Saturday, January 17, 2015

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A Little Perspective on the Current Situation (Drought!)

Will it ever snow again in the Sierra?  Probably, but not likely in the next 7 days.  Omegasaurus (see our last post if you are not familiar with this beast) will continue to dominate our weather pattern in the near future.  I'm not going to get into details about the long-range forecast, as we've had our hopes built up just to get let down a few too many times this season.


As a graduate student at the Desert Research Institute my main area of research has been drought.  So, many of you may be tired of hearing about the current drought, but where this one falls into the last 120 years of records is pretty interesting to a drought nerd like myself!  I put together an analysis from the Tahoe City COOP station.  This station is part of the US Historical Climatology Network because it has a long and consistent period of record dating back to the late 1800s.

Let me break down this figure for you.  In each panel the black line is the same, and shows the water year (September-October) percent of normal precipitation.  A red bar indicates the start of a drought period.  For the top panel a drought is classified as <100% of normal for 3 consecutive years.  The middle is same threshold, but for 4 consecutive years, and bottom has a threshold of <75% of normal for 3 consecutive years.  

Source: Dan McEvoy, Desert Research Institute

There were actually 9 years in a row below normal during the 90's, nearly the entire decade (top panel).  But, a couple of those years were 90-98% of normal, which still a lot of precipitation.  Focusing on the bottom panel, there have only been 4 cases since 1896 that have seen 3 years in a row with <75% of normal precipitation (including 2012-2014).  At this particular station there has never been 4 years in a row below 75% of normal...lets hope we don't break that record this year!

Lets not forget that we have evidence that suggests much drier periods than this one lasting for several decades, as Ben alluded to in the last post.  My analysis is based only on one weather station record.

Well, I'm off to hit the mountain bike trails in Reno, which are riding pretty awesome right now! Enjoy the weekend, and make the best of what have right now!


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