.89
0.92
1.00
1.00
1.00

---

(Million JPY)

754,952
903,576
544,042531,950
302,755
325,276
348,269

3,710,819

Future benefits: 112 billion JPY (8 billion USD)
• average expected annual damage (EAD) reduction for 50 yrs• base case: Flood protection works with the safety level of1/150 yr flood• The amount of EAD reduction for 10 flood scales based on 10
probability years selected• multiplied by the interval probability to obtain the annual
EAD reduction.

Million JPY
10,000 USD

2. COSTS: LONG-TERM INVESTMENT IN FLOOD PROTECTIONTOTAL: 610 BILLION JPY, OR 5.5BILLION USD
SOME HALF OF ANNUAL BUDGET OF SENDAI,

1941-2018 CURRENT PRICE
2-7 billion
JPY/ yr

1 billion
JPY/ yrTotal benefits

3.81 trillion JPY (26.4 billion USD)

Total costs

626 billion yen (4.4 billion USD)

Cost-benefit ratio B/C

6.1

III. HOW TO SHARE BENEFITS AND COSTSAMONG MULTI-STAKEHOLDERS

1. WHOLE-A-SOCIETY FOR INVESTING IN DRR
Local community
Local government
National government

ROLE OF LOCAL COMMUNITY IN SENDAIOPERATING GATEWOMEN LEADERSENDAI IWAKIRI ELEMENTARY SHOOLANY CHANCE OF INVOLVING PRIVATE FINANCE?
KAWAMACHI TERRACE IN NATORI CITY

2. Concept: financing investment in DRR

Ishiwatari, M., & Surjan, A. (2019). Good enough today is not enough tomorrow: Challenges of increasing
investments in disaster risk reduction and climate change adaptation. Progress in Disaster Science,25 1,

IV CONCLUSION

consideration
Issues to apply developing countries• computer resources• the datasets of hydrology, geography, and socio-economy.
Limitation• Replacing cost
• Attracting investment• Climate change

CONCLUSION
proposed methodology of economic analysis for long-term
investment in flood protection in the past at river basin scale.
for assessing the past and future benefits
consider effects of past urbanization and inflation.
Natorigawa River basin including Sendai City, Japan
70 years investment was efficient with cost-benefit ratio of 6.1
28

THANKYOUISHIWATARI.MIKIO@JICA.GO.JP