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Southwestern US Precipitation Decrease

There is considerable evidence that changing weather patterns linked to climate change are at least partly responsible for recent precipitation decrease in California and the southwestern US. There is also emerging evidence showing that climate change is shifting rainfall patterns, consistent with literature that projects climate change will lead to drying in the region by mid-century.

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Climate science at a glance

  • In the past few decades, rainfall has diminished in the western US, and the causes are an active area of research.
  • Warming in the northern Pacific contributes to weather patterns that lead to hotter-drier conditions in the western US.
  • Weather patterns linked to climate change are at least partly responsible for the dramatic precipitation decrease from 2012-2014 during the California drought.
  • Models project that climate change will lead to drying in the Southwest by mid-century.
  • There is some evidence that a drying trend linked to climate change is already underway.[1]

Southwest decreased precipitation trends and climate change

  • (Diffenbaugh et al. 2015; Park et al. 2015): Changing weather patterns due to climate change are at least partly responsible for the dramatic precipitation decrease during the two back-to-back winters in California—the winters of 2012-2013 and 2013-2014—that contributed to the severity of the California drought. Researchers have linked climate change to the circulation patterns that produced the unprecedented high-pressure weather pattern known as the “ridiculously resilient ridge” that blocked storms from the state.[2][3]
  • (Prein et al. 2016): Data from 1979 to 2014 shows up to a 25 percent decrease in precipitation in the US Southwest related to an increase in high pressure, anticyclonic conditions during this time in the North East Pacific.[4]
  • (IPCC AR5, 2013): Globally, models show that many mid-latitude and subtropical dry regions will see a decrease in precipitation by 2100 should global emissions continue to increase.[5]

Studies attribute decreases in Southwest precipitation to climate change

  • (Bonfils et al. 2020): There is an indication that climate change is already shifting rainfall in the Southwestern US. While human emissions of aerosols in the 1950s shifted the tropical rainbelt (ITCZ) and led to a wetter Western US, climate change-driven warming in the Northern Hemisphere has now offset that cooling trend, returning the Western US to drier conditions. Further warming is likely to lead to even further dry conditions.[1]
  • The strength and frequency of the MJO have increased over the past century (medium confidence) (Oliver 7 and Thompson, 2012; Maloney et al., 2019; Cui et al., 2020) because of global warming

Select a pillar to filter signals

Air Mass Temperature Increase
Arctic Amplification
Extreme Heat and Heat Waves
Glacier and Ice Sheet Melt
Global Warming
Greenhouse Gas Emissions
Land Ice and Snow Cover Decline
Land Surface Temperature Increase
Permafrost Thaw
Precipitation Falls as Rain Instead of Snow
Sea Ice Decline
Sea Surface Temperature Increase
Season Creep/ Phenology Change
Snowpack Decline
Snowpack Melting Earlier and/or Faster
Atmospheric Moisture Increase
Extreme Precipitation Increase
Runoff and Flood Risk Increase
Total Precipitation Increase
Atmospheric Blocking Increase
Atmospheric River Change
Extreme El Niño Frequency Increase
Gulf Stream System Weakening
Hadley Cell Expansion
Large Scale Global Circulation Change/ Dynamical Changes
North Atlantic Surface Temperature Decrease
Ocean Acidification Increase
Southwestern US Precipitation Decrease
Surface Ozone Change
Surface Wind Speed Change
Drought Risk Increase
Land Surface Drying Increase
Intense Atlantic Hurricane Frequency Increase
Intense Cyclone, Hurricane, Typhoon Frequency Increase
Intense Northwest Pacific Typhoon Frequency Increase
Tropical Cyclone Steering Change
Wildfire Risk Increase
Coastal Flooding Increase
Sea Level Rise
Air Mass Temperature Increase
Storm Surge Increase
Thermal Expansion of the Ocean
Winter Storm Risk Increase
Coral Bleaching Increase
Habitat Shift or Decline
Parasite, Bacteria and Virus Population Increase
Pine Beetle Outbreaks
Heat-Related Illness Increase
Infectious Gastrointestinal Disease Risk Increase
Respiratory Disease Risk Increase
Vector-Borne Disease Risk Increase
Storm Intensity Increase
Tornado Risk Increase
Wind Damage Risk Increase
What are Climate Signals?