How to Define a Drought?

Some consider drought to occur in the Colorado River Basin when water supplies reach drought level (1st red line on the left graph), and others may define it in various other ways.  The National Drought Mitigation Center at the Unversity of Nebraska/Lincoln, after declaring that drought is indeed difficult to define, says In the most general sense, drought originates from a deficiency of precipitation over an extended period of time - usually a season or more . .    We use this definition as evidence of the beginning of this 25-year drought (as of 2024), and the long-term below-drought-level of Lake Mwad (and Lake Powell, the graph on the right) as the drought's continuation.

The graph segment on the left shows the deepest and longest-term decline of Lake Mead since it started filling in 1937 to its lowest level ever - down 179 feet (54.6 m) on July 28, 2022.  Drought-level is the 1st red line from the top of the graph.

The graph segment of Lake Powell on the right is strikingly similar with Lake Powell reaching its lowest level ever on April 13, 2023, down 180 ft (54.9 m) from full pool.

Drought Updates continues this story with recent graphs of 5 years history for the lakes, 7 years for snowpack.  Cycling NASA images illustrate the extent of the drought and its water loss for Lake Powell and Lake Mead (from Satellite Images).