Flood Vulnerability, Social Risk, and Economic Damage Assessment in the Lower Karnali River Basin, Nepal

Abstract

The lower Karnali River basin is one of Nepal’s most flood-prone regions, yet it has lacked an integrated risk assessment. This study presents the first comprehensive analysis combining physical vulnerability, social vulnerability, and economic damage assessment for the corridor. Utilizing a validated 2D HEC-RAS model across eight return periods (2–500 years), we quantified impacts on 23,929 buildings, 477 km of roads, and 16,065 hectares of paddy cropland using locally calibrated depth-damage curves. Those calibrations were mainly focused on three building typologies, two road surface classes, and paddy crops at the maturity stage. A Social Vulnerability Index (SVI) was developed for 27 wards, integrating demographics, healthcare access, and education. Findings indicate total economic damages range from NPR 395 million (2-year) to NPR 3538 million (500-year), with buildings consistently accounting for the largest share (41–42%). Madhuwan Ward 6, Geruwa Ward 1, and Rajapur Ward 7 emerged as the highest combined flood risk hotspots through the integration of social vulnerability and physical hazard. The results prove that social infrastructure investment, particularly in healthcare, serves as a direct flood risk reduction measure. This research provides a spatially explicit evidence base to guide targeted mitigation, land-use policy, and social protection in the basin.

Keywords

Flood risk / HEC-RAS / Inundation / Vulnerability / Depth-damage / Socio-economic / Lower Karnali / Infrastructure

References

[1] McDermott TKJ . Global exposure to flood risk and poverty. Nat. Commun. 2022, 13, 3529. DOI: 10.1038/s41467-022-30725-6

[2] Rentschler J, Salhab M, Jafino BA . Flood exposure and poverty in 188 countries. Nat. Commun. 2022, 13, 3527. DOI: 10.1038/s41467-022-30727-4

[3] Liu Q, Du M, Wang Y, Deng J, Yan W, Qin C, et al. Global, regional and national trends and impacts of natural floods, 1990-2022. Bull. World Health Organ. 2024, 102, 410-420. DOI: 10.2471/BLT.23.290243

[4] Lindersson S, Raffetti E, Rusca M, Brandimarte L, Mård J, Di Baldassarre G . The wider the gap between rich and poor the higher the flood mortality. Nat. Sustain. 2023, 6, 995-1005. DOI: 10.1038/s41893-023-01107-7

[5] Rogers JS, Maneta MP, Sain SR, Madaus LE, Hacker JP . The role of climate and population change in global flood exposure and vulnerability. Nat. Commun. 2025, 16, 1287. DOI: 10.1038/s41467-025-56654-8

[6] Khatiwada K, Panthi J, Shrestha M, Nepal S. Hydro-Climatic Variability in the Karnali River Basin of Nepal Himalaya. Climate 2016, 4, 17. DOI: 10.3390/cli4020017

[7] Aryal D, Wang L, Adhikari TR, Zhou J, Li X, Shrestha M, et al. A Model-Based Flood Hazard Mapping on the Southern Slope of Himalaya. Water 2020, 12, 540. DOI: 10.3390/w12020540

[8] Lamichhane K, Karki S, Sharma K, Khadka B, Acharya B, Biswakarma K, et al. Unraveling the causes and impacts of increasing flood disasters in the kathmandu valley: Lessons from the unprecedented September 2024 floods. Nat. Hazards Res. 2025, 5, 875-897. DOI: 10.1016/j.nhres.2025.04.001

[9] MacClune K, Venkateswaran K, Dixit KM, Yadav S, Maharjan R, Dugar S. Risk Nexus: Urgent Case for Recovery-What We Can Learn from the August 2014 Karnali River Floods in Nepal ; ISET-International: Boulder, CO, USA, 2015; ISET-Nepal and Practical Action Nepal: Kathmandu, Nepal, 2015.

