47.3% of the Contiguous United States in Moderate or Worse Drought – 25 Apr 2013

According to the Drought Monitor, drought conditions improved recently across some of the US. As of Mar. 12, 2013, 47.3% of the contiguous US is experiencing moderate or worse drought (D1-D4) as the 2011-2012 drought extended well into 2013.  That is the lowest percentage in a number of months. The percentage area experiencing extreme to exceptional drought increased from 14.6% to 14.7%, but this is ~3% lower than it was three months ago. Percentage areas experiencing drought across the West decreased in the past month as a series of late season cyclones impacted the region.  Drought across the Southwest worsened slightly while rain from storms maintained the low-level of drought conditions in the Southeast.

My previous post preceded the series of major winter storm that affected much of the US.  In some places in the High Plains and Midwest, 12″ or more of snow fell.  With relatively high liquid water equivalency, each storm dropped almost ~1″ of water precipitation, of which the area was in sore need.  Unfortunately, these same areas required 2-4″ of rain to break their long-term drought.  In other words, while welcome, recent snows have reduced the magnitude of the drought in many areas, but have not completely alleviated them.  Ironically, a very different problem arose from these storms: flooding.

Figure 1 – US Drought Monitor map of drought conditions as of April 25th.

If we focus in on the West, we can see recent shifts in drought categories:

Figure 2 – US Drought Monitor map of drought conditions in Western US as of April 25th.

Some relief is evident in the past month (see table on left), 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.  As you can probably tell, this is a large area experiencing abnormally dry conditions for about one year now.

Here are conditions for Colorado:

Figure 3 – US Drought Monitor map of drought conditions in Colorado as of April 25th.

There is some evidence of relief evident over the past three months here.  Instead of 100% of the state in Severe drought, only 78% is today.  The central & northern mountains, as well as the northern Front Range (Denver north to the border) enjoyed the most relief since February.  The percentage area in Extreme drought also dropped significantly from 59% to 38%.  Exceptional drought shifted in space from northeastern Colorado to central Colorado while southeastern Colorado remained very dry.

Drought conditions improved somewhat across the southwestern portion of the state in the past couple of weeks.  The percentage area that is experiencing less than Severe drought conditions continues to track downward, which is a good sign.  Unfortunately, Exceptional drought conditions continued their hold over the eastern plains.

Here are conditions for the High Plains states:

Figure 4 – US Drought Monitor map of drought conditions in the High Plains as of April 25th.

The large storms that moved over this area in the past month reduced the worst drought conditions across Nebraska, South Dakota, and Wyoming.  The percentage area with Exceptional drought dropped from 27% to 7%; Extreme drought dropped from 61% to 28%; and Severe drought dropped from 87% to 70%.

With rather significant areas still experiencing moderate or worse drought across much of the US west of the Mississippi River, drought remains a serious concern in 2013.  I previously hypothesized that much of the 2012 drought was partly a result of natural climate variability and underlying long-term warming.  I wrote about NOAA’s examination into the causes of the 2012 drought a couple of weeks ago in which the authors suggested it was not heavily influenced by long-term warming.

US drought conditions are more influenced by Pacific and Atlantic sea surface temperature conditions.  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.

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 when they turn 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 we will find 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.

51.4% of the Contiguous United States in Moderate or Worse Drought – 12 Mar 2013

According to the Drought Monitor, drought conditions improved recently across some of the US. As of Mar. 12, 2013, 51.4% of the contiguous US is experiencing moderate or worse drought (D1-D4).  That is the lowest percentage in a number of months. The percentage area experiencing extreme to exceptional drought increased from 17.7% to 16.5% in the last month. Percentage areas experiencing drought across the West stayed mostly the same while snowpack generally increased. Drought across the Southwest decreased slightly and rain from storms improved drought conditions in the Southeast.

My previous post preceded a major winter storm that affected much of the US.  In some places in the High Plains and Midwest, 12″ or more of snow fell.  With relatively high liquid water equivalency, this snow represented ~1″ of water precipitation.  Unfortunately, these same areas required 2-4″ of rain to break their long-term drought.  In other words, while welcome, recent snows have not substantially reduced drought severity affecting the middle of the nation, as the following map shows.

