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by Thomas LabbéThe summer of 2018 broke a new record on the thermometer. Temperatures reached more than 30°C at the polar circle, and a large part of the northern hemisphere has been struck by a drought that brings back in memory of everybody the summer of 2003.In the memory of climate historians, the summer of 2018 would automatically refer to the summer 1540[1] which has been assessed as one of the major droughts of the millennium at the European scale. Less known is the dryness that affected North-West of Europe in 1137. Although we don’t know much about this event, the sources clearly state that something unusual had happened. Richard of Poitiers, a Cluniac monk, wrote for example in his chronicle that rivers, fountains and lakes dried up. Even more worrying for him were the fires that broke out from the bowels of the earth and no rains could extinguish them!Fuit tanta siccitas in Gallia, quanta retroactis saeculis in eadem regione unquam visa est aut audita, ita ut fontes et flumina, lacus, putei etiam siccarentur. Visus est etim ignis biennio cremare super terram, qui casu aut sponte missus per rimas arentis terrae in imis ceciderat, nec frigor, nec gelu seu imbribus extingui poterat[2].A remarkable set of monastic chronicles refers to the drought of 1137. In his overview of climate-related narratives in medieval Europe, Pierre Alexandre found at least 14 different contemporary sources that mentioned the event, in an area covering south-west France to Netherlands[3]. Chroniclers give only short descriptions of it, but they generally agreed that it lasted from March to September of this year. Orderic Vital, a monk of Saint-Evroult in Normandy, adds that the temperatures reached a continuous peak in July and August. People suffered from thirst, especially during the summer labour in the fields, and as many water bodies in the region were dry, peasants had to make long walks under the heatwave to get some water. Interestingly enough, chroniclers mostly emphasized the vulnerability of the population to thirst on the one hand, and the risk of fire on the other hand. Surely, the aforementioned strange story reported by Richard of Poitiers is a metaphor of the multiplication of fires that occurred in relation with the drought.[caption id="attachment_636" align="aligncenter" width="452"] Fig. 1. Map: Thomas Labbé.[/caption]A close look at the history of architecture gives actually some more details about the extent of the drought. In 1137, church and city fires really occurred throughout a large part of Western Europe. They shape a region that roughly overlaps the area documented by the chronicles. It is thus more than probable that these fires occurred because of the drought. For example, the cathedral of Rochester burnt in June 1137, as well as the cathedral of York. In Germany, the cathedrals of Mainz and Speyer burnt in the same vintage, when in France, fires destroyed the city of Dijon in the end of June, and the city of Amiens in the beginning of August.Finally, the pattern that we can draw with the sources at our disposal is that this little known event certainly constitutes one of the major droughts of the Medieval Climate Anomaly (MCA), the so-called warm period of the central Middle Ages. From the documentary sources, its extension covered at least England, Netherlands, Belgium, West Germany and a large part of France, where the heatwave lasted continuously in July and August (fig. 1). If we believe the dendrological data provided by the Old World Drought Atlas, the South of Scandinavia has been affected, too (fig. 2) , so this was definitely a European scale event.[caption id="attachment_660" align="alignnone" width="765"] Fig. 2: Dendrological data for 1137. Source: Ed Cook et al. 2015, OWDA.[/caption][1] Wetter O., Pfister Chr., et al., “The year-long unprecedented European heat and drought of 1540 – a worst case”, Climatic Change, 125, p. 349-363.[2] Ex chronico Richardi Pictaviensis monachi cluniacensis, Recueil des historiens des Gaules et de la France, 12, Paris, 1877, p. 415.[3] Pierre Alexandre, Le climat en Europe au Moyen Âge: contribution à l’histoire des variations climatiques de 1000 à 1425 d’après les sources narratives de l’Europe occidentale, Paris, EHESS, 1987.