VOSWMM

Climatology Editor

Click the Climatology button to open Climatology Editor. It consists of different settings.

Temperature

The Temperature page in the Climatology Editor dialog allows you to specify the source of temperature data for snowmelt computations and potential use in determining evaporation rates. There are three choices:

  1. No Data: Choose this if you’re not simulating snowmelt and don’t need daily temperatures for evaporation rate calculations.
  2. Time Series: Select this if you’ll describe temperature variations using one of the project’s time series. You need to enter or choose the name of the time series and can edit it using the Time Series Editor.
  3. External Climate File: Choose this if you’ll read min/max daily temperatures from an external climate file. You’ll also need to provide the following information:
  • Click the FileBrowse button to search for a climate file or delete to clear the file name.
  • To start reading the climate file at a specific date different from the simulation’s start date (as set in Simulation Options), check the “Start Reading File at” box and enter the starting date.
  • If using a GHCN file, specify the temperature units used by the file.

Use the External Climate File option when you want to estimate daily evaporation rates based on daily temperature data or read them directly from the file.

Evaporation

The Evaporation page in the Climatology Editor dialog is used to provide potential evaporation rates, typically in inches per day (or millimeters per day), for a study area. There are several options for specifying these rates:

  1. Constant Value: Use this if evaporation remains the same over time. Enter the constant value in the provided edit box.
  2. Time Series: Select this if evaporation rates will vary over time and are specified in a time series. select the name of the time series, and you can edit it using the Time Series Editor. The rate remains constant from one date in the time series to the next.
  3. Climate File: Choose this if daily evaporation rates will be read from the same climate file specified for temperature data. Enter values for monthly pan coefficients in the data grid (used to convert pan evaporation to actual evaporation).
  4. Computed from Temperatures: This option uses the Hargreaves’ method to calculate daily evaporation rates from daily air temperature records in the external climate file specified on the Temperature page. It also considers the site’s latitude.
  5. Monthly Averages: Use this to supply an average rate for each month of the year. Enter the value for each month in the data grid. Rates remain constant within each month.
  6. Evaporate Only During Dry Periods: Select this if evaporation can only occur during periods with no precipitation.

Additionally, this page allows you to specify a Monthly Soil Recovery Pattern, which is a time pattern adjusting the rate of infiltration capacity recovery during precipitation-free periods. It applies to all subcatchments and can account for seasonal variations in soil drying rates. The pattern factors should align with evaporation rate variations and can be edited using the Time Pattern Editor.

Wind Speed

The Wind Speed page in the Climatology Editor dialog allows you to specify average monthly wind speeds, which are used in snowmelt rate calculations during rainy conditions. You can provide wind speeds in either miles per hour (US units) or kilometers per hour (metric units). There are two options for specifying wind speeds:

  1. Climate File Data: Use wind speeds from the same climate file specified for temperature data.
  2. Monthly Averages: Set a constant average wind speed for each month of the year in the provided data grid. Default values are zero.

Snow Melt

The Snowmelt page in the Climatology Editor dialog allows you to set parameters for snowmelt calculations. These include:

  1. Dividing Temperature Between Snow and Rain: Define the temperature at which precipitation turns from snow to rain.
  2. ATI (Antecedent Temperature Index) Weight: Reflects heat transfer effects in the snowpack based on prior air temperatures. A smaller value means a thicker snowpack with slower heat transfer.
  3. Negative Melt Ratio: Defines the heat transfer coefficient in non-melt conditions compared to melt conditions.
  4. Elevation Above MSL: Specify the study area’s average elevation above sea level.
  5. Latitude: Enter the study area’s latitude for sunrise, sunset, and evaporation rate calculations.
  6. Longitude Correction: Adjust for the difference between true solar time and standard clock time based on the study area’s longitude.

Areal Depletion

The Areal Depletion page in the Climatology Editor dialog allows you to define the relationship between snowpack depth and the area covered by snow for impervious and pervious surfaces in a study area. You specify values for 10 equal increments of relative depth ratio (0 to 0.9). These values represent the fraction of each area that remains snow-covered at each depth ratio. Valid entries range from 0 to 1 and should increase with greater depth ratios.
You can use preset buttons like “Natural Area” for typical values or “No Depletion” to set all values to 1, indicating no depletion. This configuration helps accurately model snow coverage and depletion in the area.