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Estimate Atmospheric Parameters Related to Evapotranspiration

Source: R/env_data_collection_src.R
param_atmospheric.Rd

Computes vapour pressure deficit, the slope of the saturation vapour pressure curve, Priestley-Taylor potential evapotranspiration and the precipitation balance, following FAO-56.

Usage

param_atmospheric(
  env.data,
  PREC = NULL,
  Tdew = NULL,
  Tmin = NULL,
  Tmax = NULL,
  RH = NULL,
  Rad = NULL,
  G = 0,
  Alt = 600,
  alpha = 1.26,
  merge = FALSE,
  verbose = TRUE
)

Arguments

env.data

data.frame. A get_weather output or equivalent.

PREC, Tdew, Tmin, Tmax, RH, Rad

character. Column names for precipitation, dew point, minimum and maximum temperature, relative humidity and solar radiation. Defaults follow NASA POWER naming.

G

numeric. Soil heat flux (MJ/m2/day). Default 0.

Alt

numeric scalar, or character naming an elevation column in env.data. Default 600 m.

alpha

numeric. Priestley-Taylor coefficient. Default 1.26.

merge

boolean. Bind results onto env.data.

verbose

boolean. Print a summary of what was computed.

Value

A data.frame with VPD (kPa), SPV (kPa/C), ETP (mm/day) and PETP (mm/day).

Details

Elevation now works. Alt accepts either a numeric elevation or the name of a column. Previously the default Alt = 600 was never NULL, so the elevation column was never read and every site was treated as 600 m – a 26% error in atmospheric pressure at 2500 m, propagating into the psychrometric constant and ETP.

VPD is the difference between mean saturation vapour pressure (from Tmin and Tmax) and actual vapour pressure (from dew point). Values are floored at 0; negatives can only arise from a dew point above air temperature, which is unphysical and indicates a data problem. A warning is raised when this occurs.

See also

param_radiation, param_temperature, processWTH

Author

Germano Costa Neto

Examples

# \donttest{
env.data <- get_weather(lat = -13.05, lon = -56.05)
#> ---------------------------------------------------------------
#> get_weather -- downloads daily weather from NASA POWER
#> Last updated at 09/27/2026
#> ---------------------------------------------------------------
#> start.day is NULL; matched as 2024-01-26
#> end.day is NULL; matched as 2024-02-25
#> ---------------------------------------------------------------
#> get_weather() - daily weather from NASA POWER
#> https://docs.ropensci.org/nasapower
#> ---------------------------------------------------------------
#> Start .............................. Thu Oct 22 18:34:50 2026
#> Environmental units ................ 1
#> Parallel ........................... [   ]
#>   [1/1] env1 downloaded
#> Computing VPD ...................... [ x ]
#> Computing N, RTA ................... [ x ]
#> Computing n ........................ [ x ]
#> Computing TH1 ...................... [ x ]
#> Computing TH2 ...................... [ x ]
#> Computing PAR_TEMP ................. [ x ]
#> Environmental units downloaded ..... 1/1
#> Daily weather features ............. 25
#> Done ............................... Thu Oct 22 18:34:51 2026
#> Total time ......................... 0.96s
param_atmospheric(env.data, Alt = 850)
#> ---------------------------------------------------------------
#> param_atmospheric -- derives atmospheric-demand parameters
#> Last updated at 09/27/2026
#> ---------------------------------------------------------------
#> ----------------------------------------------------------------------
#> Slope of saturation vapour pressure curve (SPV, kPa/C)
#> Vapour pressure deficit (VPD, kPa)
#> Potential evapotranspiration (ETP, mm/day)
#> Precipitation balance P - ETP (PETP, mm/day)
#> ----------------------------------------------------------------------
#>          VPD       SPV       ETP        PETP
#> 1  1.0570758 0.2127664 10.701635  -9.7216352
#> 2  1.1963363 0.2115765 11.262974 -11.2229737
#> 3  1.2402607 0.2137985 10.129089 -10.1090887
#> 4  0.9479085 0.2069256  8.669066  -4.7790658
#> 5  1.1868980 0.2164249  9.598868   1.5911318
#> 6  0.9927726 0.2140709  8.947486  -1.8774863
#> 7  1.3280358 0.2268024  9.526170  11.1938296
#> 8  0.6186276 0.2023610  6.961476   1.2085238
#> 9  0.7202045 0.1957995  4.285090   6.0149101
#> 10 0.3776662 0.1847477  5.813851  25.0261486
#> 11 0.3128784 0.1788592  7.653222   4.7067785
#> 12 0.6340613 0.1897132  9.404194   2.6958056
#> 13 0.7824328 0.2029855  8.081383  -3.5813835
#> 14 0.8544113 0.2025170  8.436664   5.5833361
#> 15 0.6804262 0.2052893  9.529413   1.0205868
#> 16 0.6819151 0.2070845  5.632104  13.2778964
#> 17 0.3567582 0.1936859  6.436445  15.8835547
#> 18 0.5607959 0.1936859  5.106924  -4.1769244
#> 19 0.6908651 0.1974738  9.106010  -7.6160103
#> 20 0.7864117 0.2060269  9.878412  -9.1184117
#> 21 0.8475449 0.2098021 10.333451  -5.6034514
#> 22 0.8393412 0.2101774  9.779679  -4.2996790
#> 23 0.9634764 0.2146710  6.338395  -3.3683950
#> 24 0.4906680 0.1902060  7.794400  22.3855999
#> 25 0.3687032 0.1950424  5.491460  15.0385401
#> 26 0.5029901 0.1938363  6.300752  10.2092476
#> 27 0.5504202 0.1993139  6.708586  -3.1685857
#> 28 0.6103149 0.2042394  5.962741  -4.2327406
#> 29 0.5414807 0.1995707  4.985698  -3.4756975
#> 30 0.5193414 0.1956984  7.502888  -0.7828879
#> 31 0.7193274 0.2021532  9.547041  -7.2970405
# }