The challenge of water scarcity in Arizona is defined by two types of drought. A meteorological drought is a short-term deficit in precipitation. The more pressing issue for the Southwestern US is a hydrological drought, which is the cumulative effect of long-term precipitation shortfalls on stored water supplies like reservoirs, streamflow, and groundwater reserves. Arizona’s arid environment means that water resources are continually stressed, requiring a long-term perspective that goes beyond a single dry year’s rainfall.
Establishing Arizona’s Drought Timeline
The duration of Arizona’s current water insecurity stretches back over two decades, with the prolonged 21st-century drought starting around the year 2000. This period is recognized as part of a larger “megadrought” affecting southwestern North America. Tree-ring data indicates that the years since 2000 have been the driest multi-decade period in at least 1,200 years.
This persistence is driven by cumulative water deficit combined with rising temperatures, leading to aridification. Higher temperatures increase evaporation from reservoirs and soil, intensifying the effects of reduced precipitation. Drought is measured less by recent rainfall and more by the continuous, unrecovered drop in water storage over time.
How Drought Conditions Are Measured
Arizona’s official drought status is continuously monitored using federal, state, and local data. The widely recognized classification system is the U.S. Drought Monitor (USDM), which employs a five-category scale ranging from D0 (Abnormally Dry) to D4 (Exceptional Drought). The USDM uses a “convergence of evidence” approach, blending multiple indicators like precipitation totals, streamflow levels, soil moisture, and reports from local experts.
The state’s Drought Monitoring Technical Committee utilizes specialized indices to determine the long-term status. For instance, the Standardized Precipitation Index (SPI) is calculated at various timescales. Short-term conditions are indicated by 3- to 12-month periods, while 24- to 48-month periods reflect the long-term hydrological situation. This multi-faceted approach allows policymakers to differentiate between temporary dryness and a chronic water supply problem.
Impact on Major Water Systems
The most profound impact of the sustained drought is seen in the Colorado River system, which supplies approximately 40% of Arizona’s water. Water levels in Lake Mead, the largest U.S. reservoir, determine the severity of water cuts for Arizona and other Lower Basin states. These curtailments are triggered by specific elevation thresholds set by agreement.
The Central Arizona Project (CAP) holds the lowest priority water rights in the Lower Basin and is the first system to incur substantial cuts, often impacting the agricultural sector most heavily. Reductions are triggered by Lake Mead’s projected elevation:
- Tier Zero shortage: Below 1,090 feet.
- Tier 1 shortage: Beginning at 1,075 feet.
- Tier 2 shortage: Beginning at 1,050 feet.
- Tier 3 shortage: Beginning at 1,025 feet.
Arizona’s in-state surface water, managed by the Salt River Project (SRP) on the Salt and Verde Rivers, provides a resilient supply for the Phoenix metro area. This system includes reservoirs, such as Roosevelt Lake, which store local runoff from mountain snowpack. Reduced CAP supply pushes some users, particularly in agriculture, to increase reliance on groundwater pumping, stressing finite underground aquifers.
State-Level Water Management Strategies
Arizona has implemented several long-term policies to proactively manage its water portfolio against persistent drought. A major strategy is the Arizona Water Banking Authority (AWBA), established in 1996 to store unused Colorado River entitlement underground. The AWBA stores water in aquifers through recharge facilities, accruing credits that can be recovered during Colorado River shortages to provide a backup supply for municipal and industrial users.
The state’s 2019 Drought Contingency Plan (DCP) formalized a framework for sharing the burden of Colorado River reductions and incentivizing conservation. The DCP includes a mitigation component that uses banked water to offset some of the cuts to the CAP system. Arizona also maintains an “Assured Water Supply” program, which requires developers to demonstrate a 100-year water supply for new subdivisions.
Looking toward the future, the state is actively investigating augmentation strategies through the Water Infrastructure Finance Authority of Arizona (WIFA). These efforts include feasibility studies for large-scale projects such as ocean desalination and enhanced water recycling. These projects aim to diversify Arizona’s water portfolio and reduce the risk associated with reliance on the Colorado River and stressed groundwater sources.