Changes from the original module are written in bold text
Brings in external parameters identifying information about each time series of application rates and brings in an external variable that is the daily quantity of applied irrigation water for each of the applications. This variable is from data read-in through a new module (divrt_apply.prms.f), which is required when using this module. For these changes intcp_prms.apply.f would be used in place of intcp_prms.f and divrt_apply.prms.f would be added as a new module, and if the diversion and or return flow part (data input) of divrt_apply.prms.f is used, then musroute_prms_divretrn.f would be used in place of musroute_prms.f.
New dimensions of napply (number of application rates input), ndiv (number of diversions), and nretrn (number of returns) are needed. MAXAPPLY is the array size for napply, MAXDIV is the array size for ndiv, and MAXRETRN is the array size for nretrn in /modules/setdims/setdims.f and /modules/include/fmodules.inc.
Computes amount of intercepted rain and snow, evaporation from intercepted rain and snow, and net rain and snow that reaches the soil or snowpack.
Summer vegetation cover density for the major vegetation type on an HRU.
Winter vegetation cover density for the major vegetation type on an HRU.
Vegetation cover type designation for an HRU: 0 = bare soil, 1 = grasses, 2 = shrubs, 3 = trees.
The method of irrigation for each HRU. Method: 0=sprinkler, 1=furrow/drip. Sprinkler has interception applied; furrow/drip bypasses interception calculations. Method is determined from irr_type described below and does not have to be input.
The method of irrigation for each application rate. Method: 0=sprinkler, 1=furrow/drip. Sprinkler has interception applied; furrow/drip bypasses interception calculations. After the HRU is defined for each application rate time series, the method is stored in the above parameter (hrumeth); thus, a user does not have to input the irrigation method for each hru.
The HRU id where an application rate is applied.
Snow interception storage capacity for the major vegetation type on an HRU, in inches.
Depletion factor for reducing the depth of intercepted snow storage in excess of the maximum rain storage during a rain-on-snow event (expressed as a decimal percentage of current excess storage remaining after 24 hours of rain).
Summer rain interception storage capacity for the major vegetation type on an HRU, in inches.
Winter rain interception storage capacity for the major vegetation type on the HRU, in inches.
Total basin area, in acres [basin]
Average emissivity of air on days without precipitation. [snow]
Evaporation pan coefficient [potet]
Proportion of potential evapotranspiration that is sublimated from the snow surface. [snow]
Basin area-weighted average of application rates (hru_apply described below), in inches.
Average basin evaporation and sublimation loss from interception storage, in inches.
Current average basin interception storage, in inches.
Basin area-weighted average of application rates after interception (net_apply described below), in inches.
Average basin net precipitation, in inches.
Daily application rate for a HRU, in inches.
Evaporation and sublimation loss from interception storage on an HRU, in inches.
Interception form switch indicating whether interception is rain (0) or snow (1).
Interception switch indicating no intercepted precipitation (0) or intercepted precipitation available (1).
Current depth of interception storage on an HRU, in inches.
HRU net application rate for a HRU, in inches.
HRU net precipitation, the sum of net_rain and net_snow, in inches
Rain on an HRU (hru_rain) minus interception, in inches.
Snow on an HRU (hru_snow) minus interception, in inches.
The daily irrigation application rate, in inches. [divapp]
HRU pervious area, in acres. [basin]
Precipitation on HRU, rain and snow, in inches. [precip]
Rain on HRU, in inches. [precip]
Snow on HRU, in inches. [precip]
Measured pan evaporation. [obs]
Snowpack water equivalent on an HRU, in inches. [snow]
Potential evapotranspiration for HRU, in inches. [potet]
The computed solar radiation for HRU, in calories/cm2 . [solrad]
Average HRU temperature, in ° C. [temp]
Maximum HRU temperature, in ° F. [temp]
Indicator for whether transpiration is occurring, 0=no, 1=yes. [potet]
Interception of precipitation is computed as a function of the cover density ( covden_sum and covden_win ) and the storage available ( snow_intcp , srain_intcp , and wrain_intcp ) for the predominant vegetation on an HRU. HRU precipitation is obtained from a precipitation distribution module in the form of total precipitation ( hru_ppt ) and the amounts of hru_ppt that are in the form of rain ( hru_rain ) and snow ( hru_snow ). Net rain ( net_rain ) during the summer period is computed by
srain_intcp is the rain interception storage capacity for the major vegetation type during the summer period, in inches, and
intcp_stor is the current depth of interception storage, in inches.
