Kaushalya et al. (2026) An integrated framework for evidence-based climate adaptation planning in water-related disaster management in Malwathu Oya Basin, Sri Lanka

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2026
• Date: 2026-09-21
• Authors: Ranapura Dewage Thilini Kaushalya, Mohamed Rasmy, Katsunori Tamakawa, Toshio Koike
• DOI: 10.1016/j.ejrh.2026.104000

Research Groups

• International Centre for Water Hazard and Risk Management, Public Works Research Institute, Japan
• National Graduate Institute for Policy Studies (GRIPS), Japan

Short Summary

This study develops an integrated framework linking multi-model climate projections, hydrological simulations, and socio-economic impact assessments to support evidence-based climate adaptation planning in the Malwathu Oya Basin, Sri Lanka. It finds that future climate change will intensify hydroclimatic variability, leading to increased flood and drought risks and substantial socio-economic impacts, which can be mitigated through coordinated reservoir operations and crop diversification strategies.

Objective

• To develop and apply an integrated framework for risk-informed adaptation planning by linking multi-model climate projections, hydrological simulations, and socio-economic impact assessment in the Malwathu Oya Basin, Sri Lanka.
• To assess future flood and drought risks and identify climate-informed adaptation pathways for enhancing basin-scale disaster resilience and strengthening integrated water resources management.

Study Configuration

• Spatial Scale: Malwathu Oya Basin, Sri Lanka, covering an area of approximately 3246 square kilometers.
• Temporal Scale: Historical baseline (1980–2005) and future projection period (2050–2075).

Methodology and Data

• Models used:
  • Coupled Model Intercomparison Project Phase 5 (CMIP5) for multi-model climate projections (under RCP 8.5 scenario).
  • Water and Energy Budget–based Rainfall–Runoff–Inundation (WEB-RRI) model for seamless hydrological and inundation simulations.
  • CROPWAT software for crop water requirement estimation and water management assessment.
  • Locally developed depth–damage vulnerability curves (from Climate Resilience Improvement Project, CRIP, Sri Lanka) for socio-economic impact assessment.
• Data sources:
  • Climate data: Daily precipitation and air temperature from the Department of Meteorology, Sri Lanka.
  • Hydrological data: Daily river discharge from the Irrigation Department, Sri Lanka.
  • Agricultural data: Monthly crop yield and cultivated area from the Irrigation Department, Sri Lanka; seasonal crop coefficients from FAO.
  • Topographic data: 15 arc-second Digital Elevation Model, flow direction, and flow accumulation from HydroSHEDS (USGS).
  • Land surface data: 8-day 1 km Leaf Area Index (LAI) and Fraction of Photo-synthetically Active Radiation (FPAR) from NASA Earth Observing System Data and Information System (EOSDIS).
  • Atmospheric forcing: 3-hour 0.125° air temperature, wind speed, shortwave & longwave radiation, specific humidity, and surface pressure data from Japanese 55-year reanalysis (JRA-55) from JMA.
  • Soil data: 9 km soil data from FAO.
  • Land use data: Land Use and Policy Planning Department (LUPPD), Sri Lanka.
  • Flood data: Flood inundation areas from the Irrigation Department, Sri Lanka.
  • Population data: 2012 population data from the Census and Statistics Department, Sri Lanka; projected population data (3 arc-second) from the Global Human Settlement Layer, European Commission.
  • Infrastructure data: Flood-affected buildings (30 cm - 1 m resolution) from Microsoft/Global ML Building Footprints.
  • CMIP5 data accessed via the Data Integration and Analysis System (DIAS).

Main Results

• Climate projections (2050–2075, RCP 8.5) indicate an overall increase in annual and Northeast Monsoon (NEM) rainfall, but with greater temporal concentration and variability, leading to reduced discharges during dry months.
• Flood hazards are projected to intensify, with depths exceeding 2 meters and a 30–40% expansion of inundation extent in downstream areas.
• Socio-economic impacts are projected to increase substantially under future extreme flood scenarios: building damages and associated economic losses are expected to increase by approximately 150% to over 350%, while agricultural losses are projected to increase by 60% to 110%.
• Total flood-exposed population is projected to increase by approximately 96% to 143%, with rural communities remaining disproportionately affected.
• Drought risk is projected to increase, with more pronounced and persistent negative Standardized Streamflow Index (SSI-3) anomalies during climatologically dry months, indicating a propagation of meteorological drought into hydrological drought.
• Adaptation analysis demonstrates that coordinated reservoir operations (e.g., pre-release of 60% or more of reservoir capacity, floodwater diversion of 100–150 cubic meters per second) can significantly reduce urban flood depths (up to 1.4 meters).
• Climate-responsive cropping strategies, such as diversifying from 100% paddy to 50% paddy + 50% green gram or 100% green gram, can maintain reliable reservoir water supply during dry years and increase farmers' income by approximately 6% to 11%.

Contributions

• Developed a novel, integrated, and transferable framework that systematically links multi-model climate projections, seamless hydrological simulations, and socio-economic impact assessments for evidence-based climate adaptation planning.
• Provided a comprehensive quantification of compound hydroclimatic risks (coexisting floods and droughts) and their basin-scale socio-economic impacts in a climate-vulnerable, monsoon-dominated region (Malwathu Oya Basin, Sri Lanka).
• Highlighted the critical importance of process-based climate model evaluation (screening GCMs based on atmospheric circulation and moisture fields) for robust and physically consistent impact assessments in monsoon-driven systems.
• Evaluated practical, coordinated operational and management-based adaptation strategies (reservoir pre-release, floodwater diversion, and climate-smart cropping practices) that leverage existing infrastructure and offer low-regret pathways for enhancing basin-scale disaster resilience and strengthening Integrated Water Resources Management (IWRM) under future climate uncertainty.

Funding

• Public Works Research Institute (PWRI), Japan (research funding).
• International Centre for Water Hazard and Risk Management (ICHARM), Japan (research facilities, academic and technical guidance).
• National Graduate Institute for Policy Studies (GRIPS), Japan (academic support and open-access publication fee).
• Data Integration and Analysis System (DIAS), developed and operated under a grant-in-aid project (JPMXD0721453504) of the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Citation

@article{Kaushalya2026integrated,
  author = {Kaushalya, Ranapura Dewage Thilini and Rasmy, Mohamed and Tamakawa, Katsunori and Koike, Toshio},
  title = {An integrated framework for evidence-based climate adaptation planning in water-related disaster management in Malwathu Oya Basin, Sri Lanka},
  journal = {Journal of Hydrology Regional Studies},
  year = {2026},
  doi = {10.1016/j.ejrh.2026.104000},
  url = {https://doi.org/10.1016/j.ejrh.2026.104000}
}