WMS:GSSHA Precipitation

The GSSHA Precipitation dialog can be accessed by selecting GSSHA | Precipitation... while in the 2D Grid module. All rainfall types in GSSHA must be tied to a specific point in time by specifying the year, month, day, hour, and minute of each rainfall data point. This dialog allows specifying the type of rainfall and entering the necessary data associated with the rainfall type.

Rainfall can be input in one of the following formats, selected from the drop-down in the Rainfall event(s) section:

• "Uniform"
• "Gage"
• "Hyetograph"
• "Nexrad Radar"

Uniform

GSSHA Precipitation dialog showing the "Uniform" options.

The ability to assign uniform rainfall over the entire watershed is maintained largely as a trouble-shooting feature and is mostly used in initial model development. Real watersheds are modeled with temporally- and spatially-varying rainfall. When "Uniform" is selected from the Rainfall event(s) drop-down, the following rows appear in the spreadsheet:

• Intensity – Rainfall intensity as a decimal value in millimeters per hour.
• Duration – Rainfall duration as an integer in minutes.
• Start date/time – A date and time drop-down that allows for selecting the start time of the rainfall event. Selection can be made directly from the drop-down, or the following information can be entered in "MM/DD/YYYY H:MN:SS AM/PM" format:
  • MM – Month. Can be either one or two digits.
  • DD – Day, entered in two-digit format ("04" for the fourth day of the month).
  • YYYY &ndash Year, entered in four digit format.
  • H – Hour, can be either one or two digits.
  • MN – Minutes, entered in two digit format.
  • SS – Seconds, entered in two digit format.
  • AM/PM – Enter either "AM" or "PM".

Gage

GSSHA Precipitation dialog showing the "Gage" options.

Select the Gage option to specify single or multi-gage rainfall. Rainfall distributions for all rain gages should already be entered on a rain gage coverage in WMS. Create a separate rain gage coverage for each precipitation event. Rain gage files constructed using an editor outside of WMS can be used in two ways: reference the file in the Manage Files dialog when saving the GSSHA project file or use the Import Gage File... button to read the file and generate rain gage coverages in WMS.

Temporally Varying, Spatially Uniform (Single Gage) Rainfall

Single-gage rainfall produces a time series of rainfall for the entire watershed. Toggle on the the rain gage coverages (containing a single gage) in the dialog that will be used for writing the GAG file required by GSSHA.

Temporally Varying Multiple-Gage Rainfall

Select rain gage coverages with multiple gages defined to be used for writing the GAG file required by GSSHA. Specify whether to use Inverse distance weighting (IDW) or Thiessen polygons for determining the spatial variation in rainfall for each grid cell.

Hyetograph

GSSHA Precipitation dialog showing the "Hyetograph" options.

Select the Hyetograph option to enter a temporally varying, spatially uniform (single-gage) event without creating a rain gage coverage. Enter the average total depth (mm) of precipitation across the drainage area and the start date/time. Click on the Define Distribution... button to define the temporal distribution.

Nexrad Radar

GSSHA Precipitation dialog showing the "Nexrad Radar" options.

Select the Nexrad Radar option and click on the Import Radar Data... button to process NEXRAD rainfall data for use in GSSHA. WMS will write the GSSHA rainfall (*.gag) file using the RADAR type. For RADAR type rainfall inputs, Thiessen polygons should be selected as the interpolation method.

See Also

• WMS:Radar Rainfall
• WMS:GSSHA Snowmelt Options