Information About the National Water Model

The National Water Model

View the NOAA publication on the National Water Model here.

The National Water Model (NWM) is a hydrologic modelling framework that simulates observed and forecast streamflow over the entire continental United States (CONUS). The NWM simulates the water cycle with mathematical representations of the different processes and how they fit together. This complex representation of physical processes such as snowmelt and infiltration and movement of water through the soil layers varies significantly with changing elevations, soils, vegetation types and a host of other variables. Additionally, extreme variability in precipitation over short distances and times can cause the response on rivers and streams to change very quickly. Overall, the process is so complex that to simulate it with a mathematical model means that it needs a very high powered computer or supercomputer in order to run in the time frame needed to support decision makers when flooding is threatened.

The NWM produces hydrologic guidance at a very fine spatial and temporal scale. It complements official NWS river forecasts at approximately 4000 locations across the CONUS and produces guidance at millions of other locations that do not have a traditional river forecast.

Diagram of Water Cycle

NWM Operational Configuration:

The NWM runs ten uncoupled analyses (simulations of current conditions) with look-back periods ranging from 28 hours to 3 hours. These analyses are used to provide initial conditions for the model’s forecast runs. Over the CONUS, short-range forecasts are executed hourly, while over Hawaii / United States Virgin Islands (USVI) and Puerto Rico they are executed twice per day. Additionally, the CONUS features medium-range and long-range forecasts which are each produced four times per day. All CONUS model configurations provide streamflow for 2.7 million river reaches and other hydrologic information on 1km and 250m grids. The NWM provides complementary hydrologic guidance at current National Weather Service (NWS) river forecast locations and significantly expands guidance coverage and type in underserved locations.

WRF-Hydro Plus NHDPlusV2 Data

The core of the NWM system is the National Center for Atmospheric Research (NCAR)-supported community Weather Research and Forecasting Hydrologic model (WRF-Hydro) . It ingests forcing from a variety of sources including Multi-Radar/Muti-Sensor System (MRMS) and Stage IV Multisensor Precipitation Estimator (MPE) radar-gauge observed precipitation data, and High Resolution Rapid Refresh (HRRR) , Rapid Refresh (RAP) , North American Mesoscale Nest (NAM-Nest) , Global Forecasting System (GFS) and Climate Forecast System (CFS) Numerical Weather Prediction (NWP) forecast data. WRF-Hydro is configured to use the Noah-MP Land Surface Model (LSM) to simulate land surface processes. 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 Hydrography Dataset River analyses and forecasts are provided across a domain encompassing the CONUS, the Great Lakes Drainage Basin, Hawaii / USVI, Puerto Rico and additional hydrologically-contributing areas. Land surface output is available on a larger CONUS+ domain that extends beyond the CONUS into Canada and Mexico (roughly from latitude 19N to 58N), and covers Hawaii and Puerto Rico / USVI as well. United States Geological Survey (USGS) and United States Army Corps of Engineers (USACE) streamflow observations are assimilated into five of the analysis and assimilation configurations, with the other five serving as open-loop (non-data-assimilation) configurations. All analysis and forecast configurations benefit from the inclusion of over 5,000 reservoirs, with the CONUS short- and medium-range forecasts ingesting RFC-supplied forecasts of reservoir outflow at several hundred locations. Additionally, aiding model assessment and informing model application, three new open-loop forecast configurations (CONUS medium-range, Puerto Rico and Hawaii short-range) are initialized with conditions from the open-loop analyses.


Model Details

Operational Model Configuration

General Framework:

The NWM is run in six CONUS configurations, four Hawaii configurations and four Puerto Rico / USVI configurations:
  • CONUS
    • Standard Analysis (self-cycling with 3-hour look-back, used to initialize CONUS short- and medium-range forecasts)
    • Extended Analysis (28-hour lookback used to initialize Standard Analysis once per day)
    • Long-Range Analysis (12-hour lookback, used to initialize Long-Range forecasts)
    • Short-Range Forecast: 18-hour deterministic (single value) forecast
    • Medium-Range Forecast: Seven-member ensemble forecasts out to 10 days (member 1) and 8.5 days (members 2-7)
    • Long-Range Forecast: 30-day four-member ensemble forecast
  • Hawaii
    • Hawaii Analysis (self-cycling with 3-hour look-back, used to initialize Hawaii short-range forecasts)
    • Hawaii Short-Range Forecast: 60-hour deterministic (single value) forecast for Hawaii domain
    • Hawaii Short-Range Forecast: 48-hour deterministic (single value) forecast for Hawaii domain
    • Hawaii Short-Range Open Loop Forecast: 48-hour deterministic (single value) forecast for Hawaii domain, initialized with Open-Loop Analysis.
  • Puerto Rico / USVI
    • Puerto Rico Analysis (self-cycling with 3-hour look-back, used to initialize Puerto Rico short-range forecasts)
    • Puerto Rico Open-Loop Analysis (self-cycling with 3-hour look-back, used to initialize Puerto Rico short-range open-loop forecasts, does not ingest streamflow observations)
    • Puerto Rico Short-Range Forecast: 48-hour deterministic (single value) forecast for Puerto Rico domain
    • Puerto Rico Short-Range Open Loop Forecast: 48-hour deterministic (single value) forecast for Puerto Rico domain, initialized with Open-Loop Analysis.

