Long-term Simulations:Hydrometeorological data

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Hourly values of the following hydrometeorological data must be specified for the long-term simulation period:

  • Barometric Pressure (in Hg)
  • Relative Humidity (%)
  • Total Sky Cover (%)
  • Wind Speed (kts)
  • Dry Bulb Temperature (oF)
  • Direct Radiation (W×h/m2)
  • Global Radiation (W×h/m2)

The needed data can be obtained from a variety of sources including the National Climatic Data Center (NCDC) and commercial vendors (such as Earth Info). All seven parameters are contained in data sets referred to as Surface Airways data by most sources. These data are used to perform evapotranspiration calculations.

Because of the variety of data sources, GSSHA will read the data in a variety of formats. These are:

  • SAMSON, Surface Airways, and U.S. Army Engineer Research and Development Center/WES. The SAMSON format is developed for the NCDC historical database of Surface Airways data called SAMSON. These data files may be purchased from the NCDC in the form of a CD, which contains all historical data from 1961-1990.
  • If more recent data are required, they can also be purchased from the NCDC in the Surface Airways format. These file formats contain numerous data parameters in addition to the seven required inputs above.
  • All sources of data can be transferred to the WES format containing only the data required by the model. A sample of the ERDC/WES format is shown below. Examples of the other formats can be found in the GSSHA User’s Manual.

WES formatted data

The HMET_WES format contains the following numbers in columns 1 through 11:

1. Year (4 digit)
2. Month
3. Day
4. Hour
5. Barometric pressure (inches Hg) No Data (ND) = 99.999
6. Relative humidity percent ND=999
7. Total sky cover percent ND=999
8. Wind speed knots ND=999
9. Dry bulb temperature degrees F ND=999
10. Direct radiation Watt hour per meter squared ND=9999.99
11. Global radiation Watt hour per meter squared ND=9999.99

and appears in the following format.

1995 4 14 23 29.625 86 100 000 53 9999.9 9999.9
1995 4 15 0 29.625 83 100 003 53 9999.9 9999.9
1995 4 15 1 29.615 90 80 003 52 9999.9 9999.9

The type of hydrometeorological data and the name of the hydrometeorological data file are selected in the Continuous Simulation dialog box. WMS supports none of the hydrometeorologi­cal input data formats, and the hydrometeorological data must be assembled in software external to WMS. It is highly recommended that hydrometeorological data be converted to the WES format before use in the GSSHA model.

Missing data

In the case of missing data, the ND code, as described above, should be entered in the data set. One line of data is required for each hour of the simulation. Do not skip hours or leave blank values in a line. If no data are present, enter the Year, Month, Day, Hour, and the appropriate ND code for each missing variable for each missing hour. Upon encountering the ND codes, GSSHA fills in missing data in the following way:

  • In the case of missing pressure, total sky cover, wind speed, and dry bulb temperature, the last recorded readings are used until actual data resumes.
  • For parameters with a strong diurnal pattern, such as air temperature, relative humidity, and global and direct radiation, missing hourly values are replaced with the last good value at the same time of day. For extended no data periods, the last values from the last good day of measurements are repeated until actual data resumes.

It is important that the hydrometeorological data set begin with at least one full day of complete data; no ND codes may be present.

Many stations have no radiation data. If no radiation data are available, GSSHA will calculate radiation based on the latitude and longitude of the watershed and the time of day. The latitude/longitude and time deviation from GMT is specified in the Continuous Simulation dialog box.

Related Topics

GSSHA Wiki Main Page
Primer Main Page

Long-term Simulations
Global parameters
Infiltration model
Evapotranspiration model
Hydrometeorological data
Rainfall data