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Thursday, September 27, 2012

Climate change driving US Drought conditions towards a megadrought?

The widespread and persistent drought in the US during 2011-2012 has expanded according to the US Drought Monitor as reported on Climate Central. Are we starting to see the signs of a megadrought in the US southwest? Are human influences such as climate change contributing to or causing this widespread extreme weather event?

As of 18 September 2012, 64.82 percent of the contiguous U.S. has been declared as suffering from at least moderate drought - a new record. Extreme drought occurs across 20.74 percent, while the most severe category has ravaged 6.26 per cent of the land. And the seasonal outlook provided by NOAA provides little happy news predicting the drought will persist till the end of the year.

The drought is the worst to occurr since the dustbowl years of the 1930s and comes as North America experiences well above normal temperatures over spring and summer breaking many temperature records with the first half of 2012 being the hottest on record for the United States. July 2012 was the hottest month on record for the continental United States. But Australia and a few other places had abnormally cool month so putting the chill on a hot July for a global record.

2011 Texas drought linked to climate change

A modelling study of the 2011 Texas drought by David Rup and Philip Mote from the Oregon Climate Change Institute found that greenhouse emissions and climate change were likely to have caused the extreme temperature and drought conditions last year. The paper - Did Human Influence on climate make the 2011 Texas drought more probable? - was published July 2012 in the Bulletin of the American Meteorological Society called Explaining Extreme Events of 2011 from a Climate Perspective

We found that extreme heat events were roughly 20 times more likely in 2008 than in other La NiƱa years in the 1960s and indications of an increase in frequency of low seasonal precipitation totals. With 2008 serving as our proxy for 2011, this suggests that conditions leading to droughts such as the one that occurred in Texas in 2011 are, at least in the case of temperature, distinctly more probable than they were 40–50 years ago.

So if the drought in Texas last year was highly probably caused by climate change, I strongly suspect this years more widespead and persistent drought will also be attributed to human caused climate change.

Is this the start of a megadrought?

The persistent drought in the US has its origins in elevated sea surface temperatures in the Pacific - the strong La Nina event that has been present the last two years that brought floods to Australia. Although the La Nina effect has faded to be slowly replaced by a weak El Nino event, drought conditions are forecast to persist for the remainder of the year.

But global warming has also globally increased sea surface temperatures adding to the impact of the El Nino Southern Oscillation (ENSO) cycle, and also increased atmospheric temperatures creating stronger heatwave and drought conditions. Milder winters have resulted in less snow precipitation which leads to less spring runoff, soil moisture and groundwater replenishment.

The US southwest occasionally experiences multi-decadal megadroughts. The last two occurred during the 2nd century and the 12th century. While these megadroughts may have been caused by natural climate variation, human driven climate change will increase the frequency of extreme droughts ocurring.

Droughts like the current one, or the 2000- 2004 Drought which was assessed as the worst in 800 years may become the 'New Normal'.

"Towards the latter half of the 21st century the precipitation regime associated with the turn of the century drought will represent an outlier of extreme wetness," said the scientists in a study published in Nature Geoscience in July 2012 - Reduction in carbon uptake during turn of the century drought in western North America.

We may be seeing the start of a new megadrought in the south-western United States, or if not now, within the next 100 years with global warming the area is likely to be pushed into a megadrought. "It’s these extreme periods that can really cause ecosystem damage, lead to climate-induced mortality of forests, and may cause some areas to convert from forest into shrublands or grassland.” said Beverly Law, a co-author of the study.

Drought damages crop yields

Caption: This graphic depicts U.S corn areas located in drought areas according to the latest U.S. Drought Monitor data on August 7, 2012.

Drought impacts include reduced agricultural yield and substantial crop losses pushing up food prices and feedstock prices. In Ohio, by no means the worst affected state, corn yeilds were expected to fall 29 per cent as reported in Business Week and analysed further at Climate Progress, with some farmers facing a 60 per cent reduction in yield. In August US corn and soybean prices closed at new record highs due to crop damage from the drought. The US Department of Agriculture estimated half the corn crop was in poor or very poor condition, and 39 per cent of the soybean crop was classified in poor or very poor condition, according to this AFP report.

According to the US Agriculture Department reported on August 14 "Currently, 85% of the U.S. corn is within an area experiencing drought, along with 83% of the soybeans, 71% of the domestic cattle inventory, and 63% of the hay."

With the reduced availability of feedstocks, beef and pork producers are slaughtering their stock to minimise costs of maintaining their herds. While this may push down meat prices temporarily, the reduction to herds will act to increase prices in the future. Ridiculously, up to 40 per cent of the US corn crop is grown to produce ethanol to add to petrol.

Even that loyal farm companion, the horse, is feeling the heat of the times with economic hard times for their owners and rising cost of hay, Drought is causing horses to be abandoned according to CBS News.

