Linking Climatology, Hydrology, and Hydraulics Models

 

Computation of water runoff in the Lower Little Tennessee watershed (North Carolina and Tennessee) with the Noah Land Community Model

 

 

By Cédric H. David

 

July 25, 2006

 

 

Atmospheric observational and model output datasets and Hydrologic datasets are now available on Continental scales.  The temptation to link both on a large scale is becoming bigger and bigger.  It is now possible to use atmospheric results and hydrologic data for Hydraulic modeling and river forecasting.

 

The following explains the joint effort between CUAHSI (Consortium of Universities for the Advancement of Hydrologic Science) and NCAR (National Center for Atmospheric Research) to link atmospheric models results (NAM from NCEP) and hydrologic data (NHDPlus from USGS / USEPA) to the Noah Land Community Model, in the interdisciplinary perspective of a hydraulic forecast model.

Getting atmospheric data from Unidata

Most land surface models (including Noah) need the following 2D fields as atmospheric inputs:

  • Precipitation
  • Temperature
  • Specific humidity
  • Air pressure
  • Downward Short wave radiation
  • Downward Long wave radiation
  • Wind speed

 

These fields are very basic atmospheric model results.  They are often available at various altitudes and in numerous quantities (total, rate, etc.).  The World Meteorological Organization (WMO) has standards (WMO, 1988) that are often used in observational and model output datasets. 

 

There are global and continental atmospheric models.  Several datasets could be considered as input to Land Community Models in general, and to Noah in particular.  For the purpose of Continental Water Dynamics, we are interested in continental models.  For data assimilation, historical atmospheric data could be useful (for training) as well as atmospheric forecast data (for hydrologic forecast). 

 

The continental models that can provide with input data for Noah are:

  • RUC (Rapid Update Cycle).  Available in 20, 40 and 80 km resolution for Continental U.S. (CONUS).  A 13 km version has been announced.  RUC is a forecast and historical model.  Duration: past 7 days plus 12 hours hourly forecast.
  • NAM (North American Model).  This model is a generic slot for multiple models.  Until June 20th, Eta (from η, the vertical coordinate, characteristic of the model) was used.  Since June 20th, the WRF (Weather Research & Forecasting) model has replaced Eta in NAM.  Available in 12, 20, 40 and 80 km resolution.  NAM is a forecast model only.  Duration 84 hours of forecast every 3 hours.
  • NARR (North American Regional Reanalysis), the same model has been running without changes on the time window 1979 – today.  It is a "new" model that was run retrospectively a couple of years of ago for the period 1979-2003 and is still running operationally.  Available in 32 km.  NARR is a historical model.

 

 

Unidata designed and hosts a THREDDS (Thematic Realtime Environmental Distributed Data Services) server.  NetCDF CF-1 (Climate and Forecast convention 1) files are available for download from THREDDS for all the datasets available on the server (including NAM and RUC).  The following URL gives access to the website (see Figure 1).

 

http://motherlode.ucar.edu:8080/thredds/catalog.html

 

Figure 1 Unidata's THREDDS server

 

NetCDF files can be downloaded from any of the available datasets.  The 12 km resolution of the North American Model for Continental U.S. can be used as an example (NCEP Model Data / North American Model / CONUS 12 km).

 

Figure 2 shows what can be seen by browsing through the website to this location.

Figure 2 NAM CONUS 12km

 

Any of the 30 files are model results, every 6 hours for the past 7 days.  NAM is a forecast model only. Each file has 84 hours of forecast every 3 hours.

 

Figure 3 shows the webpage linked to the first file in Figure 2 (NAM_CONUS_12km_20060713_1200.grib2).

Figure 3 accessing the netCDF server

 

The link given on Access / 4. NetCDFServer brings to a web interface to query netCDF files (see Figure 4).

Figure 4 netCDF grid subset server

 

The netCDF grid subset server offers choices such as a time window, a bounding box, and various model result parameters.  The submit button will provide a NetCDF file with CF-1 convention, for the model a given model (here NAM 12k), with any parameters of interest, in a specified Lat-Long box.  The netCDF files are now ready to be displayed in any visualization software, ArcGIS will be demonstrated here.

Using Atmospheric Files in ArcGIS

NetCDF files are accepted natively in ArcGIS 9.2.  Figure 5 shows the display of NAM40K temperature field, with NHDPlus Hydrologic Unit Codes (HUCs) 05 and 06 (corresponding to the Ohio River Basin).  The results can be used for a particular watershed, interpolated, downsized, etc.

Figure 5 NHDPlus HUCs 05 and 06, with temperature data from NAM40km

 

The integration of atmospheric science models on spherical Earth with hydrologic and land surface information on a spheroidal Earth is non-trivial.  The geospatial referencing of the atmospheric models is not communicated in netCDF Climate and Forecast convention version 1 files.  Specific geographic and projected coordinate systems have to be created for use of both atmospheric and hydrologic data at once.

Processing of hydrologic and atmospheric datasets; results with the Noah Land Community Model

Efforts are being made towards the use of any atmospheric model results as an input to Noah.  In the first results, the atmospheric input files are coming directly out of the WRF model, to which Noah is fully coupled with.  NHDPlus hydrologic data (rivers, waterbodies) and elevation data was used as an input to Noah.  The grid resolution that was used for Noah is 100m on a spherical Earth.  The vector data from NHDPlus (rivers and waterbodies) was rasterized to 100m cells and the elevation raster data was resampled from 30m to 100m cells to create input to the Land Community Model.  Proper projections pf the NHDPlus data was created.  The use of the ArcHydro framework (Hydro IDs in particular) can provide a bridge between the outputs from Noah and lateral for a stream channel model on a spheroidal Earth. 

Conclusion

Atmospheric observational and model outputs datasets, as well as hydrographic datasets are now available on the Continental U.S.  The work presented here on a small watershed, but with data from continental scale datasets shows the possibility to upscale the process. 

 

 

References

World Meteorological Organization, 1988, Technical Regulations, Volume I -- General meteorological standards and recommended practices, 1988 edition

ISBN: 92-63-18049-0

 

 

Primary Contact:

Cédric H. David

Center for Research in Water Resources

University of Texas at Austin

e-mail: cedric.david@mail.utexas.edu

 

These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 2006 Center for Research in Water Resources.