Scientific Investigations Report 2006–5318
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5318
intercept_dpm.f
Calculate interception-evaporation components of precipitation, and calculate throughfall if throughfall data is not available or not applicable to a particular HRU due to land-cover type.
Calculate intercepted part of precipitation/irrigation (hru_intercpt) at HRUs, find total amount of moisture on foliage/canopy (hru_intercpt + hru_canopystor), compute evaporated part of precipitation/irrigation (hru_evapinter) at HRUs, reduce potential evapotranspiration (hru_potet) by amount of intercepted water that has been evaporated, save this reduced value in the variable hru_adjustpet (the amount reduced will depend on values of potential evapotranspiration and total canopy water), determine the change in interception (hru_chnginter) and the canopy storage (hru_canopystor) for the next day, and compute throughfall part of precipitation/irrigation (hru_thrufall) at HRUs. Irrigation is only added to throughfall if it is applied above the canopy; otherwise, it is later carried into the soil moisture account module (soilms_dpm.f)
July, 2004
cov_type
HRU cover type: land use/cover type, from 1-31, no units. [basin]
hru_appld
Application rate of irrigation water for HRU, in inches. [basin]
hru_irr_methd
Irrigation method for HRU: 0=above canopy, 1=all other. [basin]
hru_thrufall
HRU throughfall for day, based on throughfall data or calculated, in inches.
hru_intercpt
HRU interception for day: throughfall data or calculated, in inches.
hru_canopystor
Amount of water stored in the foliar cover/canopy for day, in inches.
hru_evapinter
Amount of intercepted water evaporated from the canopy for day, in inches.
hru_chnginter
Change in intercepted water from yesterday for a HRU, in inches.
hru_adjustpet
Potential evapotranspiration for HRU adjusted as used, in inches.
hru_irrigation
Amount of irrigation water applied to a HRU, in inches.
hru_ppt
Daily precipitation for each of the HRU, in inches. [grid]
hru_potet
Potential evapotranspiration for HRU, in inches. [potet]
tffrc
Thrufall for a HRU interpolated from throughfall site, as fraction of precipitation. [grid]
coefs
Daily values of 6 parameters for each of the crop-types, units vary. [cropcof]
The land use/cover for each HRU (cov_type) is first checked for the type of cover. For water HRUs, all calculations are skipped, and for bare-soils and impervious HRUs the hru_thrufall is set to hru_ppt and remaining calculations are skipped. For all other land uses/covers, the maximum interception capacity of the particular cover for the day is obtained from the coefs value previously calculated in cropcof_dpm.f; these values are based on Bauer and Vaccaro (1987), Leavesley and others (1983), Linsley and others (1982), and Zinke (1967).
There are two possible calculation routes. For the first, if throughfall data was available and the land cover at the HRU is the same as the throughfall site, then the fraction of precipitation that is throughfall (tffrc) is multiplied by the HRU precipitation (hru_ppt) to obtain throughfall (hru_thrufall). Hru_ppt is reduced by hru_thrufall to obtain the amount of intercepted moisture evaporated (hru_evapinter), which is then set to interception (hru_intercpt). Last, the available potential evapotranspiration for the HRU (hru_potet, stored in a new varaible hru_adjustpet that was initially set to hru_potet) is reduced by hru_evapinter divided by 1.26 (after Priestly and Taylor (1972) and Bauer and Mastin (1996)) and the remaining calculations are skipped. These relations are
hru_thrufall(i) = tffrc * hru_ppt(i)
hru_evapinter(i) = hru_ppt(i) - hru_thrufall(i)
hru_intercpt(i) = hru_evapinter(i)
hru_adjustpet(i) = maximum of (hru_potet(i) - hru_ evapinter(i)/1.26) or 0.0,
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
hru_adjustpet is the available potential evapotranspiration after being reduced due to the use of energy in the evaporation and transpiration processes, in inches,
hru_intercpt is the amount of preciptation intercepted, in inches,
hru_potet is the potential evapotranspiration for the HRU, in inches,
hru_evapinter is the amount of evaporation from the canopy storage, in inches, and
other variables are as defined above.