Analysis and Assimilation Configurations:

Standard Analysis and Assimilation

The Standard Analysis and Assimilation configuration cycles hourly and produces a real-time analysis of the current streamflow and other surface and near-surface hydrologic states across the contiguous United States (CONUS). This configuration is internally cycling, with each subsequent Standard Analysis starting from the previous hour’s run. The exception is the 19Z Standard Analysis cycle which ingests initial conditions from the Extended Analysis below. The Standard Analysis also produces restart files each hour which are used to initialize the short-, medium-, and long-range forecast simulations. Meteorological forcing data are drawn from the MRMS Gauge-adjusted and Radar-only observed precipitation products along with short-range RAP and HRRR, while stream-gauge observations are assimilated from the USGS.

Standard Open Loop Analysis and Assimilation

Identical to the Standard Analysis and Assimilation configuration above, but without the assimilation of USGS, USACE and RFC streamflow data. This configuration initializes the Open Loop Medium-Range forecast.

Extended Analysis and Assimilation

The Extended Analysis and Assimilation configuration cycles once per day and produces an analysis of the current streamflow and other surface and near-surface hydrologic states across the contiguous United States (CONUS). This configuration is internally cycling, with each subsequent Extended Analysis starting from the previous day’s run. This configuration also produces restart files which are used to initialize the 19Z Standard Analysis simulation. Meteorological forcing data are drawn from the Stage IV national mosaic of RFC MPE precipitation data along with short-range RAP and HRRR data.

Extended Open Loop Analysis and Assimilation

Identical to the Extended Analysis and Assimilation configuration above, but without the assimilation of USGS, USACE and RFC streamflow data. This configuration initializes the 19Z Open Loop Analysis simulation.

Long-Range Analysis and Assimilation

The Long-Range Analysis and Assimilation configuration cycles hourly and produces a real-time analysis of the current streamflow and other surface and near-surface hydrologic states across the contiguous United States (CONUS), using higher quality precipitation data than is available to the Standard Analysis and Assimilation. This configuration is internally cycling, with each subsequent Long-Range Analysis Standard Analysis starting from the previous hour’s run. The Long-Range Analysis also produces restart files which are used to initialize the long-range forecast simulations. Like the Long-Range configuration, it uses a simplified set of physics in comparison to the Standard and Extended Analyses. Meteorological forcing data are drawn from the MRMS Gauge-adjusted and Radar-only observed precipitation products along with short-range RAP and HRRR, while stream-gauge observations are assimilated from the USGS.

Long-Range Open Loop Analysis and Assimilation

Identical to the Long-Range Analysis and Assimilation configuration above, but without the assimilation of USGS streamflow data.

Hawaii Analysis and Assimilation

The Hawaii Analysis and Assimilation configuration cycles hourly and produces a real-time analysis of the current streamflow and other surface and near-surface hydrologic states across the Hawaii domain. This configuration is internally cycling, with each subsequent Hawaii Analysis starting from the previous hour’s run. The Hawaii Analysis also produces restart files each hour which are used to initialize the Hawaii Short-Range forecast simulation. Meteorological forcing data are drawn from the NAM-NEST NWP Model, while stream-gauge observations are assimilated from the USGS.

Hawaii Open Loop Analysis and Assimilation

Identical to the Hawaii Analysis and Assimilation configuration above, but without the assimilation of USGS streamflow data. This configuration initializes the Open Loop Hawaii Short-Range forecast.

Puerto Rico / USVI Analysis and Assimilation

The Puerto Rico Analysis and Assimilation configuration cycles hourly and produces a real-time analysis of the current streamflow and other surface and near-surface hydrologic states across the Puerto Rico domain. This configuration is internally cycling, with each subsequent Puerto Rico Analysis starting from the previous hour’s run. The Puerto Analysis also produces restart files each hour which are used to initialize the Puerto Short-Range forecast simulation. Meteorological forcing data are drawn from the NAM-NEST and HIRES WRF-ARW NWP Models, while stream-gauge observations are assimilated from the USGS.

