VIC-2L Program Schematic and Subroutine Descriptions

VIC-2L Program Schematic and Subroutine Descriptions

Standard operation of the VIC-2L is the water balance model. This model does not compute surface energy fluxes, and relies on an off-line snow model to provide information about snow accumulation and melt.

VIC-2L Optional Modes:

Full Energy Balance
Distributed Precipitation
- Constant Fractional Area of Precipitation Coverage
- Variable Fractional Area of Precipitation Coverage
Frozen Soils

VIC-2L Model Flow:

cmd_proc
check_files
get_global_param
while ( not all grid cells modeled )
- read_soilparam
- if ( grid cell to be modeled )
  - read_vegparam
  - make_in_and_outfiles
  - read_atmosdata
  - read_mu_prec
  - make_dmy
  - make_veg_var
  - make_soil_var
  - make_snow_data
  - make_frozen_soil
  - make_out_data
  - read_dist_prcp
  - rad_and_vpd
  - initialize_soil
  - initialize_veg
  - initialize_dist_prcp
  - initialize_snow
    - snow_table_albedo
  - for ( all records )
    - if ( full energy balance )
      - full_energy
    - if ( distributed precipitation )
      - Check for New Storm
      - dist_precip
    - else
      - avg_precip
  - write_data
  - close_files
  - free mu
  - free atmos
  - free dmy
  - free out_data
  - free soil_var
  - free veg_var
  - free veg_con
  - free prcp.dry
  - free prcp.wet

Subroutine Descriptions:

aero_flux_gra: computes

void aero_flux_gra(int,int,int,global_param_struct,dmy_struct, atmos_data_struct);

arno_evap: computes evaporation from bare soil.

void arno_evap(atmos_data_struct *, soil_var_struct *, soil_con_struct, global_param_struct);

avg_precip: uses the standard VIC method of applying the average precipitation over the entire grid cell. Use of this subroutine produces results comparable to the original unmodified VIC-2L water balance model.

for ( each vegetation type )
- canopy_evap
- runoff
arno_evap for bare soil
runoff for bare soil
put_data

void avg_precip(int,atmos_data_struct *,soil_con_struct,soil_var_struct *, veg_con_struct *,veg_var_struct *,snow_data_struct *, frozen_soil_struct *,dmy_struct,global_param_struct,double *);

calc_netshort: computes the net shortwave radiation for each time step.

double calc_netshort(double, int, double);

calc_trans: computes the transmissivity of the atmosphere for each time step.

double calc_trans(double, double);

canopy_evap: computes evapotranspiration and dew collection from the canopy, and evaporation from the soil layers.

void canopy_evap(atmos_data_struct *, soil_var_struct *, veg_var_struct *, soil_con_struct, veg_con_struct *, int, global_param_struct);

check_files: verifies that the files specified on the command line exist.

void check_files(infiles_struct *, filenames_struct)

close_files: closes the gridded input and output files opened in make_in_and_outfiles.

void close_files(infiles_struct, outfiles_struct);

cmd_proc: breaks the command line up into individual arguments.

filenames_struct cmd_proc(int argc, char *argv[]);

dist_precip: [DIST PRCP] uses Xu Liang's statistical method for distributed precipitation.

Fractional Area of Grid Cell that Receives Precipitation (mu)

for ( each vegetation type )
- redistribute soil moisture for new storm
- if ( precipitating )
  - compute exponentially distributed precipitation
  - canopy_evap for region that receives less precipitation
  - canopy_evap for region that receives more precipitation
- else
  - canopy_evap for no precipitation
- runoff for wet region
redistribute soil moisture on bare soil for new storm
arno_evap for bare soil which receives precipitation
runoff for bare soil which receives precipitation

Fractional Area of Grid Cell that Receives No Precipitation (1-mu)

for ( each vegetation type )
- canopy_evap for no precipitation
- runoff for no precipitation
arno_evap for bare soil receiving no precipitation
runoff for bare soil receiving no precipitation
combine evaporation and runoff for wet and dry regions
put_data

void dist_precip(int,atmos_data_struct *,soil_con_struct,soil_var_struct *, veg_con_struct *,veg_var_struct *,dmy_struct, global_param_struct,dist_prcp_struct *,double *,double);

evap_coef_gra: computes

evap_coef_gra(int,dmy_struct,global_param_struct,atmos_data_struct *, veg_con_struct *,veg_var_struct *,snow_data_struct);

evap_coef_gra_Ts: computes

evap_coef_gra_Ts(int, veg_con_struct *, atmos_data_struct *);

fltrad: computes the flat surface radiation (incoming and net shortwave) using sun-earth geometry, and tranmissivity.

double fltrad(double, double, double, int, double);

flux_Tsur_fun: computes

void flux_Tsur_fun(double, double *, double *, int, int,double, int);

flux_rtsafe: computes

double flux_rtsafe(double, double, int, int,double, int);

full_energy: solves the VIC model by computing the full energy balance.

