Certo che se si parte con il preconcetto che alluvioni = precipitazioni, allora tutto è dicibile.

Insomma: dal primo lavoro linkato (quello presentato all'EGU2011, la cui analisi arriva fino al 2000) cito anche questo caveat (gli autori del lavoro sanno bene, ovviamente, che alluvione ≠ precipitazione):

Future work will try to investigate the reasons for the decreasing trends at each of the basins, with particular emphasis on whether the river basins upstream the gauging location are intact or perhaps affected by human activities.
Dal secondo:
Caution is advised in interpreting these results as flooding is a complex phenomenon, caused by a number of factors that can be associated with local, regional, and hemispheric climatic processes.(...)
The inherent uncertainty in analysis of any set of extreme flood flows stems from the fact that accuracy of measurements is problematic (rating curves not available for the high flow range, gauges destroyed by the flood wave, observers evacuated), yet indirect determination of the highest stage is often possible. It would be useful to attempt to describe deterministically the reasons for atypical behaviour of some series (as compared to their spatial neighbourhood). Here, influence of a local event (e.g. flood resulting from a very high-intensity local storm, reservoirs, polders, flood control) could play an important role. A closer look into particularities of individual stations concerned would be needed to discriminate the driving factors. Since this information is not available in the GRDC holdings, there is a need to augment the collected data by accommodating more detailed metadata with more information about a station, including history of river development for navigation and energy generation. Analysis should also differentiate the flood generation mechanisms (snowmelt vs rainfall). In the present study, all floods were treated as one category.
Chi ha anche solo una minima conoscenza empirica dei bacini fluviali di molti territori, sa quanto i deflussi dei fiumi siano stati modificati negli ultimi decenni a causa di una miriade di attività antropiche. E gli autori lo segnalano.
Chi ha commentato traendo affettate conclusioni e associazioni viziate da bias no. Come mai?

In ogni caso: quello che l'AR4 dice è:
A warmer climate, with its increased climate variability, will increase the risk of both floods and droughts (Wetherald and Manabe, 2002; Table SPM2 in IPCC, 2007). As there are a number of climatic and non-climatic drivers influencing flood and drought impacts, the realisation of risks depends on several factors. Floods include river floods, flash floods, urban floods and sewer floods, and can be caused by intense and/or long-lasting precipitation, snowmelt, dam break, or reduced conveyance due to ice jams or landslides. Floods depend on precipitation intensity, volume, timing, antecedent conditions of rivers and their drainage basins (e.g., presence of snow and ice, soil character, wetness, urbanisation, and existence of dikes, dams, or reservoirs). Human encroachment into flood plains and lack of flood response plans increase the damage potential.
il che, di nuovo, è ben altra cosa rispetto al commento del post.

Infine:
GW e cambiamenti nel regime pluviometrico: altri studi interessanti

http://www.unicam.it/matinf/pasef/co...tietAl2004.pdf
http://www.nersc.no/~dagjs/rcourse_n..._frei_2005.pdf
http://www.cgd.ucar.edu/cas/Trenbert...nd%20proof.pdf