Researchers have developed the "Old World Drought Atlas" (OWDA), an atlas that used tree rings to map the climate history of Europe during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes.
Together with his colleagues, Edward Cook of Columbia University's Lamont-Doherty Earth Observatory based their research on cross-sections of trees from across Europe.
"Tree growth in the form of ring width is frequently limited by how much soil moisture form precipitation is available to use," Cook explained.
The researchers came up with output that recorded the wet and dry seasons in Europe over centuries, hoping that this will "lead to improvements in what to anticipate in the future," Cook added.
Previously, scientists have also developed drought atlases for North America and Asia. These atlases were able to describe periods of drought that the modern world has not yet experienced.
Although most of the droughts in Europe were already in records, the study contributed in a way that it filled in important details especially about notable past events.
From the year 1315 to 1317, the researchers concluded that most parts of Europe got more share of rain than its usual. However, in 1315, crop harvests failed across the continent. This phenomenon affected England, west to Russia, and south to Italy. The countries faced food scarcity and extreme price hike.
"The usual kinds of meat, suitable for eating, were too scarce; horse meat was precious; plump dogs were stolen. And, according to many reports, men and women in many places secretly ate their own children," English monk Johannes de Trokelowe wrote.
In 1540, central and eastern Europe experienced the worst case of drought, as described by modern researchers. Rings of trees were able to identify these dry times.
History records in Italy showed that from the year 1539 to 1540, winter felt like the weather in July, which was rain-free. Even after rains arrived, it did not contribute much to the affected areas.
Pierre de Teysseulh, a church official from France wrote that "the grapes were like roasted and the leaves of the vines had fallen to the ground like after a severe frost."
In 1616, the same region experienced drought again. People noted that the Elbe River had low levels. According to the tree rings, the dry times hit most parts of central Europe, Germany, and Switzerland.
From 1740 to 1741, unusually low winter caused crop failures and the Irish famine. "This event has been attributed to unusually low winter and spring temperatures in 1740, resulting in crop failures and subsequent famine," Cook remarked.
However, the tree rings showed evidence that this phenomenon might also be triggered by drought. 38% of the Irish population perished in the famine.
In 1893, drought damaged crops in Franc and Germany. People also died from sunstroke. There were also records in England that showed two rainless months.
One person described the drought in the Paris Figaro, writing that "never within the memory of living men has it been so hot, and especially so dry."
The tree rings used as data for the drought atlas were obtained from living trees and timbers discovered in an ancient construction more than 2 000 years old.
"Old World megadroughts and pluvials during the Common Era" – Edward R. Cook et al. – AAAS Science Advances – DOI: 10.1126/sciadv.1500561
Climate model projections suggest widespread drying in the Mediterranean Basin and wetting in Fennoscandia in the coming decades largely as a consequence of greenhouse gas forcing of climate. To place these and other "Old World" climate projections into historical perspective based on more complete estimates of natural hydroclimatic variability, we have developed the "Old World Drought Atlas" (OWDA), a set of year-to-year maps of tree-ring reconstructed summer wetness and dryness over Europe and the Mediterranean Basin during the Common Era. The OWDA matches historical accounts of severe drought and wetness with a spatial completeness not previously available. In addition, megadroughts reconstructed over north-central Europe in the 11th and mid-15th centuries reinforce other evidence from North America and Asia that droughts were more severe, extensive, and prolonged over Northern Hemisphere land areas before the 20th century, with an inadequate understanding of their causes. The OWDA provides new data to determine the causes of Old World drought and wetness and attribute past climate variability to forced and/or internal variability.
Featured image credit: Giuseppe Milo
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