California has become increasingly dry since 1895. From 2012 to 2016, the state experienced its most severe drought on record. Although conditions eased briefly afterward, comparable dry conditions returned during the 2021 water year.  

Droughts are periods of dry weather that last long enough to cause a water shortage. They have significant environmental, social, and economic repercussions. A natural feature of California’s climate, droughts have been exacerbated by human-induced warming. For more information, download the Drought chapter. 

This graph tracks drought using the Palmer Drought Severity Index (PDSI), which measures the relative dryness of a region by incorporating readily available temperature, precipitation, and soil moisture data. Positive values (blue bars) indicate “wet” months; negative values (red bars) are “dry” months. PDSI values below -3 denote severe drought, and below -6 very extreme drought.

• California has become increasingly dry since 1895. From 2012 to 2016, California experienced the most severe drought on record: thirteen of the 30 driest months occurred during this period. 

• Except for brief wet periods in the 2017 and 2019 water years, drought conditions have largely persisted through 2021.

• Droughts create conditions that threaten human health. Examples include degraded drinking water quality, air pollution from wildfires and dust storms, and increased exposures to the fungus that causes Valley Fever and to toxins produced by harmful algal blooms.

• Droughts lead to a wide range of ecological impacts, such as widespread tree deaths, larger wildfires, threatened fish populations. 

• Many of the impacts of drought on California’s ecosystems disproportionately affect people who depend on these diverse natural resources. 

• Warming temperatures and periods of low precipitation, both attributable to climate change, have increased the likelihood of extreme droughts in the state. Geography and local climate patterns determine regional variations in the extent and severity of droughts.

• Cal-Adapt, Extended Drought Scenarios
• National Oceanic Atmospheric Administration, Climate at a Glance 
• National Oceanic and Atmospheric Administration, State Climate Summaries, 2022: California  
• National Oceanic Atmospheric Administration, Storm Events Database  
• Western Regional Climate Center, West Wide Drought Tracker