Study provides new insights on drought predictions in East Africa
With more than 40 million people living under exceptional
drought conditions in East Africa, the ability to make accurate predictions of
drought has never been more important. In the aftermath of widespread famine
and a humanitarian crisis caused by the 2010-2011 drought in the Horn of Africa
-- possibly the worst drought in 60 years -- researchers are striving to
determine whether drying trends will continue. While it is clear that El Niño
can affect precipitation in this region of East Africa, very little is known
about the drivers of long-term shifts in rainfall. However, new research
described in the journal Nature helps explain the mechanisms at work behind
historical patterns of aridity in Eastern Africa over many decades, and the
findings may help improve future predictions of drought and food security in
the region.
"The
problem is, instrumental records of temperature and rainfall, especially in
East Africa, don't go far enough in time to study climate variability over
decades or more, since they are generally limited to the 20th century,"
explains first author Jessica Tierney, a geologist at the Woods Hole
Oceanographic Institution (WHOI). Tierney and her colleagues at WHOI and the
Lamont-Doherty Earth Observatory of Columbia University used what is known as
the paleoclimate record, which provides information on climate in the geologic
past, to study East African climate change over a span of 700 years.
The
paleoclimate record in East Africa consists of indicators of moisture balance
-- including pollen, water isotopes, charcoal, and evidence for run-off events
-- measured in lake sediment cores. Tierney and her colleagues synthesized
these data, revealing a clear pattern wherein the easternmost sector of East
Africa was relatively dry in medieval times (from 1300 to 1400 a.d.), wet
during the "Little Ice Age" from approximately 1600 to 1800 a.d., and
then drier again toward the present time.
Climate
model simulations analyzed as part of the study revealed that the relationship
between sea surface temperatures and atmospheric convection in the Indian Ocean
changes rainfall in East Africa. Specifically, wet conditions in coastal East
Africa are associated with cool sea surface temperatures in the eastern Indian
Ocean and warm sea surface temperatures in the western Indian Ocean, which
cause ascending atmospheric circulation over East Africa and enhanced rainfall.
The opposite situation -- cold sea surface temperatures in the western Indian
Ocean and warmer in the East -- causes drought. Such variations in sea-surface
temperatures likely caused the historical fluctuations in rainfall seen in the
paleorecord.
The
central role of the Indian Ocean in long-term climate change in the region was
a surprise. "While the Indian Ocean has long been thought of as a 'little
brother' to the Pacific, it is clear that it is in charge when it comes to
these decades-long changes in precipitation in East Africa," says Tierney.
Many
questions remain, though. "We still don't understand exactly what causes
the changes in sea surface temperatures in the Indian Ocean and the relationship
between those changes and global changes in climate,like the cooling that
occurred during the Little Ice Age or the global warming that is occurring
now," says Tierney. "We'll need to do some more experiments with
climate models to understand that better."
In the
past decade, the easternmost region of Africa has gotten drier, yet general
circulation climate models predict that the region will become wetter in
response to global warming. "Given the geopolitical significance of the
region, it is very important to understand whether drying trends will continue,
in which case the models will need to be revised, or if the models will
eventually prove correct in their projections of increased precipitation in
East Africa," says co-author Jason Smerdon, of the Lamont-Doherty Earth
Observatory.
While
it's currently unclear which theory is correct, the discovery of the importance
of the Indian Ocean may help solve the mystery. "In terms of forecasting
long-term patterns in drought and food security, we would recommend that
researchers make use of patterns of sea surface temperature changes in the
Indian Ocean rather than just looking at the shorter term El Niño events or the
Pacific Ocean," says Tierney.
In
addition, Tierney and her colleagues lack paleoclimate data from the region
that is most directly affected by the Indian Ocean -- the Horn of Africa. The
paleoclimate data featured in this study are limited to more equatorial and
interior regions of East Africa. With support from National Science Foundation,
Tierney and her colleagues are now developing a new record of both aridity and
sea surface temperatures from the Gulf of Aden, at a site close to the Horn.
"This
will give us the best picture of what's happened to climate in the Horn, and in
fact, it will be the first record of paleoclimate in the Horn that covers the
last few millennia in detail. We're working on those analyses now and should
have results in the next year or so," says Tierney.
This
research was based on work supported by the National Science Foundation and the
National Oceanic and Atmospheric Administration (NOAA).
Source: Woods
Hole Oceanographic Institution
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thank god!!! i m in south africa .....well nice Article!!!!