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Meteorology Data Command

The meteorologic model is responsible for preparing the boundary conditions that act on the watershed during a simulation. Consequently, a meteorologic model is prepared for use with one or more basin models. If the basin model contains subbasin elements, then the meteorologic model must specify how precipitation will be generated for each subbasin. Evapotranspiration should be included in the model if it is configured for continuous simulation. This would include both evaporation of free water from the vegetation surface as well as the land surface. Evapotranspiration is the combination of evaporation from the ground surface and transpiration by vegetation. Transpiration involves the process of vegetation extracting water from the soil through the plant root system. Whether by evaporation or transpiration, water is returned from the land surface or subsurface to the atmosphere. Even though evaporation and transpiration are taken together, transpiration is responsible for the movement of much more water than evaporation.

In GeoHECHMS, meteorologic boundary conditions, such as storm events, are defined using the Meteorology Data command. This command supports meteorological data such as precipitation and evapotranspiration. Evapotranspiration is only factored in for long-term continuous simulations.

Follow the steps below to use the Meteorology Data command:

  1. From the Input ribbon menu, select the Meteorology Data command.
    Meteorology Data command
  2. The Meteorology Data dialog box will be displayed.
    Meteorology Data dialog box

The following sections describe how to use the Meteorology Data command and how to interact with the above dialog box.

Selecting Meteorology

In the Select Meteorology section, the Meteorology ID entry denotes the selected meteorology. The default Meteorology ID is Default Met. The user can create a new meteorology, copy existing meteorology data to a new meteorology, and delete a meteorology. In addition, the user can navigate between meteorologies with use of the Meteorology ID dropdown entry. The user can also enter a description detailing the defined meteorology in the field adjacent to the Meteorology ID dropdown entry.
Select Meteorology section

Meteorology Specifications

In this section, the available dropdown entries are:

  • General Specifications
  • Evapotranspiration Data
  • Precipitation Data

Meteorology Specifications dropdown entry

General Specifications

If the user selects this dropdown entry, the General Specifications panel will be displayed where the user can select the precipitation and evapotranspiration types from the Precipitation type and Evapotranspiration type dropdown combo boxes as shown below.
General Specifications section

After selecting the precipitation and evapotranspiration types, the user can view the corresponding data panels using the Precipitation Data and Evapotranspiration Data panel selector.
Evapotranspiration and Precipitation entries

Note that selecting None from the Precipitation type or Evapotranspiration type dropdown combo boxes disables the Precipitation Data and Evapotranspiration Data panel selectors.
None - Evapotranspiration and Precipitation Types

Precipitation Types

The Precipitation type dropdown menu contains the following entries:

  • None
  • Frequency Storm
  • HMR52 Storm
  • Inverse Distance Weighted
  • Rain Gage
  • Rainfall Distribution
  • SCS Storm
  • Specified Hyetograph
  • Standard Project Storm

Precipitation Types

After selecting the Precipitation type, the user can define the data for the selected precipitation type from the Precipitation Data panel.

The following sections describe the Precipitation Data panel for each precipitation type.

Precipitation Type: Frequency Storm

This precipitation type is used to produce a synthetic storm from HYDRO25, TP40, and TP49 statistical data. This data is retrieved from the US National Weather Service (NWS). The objective of this precipitation type is to define an event for which the precipitation depths for various durations within the storm have a consistent exceedance probability.

When Frequency Storm is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
Frequency Storm precipitation panel

The above data panel contains the following sections:

Storm Location

This section of the data panel includes the following options:

  • Centered on current view extents
    If the user selects this radio button, the software will pick the center of the current view extent of the Map View.
  • Centered on subbasins
    If the user selects this radio button, the software will calculate and pick the center of the current subbasins present in the scenario.
  • Storm center
    If the user selects this radio button, then clicking the [Pick] button allows the user to select the storm center on the Map View. The Latitude and Longitude for the selected location are automatically filled after the selection of the storm center. The coordinate values entered have the same coordinate reference system (CRS) as the project. Using the [Clear] button, the user can clear the selected storm location.
Frequency Storm Specifications

This section of the data panel includes the following input parameters:
Frequency Storm precipitation panel - Frequency Storm Specifications section

