Hundred-year floods have occurred in Brazil, Queensland, Victoria, Sri Lanka, South Africa and the Philippines.
The year 2011 has begun with a remarkable number of high-impact floods world-wide, and much of the blame for this can be placed on the current La Niña event occurring in the Eastern Pacific. NOAA's Climate Prediction Center currently puts the La Niña event in the "strong" category, and whenever a La Niña or El Niño event reaches the strong category, major perturbations to global weather patterns occur. This typically results in record or near-record flooding in one or more regions of the globe. When one combines the impact of La Niña with the increase of global ocean temperatures of 0.5°C (0.9°F) over the past 50 years, which has put 4% more water vapor into the atmosphere since 1970, the result is a much increased chance of unprecedented floods. A 4% increase in atmospheric moisture may not sound like much, but it turns out that precipitation will increase by about 8% with that 4% moisture increase. Critically, it is the extreme rainfall events that tend to supply the increased rainfall. For example, (Groisman et al., 2004) found a 20% increase in very heavy (top 1%) precipitation events over the U.S. in the past century, and a 36% rise in cold season (October - April) "extreme" precipitation events (those in the 99.9% percentile--1 in 1000 events. These extreme rainfall events are the ones most likely to cause floods.
http://www.wunderground.com/blog/JeffMasters/show.html
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