pyet.combination.thom_oliver

pyet.combination.thom_oliver(tmean, wind, rs=None, rn=None, g=0, tmax=None, tmin=None, rhmax=None, rhmin=None, rh=None, pressure=None, elevation=None, lat=None, n=None, nn=None, rso=None, aw=2.6, bw=0.536, a=1.35, b=-0.35, lai=None, croph=0.12, r_l=100, r_s=None, ra_method=0, lai_eff=0, srs=0.0009, co2=300, ea=None, albedo=0.23, kab=None, as1=0.25, bs1=0.5, clip_zero=True)

Potential evapotranspiration calculated according to Thom and Oliver (1977).

Parameters:

• tmean (pandas.Series) – average day temperature [°C].

• wind (pandas.Series) – mean day wind speed [m/s].

• rs (pandas.Series, optional) – incoming solar radiation [MJ m-2 d-1].

• rn (pandas.Series, optional) – net radiation [MJ m-2 d-1].

• g (pandas.Series or int, optional) – soil heat flux [MJ m-2 d-1].

• tmax (pandas.Series, optional) – maximum day temperature [°C].

• tmin (pandas.Series, optional) – minimum day temperature [°C].

• rhmax (pandas.Series, optional) – maximum daily relative humidity [%].

• rhmin (pandas.Series, optional) – mainimum daily relative humidity [%].

• rh (pandas.Series, optional) – mean daily relative humidity [%].

• pressure (float, optional) – atmospheric pressure [kPa].

• elevation (float, optional) – the site elevation [m].

• lat (float, optional) – the site latitude [rad].

• n (pandas.Series or float, optional) – actual duration of sunshine [hour].

• nn (pandas.Series or float, optional) – maximum possible duration of sunshine or daylight hours [hour].

• rso (pandas.Series or float, optional) – clear-sky solar radiation [MJ m-2 day-1].

• aw (float, optional) – wind coefficient [-].

• bw (float, optional) – wind coefficient [-].

• a (float, optional) – empirical coefficient for Net Long-Wave radiation [-].

• b (float, optional) – empirical coefficient for Net Long-Wave radiation [-].

• lai (pandas.Series or float, optional) – leaf area index [-].

• croph (pandas.Series or float, optional) – crop height [m].

• r_l (pandas.Series or float, optional) – bulk stomatal resistance [s m-1].

• r_s (pandas.Series or float, optional) – bulk surface resistance [s m-1].

• ra_method (float, optional) – 1 => ra = 208/wind 2 => ra is calculated based on equation 36 in FAO (1990), ANNEX V.

• lai_eff (float, optional) – 0 => LAI_eff = 0.5 * LAI 1 => LAI_eff = lai / (0.3 * lai + 1.2) 2 => LAI_eff = 0.5 * LAI; (LAI>4=4) 3 => see Zhang et al. (2008).

• srs (float, optional) – Relative sensitivity of rl to Δ[CO2].

• co2 (float) – CO2 concentration [ppm].

• ea (float or pandas.Series or xarray.DataArray, optional) – actual vapor pressure [kPa].

• albedo (float, optional) – surface albedo [-].

• kab (float, optional) – coefficient derived from as1, bs1 for estimating clear-sky radiation [degrees].

• as1 (float, optional) – regression constant, expressing the fraction of extraterrestrial reaching the earth on overcast days (n = 0) [-].

• bs1 (float, optional) – empirical coefficient for extraterrestrial radiation [-].

• clip_zero (bool, optional) – if True, replace all negative values with 0.

Returns:

• pandas.Series or xarray.DataArray containing the calculated potential

• evapotranspiration [mm d-1].

Notes

Following Oudin et al. (2005).

\[PET = \frac{\Delta (R_{n}-G)+ 2.5 \gamma (e_s-e_a) w} {\lambda(\Delta +\gamma(1+\frac{r_s}{r_a}))}\]

\[w=2.6(1+0.53u_2)\]