Rainfall-Runoff-Inundation Prediction
at the River Basin Scale
Development of RRI Model and Its Application to Climate Change Impact
Assessment and Real-time Flood Inundation Predictions

1) Disaster Prevention Research Institute (DPRI), Kyoto University2) International Centre for Water Hazard and Risk Management (ICHARM)

Takahiro Sayama1), Yusuke Yamazaki2), Yoichi Iwami2)

Summary of Rainfall-Runoff-Inundation (RRI) Model- Since 2010 at ICHARM, Public Works Research Institute, Japan- Concept: rainfall-runoff and inundation simulation at the river basin scale- Target: real time inundation predictions and risk assessment- As of 2016, the package including Fortran source codes, English
manual, GUI (Model builder + Viewer) are available through ICHARM
webpage (http://www.icharm.pwri.go.jp/research/rri/rri_top.html)- Recent advancement: GW, detail cross section, time and space accounting,coupling with WEB-DHM (mainly SiB2 component) and RRI.
- Practical applications at ICHARM: UNESCO Pakistan Project (Indus), JICA Thai
Project (Chao Phraya), ADB Myanmar Project for hazard mapping (Irrawaddy)- Application for scientific studies: hydrologic sensitivity, climate change
impact, effects of GW etc.
2Annual Mean Change (CMIP5 : RCP8.5)(2081-2100) – (1986-2005)+ 100 mm/year

IPCC AR5 (WG1)

Annual Mean Change (CMIP5 : RCP8.5)(2081-2100) – (1986-2005)

IPCC AR5 (WG1)

Hydrologic Sensitivity

How much runoff (Q) is expected to increase, in percentageterm, with a 1% increase in rainfall (P)dQ / QεQ =dP / P(Schaake, 1990)

Elasticity of Flood Runoff and Inundation
How much runoff (Q) and inundation (∆F) volumes are expected toincrease, in percentage term, with a 1% increase in rainfall (P)dQ / QεQ =dP / P(Schaake, 1990)d∆F / ∆FεF =dP / P (Sayama, NHESS, 2015)
6Cumulative rainfall in millimeter(May to October)
998

9900

0003

005

Departure of accumulativerainfall(%) (May to October)06

21~140%

20

19

18

17

16

15

14

13

12

11

10

98

7

6

597

98

99

100

101102

103

104

105

106

Six months rainfall in the basin
in 2011 : 1400 mm
in past severe events (1995, 2006) : 1200 mm
in average years : 1000 mm

TMDApproach
STEP1 : Rainfall-Runoff-Inundation simulation with observed rainfall
2 km resolution, 52 years : 1960-2011⇒ Estimate rainfall and flood inundation volumes⇒ Estimate elastisity of flood runoff and inundation to rainfall

STEP2: RRI simulation with MRI-AGCM projection
AGCM3.2S (20 km), AGCM3.2H (60 km) – RCP 8.5 scenario⇒ Present climate (1979-2003) : 1 cases (3.2S)⇒ Future climate (2075-2099) : 4 cases (3.2S, 3.2H: 3 cases)

Rainfall-Runoff-Inundation Model
Input
Rainfall

1D Diffusion
in RiverSubsurface + Surface
Vertical Infiltration

OutputDischarge

DEM
W. LevelLand CoverInundation
Cross Sec.

2D Diffusionon Land• Two-dimensional model capable of simulating rainfall-runoff and flood inundation simultaneously• The model deals with slopes and river channels separately• At a grid cell in which a river channel is located, the model assumes that both slope and river are
positioned within the same grid cell
Sayama, T. et al.: Rainfall-Runoff-Inundation Analysis of Pakistan Flood 2010 at the Kabul River Basin,
Hydrological Sciences Journal, 57(2), pp. 298-312, 2012.

20

Three kinds of models for flood predictions
Precipitation

Rainfall-Runoff-Inundation

Rainfall-Runoff ModelDischargeFlood Inundation Model
River Routing Model
Water Level
Inundation

Motivations of using Rainfall-Runoff-Inundation Model
1.
2.
3.
4.

