Government officials are evaluating and revising disaster plans around the United States in the wake of Hurricane Katrina, just as they did after the Sept. 11 terrorist attacks. Find out what natural disasters top scientists' worry lists.

10. Total Destruction of Earth
Okay, so nobody is spending too much time worrying about what to do if the planet is annihilated, but at least one person has seriously pondered whether and when it could happen. From being sucked into a black hole to being blown up by an antimatter reaction, there are scientifically plausible risks of an event that would render this whole list moot.

9. Gulf Coast Tsunami
A fault line in the Caribbean has generated deadly tsunamis before.
Up to 35 million people could be threatened by one in the not-to-distant future, scientists say.

8. East Coast Tsunami
It seems no coast is immune to the threat of tsunami. For the Eastern United States, the likeliest scenario is waves kicked up by an asteroid splashing into the ocean. Astronomers already have their eye on one rock that could hit in the distant future, but the cosmos could hold a surprise, too.

7. Heat Waves
Heat waves kill more U.S. residents than any other natural disaster. As many as 10,000 people have died in past events. As urban areas get hotter, electricity systems are strained and the population ages, the risk grows.

6. Midwest Earthquake
It has been nearly two centuries since a series of three magnitude-8 quakes shook the then-sparsely populated Midwest, centered near New Madrid, Missouri. Another big one is inevitable. Now the region is heavily populated, yet building codes are generally not up to earthquake snuff. What?s more, geology east of the Rockies causes quakes to be felt across a much wider region. Shelves would rattle from Boston to South Carolina. Some homes along the Mississippi would sink into oblivion

5. Supervolcano
It probably won't happen for hundreds or possibly even millions of years, but nobody really knows when Yellowstone will blow again, destroying life for hundreds of miles around and burying half the country in ash up to 3 feet (1 meter) deep.

4. Los Angeles Tsunami
An earthquake fault just off Southern California could generate a major quake and a $42 billion tsunami that would strike so fast many coastal residents would not have time to escape. Add to that the unprecedented destruction from the earthquake's shaking, and the situation would be reminiscent of Hurricane Katrina.

3. Asteroid Impact
Scientists can't say when the next devastating asteroid impact will occur. Odds are it won't be for decades or centuries, but an unknown space rock could make a sucker punch any time. Many experts say planning to deal with a continent-wide catastrophe should begin now.

2. New York Hurricane
Major hurricanes have made direct hits on the boroughs before, but the interval between them is so long that people forget, and officials fear they might not take evacuation orders seriously. The larger problem: It would take nearly 24 hours to make a proper evacuation of New York City, but hurricanes move more swiftly as they race north, so real warning time could be just a few hours.

1. Pacific Northwest Megathrust Earthquake
Geologists know it's just a matter of time before another 9.0 or larger earthquake strikes somewhere between Northern California and Canada. The shaking would be locally catastrophic, but the biggest threat is the tsunami that would ensue from a fault line that's seismically identical to the one that caused the deadly 2004 tsunami in Indonesia.
As Earth gets warmer, large regions will experience heavier rain and snowfall as weather becomes generally more intense, according to a new study.

"The models show most areas around the world will experience more intense precipitation for a given storm during this century," said lead researcher Gerald Meehl of the National Center for Atmospheric Research (NCAR).

A warmer world will also mean a wetter one.

"On average the global precipitation increases in a warmer climate," Meehl toldLiveScience.

The increase in rain and snow will be on average about 10-20 percent, Meehl said. The more intense storms will most likely happen in late autumn, winter, and early spring. The largest increase in precipitation will occur over land in the tropics where the atmosphere is warming quickest.

Based on computer models, Meehl and his colleagues expect that the regions most likely to experience the more intense storms are places where large masses of moist air converge. These regions include northwestern and northeastern North America, northern Europe, northern Asia, the east coast of Asia, southwestern Australia and the south-central regions of South America.

The reason for the increase in storm intensity is that as the planet warms, the temperatures of the atmosphere and of the ocean surface go up as well, leading to increased evaporation and an increased capacity for the air to hold moisture. As this soggy air moves from ocean to land, the storms that form are heavier with rain or snow.

Even as some regions of the planet experience more intense storms, others will suffer a greater risk of drought during warmer months, the study concluded.

"As the climate gets warmer, we're going to feel these effects more and more strongly," Meehl said.

Separate research recently found that hurricanes are getting stronger but are occurring less frequently, likely due to warmer ocean temperatures.

In another recent study, NCAR researcher Jeffrey Yin used computer climate simulations to show that large-scale rain and snow storms known as frontal storms are moving polewards, driven also by global warming.

Meehl's study suggests that the planet will continue to see increased precipitation for several more decades, regardless of any changes humans make now. 

"Even if you could stabilize greenhouse gas concentrations in the atmosphere at present day levels, the system has a certain amount of thermal inertia and would take several more decades to stabilize," Meehl said. "You'd have to really decrease the rate that you're putting stuff in the atmosphere to get the concentrations to level out and that'll probably be fairly difficult politically."

