double canopy_evap(layer_data_struct *layer,
veg_var_struct *veg_var,
char CALC_EVAP,
int veg_class,
int month,
double *Wdew,
double delta_t,
double rad,
double vpd,
double net_short,
double air_temp,
double ra,
double displacement,
double roughness,
double ref_height,
double elevation,
double ppt,
double *depth,
double *Wmax,
double *Wcr,
double *Wpwp,
double *frost_fract,
float *root,
double *dryFrac,
double shortwave,
double Catm,
double *CanopLayerBnd)
/**********************************************************************
CANOPY EVAPORATION
Calculation of evaporation from the canopy, including the
possibility of potential evaporation exhausting ppt+canopy storage
2.16 + 2.17
Index [0] refers to current time step, index [1] to next one
If f < 1.0 then veg_var->canopyevap = veg_var->Wdew + ppt
and Wdew = 0.0
DEFINITIONS:
Wdmax - max monthly dew holding capacity
Wdew - dew trapped on vegetation
Modified
04-14-98 to work within calc_surf_energy_balance.c KAC
07-24-98 fixed problem that caused hourly precipitation
to evaporate from the canopy during the same
time step that it falls (OK for daily time step,
but causes oscilations in surface temperature
for hourly time step) KAC, Dag
modifications:
6-8-2000 Modified to use spatially distributed soil frost if
present. KAC
5-8-2001 Modified to close the canopy energy balance. KAC
2009-Jun-09 Moved computation of canopy resistance rc out of penman()
and into separate function calc_rc(). TJB
2012-Jan-16 Removed LINK_DEBUG code BN
2013-Jul-25 Save dryFrac for use elsewhere. TJB
2014-Mar-28 Removed DIST_PRCP option. TJB
2014-Apr-25 Switched LAI from veg_lib to veg_var. TJB
2014-May-05 Added logic to handle LAI = 0. TJB
2014-May-05 Replaced HUGE_RESIST with RSMAX. TJB
**********************************************************************/
{
/** declare global variables **/
extern veg_lib_struct *veg_lib;
extern option_struct options;
/** declare local variables **/
int i;
double f; /* fraction of time step used to fill canopy */
double throughfall;
double Evap;
double tmp_Evap;
double canopyevap;
double tmp_Wdew;
double layerevap[MAX_LAYERS];
double rc;
int flag_irr;
Evap = 0;
/* Initialize variables */
for ( i = 0; i < options.Nlayer; i++ ) layerevap[i] = 0;
canopyevap = 0;
throughfall = 0;
tmp_Wdew = *Wdew;
/****************************************************
Compute Evaporation from Canopy Intercepted Water
****************************************************/
veg_var->Wdew = tmp_Wdew;
if (tmp_Wdew > veg_var->Wdmax) {
throughfall = tmp_Wdew - veg_var->Wdmax;
tmp_Wdew = veg_var->Wdmax;
}
flag_irr = veg_lib[veg_class].irr_active[month-1];
rc = calc_rc((double)0.0, net_short, veg_lib[veg_class].RGL,
air_temp, vpd, veg_var->LAI, (double)1.0, FALSE,flag_irr);
if (veg_var->LAI > 0)
canopyevap = pow((tmp_Wdew/veg_var->Wdmax),(2.0/3.0))
* penman(air_temp, elevation, rad, vpd, ra, rc, veg_lib[veg_class].rarc)
* delta_t / SEC_PER_DAY;
else
canopyevap = 0;
if (canopyevap > 0.0 && delta_t == SEC_PER_DAY)
/** If daily time step, evap can include current precipitation **/
f = min(1.0,((tmp_Wdew + ppt) / canopyevap));
else if (canopyevap > 0.0)
/** If sub-daily time step, evap can not exceed current storage **/
