Scientific Investigations Report 2006–5318
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5318
transfer_dpm.f
Transfers part or all of the unused potential soil evaporation to potential plant transpiration.
This module was modified from Bauer and Vaccaro (1987) by Bauer and Mastin (1997). The module takes the part of potential soil evaporation not used to evaporate soil moisture from the unshaded part of the soil and adds part of it to potential plant transpiration. The amount added is based on the amount of foliar cover. The relation used is from Saxton and others (1974). The transfer is only completed for the cover types of forest, sage, grasslands, and bare soils and when the foliar cover (cover density) is less than 60 percent. Excluding HRUs with cover types of water and impervious, all of the unused potential soil evaporation is transferred to potential plant transpiration.
July, 2004
cov_type
HRU cover type: land use/cover type, from 1-31, no units. [basin]
hru_petloss
Amount of potential evapotranspiration loss--not transferred to potential plant evapotranspiration, in inches.
hru_adjustpet
Potential evapotranspiration for HRU adjusted as used, in inches. [intrcp]
coefs
Daily values of 6 parameters for each of the crop-types, units vary. [cropcof]
hru_pevsoil
Potential evaporation demand for soil evaporation, in inches. [soilev]
hru_actevsoil
Actual soil evaporation for a HRU, in inches. [soilev]
hru_snow
Amount of snow-water-equivalent for a HRU, in inches. [snowpck]
For every HRU, the module checks if its land use/cover (cov_type) is water (cov_type=10) or impervious surface (cov_type=16). If such a case exists, then the calculations are skipped for the HRU because potential evapotranspiration has been completely used by the evaporation from the water body or because the actual evapotranspiration calculations are skipped for impervious surfaces. Next, the snowpack for each HRU (hru_snow) is checked to see if there is one. If there is a snowpack for a HRU, the calculations are skipped because actual evapotranspiration calculations are not completed for snow-covered HRUs.
Next, the module checks if the land use/cover for a HRU is either sage (cov_type=3) or bare ground (cov_type=13), and the foliar cover is less than 0.60. The land use for a HRU is determined by
landcov = cov_type(i),
where
nhru is the number of HRUs,
i is the index of HRUs, with i from 1 through nhru,
cov_type is the land use/cover identification number for a HRU, and
landcov is a local temporary variable for the land cover for a HRU.
The foliar cover is the determined by
fc = coefs(landcov, 2),
where
coefs are the 6 parameters (coefficients) for each of the 31 cover-types (land uses/covers), with parameter 2 being the foliar cover for land use/cover = landcov, and
fc is a local temporary variable for the foliar cover for a HRU.
If neither of the above two cases exist, then transfer calculations are skipped for the HRU and all of the unused potential soil evaporation will be transferred to the potential plant evapotranspiration for the HRU as,
hru_adjustpet(i) = hru_adjustpet(i) - hru_actevsoil(i)
where
nhru is the number of HRUs,
i is the index of HRUs, with i from 1 through nhru,
hru_adjustpet is the potential evapotranspiration adjusted (lowered) as used for each HRU, and
hru_actevsoil is the actual soil evaporation for each HRU.
For the case that a HRU has a land use/cover of either sage or bare ground and the foliar cover is less than 0.60, only a part of the unused potential soil evaporation is transferred to potential plant evapotranspiration. The transfer amount is calculated as,
sa = hru_pevsoil(i) - hru_actevsoil(i)
trns = 1.6666 * fc
hru_adjustpet(i) = hru_adjustpet(i) * fc + trns*sa
hru_petloss(i) = sa – trns*sa
where
nhru is the number of HRUs,
i is the index of HRUs, with i from 1 through nhru,
sa is a local temporary variable that is the amount of unused potential soil evaporation,
hru_pevsoil is the potential soil evaporation for each HRU,
hru_actevsoil is the actual soil evaporation for each HRU,
trns is a local temporary variable that is the calculated transfer coefficient,
fc is as defined previously,
hru_adjustpet is the potential evapotranspiration adjusted (lowered) based on fc and trns, and
hru_petloss is the accumulated amount of potential evapotranspiration for a HRU that is not used for the day.
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.
Saxton, K.E., Johnson, H.P, and Show, R.H., 1974, Modeling evapotranspiration and soil moisture: Transactions of the American Society of Agriculutral Engineers, v. 17, No. 4, p. 673-677.
John J. Vaccaro and Henry H. Bauer
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Modified by:
Henry H. Bauer and 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.
Department of the Interior | U.S. Geological
Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065318
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