Global Warming increases the odds of worsening drought in many parts of the United States and the world. Regions such as the U.S. Southwest, where droughts are expected to get more frequent, intense, and longer lasting, are at particular risk.

Global warming contributes to drought as warmer temperatures enhance evaporation, which reduces surface water and dries out soils and vegetation. This makes periods with low precipitation drier than they would be in cooler conditions. Global warming also alters the timing of water availability and causes less precipitation to fall as snow in the Northern Hemisphere, including in key regions like the Sierra Nevada of California.

Monitoring drought impact supports policy measures that increase greenhouse gas removals and climate change adaptation of resilient ecosystems. Between 2000 and 2019, the EEA-39 region was affected by severe droughts with an annual productivity loss of 3% in impacted areas. The last decade saw the most intense drought years; notably, the years 2013 and 2016-2019 showed strong impacts on vegetation productivity. Drought impacts on forests were worst, with a 5% annual productivity loss followed by croplands (4% annual decrease) and heathlands/shrubs (3.1% decrease).

On January 17, 2014, California State Governor Jerry Brown declared a drought state of emergency. On April 2, 2017, Governor Brown lifted the drought emergency but declared that California must continue water conservation efforts. With the official conclusion of the most recent drought, which spanned water years 2012 through 2016, it is timely to compare it with other historic California droughts and also to consider some of the lingering impacts.