[10] Malla S, Ohgushi K . Flood vulnerability map of the Bagmati River basin, Nepal: A comparative approach of the analytical hierarchy process and frequency ratio model. Smart Constr. Sustain. Cities 2024, 2, 16. DOI: 10.1007/s44268-024-00041-7

[11] Fox S, Agyemang F, Hawker L, Neal J . Integrating social vulnerability into high-resolution global flood risk mapping. Nat. Commun. 2024, 15, 3155. DOI: 10.1038/s41467-024-47394-2

[12] Reimann L, Koks E, de Moel H, Ton MJ, Aerts JCJH . An Empirical Social Vulnerability Map for Flood Risk Assessment at Global Scale (“GlobE‐SoVI”). Earth’s Future 2024, 12, e2023EF003895. DOI: 10.1029/2023EF003895

[13] Aksha SK, Juran L, Resler LM, Zhang Y . An Analysis of Social Vulnerability to Natural Hazards in Nepal Using a Modified Social Vulnerability Index. Int. J. Disaster Risk Sci. 2019, 10, 103-116. DOI: 10.1007/s13753-018-0192-7

[14] Romali NS, Sulong S, Kawasaki A . A Systematic Review of Flood Damage Assessment: Insight for the Data-Scarce Regions. Water Resour. Manag. 2025, 39, 4707-4734. DOI: 10.1007/s11269-025-04265-9

[15] Kafle TP, Kafle A, Hazarika MK . Flood loss functions as decision support for guiding resilient urban development: A case study of Gaur Municipality, Nepal. J. Eng. Issues Solut. 2024, 3, 102-118. DOI: 10.3126/joeis.v3i1.65280

[16] Sharma AP, Fu X, Kattel GR . Is there a progressive flood risk management in Nepal? A synthesis based on the perspective of a half-century (1971-2020) flood outlook. Nat. Hazards 2023, 118, 903-923. DOI: 10.1007/s11069-023-06035-5

[17] Rakhal B, Adhikari TR, Sharma S, Ghimire GR . Assessment of channel shifting of Karnali Megafan in Nepal using remote sensing and GIS. Ann. GIS 2021, 27, 177-188. DOI: 10.1080/19475683.2021.1871950

[18] Bhattarai A, Bhattarai U, Maharjan KR, Devkota LP . Assessing the characteristics of extreme floods in Nepal. Proc. IAHS 2024, 387, 3-8. DOI: 10.5194/piahs-387-3-2024

[19] Dingle EH, Creed MJ, Sinclair HD, Gautam D, Gourmelen N, Borthwick AGL, et al. Dynamic flood topographies in the Terai region of Nepal. Earth Surf. Process. Landf. 2020, 45, 3092-3102. DOI: 10.1002/esp.4953

[20] Bijlmakers J, Griffioen J, Karssenberg D . Environmental drivers of spatio-temporal dynamics in floodplain vegetation: Grasslands as habitat for megafauna in Bardia National Park (Nepal). Biogeosciences 2023, 20, 1113-1144. DOI: 10.5194/bg-20-1113-2023

[21] Pradhananga S, Nepal S, Kamal SK, Hafeez M . Climate change will exacerbate seasonal flow variability in the Karnali River basin: Implications for water, energy, and agriculture sectors. Hydrol. Res. 2025, 56, 471-491. DOI: 10.2166/nh.2025.193

[22] Department of Hydrology and Meteorology (DHM) . Hydrological Monitoring System-Station No. 350 (Chisapani, Karnali River). Available online: http://www.dhm.gov.np/hydrology/ (accessed on 12 March 2026).

[23] Pandey VP, Sharma A, Dhaubanjar S, Bharati L, Joshi IR . Climate Shocks and Responses in Karnali-Mahakali Basins, Western Nepal. Climate 2019, 7, 92. DOI: 10.3390/cli7070092

[24] Halbert K, Nguyen CC, Payrastre O, Gaume E . Reducing uncertainty in flood frequency analyses: A comparison of local and regional approaches involving information on extreme historical floods. J. Hydrol. 2016, 541, 90-98. DOI: 10.1016/j.jhydrol.2016.01.017

[25] US Army Corps of Engineers, Hydrologic Engineering Center. HEC-RAS River Analysis System: 2D User’s Manual, Version 6.6 ; US Army Corps of Engineers, Hydrologic Engineering Center (HEC): Davis, CA, USA, 2024.

