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50.1% of the Contiguous United States in Moderate or Worse Drought – 3 Sep 2013

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According to the Drought Monitor, drought conditions worsened slightly across the entire US compared to three weeks ago. As of September 3, 2013, 50.1% of the contiguous US is experiencing moderate or worse drought (D1-D4), as the early 2010s drought continues month after month.  This value is about 9 percentage points lower than it was in the early spring. The percentage area experiencing extreme to exceptional drought decreased from 14.8% three weeks ago to 9.9% last week; this is approximately 10% lower than it was six months ago. The eastern third of the US was wetter than normal during August, which helped keep drought at bay.  The east coast in particular was much wetter than normal and the summer monsoon was much more active this summer compared to 2012.  Instead of Exceptional drought in Georgia and Extreme drought in Florida two years ago, there is flash flooding and rare dam water releases in the southeast.  Four eastern states experienced their top-four wettest Julys on record.  The West presents a different story.  Long-term drought continues to exert its hold over the region, as it remained warmer than normal but six southwestern states received top-20 July precipitation this year.  Meanwhile, Oregon recorded its driest July on record.  Compared to three weeks ago, drought area increased in the Midwest.

 photo USDrought20130903_zpsf4845451.gif

Figure 1US Drought Monitor map of drought conditions as of September 3rd.

If we compare this week’s maps with previous dates (here and here, for example), we can see recent shifts in drought categories.  Compared to early July and mid-August, and despite recent rain events, drought expanded or worsened in the Midwest (Iowa, Missouri, Illinois, Minnesota, and the Dakotas) as well as Louisiana, Arkansas, and Mississippi.

 photo west_drought_monitor_20130903_zps6a3a6205.png

Figure 2 – US Drought Monitor map of drought conditions in Western US as of September 3rd.

After worsening during late winter into spring 2013, drought conditions steadied during the past month.  The differences between this map and mid-August’s is the spatial shift of conditions; the total percent area values are about the same.  The area experiencing Exceptional drought decreased slightly over the West and the percent area with no drought increased slightly, but remains at low levels.  Figure 2 also shows that the percent area with no drought decreased since the start of the year (24% to 14%).

Here are the current conditions for Colorado:

 photo CO_drought_monitor_201309033_zps07464c14.png

Figure 3 – US Drought Monitor map of drought conditions in Colorado as of September 3rd.

There is clear evidence of relief evident over the past three months here.  Severe drought area dropped from 72% to 60% (this was 100% about last year!).  Extreme drought area dropped from 27% to 22% (also down from 50%+ six months ago).  Exceptional drought decreased significantly from three and six months ago.  Instead of 16% of Colorado (and as much as 17% earlier this year), Exceptional drought now covers only 3% of the state.  The good news for southeastern Colorado was the recent delivery of substantial precipitation.  I didn’t think it would be enough to completely alleviate the worst conditions, but they received enough precipitation that drought conditions improved from Exceptional to Extreme.  Their drought is not over yet, but they are finally trending in a good direction.  And for the first time in over one year, some small percentage (2%; up from 1% three weeks ago) of Colorado does not currently have any drought.  This is great news – hopefully this area expands throughout the rest of the year.

 photo midwest_drought_monitor_20130903_zpseafbaad1.png

Figure 4 – US Drought Monitor map of drought conditions in the Midwest as of September 3rd.

Drought expanded and worsened slightly in the Midwest in the past few months: the percent area with no drought decreased significantly from 91% to 52%.  The percent area with Moderate drought increased significantly from 3% to 29% this week.  Severe drought now impacts most of Iowa and small portions of Missouri, Wisconsin and Minnesota.

US drought conditions are more influenced by Pacific and Atlantic sea surface temperature conditions than the global warming observed to date.  Different natural oscillation phases preferentially condition environments for drought.  Droughts in the West tend to occur during the cool phases of the Interdecadal Pacific Oscillation and the El Niño-Southern Oscillation, for instance.  Beyond that, drought controls remain a significant unknown.  Population growth in the West in the 21st century means scientists and policymakers need to better understand what conditions are likeliest to generate multidecadal droughts, as have occurred in the past.  Without comprehensive planning, dwindling fresh water supplies will threaten millions of people.  That very circumstance is already occurring in western Texas where town wells are going dry.  An important factor in those cases is energy companies’ use of well water for natural gas drilling.  This presents a dilemma more of us will face in the future: do we want cheap energy or cheap water?  In the 21st century, we will not have both options available at the same time as happened in the 20th century.  This presents a radical departure from the past.

As drought affects regions differentially, our policy responses vary.  A growing number of water utilities recognize the need for a proactive mindset with respect to drought impacts.  The last thing they want is their reliability to suffer.  Americans are privileged in that clean, fresh water flows every time they turn on their tap.  Crops continue to show up at their local stores despite terrible conditions in many areas of their own nation (albeit at a higher price, as found this year).  Power utilities continue to provide hydroelectric-generated energy.

That last point will change in a warming and drying future.  Regulations that limit the temperature of water discharged by power plants exist.  Generally warmer climate conditions include warmer river and lake water today than what existed 30 years ago.  Warmer water going into a plant either means warmer water out or a longer time spent in the plant, which reduces the amount of energy the plant can produce.  Alternatively, we can continue to generate the same amount of power if we are willing to sacrifice ecosystems which depend on a very narrow range of water temperatures.  As with other facets of climate change, technological innovation can help increase plant efficiency.  I think innovation remains our best hope to minimize the number and magnitude of climate change impacts on human and ecological systems.


One thought on “50.1% of the Contiguous United States in Moderate or Worse Drought – 3 Sep 2013

  1. Pingback: 48.2% of US in Moderate or Worse Drought – 17 Sep 2013 (Thank You, Monsoon!) | Weatherdem's Weblog

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