Floods in the future

I've been muttering ever since the enormous floods in Australia in 2011 that I wasn't sure how well anyone could anticipate how much increased floods due to climate change could cause damage to the economies of countries so affected.

I've been poking around a bit and see that there certainly have been a lot of attempts to try to quantify this, but I guess I am just worried that predicting changed rainfall in regions is one of the less clear aspects giving current climate modelling, and while this may mean that current estimates may be overly pessimistic, they might also not be pessimistic enough.

I note this as an example of one estimate, from one IPCC page:

The impact of climate change on flood damages can be estimated from modelled changes in the recurrence interval of present-day 20- or 100-year floods, and estimates of the damages of present-day floods as determined from stage-discharge relations (between gauge height (stage) and volume of water per unit of time (discharge)), and detailed property data. With such a methodology, the average annual direct flood damage for three Australian drainage basins was projected to increase by a factor of four to ten under conditions of doubled atmospheric CO₂ concentrations (Schreider et al., 2000). 

That does sound serious.   I know nothing more of the paper; I should go looking for it.