NOAA NWC - Irma National Water Model Streamflow Forecasts

The National Water Model (NWM) [1] is a water forecasting model operated by the National Water Center (NWC) of the NOAA National Weather Service. The NWM continually forecasts flows on 2.7 million stream reaches covering 3.2 million miles of streams and rivers in the continental United States. It operates as part of the national weather forecasting system, with inputs from NOAA numerical weather prediction models, and from weather and water conditions observed through the US Geological Survey's National Water Information System. Reference materials for the computational framework behind NWM is published by NCAR [9] [10].

Hurricane Irma Forecast Data Downloads

• The NWC generates NWM streamflow forecasts for the continental US (CONUS) with multiple forecast horizons and time steps. Due to the output file sizes, these are normally not available for download more than a couple days at a time [2]. However, a 40-day rolling window of these forecasts is maintained by HydroShare at RENCI [3], and a complete retrospective (August 2016 to the present) of the NWM Analysis & Assimilation outputs is maintained as well (contact help@cuahsi.org for access).
• An archive of all NWM forecasts for the period Aug 29 to Sept 17, 2017 has been compiled at RENCI [4] [5], available as netCDF (.nc) files totaling 6.8TB. These can be browsed, subsetted, visualized, and downloaded (see [6] [7] [8]).
• To work with a complete time series the user will want to spatially subset the output files to a geographic area of interest, then merge the time step files for each forecast model. CUAHSI staff have developed JupyterHub python script examples for subsetting and working with these datasets [8], contact help@cuahsi.org for help with this.
• The NWM input parameter files and documentation are available for download. These enable re-running the NWM for the Harvey period, or for any time period covered by NWM v1.1 and 1.2 (August 2016 to this publication date in August 2018). These parameter files are also made available at [1]. The parameter zipfile includes a slightly modified version of the National Hydrography Dataset (NHD) medium resolution flowlines, catchments and waterbodies, see its own README file. The NWM version of NHD is also available as an ArcGIS Geodatabase below.
• Note from [1] that some of the NWM output files lack geographic coordinates, which are required for CF compliance. A script is provided in this resource [NWM_v1.1_nc_tools_v1.tar.gz, and another for NWM v1.2], which will incorporate the coordinates for compatibility with netCDF client apps and other tools.
• Please see NOAA contacts listed on [1] for questions about the NWM data contents, structure and formats. Contact help@cuahsi.org if any questions about HydroShare-based tools and data access.

Hydrologic Modeling Information

• The National Water Model uses a technical framework called WRF-Hydro (Weather Research and Forecasting Model-Hydro) to link weather and hydrological forecasting that is developed and maintained at the National Center for Atmospheric Research (NCAR). WRF-Hydro is described here [9] [10].
• The Terrain_RT model outputs include a variable sfcheadsubrt (surface head, or ponding depth, in mm) that can be a proxy for inundation. This is a raster layer with 250m horizontal resolution. Nonzero values above 5 to 50mm indicate wet land surface. However, the depths will be off at local scales. This is partially because of the small size of the grid cells (250m) and the coarseness of the DEM (10m) at that scale, and partly because of the way NWM performs channel routing, ie, without 2-way coupling of the channel to the landscape. In future versions of NWM, the depth will be much closer to observed values because of some changes that are forthcoming.

Organizational Information

• Rapid prototyping to develop and enhance the NWM is being carried out by the US academic community, coordinated by CUAHSI. The collaboration between the NWS and CUAHSI was initially launched in 2015 as a National Flood Interoperability Experiment [11].
• The NOAA National Water Center Innovators program has sponsored a program of Summer Institutes, organized through CUAHSI, and held annually at the National Water Center on the Tuscaloosa campus of the University of Alabama [12] [131].
• Publications of the American Water Resources Association (AWRA) have served as an information source for the National Water Model and the research supporting its development [14].
• The Environmental Systems Research Institute (Esri), continually publishes water forecast maps from the National Water Model as part of its Living Atlas [15]. Login to http://www.arcgis.com, add data from Living Atlas and search for layers of title National Water Model.

References

[1] Overview of the NWM framework and output files [http://water.noaa.gov/about/nwm]

[2] Free access to all National Water Model output for the most recent two days [ftp://ftpprd.ncep.noaa.gov/pub/data/nccf/com/nwm]

[3] NWM outputs for rolling 40-day window, maintained by HydroShare http://thredds.hydroshare.org/thredds/catalog/nwm/catalog.html

[4] Archived Irma NWM outputs via RENCI THREDDS server [http://thredds.hydroshare.org/thredds/catalog/nwm/irma/catalog.html]

[5] RENCI is an Institute at the University of North Carolina at Chapel Hill

[6] Live map for National Water Model forecasts [http://water.noaa.gov/map]

[7] NWM Forecast Viewer app [https://hs-apps.hydroshare.org/apps/nwm-forecasts]

[8] CUAHSI JupyterHub example scripts for subsetting NWM output files [https://hydroshare.org/resource/3db192783bcb4599bab36d43fc3413db/]. Contact help@cuahsi.org for help with these scripts.

[9] WRF-Hydro Overview [https://ral.ucar.edu/projects/wrf_hydro/overview]

[10] WRF-Hydro User Guide 2015 [https://ral.ucar.edu/sites/default/files/public/images/project/WRF_Hydro_User_Guide_v3.0.pdf]

[11] Conceptual Framework of the National Flood Interoperability Experiment [https://onlinelibrary.wiley.com/doi/10.1111/1752-1688.12474]

[12] Summary Report from 2016 Summer Institute [https://www.cuahsi.org/uploads/library/cuahsi_tr13_8.20.16.pdf]

[13] Summary Report from 2017 Summer Institute [https://www.cuahsi.org/uploads/library/CUAHSI_2017SI_TR14V102_DOI.pdf]

[14] Water Resources Impact: National Water Model [http://awramedia.org/mainblog/2018/02/15/awra-opens-national-water-model-issue-of-impact-for-public-download/]

[15] Esri Living Atlas [http://www.arcgis.com]