authority: folia
slug: evapotranspiration
name: Evapotranspiration
domain: land
subdomain: biosphere
authority_id: folia:evapotranspiration
parent: evaporation-from-land
aliases:
  - et
  - actual-evapotranspiration
  - aet
external_ids:
  cf_standard_name: water_evapotranspiration_flux
canonical_units: kg m-2 s-1
external_validations:
  product:
    id: mod16a2-v061
    docs_url: https://lpdaac.usgs.gov/products/mod16a2v061/
  product_alt:
    id: pml-v2
    docs_url: https://data.csiro.au/collections/collection/CIcsiro:17375v3/
  product_alt2:
    id: ecostress-l3-l4
    docs_url: https://ecostress.jpl.nasa.gov/data
  cf_standard_name:
    docs_url: https://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html
description: |
  Combined surface water flux from soil/open-water evaporation plus plant
  transpiration. Distinct from the GCOS `evaporation-from-land` parent,
  which formally names the abiotic component — operationally most
  satellite ET products report the combined quantity, because the biotic
  plant-mediated component dominates over vegetated land and cannot be
  separated from evaporation by remote sensing alone. Canonical mass flux
  is kg m-2 s-1; commonly expressed equivalently as mm/day of water
  depth (1 mm/day ≡ 1 kg m-2 day-1). Flagship products are
  Penman-Monteith / Priestley-Taylor models driven by satellite inputs:
  MOD16A2 (MODIS 500 m 8-day, NASA LP DAAC), PML-V2 (Penman-Monteith-
  Leuning, CSIRO/PML, 500 m 8-day), ECOSTRESS L3/L4 (ISS 70 m, sparse
  overpass), GLEAM (0.25° daily). Consumed by agriculture/irrigation,
  drought-monitoring, water-budget, and hydrological-model ops.
theme: hydrology
example_recipes:
  - title: "MOD16A2 8-day ET aggregated over a region (GEE)"
    tool: gee
    requires: []
    snippet: |
      // MOD16A2 ET band is in 0.1 mm / 8-day; rescale to mm
      var mod16 = ee.ImageCollection('MODIS/061/MOD16A2')
        .filterDate('2024-01-01', '2024-12-31')
        .select('ET');
      var annualET_mm = mod16.sum().multiply(0.1).rename('ET_mm_yr');
      var aoi = ee.FeatureCollection('users/me/aoi').geometry();
      var mean = annualET_mm.reduceRegion({
        reducer: ee.Reducer.mean(), geometry: aoi, scale: 500
      });
    docs_url: https://lpdaac.usgs.gov/products/mod16a2v061/
consumed_by: []
produced_by: []
demos: []
status: documented
sources:
  - https://lpdaac.usgs.gov/products/mod16a2v061/
  - https://data.csiro.au/collections/collection/CIcsiro:17375v3/
  - https://ecostress.jpl.nasa.gov/data
  - https://cfconventions.org/Data/cf-standard-names/current/build/cf-standard-name-table.html
  - Running, S.W., Mu, Q., Zhao, M., Moreno, A. 2019, MOD16A2 User's Guide V6 (NASA LP DAAC)
  - Zhang, Y. et al. 2019, Remote Sensing of Environment 222, 165-182 (PML-V2 global ET / GPP)