Application of Nature-Based Solutions (NbS) for Catchment Water Quality Management in Yala River Basin, Western Kenya.

Nature-based solutions (NbS) have emerged as innovative and sustainable approaches to address environmental challenges, including water quality degradation in river catchments. These solutions leverage natural processes and ecosystems to enhance water quality while providing co-benefits such as biodiversity conservation and climate resilience. The Yala River Basin in Kenya faces significant water quality challenges due to increased sediment yields and nutrient loading, primarily driven by agricultural activities, deforestation, and land-use changes. This study explores the application of NbS, such as riparian buffer strips, agroforestry, and wetland restoration, in mitigating water quality issues in the Yala Basin. The Soil and Water Assessment Tool Plus (SWAT+) was employed to model the impacts of NbS on water quality in the Yala Basin. SWAT+ is a robust, process-based hydrological model that simulates land use, climate, and management interventions at the catchment scale. Climate data from ISIMIP3b (Inter-Sectoral Impact Model Intercomparison Project) were used to provide high-resolution projections of climate variability and change. Baseline land-use data were derived from remote sensing and validated using ground surveys. Hydrological response units (HRUs) were defined to capture spatial heterogeneity in land cover, soil, and topography. Scenarios with and without NbS interventions were simulated to assess their impact on sediment and nutrient yields.

Preliminary results indicate that the implementation of NbS significantly reduces sediment yields and nutrient concentrations in the Yala Basin. Specifically, hydrological response units with NbS interventions demonstrated: Reduced sediment yields: Areas with riparian buffer strips and restored wetlands showed up to a 15% reduction in sediment transport compared to baseline scenarios. Decreased nutrient loads: Agroforestry practices and vegetation buffers reduced nitrogen and phosphorus runoff by approximately 4% and 7%, respectively. These reductions were particularly pronounced during peak rainfall events, demonstrating the effectiveness of NbS in mitigating runoff-related pollution.

The application of NbS in the Yala Basin demonstrates their potential to significantly improve catchment water quality while delivering ancillary ecosystem services. SWAT+ modeling highlights the ability of NbS to address sediment and nutrient-related challenges effectively, even under varying climatic conditions. These solutions not only provide immediate water quality benefits but also contribute to long-term catchment resilience to climate change and anthropogenic pressures.

Based on the findings, it is recommended that policymakers and stakeholders prioritize the integration of NbS in catchment management plans. Key recommendations include: Scaling up riparian buffer zones and agroforestry systems in critical hydrological response units. Establishing incentive programs for local communities to adopt NbS practices. Enhancing monitoring and evaluation frameworks to measure the long-term impacts of NbS on water quality. Strengthening partnerships between government agencies, research institutions, and community organizations to promote the co-design and implementation of NbS.