日本における洪水の適応策と緩和策の評価
Evaluation of adaptation and mitigation
to flooding in Japan

風間聡 So Kazama
東北大学 Tohoku University
18 October 2023
International Climate Change Symposium
Responses to Climate Change and Future Society1 Background 背景
Japanese Government has shifted to a new Integrated
Flood Management (IFM) 流域治水への変換

Water control 水の制御 Life style control生活の変容
http://www.pref.saitama.lg.jp/a1007/henkou/images/sougoutisui.jpg

https://www.kensetsunews.com/PB5001H/wp-content/uploads/2020/10/20201009_171132_81883.jpg

Catchment
Retention Basin

Retention Basin

Water Supply Reservoir Use

DamImprovement

House Storage
Diversion

Pumping station

Small Reservoir Use

River Improvement Retention Basin

Residents moving

Inundation Zone
Retarding Basin

School Storage

Sub Levee
Levee
Improvement
Building Storage
Underground Storage

Traditional IFM 総合治水

River AreaStorage
Facilities

New IFM 流域治水

Since 2014, Japan has been greatly damaged by flood.

22 Background & Purpose: Evaluation of adaptations
背景と目的： 適応策の評価
Ex. Smit et al.,(1999)

Adaptation Options

適用策分類

Traditional
Levee堤防IFM
Pumpポンプ
旧治水

PROTECT
防御

ACCOMMODATE
受容https://pbs.twimg.com/media/EGqqW
ddUwAArYwT.jpg:small

Piloti house高床Paddy dam
田んぼダム
LanduseControl
土地利用規制RETREAT
撤退
https://www.vill.noda.iwate.jp/seikatukib
annsaikenn/image/0000002133002.jpg

NewIFM流域治水

33 2D Hydraulic Model Simulation for Damageevaluation 数値計算
5 GCMs for Distribution of Extreme Rainfall
5つのGCMの再現期間降雨

2D Hydraulic Model

Probability Rainfall

水深推定

Water Depth
Economic Evaluation Manual
治水経済マニュアルによる被害額計算

Expected Annual
Damage Cost
山形の例

Example of Yamagata
100 years return period
Good agreement to the lastyear (2020) flood inundation

44 High levee Bed Excavation : higher Protection Level
治水レベルの向上 河道掘削=堤防建設
Tanaka et al.(2019) method

Protection level

治水レベル

・Protection level for each river andeach government zone 各河川整備
方針を反映

River bed excavation
to protect flood withRP X years 再現期間毎

RiverDike

河道掘削

Expressed bylower elevation

InlandInland
55 Piloti and Land use control
高床住宅と土地利用規制
5 Jyuukyo

capita/km2

10,000capita/㎢

Original LU

Piloti 高床住宅

3m below → No damage
in high dense areawith flood of 30 years return period
高人口密度地域 3m以下 被害無Landuse Control

Hazard map of Hyogo Prefecture

土地利用規制

3m over → No damage
in low dense areawith rain of 200 years return period
低人口密度地域 3m以上被害無し

ttps://lh3.googleusercontent.com/proxy/qsmiSXLMcWlc3fYQevrCYOx5IkLvRv2y4HsVVNdq_p044U9AF_Q4zPnPoub0vrc
nUYk2iPRvzR256Mp4exm3-5EFSfW366MaROn0YuX-ITifBrdSHob7G01A

6

6 Adaptation effects in different areas
県別適応策の効果（20世紀条件）
Damage reduction ratio for fluvial flooding / 20century base

Levee
improvement

Damagereduction ratio

Landusecontrol
NationalAverage

NationalAverage

Piloti building

Rice field dam
NationalAverage

NationalAverage

77 Adaptation effects on fluvial flood
外水洪水の適応策の効果 現状固定
20世紀末・適応策無しに対する被害額変化率
Change ratio for non-adaptation in the 20th century
適応策無し
No adaptation

Levee Improvement

土地利用規制Landuse control

20世紀末 20C end

0-18-18

近未来
2050

RCP2.62221

RCP8.52342

21世紀末
21C end

RCP2.616-4-5

増加

RCP8.538

1816increase

ピロティ建築
Piloti

田んぼダム
Rice field dam

全ての適応策All together

減少

20世紀末 20C end-67-8-85

近未来
2050

RCP2.6-46

14-74

RCP8.5-45

16-74

21世紀末
21C end

RCP2.6-51

8-76

RCP8.5-30

31-65

治水安全度向上decrease88 Adaptation effects on pluvial flood
内水洪水の適応策の効果 現状固定
20世紀末・適応策無しに対する被害額変化率
Change ratio for non-adaptation in the 20th century
適応策無し
No adaptation

Levee Improvement

土地利用規制Landuse control

20世紀末 20C end

0-54-31

近未来
2050

RCP2.650-25

RCP8.5

53

18

21世紀末
21C end

RCP2.635-16-7増加

RCP8.585

3630

increase

ピロティ建築
Piloti

田んぼダム
Rice field dam

全ての適応策All together

減少

20世紀末 20C end-86-10-90

近未来
2050

RCP2.6-75

38-91

RCP8.5-74

41-90

21世紀末
21C end

RCP2.6-78

23-92

RCP8.5-66

71-85

治水安全度向上decrease

99 Effect of Mitigation and Adaptation to flooding
両洪水の緩和策と適応策の効果
21世紀末 RCP8.5 適応無に対する被害軽減効果
Based on 21C end, comparing with non-adaptation with RCP8.5※外水と内水の被害額を同程度として計算: Pluvial and fluvial floods are same damage.

政策
Policy option

被害額軽減率
現状固定

SSPシナリオ

緩和策 Mitigation
治水安全度向上
Levee Improvement

22％↓
14％↓

30％↓
17％↓

排水能力向上 Pump

26％↓

26％↓

土地利用規制 Landuse Control

24％↓

19％↓

ピロティ建築 Piloti buildings

68％↓

68％↓

田んぼダム Rice field dam

7％↓

5％↓

Ex. Landuse Control=（116+130）/（138+185）=76%（24%↓）←内水含まずOnly fluvial←外水含まずOnly pluvial

1010 Summary
まとめ‣Purposes: Evaluation of Adaptation and Mitigation in Japan
to Flooding 適応策の定量評価‣Mitigation (Difference between RCPs)

22％ decrese (late 21 century)st

緩和策 22%被害減‣Single adaptation Effects for current climate

7～68 ％ decrease

単適応策

最大68%被害額減‣Integrated adaptation Effects for current climate

85 ％ decrease

組み合わせ適応策 最大85%被害額減

More detail: Tao Yamamoto et al., Climatic Change, 165:60, 2021.

11