Sweatin’ the Mediterranean Heat

Tuz Gölü, a large salt lake in central Turkey within the Konya Basin, lost half of its water volume in the last four decades. The Konya Basin itself, which hosts a third of all groundwater reserves in Turkey and is the home to eight wetland bird species on the brink of extinction, lost 1,300,000 acres of wetland and witnessed a water table drop of 1-2 meters, also in the last 40 years.

It looks grim.

But not just for Turkey. Even popular vacation areas around the Aegean were hellish this year. Greece had to declare “state of emergency” at least twice this summer: once for forest fires killing over 60 people, burning half a million acres of land, and costing $1.6 billion; and once for drought on the Cyclades Islands due to water shortages.

Morocco experienced 50% less rainfall than average this year which will likely result in half of last year’s grain harvest. And because feed prices went up as a result of this drought, Moroccan livestock was also seriously affected. Again, is this an unusual year? Actually not. This next figure, which is from Esper et al.’s (2007) paper in Geophysical Research Letters, shows a significant drop in Feb. – June PDSI (which is a standardized measure of surface moisture conditions after Palmer, 1965) since 1980 in Morocco.

Some speculate that the tragic fires in Greece may have been arson, others say better maintenance of water pipes and anticipation of the coming drought early in the previous winter would have prevented Ankara’s water shortage, and better irrigation systems in Morocco would have mitigated agricultural disaster there.

Though it is “debated” in the US, most people in Turkey consider AGW to be a given. This is generally a good attitude, of course, but it opened the door for some government and city officials to simply blame AGW for drought instead of their incompetence in dealing with it. As a result, the Turkish General Directorate of Disaster Affairs started discussing whether AGW should be listed under “natural disasters” in order to provide better risk assessment and adaptation plans, and to prohibit building new structures in “high risk” areas. Even Al Gore came to visit Istanbul this summer to give a talk at a conference called “Climate Change and its Effect on Life.”

So, is AGW to blame for Mediterranean drought? Although bad land use practices and arson share the blame, AGW is most likely the culprit. Here’s how:

The North Atlantic Oscillation is an alternation of air masses between polar and subtropical regions of the North Atlantic. When the NAO index (difference between the normalized sea level pressure anomalies in the Iceland and Azores areas, respectively) is in a positive phase, a low pressure system prevails over Iceland and a high pressure system over the Azores. This causes cooler northern seas, stronger winter storms across the Atlantic Ocean, warm wet winters in northern Europe, and cold and dry winters in Canada and Greenland. However, this also causes less rain and reduced stream flow in southeastern Europe and the Middle East. In general, when NAO is in a positive phase, the Mediterranean region receives less precipitation.

The precipitation pattern in Turkey is well correlated with the phases of the NAO index. For instance Cullen and deMenocal (2000) showed that Euphrates’ spring stream flow varies by about 50% with the NAO index. The NAO index vacillates between negative and positive phases, but its oscillations had a more annual pattern before the 20th century, and since then has become more decadal. More importantly, since the 80’s it has remained in a prolonged positive phase. This is in keeping with the precipitation drop I described for Turkey and Morocco (and the Mediterranean region) in the last several decades.

But do we know that this recent prolonged positive phase in the NAO index is not simply a part of its natural decadal variability? And is this recent positive phase actually related to global warming?

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