Continental-Scale Operational Hydrologic Modeling: Version 1.0 of the National Water Model

Version 1.0 of the National Water Model was implemented into NWS operations in late 2016.  A joint effort between the National Weather Service (NWS) Office of Water Prediction (OWP), the National Center for Atmospheric Research (NCAR) and the NWS National Centers for Environmental Prediction (NCEP), this model establishes a foundation for national-scale operational hydrologic forecasting.  It provides complementary streamflow guidance at the ~4,000 existing NWS river forecast points, and first-time streamflow guidance at close to 2.7 million additional locations.  Additionally, the system provides a suite of water resource output across seamless continental-scale 1km and 250m grids. 

Cycling hourly, the core of the uncoupled analysis and forecast system is the NCAR-supported community Weather Research and Forecasting (WRF)-Hydro hydrologic model.  A forcing engine module ingests and downscales forcing from both observation- and model-based sources, including Multi-Sensor Multi-Radar (MRMS) radar-gauge observed precipitation data and High Resolution Rapid Refresh (HRRR), Rapid Refresh (RAP), Global Forecast System (GFS) and Climate Forecast System (CFS) forecast data.  Land surface processes are simulated by the Noah-Multi Parameterization (Noah-MP) Land Surface Model (LSM) within WRF-Hydro, while separate water routing modules perform diffusive wave surface routing and saturated subsurface flow routing on a 250m grid, and Muskingum-Cunge channel routing down National Hydrogaphy Dataset Plus V2 (NHDPlusV2) stream reaches.  The land surface output domain extends beyond the CONUS into Canada and Mexico, while river analyses and forecasts are provided across a domain encompassing the Continental United States (CONUS) and hydrologically contributing areas.  Streamflow data assimilation within the Analysis and Assimilation configuration of the model leverages a nudging-based approach and ingests United Sates Geologic Survey (USGS) streamflow observations.  Additionally, three forecast configurations are executed which include a short-range 15 hour deterministic forecast, a medium-Range 10 day deterministic forecast and a long-range 30 day 16-member ensemble forecast.  All four of these configurations benefit from the inclusion of 1,260 reservoirs.

This presentation will provide a general overview of the NWM and associated evaluation activities, as well as cover plans for NWM enhancements.