Storm warning;Geography

26th November 1999 at 00:00
1999 was a bad year for natural disasters, what with floods, cyclones and earthquakes. But are things getting worse? John Stringer investigates...

The comedian Marty Feldman once per-formed a sketch where, eyes rolling and face contorted, he predicted plague and pestilence and fire from heaven, ending rather lamely with "the rest of the day will be cloudy with some sunny intervals".

At the end of one millennium and the beginning of the next, it sometimes seems as if his dire predictions are coming true. Even in Britain, which has been apparently immune to these kinds of extremes, the weather patterns seem to be changing.

But is this really the case? What we often forget is that we live on a changing planet. Continents are drifting, mountains are colliding, temperatures are changing and air masses are moving.

The Sun is the engine that powers our weather. Changes in surface temperature cause air pressures to change, making air masses move as winds. These winds in turn cause tumbling of the sea's surface water into waves. Rising clouds of water vapour form drops and fall as rain. In winter, the temperatures drop, causing ice and snow.

In any one year, there will be around 100,000 thunderstorms and 10,000 floods on our planet; over the past two decades natural disasters have claimed three million human lives and left more than a billion people homeless. But can we blame all this on the Sun?

* Volcanoes

You can't blame the Sun for volcanoes! Volcanoes are vents releasing the pent-up pressure of molten rock beneath the surface of the Earth. On April 5, 1815, Mount Tambora in Indonesia erupted, killing 92,000 people, 12,000 in the ash and lava. But 80,000 of them died later, simply because there were no rescue and relief services. Deprived of their homes, their crops and animals, most of them starved to death. This was the greatest death toll from an eruption last century, and it demonstrated the importance of detection and prediction.

In contrast, the eruption of Mount St Helens in Washington State, USA, on May 18, 1980, was pre-dicted eight weeks before. Hot gases streamed from it at 1,000 kph; lava destroyed 600sq km of forest, and ash was strewn around over 60,000sq km. Debris was found 30km away. Crops were destroyed and water made undrinkable; but because of preparation and planning, only 61 deaths could be directly attributed to the volcano. The long-term effects, however, will be more significant. Volcanoes produce huge amounts of greenhouse gases, adding to the problems of global warming.

* Earthquakes

Around the world, many earthquake centres monitor ground movement and changes in sea level and, by computer modelling of the possible outcomes, scientists aim to predict and alleviate the results of earth tremors.

But even after severe earthquakes, people are reluctant to leave a place they know. El Asnam in Algeria is hit by earthquakes on a regular basis - most recently in 1954 and 1980, in which 10,000 people were killed and 300,000 left homeless; yet it was rebuilt in 1980.

The famous San Francisco earthquake on April 18 1906, was inevitable - the city is built on a fault in the Earth's surface where two huge masses of rock are straining against each other. But nobody was prepared for the massive 'quake that shook the city on that day - 8.3 on the 10-point Richter Scale. More than 700 people were killed as poorly constructed buildings collapsed and 3,000 acres of the city were destroyed. Yet San Francisco was not rebuilt elsewhere, despite other 'quakes, including a major one on October 17 1989, that caused 67 fatalities. This event had been predicted, precautionstaken and buildings strengthened. There were few deaths in the city itself. Almost all those who died had been trapped in their cars when a motorway bridge collapsed.

Earthquakes don't kill people; buildings do. In a recent Armenian earthquake, 6,000 of the 25,000 dead were teachers and students; unlike most of the population, they were indoors when the earthquake struck. An Indian engineer has since devised a "ring" beam, built into the roof of every new school in his country that supports the roof and prevents the walls falling like a house of cards.

* Tsunami

Earthquakes and volcano eruptions also take place under the sea. When this happens, they can cause tsunamis, waves up to 300km long that travel at speeds of up to 800kph. The waves they cause may reach 30m in height in shallow water, sweeping inland to cause great loss of life and damage to property. A tsunami wiped out the Minoan civilisation in 1480BC; a giant wave hitting Chile on May 22 1960, left 2,000 dead, 3,000 injured and two million homeless.