  • Annual-partial conversion
    This dropdown combo box entry is used to select the annual to partial conversion factor to be applied. It is used to convert annual duration to partial duration precipitation frequency data.
  • Annual-partial ratio
    This read-only entry displays the corresponding ratio for the selected Annual-partial conversion entry value.
  • Precipitation data source
    This dropdown combo box entry is used to select a precipitation data source which can be used to retrieve the rainfall data for the selected storm frequency and storm duration. The dropdown entry provides the option to choose the precipitation data source for the USA, Austria, Ontario, and Germany.
  • Storm frequency
    This dropdown combo box entry is used to define the frequency of the storm in years.
  • Storm duration
    This dropdown combo box entry is used to define the duration of the storm in hours or days.
  • Intensity duration
    This dropdown combo box entry is used to define the shortest period of the storm. Usually, the Intensity duration should be set equal to the time step of the simulation. This entry must be less than the Storm duration entry.
  • Intensity position
    This dropdown combo box entry is used to specify where in the storm the period of peak intensity will occur. Changing the position does not change the total precipitation depth of the storm but does change how the total depth is distributed over time during the storm.
  • Apply TP40 reduced storm area
    This optional checkbox data entry is used to define the area that the storm occupies over the watershed for purposes of applying the TP40 reduction in the computations.

    Storm area reductions can be applied to storm events when modeling very large watersheds. For example, when modeling a 100-year storm over a 350 square mile watershed, it is unreasonable to assume that the storm occurs simultaneously over the entire watershed. In reality, storms are much smaller, and only cover a small area of a large watershed. Therefore, a storm area reduction can be defined in these situations to compute a more accurate runoff amount.
Rainfall Depth Data

The table under this section allows the user to enter the rainfall data from the US National Weather Service (NWS). Clicking the [Retrieve] button retrieves the rainfall data from the selected precipitation data source. The cells contained within the Rainfall Depth column get enabled/disabled depending upon the values selected in the Storm duration and Intensity duration dropdown combo box entries.
Frequency Storm precipitation panel - Rainfall Depth Data section

For example, if the user selects 24 Hours as the Storm duration, then all the Rainfall Depth column cells after the 24 Hours storm duration will be disabled. Similarly, if the user selects 15 Minutes as the Intensity duration, then all the Rainfall Depth entries before 15 Minutes will be disabled.

Precipitation Type: HMR52 Storm

This precipitation type can be used to compute the probable maximum precipitation (PMP) for a watershed. The concentric ellipses are used to construct the storm spatial pattern where each ellipse represents an isohyet of precipitation depth. The storm is located over the watershed by specifying the center of the pattern and the angle of the major axis of the ellipses. Total precipitation depth is computed using a specified storm area and area-duration curves. The total precipitation depth is converted to a temporal pattern based on the selected placement of the peak intensity within the storm duration. The HMR52 storm precipitation type includes several parameters to describe the location, orientation, and temporal distribution of the storm.

When HMR52 Storm is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
HMR52 Storm precipitation panel

The above data panel contains the following sections:

HMR52 PMP Storm Specifications

This section of the data panel includes the following options:

  • Centered on current view extents
    If the user selects this radio button, the software will pick the center of the current view extent of the Map View.
  • Centered on subbasins
    If the user selects this radio button, the software will calculate and pick the center of the current subbasins present in the scenario.
  • Storm center
    If the user selects this radio button, then clicking the [Pick] button allows the user to select the storm center on the Map View. The Latitude and Longitude for the selected location get automatically filled after the selection of the storm center. The coordinate values entered have the same coordinate reference system (CRS) as the project. Using the [Clear] button, the user can clear the selected storm location.
  • Storm preferred orientation & Storm actual orientation
    The preferred and actual storm orientation angles are measured in degrees increasing clockwise from North. Click the [Retrieve] button to retrieve the storm preferred orientation for the selected location. Clicking the [View] button displays the HMR52 Storm Preferred Orientation dialog box to view the storm preferred orientation data.
    Frequency Storm precipitation panel - HMR52 Storm Preferred Orientation dialog box
  • Peak intensity
    This dropdown combo box entry is used to select the 6-hour peak intensity for the HMR52 storm. This peak intensity parameter specifies the period within the 72-hour storm when the precipitation will be the greatest. The 6 hours of peak intensity can be set to begin as early as hour 24 of the storm or as late as hour 60 of the storm. The depth of rain falling during the period of peak intensity is subdivided into 1-hour increments using the 1-hour to 6-hour depth ratio parameter.
  • 1-hour to 6-hour depth ratio
    This field contains the ratio of the 1-hour to 6-hour depth during the 6-hour peak intensity period. The depth of rain falling during the period of peak intensity is subdivided into 1-hour increments using this parameter.
  • Probable maximum storm area
    This field specifies the total storm area.
HMR51 Depth-Area-Duration PMP Estimates