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

If we focus in on the West, we can see recent shifts in drought categories:

Figure 2 – US Drought Monitor map of drought conditions in Western US as of the 12th of March.

Some small relief is evident in the past couple of weeks, 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.  As you can probably tell, this is a large area experiencing abnormally dry conditions for almost a year now.

Here are conditions for Colorado:

Figure 3 – US Drought Monitor map of drought conditions in Colorado as of the 12th of March.

Drought conditions improved somewhat across the southwestern portion of the state in the past couple of weeks.  The percentage area that is experiencing less than Severe drought conditions continues to track downward, which is a good sign.  Unfortunately, Exceptional drought conditions continued their hold over the eastern plains.

Here are conditions for the High Plains states:

Figure 4 – US Drought Monitor map of drought conditions in the High Plains as of the 12th of March.

Again, even with large snowfalls in the past month, little drought relief is evident across this region.  What these states need are frequent soaking rains in the spring and summer to alleviate their long-term drought.  Agriculture certainly could use that relief this year.

And finally the area that experienced the most relief in the past month, the Southeast:

Figure 5 – US Drought Monitor map of drought conditions in the Southeast as of the 12th of March.

The shifts in the numbers in the table tell a good story.  Frequent storms tracked over this region recently, which helped bust the worst conditions (Severe and worse).  Look at the ‘None’ category now versus three months ago: the percent area doubled!  Now the rains need to continue through the rest of the year.

US drought conditions are related to Pacific and Atlantic sea surface temperature conditions.  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 Nino-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.

As drought affects regions differentially, their policy responses vary.  A growing number of water utilities recognize the need to be proactive with respect to drought impacts.  The last thing they want is their reliability to suffer.  Americans are privileged in that clean, fresh water flows when they turn their tap.  Crops continue to show up at their local stores despite terrible conditions in many areas of their own nation.  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.  Warmer conditions include warmer water today than what existed 30 years ago.  Warmer water into a plant either mean warmer water out or a longer time spent in the plant, which reduces the amount of energy the plant can produce.  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.

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.

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

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.

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.

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.

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.

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

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.

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.

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.

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

Figure 6 – ENSO 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).

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.

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

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.

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.

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.

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.

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.

Figure 7 – Arctic 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.

61% of Contiguous US in Moderate or Worse Drought

The storm systems that moved over the US since the 20th of December didn’t do much to alleviate drought conditions across the US, according to the Drought Monitor.  As of Jan 1, 2013, 61% of the contiguous US is experiencing moderate or worse drought (D0-D4).  The percentage area experiencing exceptional drought edged up slightly from 6.7% to 6.8%.  Percentage areas experiencing drought across the West stayed mostly the same at the end of December as they were the 11th of December.  Drought across the High Plains expanded slightly during the same period.  Meanwhile, drought across the Southeast and Northeast improved somewhat.  Midwest drought remained largely unchanged.

The snow that fell over the intermountain west will have to melt in the spring before conditions improve there.  Additional help will have to come this summer via the monsoon before this wide expanse of severe drought is alleviated.

The snow that fell over these areas prior to Christmas didn’t help with drought conditions – yet.  Above-average snow will also have to fall over the High Plains before conditions improve much.  It was simply too hot and dry over these states last year for one storm to significantly impact drought conditions.

According to the US Climate Prediction Center’s Seasonal Outlook issued yesterday, little relief is likely through March 2013:

As this figure shows, the edges of the drought affecting the western 2/3 of the nation could see some improvement.  Conditions over the southeast, which experienced drought for a couple of years, could also improve in the next three months.

I’ve been reading a large number of scientific papers on drought.  While extensive and severe in absolute magnitude, the current drought isn’t worse than the droughts of the 20th century (1950s and 1930s).  So far, enough precipitation has fallen in the right areas at the right times to alleviate severe impacts on societies.  In contrast, 20th century droughts affected people quickly – largely because they were unprepared for the conditions they experienced.  Those prior circumstances helped inform decision makers so that future effects would not be as severe as quickly.  That said, people would not be adequately prepared if conditions revert back to those last seen in the 1100s.  Multidecadal droughts have occurred over substantial parts of the US.  The relative wetness of the 19th and 20th centuries are not likely to continue into the 21st, especially as global temperatures continue to rise.  How will we prepare and respond?