Differential impacts of Colorado River shortage operations on agricultural adaptation and groundwater reliance in Central Arizona

Abstract

Severe Colorado River reservoir declines triggered mandatory Tier 1 delivery reductions since 2022. The resulting agricultural adaptations and groundwater impacts remain poorly quantified as the reductions fall disproportionately among water users with different delivery priorities. We compared two adjacent irrigation districts in central Arizona with contrasting Central Arizona Project (CAP) delivery priorities: the Maricopa-Stanfield Irrigation and Drainage District (MSIDD; low priority) and the Ak-Chin Indian Community (Ak-Chin; senior tribal entitlement). We integrated CubeSat imagery, Random Forest classifications, and OpenET evapotranspiration ( ET ) products within a water accounting framework to quantify changes in cultivated area, crop composition, consumptive water use, and groundwater reliance. Calibrated with historical records, the framework reproduced annual irrigation totals with normalized mean absolute error (MAE) of 2.0% at Ak-Chin and 4.7% at MSIDD. During the shortage period (2022–2024), Ak-Chin maintained > 99% cultivated area and a stable crop portfolio. In contrast, the 98% reduction in CAP deliveries to MSIDD prompted substantial agricultural adjustments, including a 25.9% contraction in cultivated area and 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 decreased by 61.1 hm³ yr⁻¹ (27.4%), with fallowing and crop switching explaining 72% and 24% of the decline, respectively. The 147.5 hm³ yr⁻¹ loss of CAP deliveries was balanced by lower irrigation volumes (73%) and additional groundwater pumping (27%). These results illustrate the role of delivery priority on fallowing, crop substitution, and groundwater use, and demonstrate a transferable framework for monitoring of agricultural adaptation and water use.