Study Finds U.S. Drought Monitor Has Overstated Drought Conditions in California for 25 Years

Study Finds U.S. Drought Monitor Has Overstated Drought Conditions in California for 25 Years

FOR IMMEDIATE RELEASE

TUESDAY, JANUARY 27, 2026 | 8:00 a.m. PT

Study Finds U.S. Drought Monitor Has Overstated Drought Conditions in California for 25 Years

IRVINE, CA - For 25 years, the U.S. Drought Monitor has significantly exaggerated drought conditions in California, providing state officials with the pretext for a range of climate-change policies that have crippled the state's water infrastructure, devastated farming, and punished its 39 million residents with skyrocketing water bills.

That's the conclusion of A Statistical Review of United States Drought Monitor, a landmark California Policy Center study published today by researchers Edward Ring and Marc Joffe.

USDM is a federally funded team of researchers at the University of Nebraska-Lincoln, the National Oceanic and Atmospheric Administration and the U.S. Department of Agriculture. Between the time it began issuing drought designations in 2000 through late 2025, the group has concluded that California has been under drought conditions roughly 61 percent of the time - a remarkable doubling of the drought rate in the previous 100 years.

That would be alarming if it were true. But using USDM's own methodology, Ring and Joffe were unable to replicate USDM's dramatic findings, and instead found drought conditions should have been designated only about 31 percent of the time using USDM's framework. In their own independent analysis, the pair found that recent climate conditions are not significantly drier than those that prevailed during much of the 20th century.

CPC's findings call into question the accuracy of the USDM and its outsized role in shaping California water policy, as well as potential methodological or institutional bias in its approach.

"The USDM's claim - that droughts are hitting California twice as often after the year 2000 as they were in the 100 years before - is objectively false," said Ring, CPC's director of water and energy policy. "While USDM sounds scientific, its team could not provide us with an algorithm that would allow independent researchers to reproduce their weekly classifications. Instead, USDM admits that its employees use their discretion when assigning drought classifications."

Ring and Joffe, a CPC visiting fellow, conducted an independent review of USDM reports from 2000-2025. The authors compared USDM findings to a century of climate records from dozens of California-based monitoring stations, including precipitation, snowpack, temperature, and reservoir storage records from the National Oceanic and Atmospheric Administration (NOAA), the U.S. Department of Agriculture, and the California Department of Water Resources.

Ring and Joffe found that USDM's drought designations in California - particularly in Southern California - have been dramatically overstated relative to historical data and actual water supply conditions.

When drought data is exaggerated, Californians pay the price. The state's sweeping water rules drive up the cost of living and doing business in the state, including the cost of housing, food and utilities. By 2030, California residents face state mandated restrictions on their daily indoor water use of about 40 gallons per person per day.

Driven by USDM data, state officials require local water districts to spend millions of dollars on staff and equipment to enforce water restrictions on customers. That starves the districts of capital that might be used instead to increase water supply and storage.

"Water policy has real economic and social consequences for millions of Californians, and the science behind these decisions matters," said Ring. "When resources are diverted to address exaggerated drought conditions, we fall further behind on investing in new water supplies and the infrastructure needed to support long-term resilience."

On January 5, 2026, for the first time in 25 years, the USDM declared the entire state of California drought-free. While long overdue, the designation is temporary. Without reform, the U.S. Drought Monitor is going to continue to overstate the frequency and severity of droughts.

Ring and Joffe call for a fundamental shift in how drought is defined and managed in California. They recommend the USDM implement immediate reforms, including improving transparency and reproducibility in its drought measurement to allow researchers to independently verify its designations.

Key Findings

1. USDM Drought Categorizations Are Statistically Inconsistent With Long-Term Climate Patterns and Not Reproducible

The USDM is designed to classify drought using percentile-based thresholds derived from historical climate data. Under USDM's own framework, drought conditions should occur approximately 30 percent of the time. However, the authors' analysis of USDM records for the period 2000-late 2025 shows that USDM designated California in drought 61 percent of the time, and Orange County 62 percent of the time - roughly double the frequency implied by the USDM's own percentile-based methodology. This pattern indicates that drought categories have been consistently inflated over time, both statewide and locally. National data also reveal significant over-categorization. This discrepancy suggests potential bias in the USDM's "convergence of evidence" approach.

2. Independently Sourced Climate Data Shows Minimal Long-Term Drying

Ring and Joffe conducted a robust analysis of drought in California, using a century of climate records from dozens of California-based monitoring stations. Variables included precipitation, snowpack, temperature, relative humidity, dew point, and vapor pressure deficit. Climate data for the period 2000-2025 show no substantial drying trend compared to prior 25-year periods. While modest variation exists between decades, the data show recent climate conditions are not significantly drier than those observed during much of the 20th century.

3. Water Storage Trends Are Mixed and Likely Not Driven Solely by Climate

The study evaluates reservoir storage levels across major California water systems. The findings reveal water availability in California has remained largely adequate, and reduced storage levels are primarily the result of regulatory decisions rather than worsening climate conditions. While some reservoirs - including San Luis, Folsom, and Oroville - show modest declines, reservoirs such as Lake Mohave, Lake Almanor, and Pardee show long-term stability. Southern California facilities such as Castaic, Perris, and Pyramid Lakes exhibit only minor declines.

4. Empirical Modeling Suggests Drought Frequency Has Increased Only Marginally

Using a statistical model calibrated against historical climate and drought data, Ring and Joffe estimate that compared to the 20th century, the actual increase in drought frequency for California in the first quarter of the 21st century is approximately 0.83 percent - far below USDM's finding of a 30.65 percent increase. This variance reinforces the conclusion that the USDM has consistently overstated drought conditions.

5. USDM Measures Only "Dryness" Not Water Availability

USDM drought classifications are based on "dryness" and do not account for water availability based on water storage trends, including reservoir storage, groundwater supplies, or system capacity. As a result, areas may be classified as being in "severe" or "exceptional" drought even when sufficient water supplies are available for residents and businesses. This disconnect has allowed USDM designations to become a regulatory trigger, despite USDM's failure to measure the factor most relevant to water security.

Recommendations

By overstating drought conditions in California and failing to account for actual water availability, the USDM has contributed to unnecessary water restrictions, discouraged long-term investment in new water supplies and infrastructure, and incentivized the declaration of water emergencies.

Recommendations include:

• Greater transparency and reproducibility in drought measurement
• Reduced reliance on USDM classifications for regulatory action
• A policy framework that prioritizes resilience over emergency-driven restrictions
• Water policy should be based on measurable water availability
• Increased investment in water supply, storage, recycling, and infrastructure

The study was prepared in coordination with the Mesa Water District in Costa Mesa and includes analysis of statewide data as well as localized impacts in Orange County.

Read the full study and recommendations at: californiapolicycenter.org/USDMstudy

CONTACT: Dawn Collier

California Policy Center

[email protected]

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