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Extreme Precipitation and Flooding Events in the Mediterranean French Alps

Reference
Wilhelm, B., Arnaud, F., Sabatier, P., Crouzet, C., Brisset, E., Chaumillon, E., Disnar, J.-R., Guiter, F., Malet, E., Reyss, J.-L., Tachikawa, K., Bard, E. and Delannoy, J.-J. 2012. 1400 years of extreme precipitation patterns over the Mediterranean French Alps and possible forcing mechanisms. Quaternary Research 78: 1-12.
Wilhelm et al. (2012) write that "mountain-river floods triggered by extreme precipitation events can cause substantial human and economic losses (Gaume et al., 2009)," and they say that "global warming is expected to lead to an increase in the frequency and/or intensity of such events (IPCC, 2007), especially in the Mediterranean region (Giorgi and Lionello, 2008)." However, they caution us in this regard, stating that "reconstructions of geological records of intense events are an essential tool for extending documentary records beyond existing observational data and thereby building a better understanding of how local and regional flood hazard patterns evolve in response to changes in climate [italics added for emphasis]."

In an effort to obtain this "better understanding," Wilhelm et al. analyzed the sediments of Lake Allos, a 1-km-long by 700-m-wide high-altitude lake in the French Alps (44°14'N, 6°42'35"E). This they did by means of both seismic survey and lake-bed coring, carrying out numerous grain size, geochemical and pollen analyses of the sediment cores they obtained in conjunction with a temporal context derived using several radionuclide dating techniques. So what did they learn?

The thirteen researchers, all hailing from France, report that their investigations revealed the presence of some 160 graded sediment layers over the last 1400 years; and they indicate that comparisons of the most recent of these layers with records of historic floods suggest that the sediment layers are indeed representative of significant floods that were "the result of intense meso-scale precipitation events." Of special interest to us in this regard is their finding of "a low flood frequency during the Medieval Warm Period and more frequent and more intense events during the Little Ice Age," which meshes nicely with the results of an analysis of a Spanish lake sediment archive that allowed Moreno et al. (2008) to infer that "intense precipitation events occurred more frequently during the Little Ice Age than they did during the Medieval Warm Period."

Wilhelm et al. additionally state that "the Medieval Warm Period was marked by very low hydrological activity in large rivers such as the Rhone (Arnaud et al., 2005; Debret et al., 2010), the Moyenne Durance (Miramont et al., 1998), and the Tagus (Benito et al., 2003), and in mountain streams such as the Taravilla lake inlet (Moreno et al., 2008)." But of the Little Ice Age, they say that "research has shown higher flood activity in large rivers in southern Europe, notably in France (Miramont et al., 1998; Arnaud et al., 2005; Debret et al., 2010), Italy (Belotti et al., 2004; Giraudi, 2005) and Spain (Benito et al., 2003), and in smaller catchments (e.g., in Spain, Moreno et al., 2008)."

In concluding their report, Wilhelm et al. say their study shows that "sediment sequences from high altitude lakes can provide reliable records of flood-frequency and intensity-patterns related to extreme precipitation events," closing with the warning that "such information is required to determine the possible impact of the current phase of global warming." And when this warning is heeded, it can be seen that the climate-model-inspired claim of the world's climate alarmists - that global warming will lead to "an increase in the frequency and/or intensity of such events" - would appear to be just the opposite of what is suggested by Wilhelm et al.'s real-world study and the real-world studies of the other scientists they cite.

Additional References
Arnaud, F., Revel, M., Chapron, E., Desmet, M. and Tribovillard, N. 2005. 7200 years of Rhone river flooding activity in Lake Le Bourget, France: a high-resolution sediment record of NW Alps hydrology. The Holocene 15: 420-428.

Belotti, P., Caputo, C., Davoli, L., Evangelista, S., Garzanti, E., Pugliese, F. and Valeri, P. 2004. Morpho-sedimentary characteristics and Holocene evolution of the emergent part of the Ombrone River delta (southern Tuscany). Geomorphology 61: 71-90.

Benito, G., Diez-Herrero, A. and Fernandez de Villalta, M. 2003. Magnitude and frequency of flooding in the Tagus Basin (Central Spain) over the last millennium. Climatic Change 58: 171-192.

Debret, M., Chapron, E., Desmet, M., Rolland-Revel, M., Magand, O., Trentesaux, A., Bout-Roumazeille, V., Nomade, J. and Arnaud, F. 2010. North western Alps Holocene paleohydrology recorded by flooding activity in Lake Le Bourget, France. Quaternary Science Reviews 29: 2185-2200.

Gaume, E., Bain, V., Bernardara, P., Newinger, O., Barbuc, M., Bateman, A., Blaskovicova, L., Bloschl, G., Borga, M., Dumitrescu, A., Daliakopoulos, I., Garcia, J., Irimescu, A., Kohnova, S., Koutroulis, A., Marchi, L., Matreata, S., Medina, V., Preciso, E., Sempere-Torres, D., Stancalie, G., Szolgay, J., Tsanis, I., Velasco, D. and Viglione, A. 2009. A compilation of data on European flash floods. Journal of Hydrology 367: 70-78.

Giorgi, F. and Lionello, P. 2008. Climate change projections for the Mediterranean region. Global and Planetary Change 63: 90-104.

Giraudi, C. 2005. Late-Holocene alluvial events in the Central Apennines, Italy. The Holocene 15: 768-773.

IPCC. 2007. Climate Change 2007 - The Physical Science Basis. Cambridge University Press, Cambridge, United Kingdom.

Miramont, C., Jorda, M. and Pichard, G. 1998. Evolution historique de la morphogenese et de la dynamique fluviale d'une riviere mediterraneenne: l'exemple de la moyenne Durance (France du sud-est). Geographie physique et Quatenaire 52: 381-392.

Moreno, A., Valero-Garces, B., Gonzales-Samperiz, P. and Rico, M. 2008. Flood response to rainfall variability during the last 2000 years inferred from the Taravilla Lake record (Central Iberian Range, Spain). Journal of Paleolimnology 40: 943-961.

Archived 30 October 2012