The table under this section allows the user to enter the precipitation depths from the HMR51 PMP (Probable Maximum Precipitation) data corresponding to different storm sizes and storm durations.
Frequency Storm precipitation panel - HMR51 Depth-Area-Duration PMP Estimates

Clicking the [Retrieve HMR51 PMP Data] button will cause the software to interpolate the values for the HMR51 Depth-Area-Duration PMP Estimates table.

Clicking the [View HMR51 PMP Data] button will display the HMR51 PMP Data dialog box that displays the graphical plots of the HMR51 PMP rainfall data.
Frequency Storm precipitation panel - HMR51 PMP Data

Precipitation Type: Inverse Distance Weighted

This precipitation type was originally designed for application in real-time forecasting systems. This precipitation type uses recording gages that are reported at regular intervals such as 15 minutes or 1 hour. It can also use gages that only report daily precipitation totals. This precipitation type can automatically switch from using close gages to using more distant gages when the closer gages stop reporting data.

When Inverse Distance Weighted is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
Inverse Distance Weighted precipitation panel

The above data panel contains the following sections:

Inverse Distance Weighted Options

This section of the data panel includes the following input parameters.

  • Search radius
    This field defines the search distance (or radius) that is used to limit the influence distance of precipitation gages. The default value for this field is 621 miles (or 1000 kilometers). The user can click the [Measure] button to measure the influence distance from the Map View.
  • Use index depth to adjust for regional bias in precipitation
    When this checkbox is checked, the Index Depth columns of the Rain Gages and the Subbasin Weighted Nodes data grids are enabled.
Rain Gages

The Rain Gages data grid lists all the rain gages defined in the model and the manner by which they are to be utilized with the Inverse Distance Weighted meteorological method.
Inverse Distance Weighted precipitation panel - Rain Gages section

  • Rain Gage ID
    This read-only data column lists all the rain gages defined in the model.
  • Use Rain Gage
    This checkbox option is used to specify that the data defined for the rain gage should be used in the Inverse Distance Weighted meteorological method.
  • Daily Gage Only
    This checkbox option is used to specify that the rain gage only contains daily total precipitation values. If the Use Rain Gage checkbox option of the current rows is unchecked, then the Daily Gage Only checkbox option will be disabled.
  • Index Depth
    This field represents the index value to adjust the gage for regional bias. The average annual precipitation total is often used as the index depth at a rain gage. This data grid column will be disabled when the Use index depth to adjust for regional bias in precipitation checkbox is unchecked.
Subbasin Weighted Nodes

This section and the corresponding data grid list all the nodes defined for each subbasin.
Inverse Distance Weighted - Subbasin Weighted Nodes section

  • Subbasin ID
    This dropdown combo box is used to select the subbasin to define the weighted nodes to be used in the Inverse Distance Weighted meteorological method. Alternatively, the user can click the [Pick] button to interactively select the subbasin from the Map View.
  • Node ID
    This editable column represents a unique name for the defined weighted node.
  • Location
    This read-only column indicates if the node location has already been placed on the Map View or not.
  • Node Weight
    This spin control field is used to define the node weight and ranges from 0.00 to 1.00.
  • Index Depth
    This column represents the index value to adjust the node for regional bias. Note that this data grid column is disabled when the Use index depth to adjust for regional bias in precipitation checkbox is unchecked.

    The [Assign] button is used to select node location on subbasin from the Map View. The user can also use the [Draw] button to draw the node location on the subbasin from the Map View. The [Delete] button can be used to delete the current row’s weighted node definition. Alternatively, the user can right-click the desired row and select the Delete Row(s) option from the context menu.

Precipitation Type: Rain Gage

This precipitation type is designed to work with time series recording and single value recording precipitation gages. Time series recording precipitation gages typically measure precipitation as it occurs and then the raw data is converted to a regular time step, such as 15 minutes or 1 hour. Single value recording precipitation gages only record the total storm depth. The user can choose from different methods to develop the weights applied to each rain gage when calculating the hyetograph for each subbasin. For increased flexibility, the total storm depth and the temporal pattern are developed separately for each subbasin.