Puerto Rico / USVI Open Loop Analysis and Assimilation

Identical to the Puerto Rico Analysis and Assimilation configuration above, but without the assimilation of USGS streamflow data. This configuration initializes the Open Loop Puerto Rico Short-Range forecast.

Forecast Configurations:

Short Range

Forced with meteorological data from the HRRR and RAP models, the Short Range Forecast configuration cycles hourly and produces hourly deterministic forecasts of streamflow and hydrologic states out to 18 hours. The model is initialized with a restart file from the Analysis and Assimilation configuration and does not cycle on its own states.

Medium Range

The Medium Range Forecast configuration is executed four times per day, forced with GFS model output. Member 1 extends out to 10 days while members 2-7 extend out to 8.5 days. This configuration produces 3-hourly deterministic output and is initialized with the restart file from the Analysis and Assimilation configuration.

Long Range

The Long Range Forecast cycles four times per day (i.e. every 6 hours) and produces a daily 16-member 30-day ensemble forecast. There are 4 ensemble members in each cycle of this forecast configuration, each forced with a different CFS forecast member. It produces 6-hourly streamflow and daily land surface output, and, as with the other forecast configurations, is initialized with a common restart file from the Analysis and Assimilation configuration.

Hawaii Short Range

Forced with meteorological data from the NAM-NEST model, the Hawaii Short Range Forecast configuration cycles four times per day and produces hourly deterministic forecasts of streamflow and hydrologic states out to 60 hours. The model is initialized with a restart file from the Hawaii Analysis and Assimilation configuration and does not cycle on its own states.

Hawaii Short-Range Open Loop

The Hawaii Short-Range open loop deterministic forecast configuration is executed two times per day using the same forcing as the Hawaii Short-Range standard configuration, but drawing initial conditions from the Hawaii Open Loop Analysis and Assimilation.

Puerto Rico / USVI Short Range

Forced with meteorological data from the NAM-NEST and HIRES WRF-ARW models, the Puerto Rico Short Range Forecast configuration cycles two times per day and produces hourly deterministic forecasts of streamflow and hydrologic states out to 48 hours. The model is initialized with a restart file from the Puerto Rico Analysis and Assimilation configuration and does not cycle on its own states.

Puerto Rico / USVI Short-Range Open Loop

The Puerto Rico Short-Range open loop deterministic forecast configuration is executed two times per day using the same forcing as the Puerto Rico Short-Range standard configuration, but drawing initial conditions from the Puerto Rico Open Loop Analysis and Assimilation.

Output:

All NWM output will be stored in NetCDF format in one of three file types:
  1. 1km gridded NetCDF (land surface variables and forcing)
  2. 250m gridded NetCDF (ponded water depth and depth to soil saturation)
  3. Point-type NetCDF (stream routing and reservoir variables)

The two gridded file types are used for two separate rectangular domains, 1) the CONUS+ (roughly from 19N to 58N) and 2) the Hawaiian Islands, while the point NetCDF file type is used for the CONUS (including adjacent hydrologically contributing areas) and the Hawaiian Islands.


Output File Contents:

A full breakdown of output file contents can be found here.


Viewing Output:

Output from the National Water Model is currently visualized on this website using the experimental interactive map, and the experimental image viewer.


Downloading Output:

The full set of NWM output data and a subset of forcing files is available on the NOAA Operational Model Archive and Distribution System (NOMADS) and the National Centers for Environmental Prediction (NCEP) FTP server at the following links:

Most NWM NetCDF output files are directly viewable using standard NetCDF visualization utilities. The exception are the channel output files containing streamflow and other variables representing processes along river reach segments. To support visualization of these variables, the latitude and longitude coordinates of the centroid of each reach are made available in a separate ESRI file geo-database (gdb), outside of the NWM outputs. The file gdb can be used in many common GIS software utilities to attach coordinates to the data. The file gdb is available here.

NCEP encourages all users to ensure their decoders are flexible and are able to adequately handle changes in content order and also any volume changes which may be forthcoming. These elements may change with future NCEP model implementations. NCEP will make every attempt to alert users to these changes prior to any implementations.

To download the National Water Model product description document, click here.


Parameter Information

A subset of the model parameter files used by the operational implementation of the NWM is available. For a description of the files available, click here. To download a tar file of the available parameter files, click here.


Contact Information

Model implementation questions
Brian Cosgrove
OWP/Analysis and Prediction Division in Silver Spring, MD

Phone: (301) 427-9513
Data flow questions
Carissa Klemmer
NCEP/NCO Dataflow Team in College Park, MD

Phone: (301) 683-0567