Similar to rain interception, interception of applied irrigation water is also computed as a function of the cover density (covden_sum) and the storage available (srain_intcp) for the predominant vegetation on an HRU. However, interception is only calculated during the summer and for sprinkler type of irrigation method (irr_type=0), and it is not calculated for drip or furrow irrigation methods (irr_type=1). The irr_type is input in the diversion-return-application input module. Application rates (apply) are first obtained from the diversion-return-application input module. HRU application rates (hru_apply) are then determined from apply and napp_to_hru, which is a list of HRUs input in diversion-return-application input module that identifies the HRUs to which each apply is to go. The amount of application water after interception (net_apply) is also calculated using equations 1 and 2, but only for the case of irr_type=0
net_rain for the winter period is computed using equations (1) and (2) but with the winter cover density ( covden_win ) substituted for covden_sum and the winter interception storage capacity for rain ( wrain_intcp ) substituted for srain_intcp . net_snow is also computed in the same manner but with the substitution of hru_snow for hru_rain , winter cover density ( covden_win ) for covden_sum , and the interception storage capacity for snow ( snow_intcp ) for srain_intcp .
The existence of intercepted precipitation is denoted by setting intcp_on to a value of 1. A value of 0 indicates no intercepted precipitation. The form of the intercepted precipitation is denoted by intcp_form, which is set to 0 for rain and 1 for snow. If precipitation is a mixture of rain and snow, rain is assumed to occur first, and interception is computed for each precipitation form. net_ppt is the sum of net_rain plus net_snow . When snow falls on intercepted rain, intcp_form is changed to 1 and net_snow is computed as above. snow_intcp is assumed to always be greater than or equal to wrain_intcp .
When rain falls on intercepted snow, a check is made on intcp_stor to determine if the current snow storage is greater than wrain_intcp or srain_intcp , depending on the season. If intcp_stor is less than or equal to this value, then intcp_form is changed to 0 and net_rain is computed as above. If intcp_stor is greater than the maximum rain storage value, intcp_form is kept as 1 and a value for snow storage in excess of rain storage, termed snow_stor, is computed by
,snow_unload is a depletion factor for reducing the depth of intercepted snow storage in excess of the maximum rain storage during a rain on snow event and is expressed as a decimal percentage of current excess storage remaining after 24 hours of rain.
Maximum interception storage for a time step is then the sum of wrain_intcp (or srain_intcp ) plus snow_stor . net_rain is computed as above with this interim maximum storage value substituted for srain_intcp in (2).
The potential evaporation or sublimation rate for intercepted precipitation ( evcan ) is computed as a function of interception form. Intercepted rain is assumed to evaporate at a free-water surface rate. If pan-evaporation data are used, then evcan equals the pan loss rate. If potential evapotranspiration ( potet ) is computed from meteorological variables, evcan is computed by
,epan_coef is the monthly evaporation-pan coefficient.
Sublimation of intercepted snow is assumed to occur at a rate proportional to potet and is computed by
,potet_sublim is the proportion of potet that is sublimated from the snow surface.
In addition to sublimation, intercepted snow can be removed from the canopy by melting. A modified energy balance that considers short- and long-wave components of the energy balance is computed for each time step. For 24-hour time steps, the energy balance is computed for an assumed 12 h daylight period. If the energy balance is negative or zero, no melt occurs. When the energy balance is positive, all or part of the melt is first used to satisfy evcan, and the remainder is added to net_snow and net_ppt .
Actual loss from interception ( intcp_evap ) is equal to the smaller value of intcp_stor or evcan plus any additional snowmelt from the canopy. If intcp_stor is not depleted in one time step, the remainder is carried over to the next time step. intcp_evap represents loss from the percentage of an HRU expressed in covden_sum or covden_win . For water balance computations, intcp_evap is adjusted to represent an HRU average value.
Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, L.G., 1983, Precipitation-runoff modeling system--User's manual: U. S. Geological Survey Water-Resources Investigations Report 83-4238, 207 p.
URL for this page is http://pubsdata.usgs.gov/pubs/of/2002/ofr02362/htdocs/intcp/intcp_prms_apply.htm
Page contact: Mark Mastin (mcmastin@usgs.gov),
253-428-3600, ext. 2609
Last modified: Friday, 11-Jan-2013 03:19:46 EST
![net_rain = [hru_rain multiplied by (1.0 minus covden_sum)] + (thrufall multiplied by covden_sum)](../../images/intcp_prms_apply-1.gif)
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