The recent drought that began in 1998 in the eastern Mediterranean Levant region, which comprises Cyprus, Israel, Jordan, Lebanon, Palestine, Syria, and Turkey, is likely the worst in the past nine centuries, according to a new NASA study.
Scientists reconstructed the Mediterranean's drought history by studying tree rings as part of an effort to understand the region's climate and what shifts water to or from the area.
Thin rings indicate dry years while thick rings show years when water was plentiful.
In addition to identifying the driest years, the team discovered patterns in the geographic distribution of droughts that provides a "fingerprint" for identifying the underlying causes.
Together, these data show the range of natural variation in Mediterranean drought occurrence, which will allow scientists to differentiate droughts made worse by human-induced global warming.
"The magnitude and significance of human climate change requires us to really understand the full range of natural climate variability," said lead author Ben Cook, from NASA's Goddard Institute for Space Studies.
"If we look at recent events and we start to see anomalies that are outside this range of natural variability, then we can say with some confidence that it looks like this particular event or this series of events had some kind of human caused climate change contribution," Cook said.
Researchers used the tree-ring record called the Old World Drought Atlas to better understand how frequently and how severe Mediterranean droughts have been in the past.
Rings of trees both living and dead were sampled all over the region, from northern Africa, Greece, Lebanon, Jordan, Syria and Turkey.
Combined with existing tree-ring records from Spain, southern France, and Italy, these data were used to reconstruct patterns of drought geographically and through time over the past millennium.
Between the years 1100 and 2012, the team found droughts in the tree-ring record that corresponded to those described in historical documents written at the time.
According to Cook, the range of how extreme wet or dry periods were is quite broad, but the recent drought in the Levant region, from 1998 to 2012, stands out as about 50 per cent drier than the driest period in the past 500 years, and 10 to 20 per cent drier than the worst drought of the past 900 years.
The 900-year record of drought variability across the Mediterranean is an important contribution that will be used to refine computer models that are used to project drought risk for the coming century, researchers said.
The study was published in the Journal of Geophysical Research-Atmospheres.
