Development of an Improved Reservoir Operation Scheme for Global Flood
Modeling (CaMa-Flood v4.20)
Abstract
Global river models are crucial for simulating and forecasting floods,
especially in regions lacking dedicated flood forecasting systems.
Reservoir operations significantly affect flow simulations, impacting
forecast accuracy. In this study, we improved a storage-outflow-type
global reservoir operation scheme of the global river hydrodynamics
model CaMa-Flood, which calculates reservoir outflow based on reservoir
storage. First, a non-linear storage-outflow function using convex and
concave curves was implemented to enhance flood control and reduce the
number of required parameters. Second, a gradual transition in the
storage-outflow function was proposed to avoid simulated outflow
instability. Third, the outflow during the water-use phase was
recalibrated to reflect water availability in dry periods, rather than
using annual mean discharge. A case study involving 85 dams in Mainland
Southeast Asia was conducted to evaluate the efficacy of the three key
modifications by comparing the proposed reservoir operation scheme
against three degraded schemes. Using a linear storage-outflow function
caused 43% of the 61 reservoirs with a flood control capacity greater
than 100 million cubic meters (MCM) to overutilize their flood control
capacity during the non-flood water-excess phase. The proposed
non-linear function reduced the number of such reservoirs to 27%. In
addition, the gradual transition of the storage-outflow function
eliminated unrealistic outflow oscillation. Furthermore, parameter
estimation for water-use outflow based on reservoir water-use capacity
and dry period river discharge enabled better utilization of reservoir
capacity during dry seasons. Overall, the proposed reservoir operation
scheme holds promise for enhancing the accuracy of global flood
simulation within global river models.