River basin trajectories under global change: earth observations and participatory hydrological modelling in the Senegal river basin

Código

I-EBHE0132

Autores

Andrew Ogilvie, Papa Malick Ndiaye, Issa Leye, Ansoumana Bodian, Soussou Sambou, Thomas Legay

Tema

WG 2.5: The Water-Energy-Food-Ecosystem (WEFE) nexus: pathways to resilience

Resumo

In West Africa, surface water dynamics of large rivers are subject to strong climatic variability and under the growing influence of large dams built to meet the growing demands for hydropower and irrigation. Understanding river basin trajectories and their impacts in alluvial floodplains are essential to evaluate the trade-offs for the Water-energy-food-ecosystems (WEFE) nexus and guide water allocation strategies. Combining the continuous advances in earth observations with participatory hydrological modelling and extensive in situ fieldwork, this research seeks to improve our understanding of surface water dynamics under global change in the Senegal River. Landsat, MODIS and Sentinel-2 earth observations were extracted to monitor surface water variations, using a site specific MNDWI classification adapted to complex, wetland environments. Validated against extensive ground truth data, the approach is upscaled using cloud computing over 2813 mosaics from 1999-2022 covering the 2250 km2 floodplain. Statistical regression models are developed to estimate flooded areas based on upstream flow values and incorporated in a combined GR4J rainfall-runoff and WEAP allocation model. Seven river basin development scenarios co-constructed with the river basin agency and projections from Cordex regional circulation models (RCMs) are simulated to assess their impact on surface water dynamics and water-energy-food-environment NEXUS indicators. Results identify large historical variations in peak flooded areas between 150,000 ha and 450,000 ha (mean 227,000 ha). Scenarios of river basin development to support navigation and hydropower objectives reveal inundated areas could decline drastically by 59% to reach around 100,000 ha. Trade-off scenarios which optimize water allocation between growing, competing demands and allow translucent releases from the future dams are shown to reduce this decline to 32% with minimal impact on hydropower production. Outputs were discussed in participatory workshops with regional stakeholders to help define optimal and equitable river basin development strategies in the Senegal river basin.