I reported on Climate Change likely to severely damage U.S. crop yields in 2009. And in 3 short years we are seeing the impact.

Drought impacting Groundwater storage

The NASA Gravity Recovery and Climate Experiment (GRACE) satellites revealed the drought has reached deep. With prolonged drought more dependence is made on groundwater from Aquifers. Water that can take hundreds to thousands of years to replenish continues to be pumped out for agriculture, industrial and domestic uses. A recent news report revealed that Drought, irrigation depletes Ogallala Aquifer at third-largest level on record according to a 2011 study.

The NASA GRACE climate satellites are able to give us accurate surface and underground water maps of the United States which reveal a substantial decline in groundwater over the last two years.

The US Geological Survey released a study in February on the decline in water in the High Plains Aquifer. Withdrawals for irrigation now account for over 16 million acre-feet per year, much more than can be replenished. Waterlevel in some arease have declined up to 100 feet in some areas over the last 60 years. The High Plains Aquifer sits under eight states - Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming.

"The High Plains Aquifer is Nature's nearly perfect water storage system: self-recharging, safe from natural disasters, readily accessed over a broad area, and with copious capacity," said USGS Director Marcia McNutt in a media release. "And yet in less than 100 years we are seriously depleting what took Nature more than 10,000 years to fill."

Caption: These maps show ground water conditions in the U.S. compared to the long-term average from August 2002 to August 2012. (Map by Chris Poulsen, National Drought Mitigation Center, based on data from the GRACE science team.)

Climate change increasing wildfire frequency and intensity

Higher temperatures and drier conditions has provided the perfect conditions for wildfires across the United States. As I reported in July 2011, The US 'normal climate' just got hotter. These changes were predicted in a study published in 2010 on Extreme Drought conditions worsening globally with climate change.

The drought and drier conditions has provided ideal fire weather, with an increase in the intensity and frequency of wildfires across the country predicted to set a new record for most acres burned. As of 18 September 8.4 million acres (3.4 million hectares) across the United States. Scientific studies show that increasing temperatures and the frequency of drought, we are seeing Changes in extent and intensity of wildfire linked to Climate change. NASA Earth Observatory reports the American west continues to burn. The NASA article states:

The size and frequency of wildfires has increased significantly in the western United States over the past few decades due largely to climate change and changing forestry practices. Climate change has decreased winter snow cover, hastened the arrival of spring, and intensified heat waves across much of the West—all factors that exacerbate wildfires. In addition, decades of aggressive fire suppression have left denser forests and abundant fuel on the ground, which makes fires more difficult to control.

Am article in Nature this month - Forest fires: Burn out - warns that the severity of fires, and insect infestations increasing with warmer temperatures, is speeding up landscape transitions. These forest ecosystems may never be the same.

Pressure needed on Congress, President for climate change action

It has taken a while to build up for the common person to see the tangible impacts of climate change, but we are seeing them now in the US Drought, the record reduction in Arctic sea ice, melting of Greenland and West Antarctic Ice Sheets, the increase in extreme weather events caused by a more active water cycle.

The devestation and loss of life of Hurricane Katrina in 2005 caused many people to look again at extreme weather events and disaster management in the richest country in the world. Climate change is now contributing to and causing more extreme weather events which will directly impact the health and mortality of US citizens and the economic productivity of the country.

Perhaps the current drought will provide an essential wakeup call to many more people in the US that action needs to be taken in reduction of carbon emissions. Without this pressure from people in the street on the politicians the well funded lobby groups will continue to hold sway over the political process that affects the fate and liveability of the whole world.

The Center for Biological Diversity is running a campaign for the defence of The Clean Air Act to be used to regulate carbon pollution, and a Clean Air cities campaign. But I'm sure there are many other active creative ways to take action directly or through lobbying or protesting.


  • Climate Central, 20 September 2012 - Drought Grows, Forecast to Persist Through Early Winter
  • NASA Earth Observatory - 19 September 2012 - American west continues to burn
  • NASA Earth Observatory - 20 September 2012 - Signs of the U.S. Drought Are Underground
  • David Rup and Philip Mote - Did Human Influence on climate make the 2011 Texas drought more probable? in Peterson, Thomas C., Peter A. Stott, Stephanie Herring, 2012: Explaining Extreme Events of 2011 from a Climate Perspective. Bull. Amer. Meteor. Soc., 93, 1041–1067. (Full Issue) doi:
  • Christopher R. Schwalm, Christopher A. Williams, Kevin Schaefer, Dennis Baldocchi, T. Andrew Black, Allen H. Goldstein, Beverly E. Law, Walter C. Oechel, Kyaw Tha Paw U& Russel L. Scott, Nature Geoscience Reduction in carbon uptake during turn of the century drought in western North America (abstract) DOI: 10.1038/NGEO1529

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