Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Drought’s growing reach: NCAR study points to global warming as key factor

11.01.2005


The percentage of Earth’s land area stricken by serious drought more than doubled from the 1970s to the early 2000s, according to a new analysis by scientists at the National Center for Atmospheric Research (NCAR). Widespread drying occurred over much of Europe and Asia, Canada, western and southern Africa, and eastern Australia. Rising global temperatures appear to be a major factor, says NCAR’s Aiguo Dai, lead author of the study.



Dai will present the new findings on January 12 at the American Meteorological Society’s annual meeting in San Diego. The work also appears in the December issue of the Journal of Hydrometeorology in a paper also authored by NCAR’s Kevin Trenberth and Taotao Qian. The study was supported by the National Science Foundation, NCAR’s primary sponsor.

Dai and colleagues found that the fraction of global land experiencing very dry conditions (defined as -3 or less on the Palmer Drought Severity Index) rose from about 10-15% in the early 1970s to about 30% by 2002. Almost half of that change is due to rising temperatures rather than decreases in rainfall or snowfall, according to Dai.


"Global climate model predict increased drying over most land areas during their warm season, as carbon dioxide and other greenhouse gases increase," says Dai. "Our analyses suggest that this drying may have already begun."

Even as drought has expanded across Earth’s land areas, the amount of water vapor in the air has increased over the past few decades. The average global precipitation has also risen slightly. However, as Dai notes, "surface air temperatures over global land area have increased sharply since the 1970s." The large warming increases the tendency for moisture to evaporate from land areas. Together, the overall area experiencing either very dry or very wet conditions could occupy a greater fraction of Earth’s land areas in a warmer world, Dai says.

Though most of the Northern Hemisphere has shown a drying in recent decades, the United States has bucked that trend, becoming wetter overall during the last 50 years, says Dai. The moistening is especially notable between the Rocky Mountains and Mississippi River. Other parts of the world showing a moistening trend include Argentina and parts of western Australia. These trends are related more to increased precipitation than to temperature, says Dai.

"Droughts and floods are extreme climate events that are likely to change more rapidly than the average climate," says Dai. "Because they are among the world’s costliest natural disasters and affect a very large number of people each year, it is important to monitor them and perhaps predict their variability."

To see how soil moisture has evolved over the last few decades, Dai and colleagues produced a unique global-scale analysis using the Palmer index, which for decades has been the most widely used yardstick of U.S. drought. The index is a measure of near-surface moisture conditions and is correlated with soil moisture content.

Since the Palmer index is not routinely calculated in most of the world, Dai and colleagues used long-term records of temperature and precipitation from a variety of sources to derive the index for the period 1870-2002. The results were consistent with those from a historical simulation of global land surface conditions, produced by a comprehensive computer model developed by scientists at NCAR, NASA, Georgia University of Technology, the University of Texas at Austin, and the University of Arizona.

By factoring out rainfall and snowfall, Dai and colleagues estimated how much of the global trend in soil moisture was due solely to rising temperatures through the extra evaporation they produce.

"The warming-induced drying has occurred over most land areas since the 1970s," says Dai, "with the largest effects in northern mid and high latitudes." In contrast, rainfall deficits alone were the main factor behind expansion of dry soils in Africa’s Sahel and East Asia. These are regions where El Nino, a more frequent visitor since the 1970s, tends to inhibit precipitation.

Anatta, NCAR Media Relations | EurekAlert!
Further information:
http://www.ucar.edu
http://www.nsf.gov

More articles from Earth Sciences:

nachricht World’s oldest known oxygen oasis discovered
18.01.2018 | Eberhard Karls Universität Tübingen

nachricht A close-up look at an uncommon underwater eruption
11.01.2018 | Woods Hole Oceanographic Institution

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>