That analysis is in line with other studies that indicate there is no way to stop the planet from growing warmer through this century.

The study was published in a recent issue of the journal Geophysical Research Letters.
Earth might seem like a more active and dangerous place than ever, given the constant media reports of multiple natural disasters recently. But a broader view reveals that it's not Mother Nature who's changed, but we humans.

Drawn by undeveloped land and fertile soil, people are flocking to disaster-prone regions.

This creates a situation in which ordinary events like earthquakes and hurricanes become increasingly elevated to the level of natural disasters that reap heavy losses in human life and property.

Meanwhile, in any given year, the death toll at the hands of Mother Nature varies greatly, as do the sorts of major deadly events.

How we die

Of the estimated 61,000 people who have died this year due to natural disasters, about 50,000 (according to today's estimate) were victims of the 7.6 earthquake that struck Pakistan Oct. 7. In 2004, by contrast, more than 60 percent of the total natural disaster deaths were caused by the tsunami in the Indian Ocean.

So far, the distribution of natural disasters for 2005 is similar to that of 2004, said Debarati Guha-Sapir, director of the Center for Research on Epidemiology of Disasters (CRED) in Brussels, Belgium. However, Guha-Sapir cautioned that it is still premature to make direct comparisons between the two years, noting that the Dec. 6 tsunami that struck Indonesia and which killed 130,000 people.

Other natural disasters for 2005 that have resulted in a major loss of life include:
  • An 8.7 magnitude earthquake that struck Indonesia on March 28, killing more than 1,600 people.
  • Hurricane Katrina, which struck the Gulf Coast in late August, killing more than 1,200 people.
  • Hurricane Stan, which triggered mudslides in countries throughout South America that killed a reported 1,153 people when it made landfall Oct. 4.
Hurricane Katrina, which caused an estimated $200 billion dollars in damage, is the costliest natural disaster so far this year. It is also the costliest natural disaster in U.S. history.

All of these numbers pale greatly in comparison to deaths caused every year by war, famine and communicable diseases.

Disasters increasing

Along with the Office of US Foreign Disaster Assistance (OFDA), CRED maintains an emergency disaster database called EM-DAT. An event is categorized as a natural disaster if it kills 10 or more people or leaves at least 100 people injured, homeless, displaced or evacuated. An event is also included in the database if a country declares it a natural disaster or if requires the country to make a call for international assistance.

According to the EM-DAT, the total natural disasters reported each year has been steadily increasing in recent decades, from 78 in 1970 to 348 in 2004.

Guha-Sapir said that a portion of that increase is artificial, due in part to better media reports and advances in communications. Another reason is that beginning in the 1980s, agencies like CRED and the US Agency for International Development (USAID) began actively looking for natural disasters.

"Like in medicine, if you go out into a village and look for cases you find much more than if you just sit back and let people come to you when they're sick," Guha-Sapir said.

However, about two-thirds of the increase is real and the result of rises in so-called hydro-meteorological disasters, Guha-Sapir said. These disasters include droughts, tsunamis, hurricanes, typhoons and floods and have been increasing over the past 25 years. In 1980, there were only about 100 such disasters reported per year but that number has risen to over 300 a year since 2000.

In contrast, natural geologic disasters, such as volcanic eruptions, earthquakes, landslides and avalanches have remained steady in recent decades.

What's going on?

Scientists believe the increase in hydro-meteorological disasters is due to a combination of natural and made-made factors. Global warming is increasing the temperatures of the Earth's oceans and atmosphere, leading to more intense storms of all types, includinghurricanes.

Natural decadal variations in the frequency and intensity of hurricanes are also believed to be a contributing factor, as are large-scale temperature fluctuations in the tropical waters of the Eastern Pacific Ocean, known as El Niño and La Niña.

People are also tempting nature with rapid and unplanned urbanization in flood-prone regions, increasing the likelihood that their towns and villages will be affected by flash floods and coastal floods.

"Large land areas are [being] covered with cement so this means the flow of water becomes very strong," Guha-Sapir said. "The runoff from the water can't get absorbed by the soil anymore, so it keeps collecting and rushing down, getting heavier and faster, and then you have much bigger floods."

People aren't just putting themselves at risk for floods, but for natural disasters of all types, including earthquakes and storms like hurricanes and typhoons.

Making disasters

"As you put more and more people in harms way, you make a disaster out of something that before was just a natural event," said Klaus Jacob, a senior research scientists at Columbia University's Lamont-Doherty Earth Observatory.

According to the World Bank's "Natural Disaster Hotspots: A Global Risk Analysis" report released in March, more than 160 countries have more than a quarter of their populations in areas of high mortality risks from one or more natural disasters. Taiwan was singled out as being the place on Earth most vulnerable to natural disasters, with 73 percent of it's land and population exposed to three or more threats.

The good news is that the number of deaths from natural disasters has decreased substantially in recent decades thanks to better disaster preparedness and prevention programs. But this statistic is tempered by the fact that more people are being injured, displaced or left homeless.

"If you don't die you need care," Guha-Sapir said. "To a certain extent we prevent people from dying but more and more people are affected."