Rainfall-runoff and inundation cannot be separated with large inundation
Kinematic wave is not suitable for flat topography
Important for representing inundation process for better river predictions
Inundation itself may be of interest in flood forecasting or risk assessment
10

Rainfall-Runoff-Inundation
Predictionof Thailand Flood 2011
(conducted on 2011/10/14)
W. Depth

Nakhon Sawan

Simulation Domain : 163,293 km2
Grid Size : 60sec (1776 x 1884 m)
Simulation Period：
2011/07/01 – 2011/11/30
Input Rainfall:2011/07/01 – 2011/10/14
3B42RT (Satellite Based Rainfall)(Every 3hours, Spatial Resolution: 0.25 deg)2011/10/14 – 2011/10/21
JMA- GSM Weekly Weather Forecasting（Forecasting Lead Time: 8 days, Update every 12 hours）
2011/11/15 – 2011/11/30(Previous year’s 3B42RT rainfall in the same period)

Ayutthaya

1 : July 1
31 : Aug 1
62 : Sep 1
92 : Oct 1
123 : Nov 1
152 : Nov 30

Bangkok11
http://www.icharm.pwri.go.jp/news/news_j/111024_thai_flood_j.html

Model Building with RRI-GUI
STEP1: HydroSHEDS data

STEP6: Visualizing simulation results
Animation of flood inundation depths

STEP2: Catchment delineation

STEP3: Modifying topographic data (optional)

STEP5: Running RRI Model

STEP4: Reading rainfall data (gauged / satellite)

Run

Time-series of flood inundation depths

Hydrograph of river discharge and water level

Longitudinal flood water level

Three Conditions of Surface / Subsurface Flow
Surface / subsurface flow conditions(A) Only overland flow
(no infiltration loss, nosubsurface flow)(B) Vertical infiltration+ Infiltration excess
overland flow(C) Saturated subsurface+ Saturation excess overlandflowβ h − km   d m I (h ≤ d m ) dm q = − [km d m + ka (h − d m )]I (d m < h ≤ d a )5− [km d m + ka (h − d m )]I + I (h − d a )3 (d a < h )n
13(Tachikawa et al., JSCE, 2004)

Annual Maximum Inundation Extent
2005

2006

2007

2008

2009

2010

2011

RRI Model

RemoteSensing(Composite)

Source: GISTDA (Thailand)
FIT

2005

0.160.08

2006

0.470.31

2007

0.180.14

2008

0.05

0.1520090.010.12

2010

0.52

0.25

2011

0.21

0.46

Avg.

0.23

0.21

Source: UNOSAT

25000

Inundation Area [km2]

Relative
Error

20000
15000
RRI

10000

RS

5000
02005 2006 2007 2008 2009 2010 2011Year

Flood Inundation Volume

Average(1019 mm)

Past Floods
1995, 2006(~1200mm)

2011 Flood(1391 mm)

no damwith dams

Flood Runoff d∆F/dP = 0.25 with dams : + 200 mm rainfall  + 50 mm (= 8.2 billion m3 ) inundation
 Available storages of Bhumipol and Sirikit dams in April 15, 2011 (six mo. before the peak) : 46 mm (=7.5 billion m3) The dams contributed to reduce the inundation by 26 mm (=4.4 billion m3)

Elasticity of Flood Runoff and InundationdQ / QεQ =dP / Pd∆F / ∆FεF =dP / P

By taking 6 month rainfall = 1200 mm as the basis,
Elasticity of peak discharge at C2: εpQ = 1.5
Elasticity of total runoff： εQ = 2.3
Elasticity of flood inundation volume: εF = 4.2

Flood inundation volume increases by 4.2 %if the monsoon rainfall increases by 1%
Sayama et al., Hydrologic sensitivity of flood runoff and inundation: 2011 Thailand floods in the Chao Phraya River basin,Nat. Hazard Earth Syst. Sci., 15, pp. 1 – 14, doi:10.5194/nhess-15-1-2015, 201516