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Floods and droughts

Too much water and too little water have always been the natural curse of agriculture. Today, despite greatly improved knowledge of weather systems, the use of meteorological satellites and advanced computer simulation of the climate, farmers are more exposed to climate extremes than ever before. While such extremes may be becoming more common as a result of climate change, vulnerability has increased for other reasons as well: population densities have increased; marginal land is increasingly used to grow inappropriate crops, leading to potential soil erosion and flash floods; deforestation has denuded steep land of its protective vegetative cover; powerful machinery has made it possible to strip land of its vegetation in a fraction of the time that used to be required; and economic pressures on farmers to increase productivity through high input farming have led to unstable and unsustainable farming practices. It will prove impossible to maximize agricultural production from limited water resources unless the factors that so accentuate the effects of natural disasters can be corrected.

Major flood disasters



Approx. no.of Deaths


The Netherlands

100 000


The Netherlands

400 000



300 000


Yellow River, China

900 000


Texas, United States

5 000


Yangtze River, China

100 000


Yangtze River, China

145 000


Yangtze River, China

142 000


Yellow River, China

870 000


Yangtze River, China



The Netherlands

2 000


Yangtze River, China

30 000



10 000


Vaiont, Italy



Morvi, India

15 000



139 000


The Philippines

6 000


Huai River, China


Source: World Commission on Water for the 21st Century,
World Water Vision: Making Water Everybody's Business,
Draft Report of the Commission, Version of 14 November 1999

According to studies made by the Munich Re Group, there were 3.2 times more major natural catastrophes - notably floods, storms and earthquakes - in the 1990s than in the 1960s, and their economic damage increased 8.6 times. The increase in the frequency and seriousness of floods, and the mudslides often associated with them, has been the most striking. During 1988-97, floods accounted for about one-third of all natural catastrophes, caused more than half of all deaths from catastrophes and were responsible for one-third of overall economic losses from catastrophes.

Floods and other natural catastrophes worldwide, 1988-97

An increasing number of people are being severely affected by floods - more than 130 million between 1993 and 1997. Environmental degradation has made a substantial contribution to the devastation caused by flooding. So have poverty and marginalization, which often require the poor to live in unsuitable and exposed conditions.

Land degradation is a major cause of the increasing impact of floods and droughts on human populations and the environment. About 70 percent of drylands and one-sixth of the world population are currently affected by land degradation. It occurs in most regions of the world but is most pronounced in the semi-arid and drought-prone regions of Africa, Asia and South America. Drought and desertification have led to major migrations in both Brazil and the Sahel. During the past three decades, many people have lost livelihoods once based on agriculture, and there has been widespread famine, malnutrition and migration.

FAO's Water for Life, published on the occasion of World Food Day in 1994, reported that:

'In many parts of the world, rainfed cropland is in poor shape. Increasing human and livestock populations have led to land degradation through soil erosion, overgrazing, bush fires, deforestation and the expansion of arable farming onto unsuitable marginal land. In arid and semi-arid areas, which cover a third of the Earth's land surface, these forms of degradation lead to desertification ...

`The cost in terms of human suffering is high. The African droughts of 1984-85 affected 30-35 million people; land degradation and desertification caused some 10 million of them, later known as environmental refugees, to be permanently displaced.'

In 1998, weather patterns associated with El Niño dried out crops in some regions, flooded them elsewhere and battered Central America with Hurricane Mitch which caused the deaths of more than 9 000 people and left nearly 3 million homeless. Honduras and Nicaragua were the hardest hit, with Honduras losing more than half its maize crop. Losses in coffee and other export crops were estimated at US$480 million.

Human-made factors greatly increased the impact of Hurricane Mitch. Mudslides poured down slopes denuded by deforestation and the cultivation of marginal land. Flooding was aggravated by poor watershed management. The most affected countries are attempting to address the structural problems that contributed to the disaster by examining land tenure practices, supporting reforestation projects and providing training in watershed management.

Severe flooding in several Asian countries and the worst drought for decades in the Near East have worsened prospects for food security. Drought was expected to lead to a 16 percent fall in cereal production for the Near East region in 1999. Losses will be far greater in the Islamic Republic of Iran, Iraq, Jordan and the Syrian Arab Republic. Unhappily, there is no evidence to suggest that these setbacks are only transitory in either Asia or the Near East.

Downstream dessication is also becoming increasingly problematic in many areas. The tragic history of the Aral Sea (see page 6) is well known; what is less well known is that a similar fate is facing farmers on the deltas of many rivers from which so much water has been used on the upper and middle reaches that little is left for those who farm and live lower down.

Floods and droughts on China's Yellow River

Draining a basin of 745 000 square kilometres which nourishes 120 million people, the Yellow River is the second longest river in China

The Yellow River in China has become a classic example of how upstream use can led to mid-stream floods and downstream dessication.

The Yellow River dries up before it reaches the sea on an increasing number of days each year, some 200 in 1997. Annual flow at the delta during 1986-94 was half what it was in the previous decade. Research has shown that upstream development and diversions, and the success of programmes of water and soil retention in the middle reaches, are responsible, and that climate change is not a significant factor.

The Yellow River has the highest sediment concentration and total load of any river in the world. It transports some 1600 million tonnes of sediment a year, most of which results from erosion on the Loess Plateau. Much of the sediment is deposited on the channel bottom when the river flows onto the great North China Plain, where the bed of the river is now up to 10 metres higher than the surrounding land, retained there by flood banks. These banks are frequently breached after heavy rains, leading to catastrophic floods which are regularly responsible for heavy loss of life and economic damage in the area.

However, water shortages on the North China Plain now amount to some 5000 million m3 for municipal and industrial uses, and 35000 million m3 for agricultural purposes. This is some 70 percent of the total long-term average flow of the Yellow River. It is the high level of abstraction in this area and downstream that causes the river to dry up so often before it reaches the sea, depriving agriculture in the delta area of the irrigation water needed to maximize production on the fertile downstream plains.

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