Modeling the historic droughts that have hit the Mediterranean basin, scientists have found that the region's latest dry period was the worst drought to have hit the area in the past 900 years. The study, published in the Journal of Geophysical Research, “highlights the concerns that climate change may be contributing to observed drying trends,” and that those impacts might already be being felt.

The researchers looked back at the records of droughts documented in tree rings from all around the Mediterranean, sampling trees from North Africa, Greece, Lebanon, Jordan, Syria, and Turkey, as well as using existing tree ring data from Spain, France and Italy. They found that the growth of the trees matched up with historical records written at the time of droughts to have hit the region between 1100 CE and 2012 CE. Although the variability between wet and dry periods was quite large, the most recent 1998-2012 drought was still found to be about 50 percent drier than the driest period in the last 500 years, and over 10 percent drier than any in the past 900.

^{For January 2012, brown shades show the decrease in water storage from the 2002-2015 average in the Mediterranean region. NASA}

The scale of the project also allowed the researchers to look at how droughts affected different regions of the Mediterranean. They found that if the east was experiencing a dry period, then it was likely that the west was going through a similar spell. This is important, because it has all sorts of implications for food and water security within the region as a whole if everyone is experiencing a drought at the same time, and could help predict where conflict over these resources might arise.

But interestingly, when the researchers then looked at how dry periods affected the north and south of the region, they found an opposite relationship. When Greece, Italy, France and Spain were in drought, the eastern areas of North Africa tended to be wet. The differences between what happens in the east and west of the region when compared to the north-south are thought to be due to airflow patterns that move the weather systems around the Med. 

Having such a long term data set will be invaluable for any future events, as it in effect provides a baseline for comparison. This means that any variability can be checked to see if drying conditions could be seen as a natural cycle, or is caused by man-made climate change.

“The magnitude and significance of human climate change requires us to really understand the full range of natural climate variability,” explains Ben Cook, from NASA's Goddard Institute for Space Studies and who led the research. “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.”