f = min(1.0,((tmp_Wdew) / canopyevap));
else
f = 1.0;
canopyevap *= f;
/* compute fraction of canopy that is dry */
if (veg_var->Wdmax > 0)
*dryFrac = 1.0-f*pow((tmp_Wdew/veg_var->Wdmax),(2.0/3.0));
else
*dryFrac = 0;
tmp_Wdew += ppt - canopyevap;
if (tmp_Wdew < 0.0)
tmp_Wdew = 0.0;
if (tmp_Wdew <= veg_var->Wdmax)
throughfall += 0.0;
else {
throughfall += tmp_Wdew - veg_var->Wdmax;
tmp_Wdew = veg_var->Wdmax;
}
/*******************************************
Compute Evapotranspiration from Vegetation
*******************************************/
if(CALC_EVAP)
transpiration(layer, veg_var, veg_class, month, rad, vpd, net_short,
air_temp, ra, ppt, *dryFrac, delta_t,
elevation, depth, Wmax, Wcr, Wpwp,
layerevap,
frost_fract,
root,
shortwave,
Catm,
CanopLayerBnd);
veg_var->canopyevap = canopyevap;
veg_var->throughfall = throughfall;
veg_var->Wdew = tmp_Wdew;
tmp_Evap = canopyevap;
for(i=0;i<options.Nlayer;i++) {
layer[i].evap = layerevap[i];
tmp_Evap += layerevap[i];
}
Evap += tmp_Evap / (1000. * delta_t);
return (Evap);
}
/******************************************************************************
* @brief Calculation of evaporation from the canopy, including the
* possibility of potential evaporation exhausting ppt+canopy storage
*****************************************************************************/
double
canopy_evap(layer_data_struct *layer,
veg_var_struct *veg_var,
bool CALC_EVAP,
unsigned short veg_class,
double *Wdew,
double delta_t,
double rad,
double vpd,
double net_short,
double air_temp,
double ra,
double elevation,
double ppt,
double *Wmax,
double *Wcr,
double *Wpwp,
double *frost_fract,
double *root,
double *dryFrac,
double shortwave,
double Catm,
double *CanopLayerBnd)
{
/** declare global variables **/
extern veg_lib_struct *vic_run_veg_lib;
extern option_struct options;
/** declare local variables **/
size_t i;
double f; /* fraction of time step used to fill canopy */
double throughfall;
double Evap;
double tmp_Evap;
double canopyevap;
double tmp_Wdew;
double layerevap[MAX_LAYERS];
double rc;
Evap = 0;
/* Initialize variables */
for (i = 0; i < options.Nlayer; i++) {
layerevap[i] = 0;
}
canopyevap = 0;
throughfall = 0;
tmp_Wdew = *Wdew;
/****************************************************
Compute Evaporation from Canopy Intercepted Water
****************************************************/
veg_var->Wdew = tmp_Wdew;
if (tmp_Wdew > veg_var->Wdmax) {
throughfall = tmp_Wdew - veg_var->Wdmax;
tmp_Wdew = veg_var->Wdmax;
}
rc = calc_rc((double) 0.0, net_short, vic_run_veg_lib[veg_class].RGL,
air_temp, vpd, veg_var->LAI, (double) 1.0, false);
if (veg_var->LAI > 0) {
canopyevap = pow((tmp_Wdew / veg_var->Wdmax), (2.0 / 3.0)) *
penman(air_temp, elevation, rad, vpd, ra, rc,
vic_run_veg_lib[veg_class].rarc) *
delta_t / CONST_CDAY;
}
else {
canopyevap = 0;
}
if (canopyevap > 0.0 && delta_t == CONST_CDAY) {
/** If daily time step, evap can include current precipitation **/
f = min(1.0, ((tmp_Wdew + ppt) / canopyevap));
}
else if (canopyevap > 0.0) {
/** If sub-daily time step, evap can not exceed current storage **/
f = min(1.0, ((tmp_Wdew) / canopyevap));
}
else {
f = 1.0;
}
canopyevap *= f;
/* compute fraction of canopy that is dry */
if (veg_var->Wdmax > 0) {
