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Five Decades of Floods and Flood Risk in the Po River Basin of Italy

Paper Reviewed
Domeneghetti, A., Carisi, F., Castellarin, A. and Brath, A. 2015. Evolution of flood risk over large areas: Quantitative assessment for the Po river. Journal of Hydrology 527: 809-823.

Setting the stage for their work, Domeneghetti et al. (2015) write that freshwater flooding is "the most impacting natural disaster in terms of number of people affected and economic damages," adding that "some studies in the literature (e.g. IPCC, 2013; Stern Review, 2007) seem to indicate that flood damages are expected to increase in the near future as a consequence of a global climate change," citing the additional studies of Hall et al. (2005) and de Moel et al. (2011). However, for some, the future is now; for according to the four Italian researchers, many people believe global warming has already increased historical flood frequencies based on reports of rising economic damages that have been attributed to flooding events over the past few decades. But is this attribution correct?

In a test of this ascription, Domeneghetti et al. set out to evaluate the spatial and temporal history of flooding events in the Po river basin in Italy over the past five decades by examining various data sets pertaining to streamflow, land-use change, demographic dynamics, asset economic values, and topography. Such analyses revealed there was a significant increase in residential growth in and around the Po river, particularly near levees and dykes, which increased the exposure of persons and property to flood risk over the period of study. However, meteorologically speaking, Domeneghetti et al. report flood events have not increased. "Consistent with previous analyses (see e.g. Montanari, 2012; Zanchettini et al., 2008)," they write, "our trend detection analysis, which we carried out on long historical series observed for the Po river, does not detect any evidence of a statistically significant change in the flood hazard along the Po river and supports the stationarity of the hydrological series during the period of interest (i.e., last five decades)."

Thus, although the risk of flooding in the Po river basin has increased over the past half-century due to various anthropogenic pressures (e.g. the expansion of urban and industrial areas into dyke-protected floodplains), actual flood events from a climatological or meteorological perspective have not -- atmospheric CO2 and temperature increases notwithstanding.

References
de Moel, H., Aerts, J.C.J.H. and Koomen, E. 2011. Development of flood exposure in the Netherlands during the 20th and 21st century. Global Environmental Change 21: 620-627.

Hall, J.W., Sayers, P.B. and Dawson, R.J. 2005. National-scale assessment of current and future flood risk in England and wales. Natural Hazards 36: 147-164.

Montanari, A. 2012. Hydrology of the Po River: looking for changing patterns in river discharge. Hydrology and Earth System Sciences 16: 3739-3747.

Zanchettini, D., Traverso, P. and Tomasino, M. 2008. Po River discharge: a preliminary analysis of a 200-year time series. Climatic Change 88: 411-433.

Posted 28 March 2016