* Storms

Thunder-clouds can grow up to 12 miles in height. Their anvil shape is caused by high winds at that height, blowing the top sideways.

Some of the water in them stays unfrozen - even at minus 40xC. But clouds also contain fragments of ice that are growing onion-like, layer by layer, and then may become too heavy to be held up by currents of air, falling to the ground as hail. If the air currents are really fast - for instance 90mph - the hailstones may grow to the size of oranges before they drop from the cloud.

In Hyderabad, India, in 1939, hailstones weighing 3.5kg fell to Earth; in 1843, 83 people and 3,000 cattle were killed by a similar storm in the Himalayas.

Lightning is a high-voltage electrical discharge between two thunder clouds, or between a cloud and the Earth. Air in the path of the lightning expands and the accompanying noise is heard as thunder.

Lightning travels at 140,000km per second, half the speed of light. While the streak is very narrow - less than two centimetres wide - it can be 43km long. You can survive being hit by lightning if it goes to Earth without passing through your heart. Park Ranger Roy Sullivan was hit by lightning seven times between 1942 and 1977.

* Floods

Flash-floods are weather's biggest killer. They are extremely difficult to forecast and may hit small areas.

On July 31 1976, huge thunderclouds formed along the edge of the Rocky Mountains in Colorado; they reached 21,000m in height. That evening, they dropped 30cms of rain into the Big Thompson River, an area that normally receives only 41cms a year. Water poured down the rocky valley, sweeping pine trees, boulders, houses and cars before it, and killing 239 people.

On August 15, 1952, a flash-flood hit the Devon village of Lynmouth after three months' rain fell in 24 hours. Some 93 buildings were destroyed and the 28 bridges across the two Lyn rivers were swept away; 34 people died as three billion gallons of water flowed through the village.

Yet neither of these two disasters can compare with the flooding that could result from global warming. Carbon dioxide and other greenhouse gases from power stations, industry, the burning of rain forests and vehicles, are forming a blanket around the Earth that traps the Sun's heat instead of allowing it to reflect into space. The Earth is getting warmer and the sea level is rising - both through expansion and because ice caps are melting. A rise of one metre in sea level will flood a third of Bangladesh.Across the world, 200-million people could be made homeless.

* Soil erosion

In the desert, many people have changed their nomadic way of life and settled permanently in one area. Previously, their transitory lifestyle allowed the arid land to recover. But the re-use of already parched ground for agricultural purposes can break down the soil structure, so it is not as fertile as it might be. Clearing trees to farm, or to use for building or burning, leaves huge areas open to erosion and without the roots that once caged the soil.

* Hurricanes and tornadoes

A hurricane (called a typhoon in the Northern Pacific and a cyclone in the Indian Ocean) originates close to the equator when a central calm "eye" is surrounded by inwardly spiralling winds. As the sea temperature rises, water evaporates into whirling, unstable storm clouds. A hurricane is a wind of force 12 or more on the Beaufort scale, and is accompanied by lighting and torrential rain. Hurricane Gilbert in the Caribbean in 1988 gusted up to 320kph. A cyclone in the Bay of Bengal in November 1970 caused the sea to rise 10 metres and crash into the Ganges delta to drown 300,000 people and a million farm animals.

The UK doesn't suffer with hurricanes. While south-east England felt the strongest winds there for 300 years in October 1987 and January 1990, they were nowhere near hurricane force.

A rising column of warm air propelled by a strong wind can become a tornado - swirling at 480kph. A tornado which cut through the three US states of Missouri, Illinois and Indiana on March 18, 1925 killed at least 700 people and injured 3,000.

* Worse to come?

The world has become more vulnerable to natural disasters. It is more densely populated and much of that population is crowded into cities, concentrating a large number of possible victims into small areas.

The Earth's climate is changing. The last decade has seen some of the hottest years ever recorded across the world. By the heedless burning of irreplaceable resources, humanity is raising the temperature - and the stakes.

We are all in this together; and the sooner we wake up to it, the more likely it is human beings will be around to see the next millennium.

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