*dryFrac = 1.0 - f * pow((tmp_Wdew / veg_var->Wdmax), (2.0 / 3.0));
}
else {
*dryFrac = 0;
}
tmp_Wdew += ppt - canopyevap;
if (tmp_Wdew < 0.0) {
tmp_Wdew = 0.0;
}
if (tmp_Wdew <= veg_var->Wdmax) {
throughfall += 0.0;
}
else {
throughfall += tmp_Wdew - veg_var->Wdmax;
tmp_Wdew = veg_var->Wdmax;
}
/*******************************************
Compute Evapotranspiration from Vegetation
*******************************************/
if (CALC_EVAP) {
transpiration(layer, veg_var, veg_class, rad, vpd, net_short,
air_temp, ra, *dryFrac, delta_t, elevation, Wmax, Wcr,
Wpwp, layerevap, frost_fract, root, shortwave, Catm,
CanopLayerBnd);
}
veg_var->canopyevap = canopyevap;
veg_var->throughfall = throughfall;
veg_var->Wdew = tmp_Wdew;
tmp_Evap = canopyevap;
for (i = 0; i < options.Nlayer; i++) {
layer[i].evap = layerevap[i];
tmp_Evap += layerevap[i];
}
Evap += tmp_Evap / (MM_PER_M * delta_t);
return (Evap);
}
double canopy_evap(layer_data_struct *layer_wet,
layer_data_struct *layer_dry,
veg_var_struct *veg_var_wet,
veg_var_struct *veg_var_dry,
char CALC_EVAP,
int veg_class,
int month,
double mu,
double *Wdew,
double dt,
double rad,
double vpd,
double net_short,
double air_temp,
double ra,
double displacement,
double roughness,
double ref_height,
double elevation,
double *prec,
double *depth,
double *Wcr,
double *Wpwp,
float *root)
/**********************************************************************
canopy_evap.c Dag Lohmann September 1995
This routine computes the evaporation, traspiration and throughfall
of the vegetation types for multi-layered model.
The value of x, the fraction of precipitation that exceeds the
canopy storage capacity, is returned by the subroutine.
UNITS: moist (mm)
evap (mm)
prec (mm)
melt (mm)
VARIABLE TYPE NAME UNITS DESCRIPTION
atmos_data_struct atmos N/A atmospheric forcing data structure
layer_data_struct *layer N/A soil layer variable structure
veg_var_struct *veg_var N/A vegetation variable structure
soil_con_struct soil_con N/A soil parameter structure
char CALC_EVAP N/A TRUE = calculate evapotranspiration
int veg_class N/A vegetation class index number
int month N/A current month
global_param_struct global N/A global parameter structure
double mu fract wet (or dry) fraction of grid cell
double ra s/m aerodynamic resistance
double prec mm precipitation
double displacement m displacement height of surface cover
double roughness m roughness height of surface cover
double ref_height m measurement reference height
Modifications:
9/1/97 Greg O'Donnell
4-12-98 Code cleaned and final version prepared, KAC
06-25-98 modified for new distributed precipitation data structure KAC
01-19-00 modified to function with new simplified soil moisture
scheme KAC
**********************************************************************/
{
/** declare global variables **/
extern veg_lib_struct *veg_lib;
#if LINK_DEBUG
extern debug_struct debug;
#endif
extern option_struct options;
/** declare local variables **/
int Ndist;
int dist;
int i;
double ppt; /* effective precipitation */
double f; /* fraction of time step used to fill canopy */
double throughfall;
double Evap;
double tmp_Evap;
double canopyevap;
double tmp_Wdew;
double layerevap[MAX_LAYERS];
