Sharma et al. (2026) Differential impacts of Colorado River shortage operations on agricultural adaptation and groundwater reliance in Central Arizona

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-10-09
• Authors: Shraddha Sharma, Zhaocheng Wang, Enrique R. Vivoni, Andrew N. French, Pierre Guillevic, Rasmus Houborg, C. A. Sanchez, Sarah Porter
• DOI: 10.1016/j.agwat.2026.110842

Research Groups

• School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ, USA
• Center for Hydrologic Innovations, Arizona State University, Tempe, AZ, USA
• Yuma Center of Excellence for Desert Agriculture, University of Arizona, Yuma, AZ, USA
• US Arid Land Agricultural Research Center, USDA Agricultural Research Service, Maricopa, AZ, USA
• Planet Labs PBC, San Francisco, CA, USA
• University of Arizona, Maricopa, AZ, USA
• Kyl Center for Water Policy, Arizona State University, Phoenix, AZ, USA

Short Summary

This study quantifies the differential impacts of Colorado River water shortages on agricultural adaptation and groundwater reliance in two central Arizona irrigation districts with contrasting water delivery priorities. It reveals that lower-priority districts experienced significant cultivated area contraction, crop switching, and increased groundwater pumping, while higher-priority districts maintained stable operations.

Objective

• To quantify how cultivated extent and crop composition changed from 2021 to 2024 across districts with contrasting Colorado River water shortage exposure.
• To determine the decrease in consumptive water use and attribute proportions of that decrease to land fallowing and crop switching.
• To assess how reductions in Colorado River deliveries were offset by lower irrigation demand and increased groundwater pumping.

Study Configuration

• Spatial Scale: Central Arizona, Pinal County, focusing on two adjacent irrigation districts: Ak-Chin Indian Community (85 km²) and Maricopa-Stanfield Irrigation and Drainage District (MSIDD, 420 km²). Analysis conducted at field-level (3 m and 30 m resolution).
• Temporal Scale: Study period from 2018 to 2024, with a focus on the Colorado River shortage period (2022–2024) using 2021 as the baseline year. Historical groundwater data from 2005.

Methodology and Data

• Models used:
  • Random Forest algorithm for crop type classification.
  • OpenET multi-model framework (Ensemble ET product, including ALEXI/DisALEXI, eeMETRIC, geeSEBAL, SSEBop, PT-JPL, SIMS) for evapotranspiration estimation.
  • Water accounting framework utilizing a calibrated irrigation efficiency factor (L) to infer groundwater withdrawals.
• Data sources:
  • Remote Sensing: PlanetScope imagery (3 m resolution, daily, multispectral), Planet Fusion product (3 m resolution, daily, cloud-free, gap-filled surface reflectance), OpenET platform (Collection v2.1, 30 m spatial resolution, monthly ET estimates).
  • Ground Observations: Arizona Meteorological Network (AZMET) daily meteorological data (precipitation, reference evapotranspiration), eddy covariance (EC) towers (daily actual ET), Arizona Department of Water Resources (ADWR) Groundwater Site Inventory database (groundwater levels), Central Arizona Project (CAP) and ADWR water delivery records, Ak-Chin field boundary and crop-type records.
  • Benchmark/Reference Data: U.S. Department of Agriculture (USDA) Cropland Data Layer (CDL, 30 m, annual) and Crop Sequence Boundaries (CSB, vector dataset).

Main Results

• The Ak-Chin Indian Community (senior water priority) maintained over 99% of its cultivated area and a stable crop portfolio during 2022–2024, with Ensemble ET changing by only -3.1 hm³ (-4.6%) between 2021 and 2024.
• The Maricopa-Stanfield Irrigation and Drainage District (MSIDD, junior water priority) experienced a 98% reduction in CAP deliveries (from 150.6 hm³ yr⁻¹ in 2021 to 3.1 hm³ yr⁻¹ in 2024).
  • MSIDD's cultivated area contracted by 25.9% (from 204.7 km² in 2021 to 151.7 km² in 2024), with larger fields disproportionately fallowed.
  • Agricultural adaptation in MSIDD included a shift from high- to lower-water-use crops, with alfalfa area decreasing by 38.6% and barley area increasing by 112.7%.
  • Ensemble ET in MSIDD decreased by 61.1 hm³ yr⁻¹ (27.4%) from 2021 to 2024, with fallowing explaining 72% of the decline and crop switching explaining 24%.
  • The 147.5 hm³ yr⁻¹ loss of CAP deliveries to MSIDD was offset by lower irrigation volumes (73%) and additional groundwater pumping (27%).
  • Inferred groundwater pumping in MSIDD increased by 62.0 hm³ yr⁻¹ between 2021 and 2023.
  • Groundwater depth-to-water (DTW) records from 14 index wells in the study area showed a clear regime shift, with 12 of 14 wells transitioning from rising water tables (median: -0.59 m yr⁻¹) before 2021 to declining water tables (median: +0.85 m yr⁻¹) after 2021.
• The OpenET-based water accounting framework, calibrated with historical records, reproduced annual irrigation totals with a normalized mean absolute error (MAE) of 2.0% at Ak-Chin and 4.7% at MSIDD.

Contributions

• Presents the first attempt to quantify and reveal the differential impacts of Colorado River water shortage operations on agricultural adaptation in the Colorado River Basin since 2022.
• Develops and demonstrates a transferable, end-to-end analytical framework for monitoring agricultural adaptation and water use, integrating high-resolution CubeSat imagery, satellite evapotranspiration products, and water accounting.
• Provides valuable insights into the role of water delivery priority in shaping agricultural responses, including fallowing, crop substitution, and increased groundwater reliance.
• Offers critical data to inform future groundwater modeling for the Pinal Active Management Area (AMA), highlighting that actual agricultural responses to shortages (e.g., earlier elimination of CAP Ag Pool deliveries, higher groundwater pumping) have outpaced previous model projections.

Funding

• Research Seed Grant from Arizona State University (ASU).
• Arizona Water Innovation Initiative (AWII).
• Fulton Founder in Residence Fellowship from Ira A. Fulton Schools of Engineering at ASU (Zhaocheng Wang).
• Lincoln Institute’s Babbitt Center for Land and Water Policy Dissertation Fellowship Program (Zhaocheng Wang).

Citation

@article{Sharma2026Differential,
  author = {Sharma, Shraddha and Wang, Zhaocheng and Vivoni, Enrique R. and French, Andrew N. and Guillevic, Pierre and Houborg, Rasmus and Sanchez, C. A. and Porter, Sarah},
  title = {Differential impacts of Colorado River shortage operations on agricultural adaptation and groundwater reliance in Central Arizona},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2026.110842},
  url = {https://doi.org/10.1016/j.agwat.2026.110842}
}