For the second calculation route, if there was no throughfall data or the land cover at the HRU was not the same as the throughfall site, then the HRU is checked to determine if there is irrigation for this HRU and the irrigation method. If the irrigation is applied above the canopy, the amount of irrigation is determined from the application rate (hru_appld) and the part of the application rate for today (coefs). This calculation is
hru_irrigation(i) = hru_appld(i) * coefs(landcover,5)
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
hru_irrigation is the application rate for the day for the HRU, in inches,
hru_appld is the annual application rate for the HRU, in inches,
coefs is the daily multiplying factor for irrigation application (apmult) calculated in cropcof, and
other variables are as defined above.
For either of the 2 throughfall conditions defined above the following conditions are checked: 1) there was precipitation (hru_ppt greater than 0) or 2) if there is water remaining on the canopy from yesterday (hru_canopystor greater than 0). If neither of these conditions hold, then the interception calculations are skipped for this HRU.
If the precipitation condition holds, then the maximum amount of precipitation that can be intercepted is calculated as
mxtnr = mxnt – hru_canopystor(i),
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
mxtnr is the maximum amount of precipitation that can be intercepted, in inches,
mxnt is the growing season derived maximum amount of storage for the HRU’s land cover, in inches, and
hru_canopystor is the water currently stored in the canopy.
The interception (hru_intercpt) is then calculated as the minumum of the precipitation (hru_ppt) plus irrigation (hru_irrigation) or mxntr. Irrigation is not included in the calculations if the water is applied below the canopy, such as in drip irrigation. The total amount of water stored in the canopy is calculated as
ptn = hru_intercpt(i) + hru_canopystor(i),
where
ptn is the amount of water stored in the canopy, in inches, and
other variables as defined above.
The evaporation of the canopy storage (hru_evapinter) is calculated as the minimum of ptn or hru_potet. To preserve the original amount potential evaotranspiration for the HRU (hru_potet) for information purposes and for water budget information, a new variable, hru_adjustpet, is calculated. This variable was set to hru_potet at the beginning of the run part of the module and was also described above for the case of throughfall data. The variable represents the available PET for each HRU after it has been adjusted (reduced) for the use of energy in each of the appplicable land-surface process. This module represents the first invocation of hru_potet and hru_adjustpet. Thus, it is calculated as
hru_adjustpet(i) = hru_potet(i) - hru_evapinter(i),
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
hru_adjustpet is the available potential evapotranspiration after being reduced due to the use of energy in the evaporation and transpiration processes, in inches,
hru_potet is the potential evapotranspiration for the HRU, in inches, and
hru_evapinter is the amount of evaporation from the canopy storage, in inches.
The new amount of water remaining on the canopy (remnew) is,
remnew = ptn - hru_evapinter(i),
where
remnew is the new amount of water remaining on the canopy, in inches, and
other variables as defined above.
Before setting the new value of canopy storage, the change in intercepted moisture (storage) is calculated as
hru_chnginter(i) = remnew - hru_ canopystor (i),
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
hru_chnginter is the change in intercepted mositure, in inches, and
other variables as defined above.
The canopy storage for the next day is then set to remnew, and hru_thrufall is calculated as hru_ppt minus hru_intercpt.
Bauer, H.H., and Mastin, M.C., 1997, Recharge from precipitation in three small glacial-till mantled catchments in the Puget Sound Lowlands: U. S. Geological Survey Water-Resources Investigations Report 96-4219, 119 p.
Bauer, H.H., and Vaccaro, J.J., 1987, Documentation of a deep percolation model for estimating ground-water recharge: U. S. Geological Survey Open-File Report 86-536, 180 p.
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, 245 p.
Linsley, R.K., Kohler, M.A., and Paulhus, J.L.H., 1982, Hydrology for engineers: McGraw-Hill Book Company, Third Edition, New York, New York, 508 p.
Pearce, A.J., Rowe, L.K., and Stewart, J.B., 1980, Nighttime, wet canopy evaporation rates and the water balance of an evergreen mixed forest: Water Resources Research, v. 6, no. 5, p. 955-959.
Priestly, C.H.B., and Taylor, R.J., 1972, On the assesment of surface heat flux and evaporation using large scale parameters: Monthly Weather Review, v. 100, p. 81-92.
Zinke, P.J., 1967, Forest interception studies in the United States, in Soper, W.E., and Lull, H.W., eds., Forest hydrology: Proceedings of a National Science Foundation Advanced Science Seminar, Oxford, Pergamon Press Ltd., p. 137-161.
John J. Vaccaro and Henry H. Bauer
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Modified by:
John J. Vaccaro
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Telephone: 253-552-1620
Fax: 253-552-1581
Email: jvaccaro@usgs.gov
U.S.
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