Bonacci et al. (2026) Analysis of Annual Water Level Variability in the Mead and Powell Reservoirs of the Colorado River

Identification

• Journal: Water
• Year: 2026
• Date: 2026-01-14
• Authors: Ognjen Bonacci, Ana Žaknić‐Ćatović, Tanja Roje-Bonacci
• DOI: 10.3390/w18020224

Research Groups

• Faculty of Civil Engineering, Architecture and Geodesy, Split University, Split, Croatia
• Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Canada

Short Summary

This study analyzes long-term water level variability in the Mead and Powell reservoirs of the Colorado River, revealing significant declining trends, especially post-2003, driven by climate change and increased consumption, with Lake Mead experiencing a more pronounced and concerning decrease.

Objective

• To analyze water-level trends and variations in Lakes Mead and Powell on an annual time scale using several less commonly applied concepts and analytical methods.

Study Configuration

• Spatial Scale: Colorado River Basin, focusing on Lake Mead (Hoover Dam) and Lake Powell (Glen Canyon Dam). Lake Mead surface area: 639 km²; Lake Powell surface area: 689 km².
• Temporal Scale:
  • Lake Mead: Daily data from 2 February 1935, annual analysis for 1938–2024.
  • Lake Powell: Daily data from 28 December 1963, annual analysis for 1964–2024.
  • Regression analysis: 1964–2024, with subperiods 1964–2006 and 2007–2024.

Methodology and Data

• Models used:
  • Linear Regression (for inter-reservoir relationship)
  • Pearson’s linear correlation coefficient (R) and coefficient of determination (R²)
  • Rescaled Adjusted Partial Sums (RAPS) method (for detecting fluctuations and subperiods)
  • F-test (for differences in variances)
  • t-test (for differences in average values)
  • Day-to-day (DTD) method (for water-level variability)
  • Standardized Hydrological Index (SHI) (for drought assessment)
• Data sources:
  • Daily water-level data from U.S. Geological Survey Nevada Water Science Center (Lake Mead)
  • Daily water-level data from U.S. Geological Survey Utah Water Science Center (Lake Powell)

Main Results

• Both Lake Mead and Lake Powell exhibit clear declining trends in water levels, particularly after 2003.
• Lake Mead shows a more severe decline, with extreme drought conditions (SHI < -2.0) observed in 2022–2024.
• RAPS analysis identified three statistically distinct subperiods for both reservoirs, with a sharp and significant decline in water levels during the most recent period (2003–2024).
  • Lake Mead average annual water levels: 352.1 m a.s.l. (1938–1971), 363.3 m a.s.l. (1972–2002), 334.5 m a.s.l. (2003–2024).
  • Lake Powell average annual water levels: 1078.9 m a.s.l. (1964–1972), 1116.7 m a.s.l. (1973–2002), 1096.4 m a.s.l. (2003–2024).
• The DTD method confirmed Lake Powell's regulating influence on Lake Mead, reducing its average DTD variability from 0.197 m (1938–1964) to 0.0855 m (1965–2024).
• Regression analysis revealed that for comparable Lake Powell levels, Lake Mead's mean annual water levels in 2007–2024 were approximately 22 m lower than in 1964–2006, indicating increased system losses. The coefficient of determination (R²) for this relationship also declined from 0.888 to 0.580 in the later period.
• The SHI indicates an accelerating intensification of drought conditions over the last two decades for both reservoirs.

Contributions

• Provides a comprehensive analysis of long-term water-level dynamics in the critical Mead and Powell reservoirs using a suite of less commonly applied hydrological methods (RAPS, DTD, SHI).
• Quantitatively demonstrates the regulatory impact of Lake Powell on Lake Mead's day-to-day water level variability.
• Identifies statistically significant shifts in water level regimes, highlighting a pronounced and concerning decline in both reservoirs since 2003.
• Offers empirical evidence of changing system-level coupling between the two reservoirs, indicating increased downstream water losses in the more recent period.
• Underscores the urgent need for revised water-management policies and consumption patterns in the Colorado River Basin in light of observed hydrological realities and climate projections.

Funding

This research received no external funding.

Citation

@article{Bonacci2026Analysis,
  author = {Bonacci, Ognjen and Žaknić‐Ćatović, Ana and Roje-Bonacci, Tanja},
  title = {Analysis of Annual Water Level Variability in the Mead and Powell Reservoirs of the Colorado River},
  journal = {Water},
  year = {2026},
  doi = {10.3390/w18020224},
  url = {https://doi.org/10.3390/w18020224}
}