Material and methods for evaluating the man-induced component of water shortages (late 18th - early 20th century) | Les basses eaux, un indicateur complexe de l'histoire climatique. Matériel et méthodes pour l'évaluation de la composante humaine des pénuries d'eau

[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAU

International audience

Английский. Over the past two decades studies on climate history have contributed to improving knowledge on past droughts, particularly through the study of pro pluvia rogation ceremonies (e.g. Martin-Vide and Barriendos 1995, Piervitali and Colacino, 2001, Garnier, 2010). Simultaneously, other authors have proposed studying social responses to past climatic events as well as their economic or agricultural impacts (Pfister, 2010). As such, since climate history relies heavily on written sources based on specific societal reactions such as mentions or complaints of extreme climate events or catastrophes these approaches are not independent from each other. For droughts, written sources describing low flows or exceptional drying of streams are indisputable indicators of periods of low precipitation. However, deducing the severity of an event or comparing dry episodes is less obvious. We postulate that the sensitivity of a society to such phenomena may fluctuate over time, due to its stronger or weaker dependency on water flow, which in turn depends on the way in which it exploited water resources, or even to what extend it exerted pressure on water resources and exacerbated the situation. For example, in the Cévennes (Southern France) some crises caused by water scarcity during the nineteenth century had an incontestable social component (Jacob-Rousseau, 2005). In this context, a better knowledge of the hydrological consequences of agricultural or industrial water exploitation in the past could shed a critical light on useful sources in climate history. It could also provide the basis for discussing results obtained from modelling reconstructed low-flow periods. The purpose of this paper is to present research we initiated on the pressures exerted on water resources in the past (late 18th-early 20th centuries) for various catchments in south-eastern France. We will present a critical analysis of archival documents, which in France can be addressed at different spatial or temporal resolutions including statistics on industrial or agricultural water use, agricultural statistics or cadastral information. We will then demonstrate which type of approaches and data processing is appropriate for developing indicators both in order to identify real pressures and to evaluate how water withdrawal could have influenced low flow in the past. Finally, we will present some case studies on the temporal and spatial impacts of droughts in watersheds. This will enable a critical comparison of the geographic context and the textual information.