Scientific Investigations Report 2006–5318
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5318
netrad_dpm.f
Declare, initialize, and run module for calculating net radiation.
Calculates the net radiation for a fir forest from incoming shortwave radiation (solar + sky reflected, as would be measured by a pyrenometer). Formulation also applied to cover types of water, grass, sage, barren soils, and impervious surfaces. The formulas are from Giles and others (1984) and Spittlehouse and Black (1981). The module is also based on modifications of Bauer and Vaccaro (1987) by Bauer and Mastin (1997)
July, 2004
slrxfmx
Maximum of observed daily incoming solar radiation, monthly, in fractions.
cov_type
HRU cover type: land use/cover type, from 1-31, no units. [basin]
hru_netrad
Daily net radiation for each of HRUs, in cal/cm2/dy.
tmaxf
Daily maximum temperature for each of the HRUs, in degrees Fahrenheit. [grid]
tminf
Daily minimum temperature for each of the HRUs, in degrees Fahrenheit. [grid]
hru_solrad
Daily incoming solar radiation for each of the HRUs, cal/cm2/dy. [grid]
slrexthz
Solar radiation for horizontal surface for day, in langleys. [extrad]
frcdylt
Fraction of day with sun—daylight, in fractions. [extrad]
The run part of the module first sets certain constants that include: albedo, emissivity of vegetation, the Stefan-Boltzman constant (stefboltz--117.13 E-09, in cal/cm2/day), and two empirical coefficients, C and D.
The cover type (land use/cover—cov_type) is then checked if it is for conifer forests, water, bare soils, or impervious surfaces (cov_type=3, 10, 13, and 16) in order to do net radiation calculations, otherwise the HRU is skipped, the hru_netrad is set to zero, and the next HRU is checked.
For the case of the correct cov_type, the average temperature during daylight hours is calculated as,
tavf = (tminf(i)+2.0 * tmaxf(i)) / 3.0
where,
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
tavf is the average temperature for daylight hours, in degrees Farenheit,
tmaxf is the HRU daily maximum temperature (degrees Farenheit), and
tminf is the HRU daily minimum temperature (degrees Farenheit).
After tavf is calculated for a HRU, it is coverted first to degrees Celsisus (tavc) and then to degrees Kelvin (tavk). Tavk is then used to compute the Stephan-Boltzman black body radiation as,
stefan = stefboltz * tavk4.
Net shortwave radiation is calculated as,
slrnetsw = (1-albedo) * hru_solrad(i),
where,
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
albedo is the albedo for the four land covers, and
and hru_solrad is the daily incoming solar radiation for each of the HRUs, cal/cm2/dy, previously calculated.
The emissivity of air is calculated as,
emair= 1.0 – 0.261 * e**(-0.00077*tavc2),
where,
emair is the emissivity of air,
tavc as previously defined, and
other values are constants.
Slrxfmx, which is the maximum of observed incoming solar radiation expressed as a fraction of extraterrestrial radiation on a horizontal surface (maximum solar radiation/slrexthz-for clear sky and varies slightly with month of year) is used to modify the daily calculated value of slrexthz (extraterrestrial solar radiation on horizontal surface). The resulting value, slrrdmx is the used to calculate a ratio (slrratio=slrexthz/slrxfmx(imo)) Using the ratio, the net longwave radiation can then be calculated as,
slrnetlw = frcdylt(i) * (C+D*slrratio) * emveg * emair-1) * stefan,
where,
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
emair and emveg are the emissivities previously defined,
C and D are constants (0.1, 0.9, respectively),
frcdylt(i) is the fraction of day with sun calculated in the extrad_dpm module,
slrratio is the ratio defined above, and
stefan is the black-body radiation defined previously.
Now that the net shortwave and logwave radition have been calcuted for the HRU, they are added to obtain the net radiation for the HRU,
hru_netrad(i) = slrnetlw + slrnetsw
where,
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
hru_netrad(i) is the net radiation for a HRU covered by conifer forests, water, bare soils, or impervious surfaces (otherwise = 0.0), in cal/cm2/dy, and,
slrnetlw, slrnetsw are the net longwave and shortwave radiation values for this day and this HRU as previously defined.
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.
Giles, D.G., Black, T.A., and Spittlehouse, D.L., 1984, Determination of growing season soil water deficits on a forested slope using water balance analysis: Canadian Journal of Forest Research, v. 15, p. 107-114.
Spittlehouse, D.L., and Black, T.A., 1981, A growing season water balance model applied to two Douglas fir stands: Water Resources Research, v. 17, no. 6, p. 1,651-1,656.
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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