layer_data_struct *tmp_layer;
veg_var_struct *tmp_veg_var;
/**********************************************************************
CANOPY EVAPORATION
Calculation of evaporation from the canopy, including the
possibility of potential evaporation exhausting ppt+canopy storage
2.16 + 2.17
Index [0] refers to current time step, index [1] to next one
If f < 1.0 than veg_var->canopyevap = veg_var->Wdew + ppt and
Wdew = 0.0
DEFINITIONS:
Wdmax - max monthly dew holding capacity
Wdew - dew trapped on vegetation
Modified
04-14-98 to work within calc_surf_energy_balance.c KAC
07-24-98 fixed problem that caused hourly precipitation
to evaporate from the canopy during the same
time step that it falls (OK for daily time step,
but causes oscilations in surface temperature
for hourly time step) KAC, Dag
**********************************************************************/
if(options.DIST_PRCP) Ndist = 2;
else Ndist = 1;
Evap = 0;
for(dist=0;dist<Ndist;dist++) {
/* Initialize variables */
for(i=0;i<options.Nlayer;i++) layerevap[i] = 0;
canopyevap = 0;
throughfall = 0;
/* Set parameters for distributed precipitation */
if(dist==0) {
tmp_layer = layer_wet;
tmp_veg_var = veg_var_wet;
ppt = prec[WET];
tmp_Wdew = Wdew[WET];
}
else {
tmp_layer = layer_dry;
tmp_veg_var = veg_var_dry;
ppt = prec[DRY];
mu = (1. - mu);
tmp_Wdew = Wdew[DRY];
}
if(mu > 0) {
/****************************************************
Compute Evaporation from Canopy Intercepted Water
****************************************************/
/** Due to month changes ..... Wdmax based on LAI **/
tmp_veg_var->Wdew = tmp_Wdew;
if (tmp_Wdew > veg_lib[veg_class].Wdmax[month-1]) {
throughfall = tmp_Wdew - veg_lib[veg_class].Wdmax[month-1];
tmp_Wdew = veg_lib[veg_class].Wdmax[month-1];
}
canopyevap = pow((tmp_Wdew / veg_lib[veg_class].Wdmax[month-1]),
(2.0/3.0))* penman(rad, vpd * 1000., ra, (double) 0.0,
veg_lib[veg_class].rarc,
veg_lib[veg_class].LAI[month-1],
(double) 1.0, air_temp,
net_short, elevation,
veg_lib[veg_class].RGL) * dt / 24.0;
if (canopyevap > 0.0 && dt==24)
/** If daily time step, evap can include current precipitation **/
f = min(1.0,((tmp_Wdew + ppt) / canopyevap));
else if (canopyevap > 0.0)
/** If sub-daily time step, evap can not exceed current storage **/
f = min(1.0,((tmp_Wdew) / canopyevap));
else
f = 1.0;
canopyevap *= f;
tmp_Wdew += ppt - canopyevap;
if (tmp_Wdew < 0.0)
tmp_Wdew = 0.0;
if (tmp_Wdew <= veg_lib[veg_class].Wdmax[month-1])
throughfall += 0.0;
else {
throughfall += tmp_Wdew - veg_lib[veg_class].Wdmax[month-1];
tmp_Wdew = veg_lib[veg_class].Wdmax[month-1];
}
/*******************************************
Compute Evapotranspiration from Vegetation
*******************************************/
if(CALC_EVAP)
transpiration(tmp_layer, veg_class, month, rad,
vpd, net_short, air_temp, ra,
ppt, f, dt, tmp_veg_var->Wdew, elevation,
depth, Wcr, Wpwp, &tmp_Wdew,
&canopyevap, layerevap, root);
}
tmp_veg_var->canopyevap = canopyevap;
tmp_veg_var->throughfall = throughfall;
tmp_veg_var->Wdew = tmp_Wdew;
tmp_Evap = canopyevap;
for(i=0;i<options.Nlayer;i++) {
tmp_layer[i].evap = layerevap[i];
tmp_Evap += layerevap[i];
}
Evap += tmp_Evap * mu / (1000. * dt * 3600.);
}
return (Evap);
}
