Wintertime droughts are increasingly common in the Mediterranean
region, and human-caused climate change is partly responsible,
according to a new analysis by NOAA scientists and colleagues at
the Cooperative Institute for Research in Environmental Sciences
(CIRES). In the last 20 years, 10 of the driest 12 winters have
taken place in the lands surrounding the Mediterranean Sea.
"The magnitude and frequency of the drying that has occurred is too
great to be explained by natural variability alone," said Martin
Hoerling, Ph.D. of NOAA's Earth System Research Laboratory in
Boulder, Colo., lead author of a paper published online in
the Journal of
Climatethis month. "This is not encouraging news for a region
that already experiences water stress, because it implies natural
variability alone is unlikely to return the region's climate to
normal."
The Mediterranean region accumulates most of its precipitation
during the winter, and Hoerling's team uncovered a pattern of
increasing wintertime dryness that stretched from Gibraltar to the
Middle East. Scientists used observations and climate models to
investigate several possible culprits, including natural
variability, a cyclical climate pattern called the North Atlantic
Oscillation (NAO), and climate change caused by greenhouse gases
released into the atmosphere during fossil fuel use and other human
activities.
Climate change from greenhouse gases explained roughly half the
increased dryness of 1902-2010, the team found. This means that
other processes, none specifically identified in the new
investigation, also have contributed to increasing drought
frequency in the region.
The team also found agreement between the observed increase in
winter droughts and in the projections of climate models that
include known increases in greenhouse gases. Both observations and
model simulations show a sudden shift to drier conditions in the
Mediterranean beginning in the 1970s. The analysis began with the
year 1902, the first year of a recorded rainfall dataset.
In this analysis, sea surface temperature patterns emerged as the
primary reason for the relationship between climate change and
Mediterranean drought. In recent decades, greenhouse-induced
climate change has caused somewhat greater warming of the tropical
oceans compared to other ocean regions. That pattern acts to drive
drought-conducive weather patterns around the Mediterranean. The
timing of ocean temperature changes coincides closely with the
timing of increased droughts, the scientists found.
The Mediterranean has long been identified as a "hot spot" for
substantial impact from climate change in the latter decades of
this century because of water scarcity in the region, a rapidly
increasing population, and climate modeling that projects increased
risk of drought.
"The question has been whether this projected drying has already
begun to occur in winter, the most important season for water
resources," Hoerling said. "The answer is yes."
Climate is a global phenomenon with global impacts on food prices
and water security, and NOAA researchers are engaged in
understanding changes in climate across many regions of the world.
In the Mediterranean, winter drought has emerged as a new normal
that could threaten food security. Lessons learned from studying
climate in that region may also be relevant for the U.S. West
Coast, which has a similar climate to the Mediterranean region of
Europe and North Africa.
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NOAA Headquarters:
Thanks to NOAA Headquarters for this article.