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55.7% of the Contiguous United States in Moderate or Worse Drought – 12 Feb 2013

According to the Drought Monitor, drought conditions are relatively unchanged in the past two weeks. As of Feb. 12, 2013, 55.7% of the contiguous US is experiencing moderate or worse drought (D1-D4). The percentage area experiencing extreme to exceptional drought increased from 19.4% to 17.7% in the last two weeks. Percentage areas experiencing drought across the West stayed mostly the same while snowpack increased. Drought across the Southwest decreased slightly. Meanwhile, storms improved drought conditions in the Southeast.

This post precedes a significant snow event across the High and Great Plains.  The NWS expects up to a foot of snow in some areas of the Plains over the next couple of days, which will provide about 1″ of liquid water equivalent.  Since these areas currently suffer from a 2-4″ liquid water deficit, this storm will not break the short-term drought.  Moreover, long-term drought will only be broken by substantial spring and summer rainfall.  After one or two more Drought Monitor updates, we should see some welcome differences in these maps.

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Figure 1 – US Drought Monitor map of drought conditions as of the 12th of February.

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Figure 2 – US Drought Monitor map of drought conditions in Western US as of the 12th of February.  Some small relief is evident in the past week, including some changes in the mountains as storms recently dumped snow across the region.  Mountainous areas and river basins will have to wait until spring for snowmelt to significantly alleviate drought conditions.

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Figure 3 – US Drought Monitor map of drought conditions in Colorado as of the 12th of February.  Drought conditions held mostly steady across the state in the past week.  For the first time in over a month, less than 100% of CO is experiencing Severe drought conditions.  This improvement occurred over the southwestern portion of the state due to mid-season snow storms.  Unfortunately, Exceptional drought conditions expanded over the northeastern plains.

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Figure 4 – US Drought Monitor map of drought conditions in Southeast US as of the 12th of February.  As mentioned above, drought conditions contracted a little and grew less severe in the past couple of weeks.  The worst hit area, in central Georgia, has experienced the longest duration drought conditions on this map.

Cooler than normal sea-surface temperatures (SSTs) are present in the eastern Pacific, according to current MJO and ENSO data.  Additionally, eastern Pacific SSTs are cooler than the climatic average due to the current negative phase of the IPO.  This in turn is due in part to global warming, which is causing warmer western Pacific and Indian Ocean SSTs than usual.  The cool SSTs in the eastern Pacific initiate and reinforce air circulations that generally keep precipitation away from the Southwest and Midwest US.  This doesn’t mean that drought will be ever-present; only that we are potentially forcing the climate system toward more frequent drought conditions in these regions.  Some years will still be wet or normal; other years (increasing in number) will be dry.  This counters skeptics who claim that more CO2 and warmer temperatures are better for plants.  If there is no precipitation, plants cannot take advantage of longer growing seasons.  Moreover, we will experience years with increased food pressure.  These conditions’ extent in the future is up to us and our climate policy (or lack thereof).

While MJO, ENSO, and IPO are all in phases that tend to deflect storm systems from the Southwest, this week’s storm demonstrates that the conditions are not ever-present.  Weather variability still occurs with the dryer regime.  Put another way, weather is not climate.


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57.7% of Contiguous US in Moderate or Worse Drought – 29 Jan 2013

According to the Drought Monitor, drought conditions are relatively unchanged in the past two weeks. As of Jan. 29, 2013, 57.7% of the contiguous US is experiencing moderate or worse drought (D0-D4). The percentage area experiencing extreme to exceptional drought increased from 19.3% to 19.4%. Percentage areas experiencing drought across the West stayed mostly the same at the end of January as they were at in the middle. Drought across the Southwest decreased slightly. Meanwhile, drought across the Southeast grew due to relative lack of precipitation.

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Figure 1 – US Drought Monitor map of drought conditions as of the 29th of January.

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Figure 2 – US Drought Monitor map of drought conditions in Western US as of the 29th of January.  Some small relief is evident in the past week, but note the lack of change of drought conditions across the regions, despite recent snows throughout the mountains.  Mountainous areas and river basins will have to wait until spring for snowmelt to help start to alleviate drought conditions.

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Figure 3 – US Drought Monitor map of drought conditions in Colorado as of the 29th of January.  Drought conditions held steady across the state in the past week.  100% of Colorado experienced Severe or worse drought conditions for the past three weeks.

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Figure 4 – US Drought Monitor map of drought conditions in Southeast US as of the 29th of January.  As mentioned above, drought conditions expanded and worsened in the past couple of weeks.  The worst hit area, in central Georgia, has experienced the longest duration drought conditions on this map.  Drought has expanded and contracted around this area during that time.

The latest seasonal (three-month) outlook from the National Weather Service predicts enhanced chances for above-average temperature and below-average precipitation for the central US.  This means that drought conditions are likely to continue for at least another three months and probably longer if prevailing conditions do not change.  One of the major weather stories of 2012 was drought; 2013 is shaping up to have the same story.

What is causing this?  A combination of factors: the Arctic Oscillation (AO), the Madden-Julian Oscillation (MJO), the El-Nino and Southern Oscillation (ENSO), the Interdecadal Pacific Oscillation (IPO), and background climate warming.

As I discussed in my last drought post:

The lack of sea ice in the Arctic back in September is part of what caused the negative phase of the AO.  The Arctic Ocean absorbed solar radiation instead of reflecting it back to space.  The ocean then slowly released that heat to the atmosphere before new ice could form.  That extra heat in the atmosphere changed how and where the polar jet stream established this winter.  Instead of a tight loop near the Arctic Circle, the jet stream has grown in North-South amplitude, allowing cold air to pour to latitudes more southerly than usual and warm air to move over northern latitudes.  The large amplitude jet has kept the normal type of storms from moving over locations that used to see them regularly during the winter.

