Background
The authors introduce their study by writing that "regional climate models project that future climate warming in Central Europe will bring more intense summer-autumn heavy precipitation and floods as the atmospheric concentration of water vapor increases and cyclones intensify," citing the studies of Arnell and Liu (2001), Christensen and Christensen (2003) and Kundzewicz et al. (2005).

What was done
In an exercise designed to assess the reasonableness of these projections, Stewart et al. further write that "a complete record of paleofloods, regional glacier length changes (and associated climate phases) and regional glacier advances and retreats (and associated climate transitions) are derived from the varved sediments of Lake Silvaplana (ca. 1450 BC-AD 420; Upper Engadine, Switzerland)," while indicating that "these records provide insight into the behavior of floods (i.e. frequency) under a wide range of climate conditions."

What was learned
The five researchers report uncovering pertinent data from the period they investigated that suggested "an increase in the frequency of paleofloods during cool and/or wet climates and windows of cooler June-July-August temperatures," which finding further suggests - as they also note - that the frequency of flooding "was reduced during warm and/or dry climates."

What it means
Reiterating the fact that "the findings of this study suggest that the frequency of extreme summer-autumn precipitation events (i.e. flood events) and the associated atmospheric pattern in the Eastern Swiss Alps was not enhanced during warmer (or drier) periods," Stewart et al. acknowledge that "evidence could not be found that summer-autumn floods would increase in the Eastern Swiss Alps in a warmer climate of the 21st century," pretty much debunking the projections of the regional climate models that have suggested otherwise.

References
Arnell, N. and Liu, C. 2001. Hydrology and water resources. In: McCarthy, J.J., Canziani, O.F., Leary, N.A., Dokken, D.J. and White, K.S. (Eds.), Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom.

Christensen, J.H. and Christensen, O.B. 2003. Climate modeling: severe summertime flooding in Europe. Nature 421: 805-806.

Kundzewicz, Z.W., Ulbrich, U., Brucher, T., Graczyk, D., Kruger, A., Leckebusch, G.C., Menzel, L., Pinskwar, I., Radziejewski, M. and Szwed, M. 2005. Summer floods in Central Europe - climate change track? Natural Hazards 36: 165-189.