Summers Were Wetter in the Middle Ages Than They Are TodayScienceDaily (Mar. 25, 2010) — The severe epidemic of plague known as the "Black Death" caused the death of a third of the European population in the 14th century. It is probable that the climatic conditions of the time were a contributory factor towards the disaster. "The late Middle Ages were unique from the point of view of climate," explains Dr Ulf Büntgen of the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) in Birmensdorf, Switzerland. "Significantly, there were distinct phases in which summers were wetter than they are today."
...
Using dendrochronology, the researchers have been able to demonstrate, for example, that a ridge beam in an old timber-framed house in the city of Kassel must have come from a tree felled in 1439. In this technique, the pattern of annual growth rings is compared with those in already dated wood samples. "We can thus determine the exact age of every beam," says Büntgen, describing the process. The ridge beam can also provide information on whether past summers in Kassel were wet or dry. "If a summer tended to be wet, the trees generally grew faster, thus resulting in wider growth rings," Esper explains. However, the information available from one beam is not enough to allow reliable conclusions about the climate in Kassel in 1439 to be reached. A large number of wood samples are required.
...
The late Middle Ages were characterized by two distinct wet periods in Central Europe in the 13th and 14th centuries, separated by dry summer weather between 1300 and 1340. "The increase in summer rainfall between 1350 and 1370 is remarkable and occurred exactly at the time when the plague broke out and spread across the entire European continent," Büntgen specifies. This was followed by a generally drier phase from the late 15th century to the early 18th century. More wet summers occured at the beginning and at the end of the 18th century, while a trend towards a drier climate has developed over the last 200 years.
...