MRI-AGCM 3.2S Precipitation based Flood Damage Assessment Study for Lower West

Rapti River Basin

International Conference on Flood Resilience Experiences in Asia and Europe

Duminda Perera1, Akiko Hiroe1, Dibesh Shrestha2, Kazuhiko Fukami1 ,Divas Basnyat2, Surendra Gautam2, Akira Hasegawa1, Toshiya Uenoyama1, Shigenobu Tanaka1

1International Centre for Water Hazard and Risk Management, 2Nepal Development Research Institute

5-7 September 2013 Exeter United Kingdom

Abstract

The study focused on future agriculture and households’ damages induced by extreme flood events projected by IPCC SRES A1B scenario by MRI-AGCM 3.2s. An integrated modelling approach was executed to achieve the target by utilizing high resolution 20 km MRI-AGCM 3.2s results with two watershed hydrological models. Bias corrected MRI-AGCM 3.2s precipitation outputs for Present-SPAC (1980-2004), and Future-SFAC (2075-2099) were used to generate river runoff by PDHM (Parameter Distributed Hydrological model). A frequency analysis was carried out to obtain 50 years return period river runoffs for the Lower West River Basin (LWRB) using simulated river runoffs by PDHM model. Flood inundation simulations for 50 years return period events of Present and Future were carried out by Rainfall, Runoff and Inundation model - RRI followed by a flood damage assessment for the flood hazards.

References Perera E.D.P., Hiroe A., Fukami K., Uenoyama T., Tanaka S. (2013). Climate change impact study on flood risk in lower West Rapti river basin using MRI-AGCM outputs. Journal of Japan Society of Civil Engineers, Ser B1 (Hydraulic Engineering), Vol.69(4),451-456.

METHODOLOGY

Flood risk assessment is carried out by combining flood hazard information (Perera et al. 2013) with exposure and vulnerability data. A household level socio-economic survey was conducted in six VDCs to assess the socio-economic status and vulnerability of the local communities and to assess the damages/losses faced by the communities in previous flood events. These data were then analysed to prepare the flood-damage (loss) functions for agriculture and households’ damages across the study area. Finally damage functions were combined with inundation depth and distribution results to achieve damages.

Table 1. Frequency analysis results

CONCLUSION

50 year return period floods’ damages were estimated and increment ratios based on 2007 flood event was calculated. The inundation and damage distributions at extreme flood events suggest that in Future, the VDCs will be severely affected unless proper structural and non-structural counter measures are established. The potential agricultural damages in Future will cause high economic losses ultimately can lead to social catastrophes. Applying an integrated hydrological and socio-economic approach, study was able to show potential agriculture and household damages despite the uncertainties.

INTRODUCTION

Damage assessment

A rural area located in the LWRB near the Nepal-India border which faces recurrent flood disasters where significant losses of property, lives and livelihood of the local population occurred was focused in this study (Figure.1). Rural communities are more vulnerable to climatic extremes than the rich because they have less protection, fewer alternatives and a lower adaptive capacities since they are more reliant on primary productions. Recent extreme flood events in LWRB were reported in 1984, 1989, 1998 and 2007. The main problems in the study area are due to annual inundations, bank erosions, high sediment loads and river course shifting. Flood inundation is both due to the mainstream and local heavy rainfall contributing to high flows in the tributaries. The study area covered six Village Development Committees (VDCs) namely Kamdi, Bankatti, Phattepur, Betahani, Holiya and Gangapur.

Figure 1. West Rapti river and study area

Figure 3. Methodology

Figure 2. Land cover, VDCs and LWRB in the

study area Figure 4. Peak inundation distributions (a): 2007

flood, (b): SPAC 50 year flood, (c): SFAC 50 year flood

Threshold 1500

m3/s

Frequency

in 25 years

Probable discharge at

RRI Inlet (m3/s)

25 years

return

period

discharge

50 years

return

period

discharge

MRI-GCM

3.1S

SP0AC 38 3272 3629

SN0AC 38 4086 4600

SF0AC 53 3544 3911

MRI-GCM

3.2S

SPAC 30 4107 4658

SNAC 37 7058 8171

SFAC 66 7723 8806

Based on observed

rainfalls 43 3906 4354

2007

flood

A2007 (km2)

SPAC

flood

ASPAC (km2)

SFAC

flood

ASFAC (km2)

ASPAC A2007

ASFAC A2007

60 106 133 1.8 2.2

Table 2. Inundation area exceeding 30 cm at flood peaks and increment ratios

Figure 5. Agriculture damage curve

Figure 6. Agriculture damage for each VDC and comparison with

2007 flood

Figure 7. Agriculture damage

distribution for SPAC and SFAC

Figure 8. Household damage curve

Figure 9. Household damage for

each VDC and comparison

with 2007 flood

Figure 10. Agriculture damage

distribution for SPAC and

SFAC

SPAC SFAC