When Rain Gage is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
Rain Gages precipitation panel

The above data panel contains the following sections:

Rain Gage Specifications

This section of the data panel includes the following options.

  • Define index depth to adjust for regional bias in precipitation
    This checkbox option allows the user to adjust the regional bias in the rainfall depth to be used for each rain gage and subbasin. This is helpful when there are regional trends in precipitation patterns. Using this option requires the specification of an “index” value for each precipitation gage and each subbasin. The average annual precipitation total is often used as the index at a rain gage, and the estimated average annual precipitation over a subbasin area is often used as the index for a subbasin. Alternatively, the monthly average values may be used at each rain gage and subbasin. The index values are used to adjust the precipitation data for regional trends before calculating the weighted depth and weighted timing.
  • Define rain gage total depth (override)
    This checkbox option allows the user to override the precipitation depth at each rain gage. Without this override, the total depth defined at a rain gage is the sum of the values in the rain gage time series. With this override, the values in the rain gage time series are proportionally adjusted to have a sum equal to the specified total rain depth.
Subbasin Index Depths (Optional)

This optional section contains a data grid that is used to define an Index Depth for each subbasin. This section is disabled if the Define index depth to adjust for regional bias in precipitation checkbox is unchecked. For the Index Depth option to work, the user must enter an index value for each subbasin and rain gage.
Rain Gages precipitation panel - Subbasin Index Depth (Optional)

Time Series Rain Gage Specifications (Optional Override)

This section contains a data grid that is used to define a total depth and index depth for each rain gage defined within the Meteorological Model for the current scenario. This section is disabled if both the Define rain gage total depth(override) and the Define index depth to adjust for regional bias in precipitation checkbox options are unchecked.
Rain Gages precipitation panel - Time Series Rain Gage Specifications (Optional Override)

Single Value Rain Gage Specifications

This section contains a data grid that allows the user to manually define single value rain gages. In the Single Value Rain Gage ID column, the user can manually enter a unique ID for a single value rain gage.
Rain Gages precipitation panel - Single Value Rain Gage Specifications

Subbasin Weighted Rain Gages

This section allows the user to define how much weight each rain gage has for each subbasin.
Rain Gages precipitation panel - Subbasin Weighted Rain Gages

  • Select Subbasin ID
    This dropdown combo box lists all the subbasins contained within the scenario. If a subbasin is currently selected on the Map View, it is shown selected in this entry. Otherwise, the last selected subbasin is shown selected. The [Pick] button allows the user to manually select the subbasin from the Map View.
  • Rain Gage ID
    This read-only data column lists all the rain gages (i.e., time series and single value) defined in the scenario.
  • Rain Gage Type
    This read-only field lists the type of rain gage that is defined. It is either Time Series or Single Value.
  • Use Rain Gage
    This checkbox entry allows the user to specify whether to use the rain gage for the selected subbasin or not.
  • Gage Depth Weight
    This spin control allows the user to define the depth weight for the rain gage. Note that this cell is disabled if the Use Rain Gage checkbox is unchecked.
  • Gage Time Weight
    This spin control allows the user to define the time weight for the rain gage. This cell is disabled for single value rain gages or if the Use Rain Gage checkbox is unchecked.

Precipitation Type: Rainfall Distribution

This precipitation type is a region-based temporal rainfall distribution of different areas. The data used in this precipitation type is created by historical storm events and the statistical analysis for each climate region and then grouped by different durations (6-hr, 12-hr, 24-hr, etc), quartiles (1st, 2nd, 3rd, 4th), and percent of occurrence (10%, 20%, 30%, etc.). The characteristics curve of rainfall distribution is a relationship between fractional rainfall intensity and elapsed time. These storm distributions contain the cumulative fractional rainfall depth that ranges from 0 to 1 and the incremental fractional intensity rainfall distribution.

When Rainfall Distribution is selected for the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
Rainfall Distribution precipitation panel

The above data panel contains the following sections:

Rainfall Distribution Specifications

This section of the data panel includes the following parameters.

