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Blog of the California Institute for Water Resources | Univ of California | Ag & Natural Resources
by Julie M Barnes
on July 17, 2019 at 9:32 AM
Greetings! I've never heard of atmospheric rivers before, which seem pretty cool. My question is, does your organization suspect or believe that the lack of the atmosphere rivers over the past decades are a contributing cause for the drought in California? If so, is there a reason that the atmospheric rivers disappear for periods of time?
Reply by Faith Kearns
on July 18, 2019 at 10:48 AM
Posted on behalf of Tashiana:  
We too think learning about atmospheric rivers can be pretty cool! You ask a great question – we do see that an absence (or weak) of atmospheric rivers (ARs) contributes to California’s droughts. In fact, ARs are sometimes referred to as “drought busters” since they can abruptly end droughts. However, even within drought periods, we’ve seen localized hazards resulting from ARs that are large enough and last a long time after making landfall.  
Research shows there are a number of factors that determine whether or not an AR forms and reaches the western U.S. Key factors involve available water vapor (at the start and as the AR moves), the strength and direction of winds, and the presence of an extratropical cyclone (storm system) which helps the water vapor converge into a narrow river-like feature. We are, however, looking to ongoing research to help explain why we see multi-year hiatuses when it comes to larger ARs.  
Climate models suggest we’ll see an increase in atmospheric water vapor because as the atmosphere warms it can hold more water. This means more “fuel” available for ARs. For this region, it’s suggested there will be an overall increase in AR severity. More pronounced swings (“whiplash”) between dry and wet years are also projected in the future.
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