Hell and High Water

The last few years have been the worst period on record for environment disasters and experts are predicting far worse to come.

Here is how to become a disaster statistic. Move to a shantytown on an unstable hillside near a tropical coast. Crowd together as more and more people arrive. Wait for the world to get a little warmer. More evaporation means more rain, which means the slopes will get progressively more waterlogged. One day, the land will turn to mud and the neighbourhood will begin to go downhill. Literally. And if the slope is steep enough, the landslide will accelerate to more than 200 miles an hour. Peter Walker, of the international federation of Red Cross and Red Crescent societies, has seen it all too often. “First, your house has been washed away. Second, the land that you farmed has disappeared. Third, the other bits of land you might have been able to farm are now useless.

In the last decade, floods, droughts, windstorms, earthquakes, avalanches, volcanic eruptions and forest fires have become increasingly common. There has been disastrous flooding in Asia, Africa, Central and South America and

Oceania. Even prosperous Europe has suffered and large areas of France, Britain and Germany have all been under water. Storms have been getting worse everywhere too, with a growing number of hurricanes hitting the US, the Caribbean and Central America. Drought has affected large areas of Sub-Saharan Africa for years and many other zones are becoming drier. For example, the Yellow River, once notorious for flooding the Chinese landscape, failed to reach the sea at all on 226 days in 1997. A number of nations have already been in armed conflict over water, and drought in the West of the US has resulted in enormous forest fires.

Volcanic eruptions and earthquakes have always been a threat in certain parts of the world. A volcanic eruption virtually wiped out the small Caribbean island of Montserrat in 1997 and there have been serious earthquakes in Greece, Turkey and El Salvador. The quake that rocked the small Central American country of El Salvador in 2001 came as the people were still rebuilding their houses and recovering from 1998's Hurricane Mitch. So why is nature beginning to turn on us? One answer is overpopulation. Population of the world is growing at the rate of 10, 000 people an hour, 240, 000 every day, nearly 90 million a year, with most of the growth in the developing world.

Text 7

With low buildings the variety of possible shapes is much greater than with taller buildings. In addition to the familiar box shapes, which is also used in very tall buildings, low buildings may use cathedral-like forms, vault, or domes. A simple single-story structure might consist of a reinforced-concrete slab laid directly on the ground, exterior manor walls supported by the slab (or by a spread footing cast continuously around the perimeter of the building), and a roof. For low building, the use of interior columns between masonry load-bearing walls is still the most common construction method. Spaced columns supported by the slab or by individual spread footing may be used, however; in that case the exterior walls can be supported by or hung between the columns. If the roof span is short, abutting planking made of wood, steel, concrete, or other material can be used to form the roof structure. Each structural material has a particular weight-to-strength ratio, cost and durability. As a general rule, the greater the roof span, the more complicated the structure supporting the roof becomes and the narrower the range of suitable materials. Depending on the length of the span, the roof may have one-way framing beams or two- way framing (beams supported on larger girders spanning the largest dimension). Trusses can be substituted for either method. Trusses, which can be less than 30 cm (12 in) or more than 9 m (30ft) deep, are formed by assembling tension and compression members in various triangular patterns.

They are usually made of timber or steel, but reinforced concrete may be used. The structure of a simple one-story building may also consist of the wall and roof framing combined by being either fastened together or shaped in one piece. The possible structural shapes are almost infinite and include the three sides of a rectangle fastened together into a unit called a bent, the familiar church form of vertical sides and sloping roof, the parabola and the semicircle or dome. The supporting structure and exterior walls, floor, and roof may also be made as a unified whole, much like a rectangular pipe with closed or open ends. These may be cast in reinforced plastic.

Text 8