An active MJO is keeping trade winds stronger than they otherwise would be, which piles up warm ocean water in the western tropical Pacific Ocean.  This causes cool, deep ocean water to rise in the eastern Pacific, as seen in Figure 5.

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Figure 5Madden-Julian Oscillation conditions as of 2 Feb 2013 from NOAA-CPC.

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Figure 6ENSO conditions as of 2 Feb 2013 from NOAA-CPC.

Cooler than normal sea-surface temperatures (SSTs) are present in the eastern Pacific due to the current MJO and ENSO data.  Additionally, eastern Pacific SSTs are cooler than the climatic average due to the current negative phase of the IPO.  This in turn is due in part to global warming, which is causing western Pacific and Indian Ocean SSTs warmer than usual.  The cool SSTs in the eastern Pacific initiate and reinforce air circulations that generally keep precipitation away from the Southwest and Midwest US.  This doesn’t mean that drought will be ever-present; only that we are potentially forcing the climate system toward more frequent drought conditions in these regions.  Some years will still be wet or normal; other years (increasing in number) will be dry.  This is a counter to skeptics who claim that more CO2 and warmer temperatures are necessarily better for plants.  If there is no precipitation, plants cannot take advantage of longer growing seasons.  Moreover, we will experience years with food pressure.  These conditions’ extent in the future is up to us and our climate policy (or lack thereof).


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58.9% of Contiguous US in Moderate or Worse Drought – 15 Jan 2013

The storm systems that moved over the US in the past month alleviated some of the drought conditions across the US, according to the Drought Monitor. As of Jan 15, 2013, 58.9% of the contiguous US is experiencing moderate or worse drought (D0-D4). The percentage area experiencing extreme to exceptional drought decreased from 21.3% to 19.4%. Percentage areas experiencing drought across the West stayed mostly the same in the middle of January as they were at the end of December. Drought across the High Plains expanded slightly during the same period. Meanwhile, drought across the Southeast and Midwest shrank due to the aforementioned storm systems.

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Figure 1 – US Drought Monitor map of drought conditions as of the 15th of January.

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Figure 2 – US Drought Monitor map of drought conditions in Western US as of the 15th of January.  Note the lack of change of drought conditions across the regions, despite recent snows throughout the mountains.  Mountainous areas and river basins will have to wait until spring for snowmelt to help start to alleviate drought conditions.

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Figure 3 – US Drought Monitor map of drought conditions in Midwest US as of the 15th of January.  This region also has not seen any meaningful shift in drought conditions recently.  The Plains will likely have to wait until spring and summer for drought relief.  This sector of the country does plant a significant amount of crops.  The winter wheat crop has already been devastated.

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Figure 4 – US Drought Monitor map of drought conditions in Colorado as of the 15th of January.  Drought conditions worsened slightly across the state in the past week.  Now, 100% of Colorado is experiencing Severe or worse drought conditions.  The percentage area with Extreme drought conditions is 5% higher than last week.  There was no significant difference in Exceptional drought area since last week.

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Figure 5 – US Drought Monitor map of drought conditions in Colorado as of July 31, 2012.  This figure shows how extensive the current drought is – both in space and time.  Severe or worse drought has afflicted close to 100% of the state for almost six months now.  While specific regions of the state have received some rain or snow, it hasn’t been enough to break the drought yet.  The percent area with Extreme or worse drought has decreased from 73.67% on July 24th to 65.35% on July 31st to 58.64% on January 15th.  The southeast part of the state has seen the worst of conditions, as Figure 5 and 6 demonstrate.

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Figure 6 – US Drought Monitor map of drought conditions in Colorado as of June 14, 2011.  Eighteen months ago, more than half of Colorado was drought-free.  As you can see, the southeast part of the state has seen Severe or worse drought conditions for a long time now.

The US is not likely to see drought relief through March (drought predictions are accurate for ~3 months at a time) .  A negative Arctic Oscillation (AO; Figure 7) is challenging the return to ENSO-neutral conditions, which should allow normal precipitation to fall over the US.  The AO has been negative in previous winters and it has caused the severe winter storms that affected the northeastern US as well as UK (record wet year in 2012) and Scandinavia.

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Figure 7Arctic Oscillation time series from NOAA’s Climate Prediction Center.

The lack of sea ice in the Arctic back in September is part caused the negative phase of the AO.  The Arctic Ocean absorbed solar radiation instead of reflecting it back to space.  The ocean then slowly released that heat to the atmosphere before new ice could form.  That extra heat in the atmosphere changed how and where the polar jet stream established this winter.  Instead of a tight loop near the Arctic Circle, the jet stream has grown in N/S amplitude, allowing cold air to pour to latitudes more southerly than usual and warm air to move over northern latitudes.  The large amplitude jet has kept the normal type of storms from moving over locations that used to see them regularly during the winter.

Hence, the drought we see now over the US is causally linked to the Arctic Oscillation as well as the long-lasting, moderate La Niña (2010-2012).  Both of the natural variations exist on top of the background climate, which we are warming (this is why there was record low Arctic sea ice in 2012).  We will continue to see the climate modulate normal weather conditions until we stop emitting greenhouse gases.  As I’ve written, that isn’t likely to happen any decade soon.

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