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')

Metadata

Release files for ETo 2.2.0

For a detailed explanation of source distributions (sdists) and built distributions (wheels), please see the package formats documentation.

Source distribution (sdist)

Source distribution for ETo 2.2.0
File	Size	Uploaded
eto-2.2.0.tar.gz	124.6 kB	Oct 2, 2026	Details

Built distribution (wheel)

Table of built distributions (wheels) for ETo 2.2.0
File	Interpreter	ABI	Platform	Reset
eto-2.2.0-py3-none-any.whl 126.9 kB Oct 2, 2026	Python 3	none	any	Details

Total release size: 251.6 kB

Release files / eto-2.2.0.tar.gz

Download URL	eto-2.2.0.tar.gz
Size	124.6 kB
Tags	Source
SHA-256 checksum How to use checksums	`e80296d32b3bbdb687e0c35f9c3fd0cee61b3f407908bf29289b88470ffdce9d`
BLAKE2b-256 checksum How to use checksums	`48cf07a7a6bffed98373038a41f47c5743d72291d0340a500c4490d43d2db7e6`
Upload date	Oct 2, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`uv/0.8.7`

Release files / eto-2.2.0-py3-none-any.whl

Download URL	eto-2.2.0-py3-none-any.whl
Size	126.9 kB
Tags	Python 3
SHA-256 checksum How to use checksums	`86a5f66aa92d483cdd2c945195783c92cbea0f8c0f99585f541c599b3cb3383c`
BLAKE2b-256 checksum How to use checksums	`765588020900e90822f7c015a2ea44c650a7a868295330893db180a219879fc6`
Upload date	Oct 2, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	No
Uploaded via	`uv/0.8.7`