California has become increasingly dry since 1895. A three-year stretch of dry years (2020 to 2022) ended with a series of storms beginning in December 2022.

Droughts are periods of anomalously dry weather that lasts long enough to cause a water shortage. They have significant environmental, social, and economic impacts. Droughts are a natural feature of California's climate and are becoming even drier due to human-induced warming. More severe droughts are part of a climate pattern occurring more frequently in California called weather whiplash -- dramatic shifts between heavy rainfall and severe droughts. 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 on record occurred during this period. 

• Except for brief wet periods in the 2017 and 2019 water years, drought conditions have largely persisted through 2021 and 2022.

• 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 produce a range of ecological impacts, such as widespread tree deaths, increased wildfire activity, impaired surface water quality, and threats to fish and other aquatic populations. 

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

• Warming temperatures and periods of low precipitation have increased the likelihood of extreme droughts in the state. Local climate patterns and water availability determine regional variations in the extent and severity of droughts.

• Cal-Adapt, Extended Drought Scenarios
• Department of Water Resources, California Water Watch
• 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