Multi-decadal water resource variations in France : connexion with the Altantic Multidecadal Variability

Abstract:

Hydrological cycles have strong temporal variations. Analysis of the long-term observations can help detect trends that may be consistent with theses projected in the context of climate change and thus help awareness of stakeholders. However, one must remain cautious on the analysis of these trends when they are estimated on the basis of a few decades, because the water cycle can have strong multi-decadal variations.

Indeed, in France, long observed series shown that river flows generally exhibit large multidecadal variation since the late 19th century to the present, especially in spring. Differences of means between 21 yr periods of the 20th century as large as 40% are indeed found for many gauging stations.
Such multi decadal variations were also found on glaciers, but are difficult to detect on the groundwater resource, which might be linked to the recharge processes.
Multi-decadal spring river flow variations are associated with variations in spring precipitation and temperature. These multi-decadal variations in precipitation are themselves found to be driven by large-scale atmospheric circulation, more precisely by a multi-decadal oscillation in a sea level pressure dipole between western Europe and the eastern Atlantic. It is suggested that the Atlantic Multidecadal Variability (AMV), the main mode of multi-decadal variability in the North Atlantic–Europe sector, controls those variations in large-scale circulation and is therefore the main ultimate driver of multi-decadal variations in spring river flows.
Impact of such teleconnection for the management of the water resource is important, since the threshold alert used by stakeholder vary also at multi decadal scale.
Moreover, such natural variabilities are not well reproduced by climate model, especially because of weak teleconnection between the simulated AMV and the simulated precipitation over France. Statistical methods could help correct such bias, and are currently assessed on the 20th century.