  • Rainfall distribution
    This field displays information about the type of rainfall distribution selected. Clicking the [Select] button displays the Rainfall Distribution dialog box.
    Rainfall Distribution precipitation panel - Rainfall Distribution dialog boxThe above dialog box allows the user to select different available rainfall distributions. Refer to this article to learn more about the Rainfall Distribution dialog box.
  • Rainfall description
    This field displays the description corresponding to the selected rainfall distribution.
    Rainfall Distribution precipitation panel - Rainfall Distribution Specifications section
  • Storm duration
    This field displays the corresponding value of a storm duration (in hours) for the selected rainfall distribution.
Precipitation Assignment

This section of the data panel includes the following input parameters:
Rainfall Distribution precipitation panel - Precipitation Assignment panel

  • All subbasins same precipitation
    After selecting this radio button, the user can assign the same amount of precipitation to all the subbasins present within the model.
  • Individual subbasin precipitation
    After selecting this radio button, the user can specifically mention the amount of precipitation for all the individual subbasins present within the model.

Precipitation Type: SCS Storm

Drainage planning in the United States is often performed using hypothetical storms developed by the Soil Conservation Service (SCS), now known as the Natural Resources Conservation Service (NRCS). These storms were developed by the SCS as averages of rainfall patterns; they are represented in a dimensionless form. The SCS designed this storm method for a small drainage area. This precipitation type intends to estimate both peak flow rate and runoff volume from precipitation of a “critical” duration.

When the SCS Storm is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
SCS Storm precipitation panel

The above data panel contains the following sections:

Precipitation Frequency Estimate Retrieval

This section of the data panel includes the following options.

  • Centered on current view extents
    If the user selects this radio button, the software will pick the center of the current view extent of the Map View.
  • Centered on subbasins
    If the user selects this radio button, the software will calculate and pick the center of the current subbasins present in the scenario.
  • Site location
    If the user selects this radio button, then clicking the [Pick] button allows the user to retrieve NOAA Atlas 14 precipitation data. The Latitude and Longitude for the selected location get automatically filled after the selection of the site location. The coordinate values entered have the same coordinate reference system (CRS) as the project. Using the [Clear] button, the user can clear the selected site location.
  • Precipitation data source
    This dropdown combo box entry is used to select a precipitation data source which can be used to retrieve the rainfall data for the selected storm frequency and storm duration. The dropdown entry provides the option to choose the precipitation data source for the USA, Austria, Ontario, and Germany.
  • Storm recurrence interval
    From this dropdown combo box, the user can select a storm reoccurrence interval.
  • Storm duration
    From this dropdown combo box, the user can select storm duration.

The [Retrieve Data] button allows the user to retrieve the rainfall data for the selected precipitation data source.

SCS Precipitation Data

This section of the data panel includes the following input parameters.
SCS Storm precipitation panel - SCS Precipitation Data section

  • SCS storm distribution
    This dropdown combo box entry is used to select the SCS storm distribution. The available options within this dropdown are Area-Dependent, Type I, Type IA, Type II, and Type III.
  • Rainfall depth
    This field is used to define the rainfall depth from the NOAA Atlas 14. Clicking the […] button displays the NOAA rainfall data web page for the current map location. Note that this button is disabled for precipitation data sources except for NOAA Atlas 14.
Apply storm area reduction

Storm area reductions can be applied to storm events when modeling very large watersheds. For example, when modeling a 100-year storm over a 350 square mile watershed, it is unreasonable to assume that the storm occurs simultaneously over the entire watershed. In reality, storms are much smaller, and only cover a small area of a large watershed. Therefore, a storm area reduction can be defined in these situations to compute a more accurate runoff amount.

If the user selects the Apply storm area reduction check box option, the following fields get activated:
SCS Storm precipitation panel - Apply storm area reduction section

  • Storm area
    This field is used to define the area that the storm occupies over the watershed.
  • TP40 storm area reduction
    This radio button option is used to define the area that the storm occupies over the watershed for purposes of applying the TP40 reduction in the computations.
  • User-defined area reduction
    This radio button entry allows the user to define a storm area reduction factor of the subbasin drainage area versus the storm area reduction factor to be applied to the subbasin. Clicking the […] button will display the Storm Area Reduction Curve Data dialog box that allows the user to define the paired data values for storm area reduction.
    SCS Storm precipitation panel - Storm Area Reduction Curve Data

Precipitation Type: Specified Hyetograph

This precipitation type allows the user to specify the exact rain gage time series to use for the hyetograph at each subbasin. This precipitation type is useful when precipitation data is processed externally and imported without modification. This method is also useful when a single rain gage can be used to represent a storm event.

