ETo

A Python package for calculating reference and crop evapotranspiration

ETo calculates reference evapotranspiration (ETo) and crop evapotranspiration (ETc) using the UN-FAO 56 paper methodology. It estimates missing meteorological parameters from available data and supports daily, hourly, and monthly time steps.

Features

• FAO 56 Penman-Monteith reference ET (short and tall reference crops)
• Hargreaves simplified daily ET
• Crop evapotranspiration — single Kc, dual Kc (Kcb + Ke), and water stress adjustment (Ks)
• Built-in crop coefficients for 23 major crops (FAO 56 Table 12)
• Automatic parameter estimation with quality tracking
• Input validation with configurable warnings
• Derived outputs — VPD, T_dew (back-calculated), clear-sky radiation

Documentation

Full documentation is available at mullenkamp.github.io/ETo.

Installation

pip install eto

or:

conda install -c mullenkamp eto

The only dependency is NumPy.

Quick Example

import numpy as np
from eto import ETo

data = {
    'T_min': np.array([10.0, 12.0, 8.0]),
    'T_max': np.array([25.0, 28.0, 22.0]),
}
dates = np.arange('2020-01-01', '2020-01-04', dtype='datetime64[D]')

et = ETo(data, freq='D', z_msl=500, lat=-43.6, dates=dates)

# Reference ET
eto = et.eto_fao()  # np.ndarray of ETo in mm

# Crop ET (single Kc)
etc = et.etc(crop='maize_grain', stage='mid')  # ETc = Kc × ETo

# Tall reference crop (ASCE alfalfa)
etr = et.eto_fao(ref_crop='tall')