2011: Year of the flood

On August 1, 2011 by Colin

I heard Bill McKibben describe this first…this article on 2011’s extreme weather ends with sobering statistics on how our human-warmed atmosphere is leading directly to heavy flooding and snowfall. Those of us who dealt with high water this year had better get used to it!

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… 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.

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