WUE.metrics {bigleaf}

Water-Use Efficiency Metrics

Description

Calculation of various water use efficiency (WUE) metrics.

Usage

WUE.metrics(
  data,
  GPP = "GPP",
  NEE = "NEE",
  LE = "LE",
  VPD = "VPD",
  Tair = "Tair",
  constants = bigleaf.constants()
)

Arguments

data

Data.frame or matrix containing all required variables

GPP

Gross primary productivity (umol CO2 m-2 s-1)

NEE

Net ecosystem exchange (umol CO2 m-2 s-1)

LE

Latent heat flux (W m-2)

VPD

Vapor pressure deficit (kPa)

Tair

Air temperature (deg C)

constants

Cmol - molar mass of carbon (kg mol-1)
umol2mol - conversion micromole (umol) to mole (mol)
kg2g - conversion kilogram (kg) to gram (g)

Details

the following metrics are calculated:

Water-use efficiency (WUE):

WUE = GPP / ET

Water-use efficiency based on NEE (WUE_NEE):

WUE_NEE = NEE / ET

Inherent water-use efficiency (IWUE; Beer et al. 2009):

IWUE = (GPP * VPD) / ET

Underlying water-use efficiency (uWUE; Zhou et al. 2014):

uWUE= (GPP * sqrt(VPD)) / ET

All metrics are calculated based on the median of all values. E.g. WUE = median(GPP/ET,na.rm=TRUE)

Value

a named vector with the following elements:

WUE

Water-use efficiency (gC (kg H20)-1)

WUE_NEE

Water-use efficiency based on NEE (gC (kg H20)-1)

IWUE

Inherent water-use efficiency (gC kPa (kg H20)-1)

uWUE

Underlying water-use efficiency (gC kPa^0.5 (kg H20)-1)

Note

Units for VPD can also be hPa. Units change accordingly. WUE_NEE is calculated based on the absolute value of NEE (the sign convention does not matter here).

References

Beer, C., et al., 2009: Temporal and among-site variability of inherent water use efficiency at the ecosystem level. Global Biogeochemical Cycles 23, GB2018.

Zhou, S., et al., 2014: The effect of vapor pressure deficit on water use efficiency at the sub-daily time scale. Geophysical Research Letters 41.

See Also

stomatal.slope for a measure of intrinsic WUE

Examples

## filter data for dry periods and daytime at DE-Tha in June 2014
DE_Tha_Jun_2014_2 <- filter.data(DE_Tha_Jun_2014,quality.control=FALSE,
                                 vars.qc=c("Tair","precip","VPD","H","LE"),
                                 filter.growseas=FALSE,filter.precip=TRUE,
                                 filter.vars=c("Tair","PPFD","ustar"),
                                 filter.vals.min=c(5,200,0.2),
                                 filter.vals.max=c(NA,NA,NA),NA.as.invalid=TRUE,
                                 quality.ext="_qc",good.quality=c(0,1),
                                 missing.qc.as.bad=TRUE,GPP="GPP",doy="doy",
                                 year="year",tGPP=0.5,ws=15,min.int=5,precip="precip",
                                 tprecip=0.1,precip.hours=24,records.per.hour=2)

## calculate WUE metrics in the filtered periods
WUE.metrics(DE_Tha_Jun_2014_2)