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Future droughts will be shockers, study says

1970s Sahel disaster will seem mild compared to areas by 2030s, models project

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Image: Map of drought potential
Courtesy Wiley Interdisciplinary Reviews, redrawn by UCAR
This map illustrates the potential for drought by 2039, based on current projections of future greenhouse gas emissions. The map uses the Palmer Drought Severity Index, which assigns positive numbers when conditions are unusually wet, and negative numbers when conditions are unusually dry. A reading of -4 or below is considered extreme drought. Blue or green regions will likely be at lower risk, while those in the red and purple spectrum could face more unusually extreme drought. staff and news service reports staff and news service reports
updated 10/19/2010 5:30:36 PM ET 2010-10-19T21:30:36

Increasingly dry conditions across much of the globe — including the U.S. — are likely over the next 30 years, a new study predicts. Moreover, by the year 2100 drought in some regions could be unprecedented in modern times.

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Increasing drought has long been forecast as a consequence of warming temperatures, but the study from the National Center for Atmospheric Research projects serious impacts as soon as the 2030s. Impacts by century's end could go beyond anything in the historical record, the study suggests.

"We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community," study author Aiguo Dai said in a statement. "If the projections in this study come even close to being realized, the consequences for society worldwide will be enormous."

To get an idea of how severe droughts might get, scientists use a measure called the Palmer Drought Severity Index, or PDSI. A positive score is wet, a negative score is dry and a score of zero is neither overly wet nor dry.

The most severe drought in recent history, in the Sahel region of western Africa in the 1970s, had a PDSI of -3 or -4.

By contrast, the study indicates that by 2100 some parts of the U.S. could see -8 to -10 PDSI, while Mediterranean areas could see drought in the -15 or -20 range.

"Historical PDSI for the last 60 years show a drying trend over southern Europe but nothing like those values at the end of this century," Dai said. "Decadal mean values of PDSI have not reached -15 to -20 levels in the past in any records over the world."

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By the 2030s, the central and western U.S. could see average readings dropping to -4 to -6, the study projected.

Areas likely to experience significant drying include:

  • the western two-thirds of the United States;
  • much of Latin America, especially large parts of Mexico and Brazil;
  • regions bordering the Mediterranean Sea;
  • large parts of southwest Asia;
  • southeast Asia, including China and neighboring countries;
  • most of Africa and Australia.

While Earth is expected to get dryer overall, some areas will see a lowering of the drought risk. These include: much of northern Europe; Russia; Canada; Alaska; and some areas of the Southern Hemisphere.

That doesn't necessarily mean that agriculture will migrate from the drought areas to these places in the high latitudes, Dai wrote.

"The high-latitude land areas will experience large changes in terms of warmer temperatures and more precipitation, and thus may indeed become more habitable than today," he wrote. "However, limited sunshine, short growing season, and very cold nighttime temperature will still prevent farming over most of these high-latitude regions."

Courtesy Wiley Interdisciplinary Reviews, redrawn by UCAR
This map showing drought patterns over the last decade uses the Palmer Drought Severity Index, which assigns positive numbers when conditions are unusually wet for a particular region, and negative numbers when conditions are unusually dry.

The study's findings are based on 22 computer models and the best current predictions of climate-warming greenhouse gas emissions. This could change depending on actual greenhouse emissions in the future as well as natural climate cycles such as El Nino, Dai said.

The study appears this week in the journal Wiley Interdisciplinary Reviews: Climate Change. It was supported by the National Science Foundation.

Reuters contributed to this report.

Discuss: Future droughts will be shockers, study says

151 total comments

1970s Sahel disaster will seem mild compared to areas by 2030s, models project


Despite the anti-intellectualism movement and conspiracy theories among conservatives, most won't deny climate change in the past and therefore in the future. What they don't believe is that it is caused by human activity. They don't want to create plan B or C because this would mean sincere research into cause, which may not support their position.

Also, I suspect some pre-destination among conservatives, more specifically the End of Times. So if we predict drought that just supports their religious beliefs. I will say it is interesting that 2050 is when Isaac Newton predicts the end, but why a person would not at least try to make a better world for future generations (their children) is beyond me.

Resbot Nermo

No need to worry about overpopulating the world. This is natures way of thinning the herd.

Resbot Nermo, with 16

Republican Free Market Advocates need to wake up and travel the United States before they discredit global warming. In my line of work. I have traveled most of the lower 48 states and the environmental destruction is overwhelming. What the scientists are saying is absolutely right. You can see preliminary effects of drying along Colorado's front range, in all of Wyoming, all of Montana. Most parts of New Mexico, Northern Arizona, Western Kansas, and Nebraska, and South Dakota. The snow fall and rain fall have dropped substantially. The aquifers have been pumped so low ground is collapsing and causing structural damage to buildings. Forests are dying. Farm land is going to waste. In Florida the sea is changing dramatically, with dying coral and changes in marine animals. I have been to Gulf Tidal Flats where one can actually see that the oceans have risen by 1 foot from historic levels due to melting icecaps. What the USA needs to do is to sober up to the fact that Capitalism ain't workin and we need to try something else world wide. The USA is an energy hog. Our country needs to take the lead. Americans need to police car manufacturers and insist on making a zero polluting vehicle. Every coal burning power plant in the nation needs to be shut down. Appliance makers, and HVAC equipment makers need to greatly improve efficiency. American Cities like LA need to be criminally prosecuted for dumping so much pollution into the air that it poisons an entire continent. Several mathematicians have won Nobel Prizes in statistics proving the validity of Global Warming. People are not trying to get rich off the Green Movement they are trying to prevent a catastrophe. What does it take to get action and put aside ignorance? The GOP needs to shut up; pay taxes; start acting in the best interests of the USA ' and stop spreading false propaganda.


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