Attainable evapotranspiration — Arizona

A peer-conditioned ET benchmark for field-scale water-use efficiency

Irrigated agriculture consumes roughly 74% of Arizona’s water withdrawals. In a state operating under the 1980 Groundwater Management Act and shrinking Colorado River allocations, the field-scale potential for structurally attainable reductions in consumptive use has been largely unquantified. Satellite-derived ET products have made the observational side cheap and consistent — but translating those measurements into prescriptive, decision-relevant benchmarks is the open problem.

Approach

Repositioning ET from descriptive flux to prescriptive diagnostic

Attainable Evapotranspiration (AtET) is a peer-conditioned benchmark that asks, for every field: what is the ET observed among the most water-efficient yet productive peers under comparable biophysical conditions? The gap between a field’s actual ET and its AtET becomes a per-field diagnostic — a number a grower, irrigation district, or state agency can act on.

Inputs (all public, all open)

  • OpenET — satellite-derived ET ensemble.
  • Sentinel-2 — NDVI time series for phenology and crop-vigor signals, pulled via Google Earth Engine.
  • PRISM — gridded climate covariates.
  • NRCS SSURGO/STATSGO — soil context.
  • USDA NASS / CDL — crop classification and county-level yield.

Peer-group construction

For every target field a peer set is assembled using similarity in crop, soil, climate, and management context. AtET is derived from the high-yielding, low-ET tail of that peer distribution — explicitly conditioning on productive peers, not just thrifty ones. Choice of percentile and matching radius is reported alongside results so the diagnostic is auditable.

Robustness — the rank-invariance result

Across alternative benchmark percentiles, peer-group constructions, and study years, the spatial and crop-wise rank-ordering of AtET gaps is invariant. That stability is the methodological argument that ET is more than a descriptive flux — it carries a reproducible agronomic signal that can be reframed as a diagnostic metric.

Bokati, Shah, Kumar — Journal of Environmental Management, in review (JEMA-D-26-11477)

Key findings (Arizona, 2020–2024, five major crops)

  • 87.8% of agricultural fields exhibit a non-zero AtET gap.
  • Median AtET gap = 290.7 mm.
  • Annual reduction potential of 301,600 to 462,570 acre-feet across six of Arizona’s Active Management Areas — comparable to the annual municipal demand of a mid-sized metropolitan area.

Full dashboard

The county-level summary alongside is a starter view. The complete field-level dashboard — with crop filters, AMA aggregates, percentile sensitivity, and individual-field lookups — lives at:

atet.waterdmd.info

Generated outputs

  • Field-level AtET and AtET-gap estimates for Arizona’s irrigated fields across 2020–2024 and five major crops.
  • AMA-level aggregates of attainable reductions in consumptive use.
  • Open-source dashboard for field-level evaluation of conservation opportunities (atet.waterdmd.info).
  • A portable benchmarking workflow that can be applied to other irrigated regions using the same public inputs.

Funding

  • Advanced Water Observatory and Decision Support System (AWODSS).
  • Arizona Water Innovation Initiative (AWII) — azwaterinnovation.asu.edu. A multi-year partnership with the State of Arizona led by ASU’s Julie Ann Wrigley Global Futures Laboratory.

Status

Methods paper in review at Journal of Environmental Management.

County-level reduction potential

Choropleth of annual AtET-gap reduction potential by Arizona county, in acre-feet per year. Use the year tabs to scrub 2019–2024. Click any county to see the year-by-year time series.
Scope: the five paper crops (alfalfa, barley, corn, cotton, wheat) summed statewide. Counties shown gray have no AtET-modeled cropland. The paper’s headline figure of 301,600–462,570 acre-feet/year is the subset of this total falling within Arizona’s six Active Management Areas — the full dashboard at atet.waterdmd.info reports the AMA breakdown and field-level details.