From the chronicle to the database record: Evaluating documentary evidence on medieval climate in Euro-Climhist

With Euro-Climhist (www.euroclimhist.unibe.ch), documentary and instrumental evidence on weather and climate is made accessible through a user-friendly database query, including daily weather observations as well as extreme events and long-term climatic development. Module 1 is already open to the public after a new release in November 2015. It comprises weather and climate information for Switzerland (1501-1999). Module 2 is currently in preparation and will be dedicated to weather and climate in Europe during the Middle Ages (1000-1500). Further modules are in the planning stage following the area of modern countries and starting from 1500.
In relation to the context in which documentary evidence was generated we need to distinguish between individual and institutional sources: Sources produced by individuals may have a very high – in some cases even daily or sub-daily – resolution including narratives of any weather elements, which seem to be needed for describing a climatic event. At best, they also refer to societal consequences of extreme events and to measures taken by the authorities and households. In contrast, authors are subjective in the selection, and to some extent also in the interpretation of events. Usually, the records include gaps and they end at the latest with the death of the observer. Original records written down within the lifetime of a chronicler are in most cases correct. Records copied from older annals, chronicles, and other compilations (i.e. chronological arrangements of texts on climatic anomalies and (natural) disasters originating from different sources) are error-prone, particularly with regard to dating. Therefore, Euro-Climhist strictly distinguishes between contemporary and non-contemporary records.
Sources produced by institutions (e.g. hospitals, bishoprics, municipalities, military, ecclesiastical, or civil authorities) constitute the second category of documentary evidence. Institutional bodies were typically not primarily interested in describing climate and they often kept detailed accounts in order to document their agricultural activities in case of auditing or enquiry. The date of those activities depended on climate and weather and, therefore, constitute relevant information for historical climatology. In communities with wine production, grape harvest dates were fixed according to the grape ripening to provide a correct delivery of the tithes to the benefitted authorities. The same procedure is known for the beginning of the grain harvest. The administrative routines involved some standardization in the way records were kept, and more importantly, institutions unlike individuals often worked in the same way for centuries and in doing so they generated very long records. They are easily quantified and statistically related to instrumental measurements, unless there is a sufficient overlap between the proxy and the instrumental series. Temperatures and precipitation in the pre-instrumental period may be estimated in this way, albeit just for periods of several months.
This paper will focus on the ongoing work for Module 2, because medieval sources force the research group to develop specific expertise both in historical source criticism and in processing the data for an online database, which can be used by professional medievalists as well as by natural scientists and lay users. It will be shown, which problems might occur with translating, interpreting, comparing, geo coding, dating and categorizing the single records.