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snow.sno

Purpose

snow.sno is the snow parameter database. Each row defines a named set of snow accumulation and melt parameters. HRUs reference a row by name through the snow column of hru-data.hru, which the reader resolves to an index into the snodb array. If hru-data.hru carries null for an HRU's snow entry, that HRU uses the default snow_parameters values.

Source

Format

List-directed reads (free format, whitespace-separated). The first two lines are skipped. From line three to end of file each line is one snow parameter row. The reader counts records on a first pass, allocates snodb(0:imax), then reads each row into snodb(isno).

  • Line 1: title (skipped). Editor convention: snow.sno: written by SWAT+ editor ....
  • Line 2: column header (skipped). Editor convention: name fall_tmp melt_tmp melt_max melt_min tmp_lag snow_h2o cov50 snow_init.
  • Line 3+: one row per parameter set, 9 fields each.

The fields appear in the order declared in type snow_parameters:

# Field Type Units Default Description
1 name char(40) - (none) Parameter set name. Referenced from the snow column of hru-data.hru.
2 falltmp real deg C 0.0 Snowfall temperature. Precipitation falls as snow when the mean air temperature is at or below this threshold.
3 melttmp real deg C 0.5 Snowmelt base temperature. Snowmelt only occurs when the snowpack temperature exceeds this value.
4 meltmx real mm/deg C/day 4.5 Maximum melt rate factor for snow during the year (occurs near 21 June).
5 meltmn real mm/deg C/day 0.5 Minimum melt rate factor for snow during the year (occurs near 21 December).
6 timp real none 0.8 Snowpack temperature lag factor (0 to 1). Higher values give more weight to the current day's air temperature.
7 covmx real mm H2O 25.0 Snow water content above which the ground is fully covered by snow.
8 cov50 real none 0.5 Fraction of covmx at which the ground is 50% snow-covered. Shape factor for the snowpack areal depletion curve.
9 init_mm real mm H2O 0.0 Initial snow water content at the start of the simulation.

The defaults above are the values assigned in type snow_parameters at declaration. They are not values the reader supplies, so every row of snow.sno must list all nine fields.

Example

refdata/Ames_sub1/snow.sno:

snow.sno: written by SWAT+ editor v2.3.3 on 2023-10-25 08:58 for SWAT+ rev.60.5.7
name                  fall_tmp      melt_tmp      melt_max      melt_min       tmp_lag      snow_h2o         cov50     snow_init
snow001                1.00000       0.50000       4.50000       4.50000       1.00000       1.00000       0.50000       0.00000

One parameter set named snow001. Note that the example value for meltmn (column 5) is 4.5, identical to meltmx. The defaults shipped in source set meltmn = 0.5.

  • hru-data.hru. References a snow.sno row by name in its snow column. null selects the type defaults.
  • file.cio. Names the snow.sno file in the init group via in_parmdb%snow. Set to null to skip reading (no snow database is loaded; HRUs that point at a snow name will fall back as described above).