(top) Multiyear average scPDSI for 1980–2012 with regions of recent and persistent drought outlined in dashed black lines: WestMED (32°N–42°N, 10°W–0°), Greece (36°N–43°N, 19°E–26°), and the Levant (30°N–37°N, 33°E–40°E). (bottom) Also shown are the regional average scPDSI time series from these regions for 1950–2012 (red line is a 10 year loess smoother). Graphic: Cook, et al., 2016 / Journal of Geophysical Research: Atmospheres

By Stacy Morford
1 March 2016

(Earth Institute) – In the years before the Syrian conflict erupted, the region’s worst drought on record set in across the Levant, destroying crops and restricting water supplies in the already water-stressed region. A new study shows that that drought, from 1998-2012, wasn’t just the most severe in a century of record-keeping—it was the Levant’s most severe drought in at least 500 years and likely more than 900 years.

The study, published in the Journal of Geophysical Research: Atmospheres, is the first to quantitatively evaluate droughts across the Mediterranean region during the past 900 years at a high level of detail. It doesn’t identify a cause of the recent Syrian drought, but it does provide independent support for studies that have suggested global warming may already be having an effect there, said lead author Benjamin Cook, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory and NASA Goddard Institute for Space Studies.

“We can now say with some degree of confidence that what we’re seeing in that part of the Mediterranean is likely separable from natural variability,” Cook said. “If climate change is having an impact and is making droughts worse, then we should see this in the record over several centuries—and we do.”

Cook and his colleagues are among the first scientists to analyze data from the 2015 Old World Drought Atlas, which maps dryness and wetness year-by-year across the Mediterranean over the past millennium based on tree ring records. The results provide new insight into climate patterns that can help scientists develop better drought risk assessments and improve understanding both of the bounds of natural climate variability and what may be the emerging influence of greenhouse gases.

Drying in the Levant

Climate models suggest that the Levant is likely to grow drier as global temperatures rise. Some studies suggest that may already be happening. A 2015 study that linked the recent Syrian drought to the start of the civil war there determined that increasing levels of greenhouse gases from human activities like the burning of fossil fuels had likely increased the probability of such a severe and persistent drought in the region, making it two to three times more likely.

“After the release of the Old World Drought Atlas last year, we have been eagerly awaiting research like this that places recent droughts in the context of variability over the past millennium, far longer than the century or so that can be analyzed with weather station records,” said Richard Seager, a climate scientist at Lamont and co-author of the 2015 Syria drought study.

“Cook and colleagues’ result is consistent with human-driven climate change and drying of the Middle East having contributed to the severity of the drought. This also raises confidence in climate models that indicate the eastern Mediterranean will be a hot spot of aridification due to rising greenhouse gases and that this change is already underway,” Seager said. [more]

Syria’s Drought Likely Its Most Severe in More than 900 Years

ABSTRACT: Recent Mediterranean droughts have highlighted concerns that climate change may be contributing to observed drying trends, but natural climate variability in the region is still poorly understood. We analyze 900 years (1100–2012) of Mediterranean drought variability in the Old World Drought Atlas (OWDA), a spatiotemporal tree ring reconstruction of the June-July-August self-calibrating Palmer Drought Severity Index. In the Mediterranean, the OWDA is highly correlated with spring precipitation (April–June), the North Atlantic Oscillation (January–April), the Scandinavian Pattern (January–March), and the East Atlantic Pattern (April–June). Drought variability displays significant east-west coherence across the basin on multidecadal to centennial timescales and north-south antiphasing in the eastern Mediterranean, with a tendency for wet anomalies in the Black Sea region (e.g., Greece, Anatolia, and the Balkans) when coastal Libya, the southern Levant, and the Middle East are dry, possibly related to the North Atlantic Oscillation. Recent droughts are centered in the western Mediterranean, Greece, and the Levant. Events of similar magnitude in the western Mediterranean and Greece occur in the OWDA, but the recent 15 year drought in the Levant (1998–2012) is the driest in the record. Estimating uncertainties using a resampling approach, we conclude that there is an 89% likelihood that this drought is drier than any comparable period of the last 900 years and a 98% likelihood that it is drier than the last 500 years. These results confirm the exceptional nature of this drought relative to natural variability in recent centuries, consistent with studies that have found evidence for anthropogenically forced drying in the region.

Spatiotemporal drought variability in the Mediterranean over the last 900 years



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