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Colorado’s Hot, Dry September Follows Hot, Dry Summer: Get Used To It

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For those of us living in Colorado, we know that this summer was warmer and drier than normal.  We further know that September was one of the warmest and driest on record.  And just like the rest of the world, if we don’t stop forcing the climate system with our global warming pollution, this summer and this September will become the new normal.  Even hotter and drier years are on tap if that happens. I’m going to start on a local level.  The Denver metro area recorded its 5th driest and 7th warmest September on record in 2010.  The climatological period is 1971 to 2000; the length of reliable records date back to 1872.  September 2010 was thus in the top 5 driest and top 10 warmest out of more than 125 other Septembers.  In other words, it was very significant.  Some of the details of that warmth should be noted:

THERE WERE 8 NINETY DEGREE DAYS WHICH WAS 6 ABOVE THE NORM. FOR THE SEASON NOW…THERE HAVE BEEN 49 90 DEGREE DAYS WHICH IS 16 ABOVE NORMAL. ONE NOTEWORTHY STATISTIC WAS THAT DURING SEPTEMBER 2010 THERE WERE 25 DAYS THAT RECORDED TEMPERATURES OF 80 DEGREES OR HIGHER. ACCORDING TO LOCAL CLIMATOLOGICAL RECORDS…THAT IS THE HIGHEST NUMBER OF 80 DEGREE TEMPERATURES FOR SEPTEMBER IN DENVER SINCE 1872.

That’s part of how you get the 7th warmest September on record.  More importantly, overnight lows tend to drive records like this.  Higher overnight lows help keep daytime highs higher and month-long temperatures on pace for record highs. And how dry was it?

BETWEEN THE 18TH AND 22ND OF SEPTEMBER…THE DENVER INTERNATIONAL AIRPORT COLLECTED A TOTAL OF ONLY 0.06 INCH OF MOISTURE. THE REMAINING 25 DAYS OF THE MONTH WERE TOTALLY DRY…NOT EVEN A TRACE OF LIQUID. BETWEEN AUGUST 8TH AND SEPTEMBER 30TH ONLY 0.08 INCH OF RAINFALL WAS TALLIED.

Eight-hundredths of an inch of precipitation is incredibly low for a nearly two-month time period.  Combined with the heat, it’s what has led to my lawn and garden to nearly stop growing and turn brown.  Obviously, it also puts stress on local water supplies. Let’s look at this in a slightly different way.  When all the hourly temperature readings are averaged over the entire month of September, the average temperature for the month registered 67.0F.  Compared to 30 years of climatological records, that was 4.6F above normal.  When you read a number like that, you should keep in mind that the most likely set of climate model solutions project that level of warming for Colorado to become the new normal this century.  Left unchecked, global warming will make this September’s near-record heat and lack of precipitation just an average year in just a few decades’ time.  I want to share this graphic again, which shows the number of weeks per year which have high temperatures over 100F. I don’t think 2 months of 100F highs sounds like a future that I want to experience. How about you? Changing gears a little bit, I wanted to discuss Colorado temperatures and precipitation for September and the summer. According to NOAA’s NCDC, Colorado recorded its 112th warmest out of 116 Septembers.  So the heat didn’t just affect Denver or the Front Range metro area.  Colorado also recorded its 18th driest out of 116 Septembers.  A quick aside: Wyoming recorded its all-time driest September in 2010 while Minnesota recorded its all-time wettest September.  Those kind of seemingly paradoxical simultaneous conditions are exactly the kind of phenomenon projected to occur more and more often in the upcoming decades.  In other words, get used to it. Additional data from the NCDC shows that Colorado recorded its 106th warmest July-September on record.  In fact, take a long look at the map at that link.  An overwhelming majority of states across the continental U.S. had above average Jul-Sep temperatures.  A majority of states had their top-10 warmest Jul-Sep temperatures out of the past 116 years.  Two saw their all-time warmest Jul-Sep periods ever.  Again, these kind of conditions are only expected to occur with more frequency in the future … unless we stop our global warming pollution.  Colorado’s Jul-Sep precipitation was much closer to normal.  How is that, you might ask, when September was so dry?  Because July and August both came close to being notably wetter than normal. Some of these numbers may not seem that impressive or may not trigger some level of concern by themselves.  Think about them in context of water supplies, agriculture and ecosystem health and they should become worrisome.  These trends aren’t likely to go away.  In fact, just the opposite, they’re likely to get worse and do so soon.  How will millions of Front Range residents cope with dwindling water supplies, especially when farmers will want and need to grow crops for food.  While we might be able to adjust, countless flora and fauna species are accustomed to long-term stable climate conditions.  They’re not going to be able to adjust to radically different conditions on time-scales of years to decades.  Their health and survival now largely depend on our decisions and actions. You can do something tomorrow.  Find a 350.org event near you and help put pressure on decision makers to actually start making some decisions. Cross-posted at SquareState.

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