The same paper quotes a number of studies which demonstrate, without question, increased winter rainfall overall, and higher rainfall per rainy day, over the examined period (as well as a warming effect which is bigger than the global average). It is not unimagineable that these increases have not provoked any increase in major flooding; but it is powerfully counter-intuitive.

Something being "powerfully counter-intuitive" has led to some poor scientific thinking before.

While studies of damage up to now may be ambiguous about a link, all the studies with future projections I found show a link.

Increased crop damage in the US from excess precipitation under climate change

We compute that US corn production losses due to this factor, already significant under current climate, may double during the next thirty years, causing additional damages totaling an estimated $3 billion per year.

ingentaconnect The Impacts of Socioeconomic Development and Climate Change on Se...

...The climate change scenarios respectively project 13.5% and 21.5% increases in annual precipitation. The first simulation increases only the mean value of annual precipitation; the second simulation assumes that the mean and standard deviation of annual precipitation change in the same proportion. Results show that the growth in reported losses from weather-related natural disasters is due mainly to three socioeconomic factors: inflation, population growth and growth in per capita real wealth. However, weather variables such as precipitation and the number of hurricanes per period also clearly affect losses. The three stage least squares (3SLS) simultaneous equation model shows that a 1% increase in annual precipitation would enlarge catastrophe loss by as much as 2.8%...

The IPCC mentions the last one, and also: AR4 WGII Chapter 3: Fresh Water Resources and their Management - 3.5.2 How will climate change affect flood damages?

Another study examined the potential flood damage impacts of changes in extreme precipitation events using the Canadian Climate Centre model and the IS92a emissions scenario for the metropolitan Boston area in the north-eastern USA (Kirshen et al., 2005b). They found that, without adaptation investments, both the number of properties damaged by floods and the overall cost of flood damage would double by 2100 relative to what might be expected with no climate change, and that flood-related transportation delays would become an increasingly significant nuisance over the course of the century. The study concluded that the likely economic magnitude of these damages is sufficiently high to justify large expenditures on adaptation strategies such as universal flood-proofing for all flood plains.

This finding is supported by a scenario study of the damage due to river and coastal flooding in England and Wales in the 2080s (Hall et al., 2005), which combined four emissions scenarios with four scenarios of socio-economic change in an SRES-like framework. In all scenarios, flood damages are predicted to increase unless current flood management policies, practices and infrastructure are changed. For a 2°C temperature increase in a B1-type world, by the 2080s annual damage is estimated to be £5 billion as compared to £1 billion today, while with approximately the same climate change, damage is only £1.5 billion in a B2-type world. In an A1-type world, with a temperature increase of 2°C, the annual damage would amount to £15 billion by the 2050s and £21 billion by the 2080s (Hall et al., 2005; Evans et al., 2004).

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).

I also found a more recent study from Spain, Flood risk and climate change. An estimation for the catchment area of the River Urola from 2009. It has a crappily worded summary so I won't quote it, but in the scenarios they investigated, not only did climate change increase damage significantly, but extra flood damage due to climate change dwarfed extra flood damage due to socio-economical change.

_{*Lunatic*, n.
One whose delusions are out of fashion.}