Streamflow simulation improvements enabled by a state-of-the-art algorithm for reservoir routing in the U.S. National Water Model

This study investigates whether improvements could be achieved for the United States National Water Model (NWM) by using a data-driven reservoir operation simulation algorithm, that is, the generic data-driven reservoir operation model (GDROM), to replace the existing reservoir representation in NWM for reservoir routing in streamflow simulation. The evaluations of NWM versus NWM + GDROM are conducted using 41-year NWM retrospective simulation products during 1979 to 2020. The results show that NWM + GDROM exhibits significant improvement to NWM in both the entire Contiguous U.S. (CONUS) and various regions. It is found that the accuracy of reservoir inflow and storage values affects the NWM + GDROM improvement. When driven by observed storage (which is usually more accurate than modeled storage) or more accurately simulated inflow, NWM + GDROM produces more significant improvements in reservoir outflow simulations in all the study CONUS regions. Especially, since high flows are more accurately simulated by NWM than low flows, NWM + GDROM has larger improvement for the simulation of high flows than low flows.