evap_coef_pilp_gra
snow_met
if ( snow AND ( currently snowing OR still snow present ) )
- compute snow albedo
- compute 2 m wind
- compute lresist
- met_inline
- melt_brent
- convert snow units ( to mm/hr and W/m²)
- cover vegetation with snow
- compute energy balance with snow
- check for presence of snow
- for ( each vegetation type )
  - runoff
- convert runoff
- for ( each vegetation type )
  - compute soil moisture
else
- [second try]?? ( looks like avg_precip)
- for ( each vegetation type )
  - prepare dew and soil moisture values
  - canopy_evap
  - runoff
- for ( bare soil )
  - arno_evap
  - runoff
- convert units
- aero_flux_pilp_gra

get_global_param: reads global parameters from the global parameter file.

global_param_struct get_global_param(FILE *);

initialize_dist_prcp: [DIST PRCP] gives initial values to the distributed precipitation variable array.

void initialize_dist_prcp(dist_prcp_struct *,soil_con_struct,veg_con_struct *, global_param_struct);

initialize_soil: gives initial values to the soil variable array.

void initialize_soil(soil_var_struct *, soil_con_struct, int);

initialize_veg: gives initial values to the vegetation variable array.

void initialize_veg( veg_var_struct *, veg_con_struct *, global_param_struct);

in_shortwave: computes the incoming shortwave radiation.

double in_shortwave(float, int, double);

make_dmy: creates a structure which stores the day, month and year of the current time step.

dmy_struct *make_dmy(global_param_struct);

make_frozen_soil: [FROZEN] creates an array of frozen soil variables for each vegetation type. This array is modified each time step, so it is used to record values from the previous time step.

frozen_soil_struct *make_frozen_soil(int);

make_in_and_outfiles: creates file names for girdded input and output files which depend on the latitude and longitude of the current grid cell.

void make_in_and_outfiles(infiles_struct *, filenames_struct, soil_con_struct, outfiles_struct *);

make_out_data: creates an array of output variables for each vegetation type. This array is modified each time step, so it is used to record values from the previous time step.

out_data_struct *make_out_data(int);

make_snow_data: [FULL][FROZEN] creates an array of snow variables for each vegetation type. This array is modified each time step, so it is used to record values from the previous time step.

snow_data_struct *make_snow_data(int);

make_soil_var: creates an array of soil variables (moisture) for each vegetation type. This array is modified each time step, so it is used to record values from the previous time step.

soil_var_struct *make_soil_var(int);

make_veg_var: creates an array of vegetation variables (evaporation, dew) for each vegetation type. This array is modified each time step, so it is used to record values from the previous time step.

veg_var_struct *make_veg_var(int);

melt_brent: computes snow melt, and pack characteristics.

double melt_brent(double, atmos_data_struct *, snow_data_struct *);

met_inline: computes psychometric constant, atmospheric vapor pressure, and atmospheric density for use with the snow melt model.

void met_inline(atmos_data_struct *);

net_out_longwave: computes net longwave radiation for each time step.

double net_out_longwave(double,double,double,double);

open_file: opens input and output files.

FILE *open_file(char string[], char type[]);

penman: computes daily evapotranspiration using the combination equation.

double penman(double, double, double, double, double, double, double, double, float);

priestly: computes evaporation using the priestly method.

double priestley(double, double);

put_data: converts units on output variables, and writes them to gridded output files.

void put_data(out_data_struct *, soil_var_struct *, veg_var_struct *, veg_con_struct *);

rad_and_vpd: computes radiation and atmospheric vapor content.

void rad_and_vpd(atmos_data_struct *, soil_con_struct, int, dmy_struct *);

read_atmosdata: reads atmospheric data for all time steps within a grid cell

atmos_data_struct *read_atmosdata(FILE *, FILE *, int *);

read_dist_prcp: [DIST PRCP] creates an array of distributed precipitation variables for each vegetation type. This array is modified each time step, so it is used to record values from the previous time step.

dist_prcp_struct read_dist_prcp(int);

read_mu_prcp: [DIST PRCP] reads radar generated precipitation and variable values for the fractional area of precipitation coverage (mu).

double *read_mu_prec(int,atmos_data_struct*,FILE*);

read_soilparam: reads soil parameters for a grid cell.

soil_con_struct read_soilparam(FILE *);

read_vegparam: reads vegetation parameters for all vegetation types within a grid cell.

veg_con_struct *read_vegparam(FILE *, int);

runoff: computes runoff from the current grid cell.

void runoff(soil_var_struct *, soil_con_struct, double, double, double);

shrad: computes the surface radiation (incoming and net shortwave) using sun-earth geometry, tranmissivity, and surface characteristics.

double shrad(double, double, double, double, double, int, double);

snow_met: computes snow pack albedo based on coldcontent, and days since last snow fall.

void snow_met(atmos_data_struct *,snow_data_struct *);

snow_table_albedo: creates a table of snow albedo values based on age of snow pack.

void snow_table_albedo();

svp:.

double svp(double);

svp_slope:.

double svp_slope(double);

write_data: writes output data to gridded files. Output data for the water balance model includes: evaporation, moisture for the upper and lower layers, runoff, and baseflow.

Hydrology Homepage / University of Washington / VIC Administrator