Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

A continent split by climate change: New study projects drought in southern Africa, rain in Sahel

24.05.2005


A new analysis of Africa’s past and future climate shows that the Sahel region, which experienced catastrophic drought until rains returned in the 1990s, could experience wetter monsoons for decades to come. However, drought across southern Africa is projected to intensify further. Oceanic warming consistent with an increase in greenhouse gases appears to be a factor in these expected 21st-century changes to Africa’s monsoons.



James Hurrell of the National Center for Atmospheric Research (NCAR) will present the findings on May 24 in New Orleans at the spring meeting of the American Geophysical Union. The study, conducted with Martin Hoerling (National Oceanic and Atmospheric Administration), was supported by NOAA and the National Science Foundation, NCAR’s primary sponsor.

The analysis, which draws on 60 simulations of global climate from five computer models, provides new evidence linking drought in southern Africa to the warming of the Indian Ocean. However, it contradicts earlier studies that also connected the Sahelian drought of northern Africa to the Indian Ocean. Instead, the new results point to a late 20th-century cooling of the North Atlantic Ocean as having been key to Sahelian drought. A subsequent switch to North Atlantic warming, partly consistent with the impact of greenhouse gas increases, is the main factor behind the Sahel’s recent swing from drought to moist conditions, the researchers believe.


"Changes in the Indian and Atlantic oceans are causing large regional effects in Africa, and these have substantial impacts on people. Now we can explain these climatic effects," says Hurrell.

Recurrent drought since the 1970s has plagued southern Africa, including Angola, Zambia, and Zimbabwe. Meanwhile, the nearby Indian Ocean has warmed more than 1 degree Celsius (0.6 degree Fahrenheit) since 1950. As showers and thunderstorms develop in the rising air above the warming ocean, says Hurrell, they help lead to sinking air and drought in a surrounding ring that includes southern Africa.

"In our models, the Indian Ocean shows very clear and dramatic warming into the future, which means more and more drought for southern Africa," says Hurrell. "It is consistent with what we would expect from an increase in greenhouse gases."

Hurrell and Hoerling compared model results from 1950-99 to several control runs that omitted the Indian Ocean warming. None of those runs showed the magnitude of drying that actually occurred in southern Africa. When the models did include the Indian Ocean warming, southern Africa consistently dried out. The models also project that by 2049, monsoons across southern Africa could be 10% to 20% drier than the 1950-99 average.

A different process appears to shape rainfall in the Sahel. When sea-surface temperatures are warmer in the South Atlantic than in the North, it pulls the Sahelian monsoon cycle south as well, depriving the region of its usual rains.

"This was the situation during much of the latter half of the 20th century." says Hurrell. "We believe the North Atlantic Ocean cooling was natural and masked an expected greenhouse-gas warming effect."

Since 1990, the sea-surface temperature pattern has reversed, warming more rapidly in the North Atlantic than in the South. The models examined by Hurrell and Hoerling show this trend intensifying in future decades. They project that the Sahel monsoon will be some 20% to 30% wetter by 2049 compared to the 1950-99 average.

The warming of Indian Ocean waters is well beyond the range expected from natural processes. This strengthens the case that greenhouse gases are involved, says Hurrell. In the Atlantic, natural variability affects ocean temperatures more strongly, making it more difficult to attribute changes there to greenhouse-gas effects.

Paleoclimate records show that even greater climate swings have occurred in Africa’s monsoons, most likely related to past variations in solar output and in Earth’s orbit. "From a paleoclimate perspective, the recent African dryings appear to be neither unusual nor extreme," says Hurrell.

Monsoon rains, critical to life in much of Africa, shift north and south with the seasons. They normally reach the Sahel from July to September and the southern part of the continent from February into April. Low-pressure centers moving west from the Sahel during the monsoon often serve as seed for tropical storms and hurricanes in the North Atlantic. Hurrell’s work does not address the possible impact of increased rains in the Sahel on future Atlantic hurricane activity.

For their study, Hurrell and Hoerling examined output from computer models at NCAR, NASA, NOAA, the European Centre for Medium-Range Weather Forecasts, and France’s National Center for Meteorological Research (CNRM).

Anatta | EurekAlert!
Further information:
http://www.ucar.edu

More articles from Ecology, The Environment and Conservation:

nachricht International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht World Water Day 2017: It doesn’t Always Have to Be Drinking Water – Using Wastewater as a Resource
17.03.2017 | ISOE - Institut für sozial-ökologische Forschung

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

When Air is in Short Supply - Shedding light on plant stress reactions when oxygen runs short

23.03.2017 | Life Sciences

Researchers use light to remotely control curvature of plastics

23.03.2017 | Power and Electrical Engineering

Sea ice extent sinks to record lows at both poles

23.03.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>