When the Specified Hyetograph is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
Specified Hyetograph precipitation panel

The above data panel contains the following sections:

Specified Hyetograph Options

The Scale rain gage hyetograph to defined total rainfall depth (Optional Total Depth Override) checkbox option is used to enable adjustment of the precipitation depth for each rain gage. Checking this option also enables the Optional Total Depth Override column of the Subbasin Rain Gages table.

Subbasin Rain Gages

The following data columns are provided in the data grid of this section.

  • Subbasin ID
    This column lists all the subbasins contained within the scenario.
  • Rain Gage ID
    This column contains a dropdown combo box in each cell that lists all the defined rain gages. Clicking the […] button will display the Rain Gage Data dialog box which allows the user to define time series rain gage data. Refer to this article in our knowledge base to learn more about Rain Gage Data dialog box.
  • Optional Total Depth Override
    This data column is enabled if the Scale rain gage hyetograph to defined total rainfall depth (Optional Total Depth Override) checkbox is checked. Otherwise, this data column is grayed out (i.e., disabled). This field gives the user the option to define a total rainfall depth for each subbasin.

Precipitation Type: Standard Project Storm

This precipitation type provides precipitation versus time relationship that is designed to be reasonably representative of major storms that have occurred or might occur in the area of concern. It is developed by studying the major storm events in the region, excluding the most extreme.

When Standard Project Storm is selected as the Precipitation type, the following data panel will be displayed for the Precipitation Data selector.
Standard Project Storm precipitation panel

The above data panel contains the following sections:

Probable Maximum Index Precipitation Data

This section of the data panel includes the following input parameters:

  • Storm distribution type
    This dropdown combo box entry is used to select the storm distribution. The available entries in this dropdown are Southwest Division and Standard.
  • Index Rainfall depth
    This field is used to define the rainfall depth. When the user clicks on the […] button, the Probable Maximum Index Precipitation dialog box will be displayed where the user can view the probable maximum index precipitation data.
    SCS Storm precipitation panel - Probable Maximum Index Precipitation dialog box
  • Storm area
    This field is used to define the area that the storm occupies over the watershed.
Probable Maximum Index Precipitation Retrieval

This section of the data panel includes the following options.

  • Centered on current view extents
    If the user selects this radio button, the software will pick the center of the current view extent of the Map View.
  • Centered on subbasins
    If the user selects this radio button, the software will calculate and pick the center of the current subbasins present in the scenario.
  • Site location
    If the user selects this radio button, then clicking the [Pick] button allows the user to retrieve NOAA Atlas 14 precipitation data. The Latitude and Longitude for the selected location get automatically filled after the selection of the site location. The coordinate values entered have the same coordinate reference system (CRS) as the project. Using the [Clear] button, the user can clear the selected site location.

    The [Retrieve Probable Maximum Index Precipitation] button retrieves the probable maximum index precipitation data for the selected location.

Subbasin Transposition Factors

The data grid of this section has two columns. The Subbasin ID column lists all the subbasins contained within the scenario, and the Transposition Factor column accounts for the location of each subbasin contained in the scenario, relative to the center of the storm.
SCS Storm precipitation panel - Subbasin Transposition Factors

Evapotranspiration Types

The Evapotranspiration type dropdown menu contains the following entries:

  • None
  • Annual Evapotranspiration
  • Monthly Average
  • User-Defined

Evapotranspiration Types

After selecting the Evapotranspiration type, the user can define the data for the selected evapotranspiration type from the Evapotranspiration Data panel.

The following sections describe the Evapotranspiration Data panel for each evapotranspiration type.

Evapotranspiration Type: Annual Evapotranspiration

This evapotranspiration type is designed to work with a maximum daily rate combined with an optional pattern of variation throughout the year. Each basin has its evaporation rate information.

Specifying only a daily rate can produce good results for simulations lasting a few days to weeks. The optional pattern can be used to adjust the applied evapotranspiration rate during simulations lasting weeks to years. The evapotranspiration for each day of the simulation is computed by multiplying the evapotranspiration rate by the percentage interpolated from the defined percent pattern.

