The Value of Long-term Streamflow Forecasts in Adaptive Reservoir Operation: The case of High Aswan Dam in the Transboundary Nile River Basin

Abstract:

Transboundary river basins are experiencing extensive dam development that imposes challenges to future water management, especially for downstream nations. Thus, adapting the operation of existing reservoirs to such challenges is indispensable to cope with potential alterations in flow regime along with pressure from growing population and increasing water demand. Our study proposes a Forecast-based Adaptive Reservoir Operation (namely FARO) framework, which harnesses long-term climate forecasts to improve real‐time reservoir operations and mitigate the risk of water shortage in the future. The FARO approach comprises two main components; 1) streamflow simulator (using hydrological model); and 2) Model Predictive Model (MPC) to optimize reservoir operation. A timely and compelling example to implement our FARO framework is the upstream development in the Nile River Basin (NRB) where the Grand Ethiopian Renaissance Dam (GERD) is being constructed. Informing the operation of downstream dams, e.g., High Aswan Dam (HAD), by streamflow forecasts becomes a prominent keystone for facing anticipated challenges. A suite of eight models from North American Multimodel Ensemble (NMME) are used to generate monthly precipitation and temperature forecasts of five year period (1998–2002) at up to 12 months of lead time. The NMME forcing are used to drive the Variable Infiltration Capacity (VIC) model and produce the monthly streamflow forecast in the Blue Nile basin. The FARO results indicated that HAD can benefit from forecast streamflow up to 10-month lead-time, beyond which the forecast information does not significantly improve the reservoir operation. During GERD operation, FARO showed higher value of forecast information for HAD operation in the post-flooding season from September through November. Our study underlined the importance of available forecast information in adapting reservoir operation and thus the potential to negotiate GERD filling decisions, inform annual expectations of available streamflow, and ease regional tensions during the filling/operation of the GERD reservoir.