New paper finds mechanism by which the Sun controls floods in the European Alps

A new paper published in Geophysical Research Letters reconstructs floods in the European Alps over the past 2000 years and finds flooding increased during periods of solar minimums. The authors find, "The all-season flood frequency...increased during solar minima, suggesting solar-induced circulation changes resembling negative conditions of the North Atlantic Oscillation [NAO] as controlling atmospheric mechanism." The paper corroborates several other published papers finding that flooding is more common during cool periods with low solar activity in comparison to warm periods, the opposite of claims by climate alarmists. The paper adds to many others finding amplification mechanisms by which small changes in solar activity can have large amplified effects on climate, via ocean oscillations such as the North Atlantic Oscillation, atmospheric oscillations such as the Madden-Julian Oscillation, Quasi-biennial Oscillation, Aleutian Low, and Eurasian pattern, as well as via stratospheric ozone, and sunshine hours/clouds.

A 2000-year long seasonal record of floods in the southern European Alps

Stefanie B. Wirth et al

Abstract: Knowledge of past natural flood variability and controlling climate factors is of high value, since it can be useful to refine projections of the future flood behavior under climate warming. In this context, we present a seasonally resolved 2000-year long flood-frequency and -intensity reconstruction from the southern Alpine slope (North-Italy) using annually laminated (varved) lake sediments. Floods occurred predominantly during summer and autumn, whereas winter and spring events were rare. The all-season flood frequency, and particularly the occurrence of summer events, increased during solar minima, suggesting solar-induced circulation changes resembling negative conditions of the North Atlantic Oscillation as controlling atmospheric mechanism. Furthermore, the most extreme autumn events occurred during a period of warm Mediterranean sea-surface temperature. Interpreting these results in regard to present climate change, our dataset proposes for a warming scenario a decrease in summer floods but an increase in the intensity of autumn floods at the South-Alpine slope.