[26] US Army Corps of Engineers, Hydrologic Engineering Center. 1D vs. 2D Hydraulic Modeling ; US Army Corps of Engineers, Hydrologic Engineering Center (HEC): Davis, CA, USA, 2024.

[27] Hawker L, Uhe P, Paulo L, Sosa J, Savage J, Sampson C, et al. A 30 m global map of elevation with forests and buildings removed. Environ. Res. Lett. 2022, 17, 024016. DOI: 10.1088/1748-9326/ac4d4f

[28] National Disaster Risk Reduction and Management Authority (NDRRMA). A Preliminary Loss and Damage Assessment of Flood and Landslide, September 2024 ; Government of Nepal, National Disaster Risk Reduction and Management Authority (NDRRMA): Kathmandu, Nepal, 2024.

[29] The Small Earth Nepal Flood Risk Assessment in Lower Karnali Watershed Region: Research Sharing Validation Workshop 2026. Available online: https://smallearth.org.np/activities/research-sharing-validation-workshops/ (accessed on 12 March 2026).

[30] Dottori F, Alfieri L, Bianchi A, Skoien J, Salamon P . River Flood Hazard Maps for Europe and the Mediterranean Basin Region. 2024. Available online: https://data.jrc.ec.europa.eu/dataset/1d128b6c-a4ee-4858-9e34-6210707f3c81 (accessed on 14 January 2026).

[31] Banstola P, Krishna P, Sapkota B . Flood Risk Mapping and Analysis Using Hydrodynamic Model HEC-RAS: A Case Study of Daraudi River, Chhepatar, Gorkha, Nepal. Grassroots J. Nat. Resour. 2019, 2, 25-44. DOI: 10.33002/nr2581.6853.02033

[32] Haque S, Ikeuchi K, Shrestha BB, Kawasaki A, Minamide M . Establishment of flood damage function model for rural roads: A case study in the Teesta River basin, Bangladesh. Prog. Disaster Sci. 2023, 17, 100269. DOI: 10.1016/j.pdisas.2022.100269

[33] Shrestha BB, Kawasaki A, Zin WW . Development of flood damage functions for agricultural crops and their applicability in regions of Asia. J. Hydrol. Reg. Stud. 2021, 36, 100872. DOI: 10.1016/j.ejrh.2021.100872

[34] Van Westen CJ, Straatsma M, Turdukulov U, Feringa WF, Sijmons K, Bakhtadze K, et al. Atlas of Natural Hazards and Risks of Georgia ; Caucasus Environmental NGO Network (CENN): Tbilisi, Georgia, 2012.

[35] Adger WN . Vulnerability. Glob. Environ. Change 2006, 16, 268-281. DOI: 10.1016/j.gloenvcha.2006.02.006

[36] Adhikari M, Pantha S, Gouli MR, Dulal B, Manadhar B, Sedhain A, et al. Exposure of public and private infrastructure to flood hazards in the Mohana-Khutiya River Basin, Nepal. H2Open J. 2025, 8, 443-464. DOI: 10.2166/h2oj.2025.024

[37] Nepal S, Kaushal CGC . Flood Inundation Mapping of Bagmati River and Impact Assessment on Building Infrastructures on Terai Plains of Nepal. J. Adv. Coll. Eng. Manag. 2024, 9, 95-104. DOI: 10.3126/jacem.v9i1.71425

[38] Mester B, Frieler K, Korup O, Desai B, Schewe J . Socioeconomic predictors of vulnerability to flood-induced displacement. Nat. Commun. 2025, 16, 8296. DOI: 10.1038/s41467-025-64015-8