When Annual Evapotranspiration is selected as the Evapotranspiration type, the following data panel will be displayed for the Evapotranspiration Data selector.
Annual Evapotranspiration panel

The above data panel contains the following sections:

Annual Evapotranspiration Specifications

The following data columns are provided in the data grid of this section.

  • Subbasin ID
    This read-only column lists all the subbasins contained within the project.
  • Daily Evapotranspiration Rate
    This column is used to define the daily evapotranspiration rate for subbasins.
  • Percent Weighting Pattern (Optional) ID
    This column contains a dropdown combo box for each subbasin that allows the user to select an already defined weighting pattern to be applied to the defined Daily Evapotranspiration Rate for the subbasin. Clicking the […] button will display the Evapotranspiration Weighting Pattern Data dialog box that allows the user to define the paired data values for the evapotranspiration weighting pattern as shown below.
    Annual Evapotranspiration panel - Evapotranspiration Weighting Pattern Data dialog box

Evapotranspiration Type: Monthly Average

This evapotranspiration type is designed to work with measured pan evaporation data. However, it can also be used with the data collected by the eddy correlation technique or other modern methods. Regardless of how the evapotranspiration data is collected, it is typically presented as the average depth of evaporated water each month.

When the Monthly Average is selected as the Evapotranspiration type, the following data panel will be displayed for the Evapotranspiration Data selector.
Monthly Average evapotranspiration panel

The above data panel contains the following sections:

Monthly Average Evapotranspiration Specifications
  • Apply to all subbasins
    This radio button option is used to apply the defined evapotranspiration rate data to all subbasins.
  • Apply different rates to each subbasin
    This radio button option is used to define a separate evapotranspiration rate for each subbasin.
Monthly Average Evapotranspiration Rate Data

In the Select subbasin dropdown combo box, all the subbasins within the model are listed. This allows the user to select a specific subbasin and define unique evapotranspiration data for that subbasin. If the Apply to all subbasins radio button is selected, the Select subbasin dropdown combo box lists will be disabled.

The following data columns are provided in the data grid of this section.

  • Evapotranspiration Rate
    This data column represents the evapotranspiration rate to be applied monthly.
  • Pan Coefficient
    This data column represents the pan coefficient to be applied monthly. The evapotranspiration rate is multiplied by the pan coefficient to determine the final potential rate for each month.

Evapotranspiration Type: User-Defined

This evapotranspiration type allows the user to specify an exact time series to use for the potential evapotranspiration. It is also useful when a single evapotranspiration observation measurement is used over a subbasin.

When User-Defined is selected as the Evapotranspiration type, the following data panel will be displayed for the Evapotranspiration Data selector.
User Defined evapotranspiration panel

The above data panel contains the following sections:

User-Defined Evapotranspiration Specifications
  • Apply to all subbasins
    This radio button option is used to apply the defined evapotranspiration rate data to all subbasins.
  • Apply different rates to each subbasin
    This radio button option is used to define a specific evapotranspiration rate for each subbasin.
Evapotranspiration Assignment to All Subbasins

Note that this section is disabled (i.e., grayed out) if the Apply different rates to each subbasin radio button entry is selected. Otherwise, if this section is enabled, all subbasins are assigned the same evapotranspiration time series gage.

The Evapotranspiration gage ID dropdown combo box lists all the evapotranspiration time series gages contained within the model. This allows the user to select a specific gage to define unique evapotranspiration data to all the subbasins within the scenario. Clicking the […] button will display the Evapotranspiration Time Series Gages Data dialog box that allows the user to define evapotranspiration time series gage data as shown below.
User-Defined evapotranspiration panel - Evapotranspiration Time Series Gage Data dialog box

Individual Evapotranspiration Subbasin Assignment

This section is disabled (i.e., grayed out) if the Apply to all subbasins radio button is selected. Otherwise, if this section is enabled, each subbasin is assigned its own evapotranspiration time series gage.

The following data columns are provided in the data grid of this section.

  • Subbasin ID
    This read-only column lists all the subbasins contained within the project.
  • Evapotranspiration gage ID
    This dropdown combo box allows the user to select a specific gage to define and assign unique evapotranspiration data to all subbasins contained within the project.

After specifying all of the necessary precipitation and evapotranspiration data for the specified scenario, the user should compute the analysis to incorporate the defined meteorology data into the project.

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