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What the heck is it with all the floods? Just in 2007 alone, monsoons sparked catastrophic floods that displaced 10 million people in India; England and Wales saw their wettest summers ever recorded in more than two centuries of recordkeeping; China's heavy rains in early June killed 120 in flooding and landslides. And that's not all -- Mozambique, Uruguay and Sudan suffered remarkable floods, while experts warned that more extreme weather is likely to come if global warming continues unabated.

The United Nations calls extreme weather a sign of global warming, and it blamed the year's record hot average global temperature for spawning flooding, deadly heat waves and wildfires. (See: www.thedailygreen.com/2007/08/08/list-of-weird-weather-extremes/4917/)

There's a 90 percent chance we'll see more frequent heavy rainfalls and heat waves this century, according to a worldwide consortium of scientists and government officials known as the Intergovernmental Panel on Climate Change. Already, it reports, "the frequency of heavy precipitation events has increased over most land areas."

What gives? First, there's a simple principle. Warm air holds more moisture than colder air. So as the planet warms, more moisture is suspended in air... then periodically falls to the ground.

Then there are societal issues compounding matters: people like to build in floodplains, that nice relatively flat land that unfortunately historically served as an overflow basin for when rivers breached their banks. Asphalt and concrete – and just about any kind of development, even adding a deck or patio -- exacerbate matters; when rain falls, it can't soak into the ground. Water careens down roads and into streams at rates far faster than historically, scouring out the banks and flushing away fish. Porous pavement and other green advances in development can alleviate these problems somewhat.

Perhaps one of the most unexpected results of climate change for the general public is this flooding. It seems counter-intuitive with warming. If the Earth is warmer, we should have droughts and less water, right? Well, because of increased evaporation and altered weather patterns, you indeed can get bigger floods and drier droughts – all in the same place.

How all of this may play out in your region depends on where you live. Experts predict global warming will increase the risk of flash floods in the Southwest, impact spring flooding in the Northeast, and increase fall and winter flooding on the Pacific Coast. The hurricane region -- Mid-Atlantic, Southeast, Gulf Coast – is at risk of coastal flooding in summer.

Health officials worry about the health implications such as the potential for floods to break sewer lines and overwhelm treatment facilities, contaminating drinking water. Major floods in places near the Equator have brought water-related diseases such as malaria and dengue hemorrhagic fever.

For more info:

* Extreme Weather is Sign of Global Warming: www.thedailygreen.com/2007/08/08/un-extreme-weather-is-sign-of-global-warming/4915/

* Linkages between climate change and flooding and landslides: tinyurl.com/yvprf6

* More about porous pavement: www.forester.net/sw_0503_advances.html

* Health consequences of increased flooding and climate change: www.eesi.org/publications/Briefing%20Summaries/06.03.98flooding.pdf

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