Wetland ecosystem services in the Kalu Oya basin, Sri Lanka

Context

This project focuses on wetland ecosystem modelling and economic valuation in the Kalu Oya and Mudun Ela basins in Sri Lanka. These areas are highly urbanised and prone to flooding due to rapid land use change, sea level rise and enhanced climate extremes. Wetlands provide essential local and global ecosystem services such as flood mitigation, carbon sequestration, and water quality improvement. The project is part of the Reversing Environmental Degradation in Africa and Asia (REDAA) programme, funded by the UK government, and aligns with efforts by JICA-ORI to assess flood mitigation strategies under changing climate and socioeconomic conditions.

What we did

The project, ran from November 2023 to March 2025, and aimed to evaluate wetland ecosystem services using open-access tools such as Co$tingNature and WaterWorld. It  quantified these services, estimated their economic value, and modelled potential impacts of climate change and land use changes. Additionally, it invested in long-term data collection infrastructure based on www.freestation.org open source designs and provided training on the tools used, ensuring that local stakeholders can continue using the findings beyond the project's duration. 

Key Outcomes

The project has delivered a comprehensive assessment of wetland ecosystem services in the region, supporting more informed land-use planning and policy decisions. It has also enhanced awareness and capacity among stakeholders regarding wetland conservation. A key output is an open-access Co$tingNature/local application tailored for the Kalu Oya and Mudun Ela basins, facilitating ongoing monitoring and management of wetland resources.

• We have built an instance of Co$tingNature/local for the basin, available here, including economic valuation

• We have carried out a range of analyses on baseline and scenario land use  for the basin, described under outputs below

Key Conclusions

The Kalu Oya and Mudun Ela Basins, highly urbanized areas near Colombo, are vulnerable to flooding due to land-use changes and their low-lying coastal location. The remaining wetlands serve as vital natural flood buffers, contribute to water quality improvement, carbon sequestration, and provide benefits for agriculture, fisheries, and recreation.

The high Total Economic Valuation (TEV) of wetlands and tree-covered areas in the basins, suggesting that conservation investments in these areas should be prioritized to maximize ecosystem service returns. The TEV is highly sensitive to the valuation of specific services like water resources and pollution dilution, underscoring the importance of accurate local valuations for informed investment.  The project concludes that avoiding development in conservation priority areas and implementing effective sustainable urban drainage are crucial for managing rising flood and heat risks. Where wetland degradation continues due to unregulated land-use changes and insufficient conservation, there is a need for policymakers to integrate economic valuation outcomes into targeted interventions for wetland protection.

Example analyses

Outputs

• Tools

  • Co$tingNature/local instance for Kalu Oya and Mudun Ela basin

• Training:

  • Mapping natural capital and ecosystem services with Co$tingNature: Kalu Oya within the Sri Lanka and global context | Sinhala version |

  • Current and future ecosystem services and their valuation in the Kalu Oya and Mudun Ela Basins using Co$tingNature/local | Sinhala version |

  • Practical using Co$tingNature/global, Co$tingNature and Co$tingNature/local  | Sinhala version |

  • Low cost environmental sensing with FreeStation | Sinhala version |

  • Practical analysing FreeStation weather and stage data | Sinhala version |

• Reports

  • Wetland ecosystem modelling and valuation in Kalu Oya Basin, Sri Lanka: a literature review

  • Wetland ecosystem modelling and valuation in Kalu Oya Basin, Sri Lanka: baseline ecosystem services modelled with Co$tingNature/local

  • Climate and land use change impacts for the Kalu Oya/Mudun Ela basins, using Co$tingNature/local

  • Total Economic Valuation of Wetland Ecosystems in the Kalu Oya and Mudun Ela Basins, Sri Lanka

• Data

  • Live weather and flood level monitoring in the Kalu Oya

Partners

The project is led by the International Water Management Institute (IWMI) in collaboration with the Sri Lanka Land Development Corporation (SLLDC), King’s College London, and AmbioTEK, UK. It also involves the Japan International Cooperation Agency – Ogata Research Institute (JICA-ORI). Funding is provided by the UK’s Foreign, Commonwealth and Development Office (FCDO), managed by the International Institute for Environment and Development (IIED) as part of the Reversing Environmental Degradation in Africa and Asia (REDAA) programme.