What Caused the Floods of 2002? (We May Know in 2100)

Article excerpt

Throughout the world at anytime, a river somewhere is in flood and its waters are threatening communities, their properties and even their lives. Few of these events are reported due to their local impact. However, the floods in Central Europe and China have drawn international attention.

Floods in more than 80 countries have caused hardship for more than 17 million people worldwide since the beginning of 2002, according to the World Meteorological Organization (WMO). Almost 3,000 people have lost their lives, while property damage has amounted to over $30 million. The total area affected is over 8 million square kilometres, almost the size of the United States.

At the other end of this extreme water overload are droughts that have been and are still taking place around the world. Serious droughts are occurring in the Southern African Development Coordination (SADC) countries of southern and central Africa, resulting in starvation and a global outcry for food aid. In North America, over 37 per cent of the United States is suffering from severe drought, with the longest-lived in the southeastern States. At the same time, since mid-June 2002, much of Europe has received between 200 and 500 millimetres of rain; between 100 and 400 mm fell within a few days from England southeastward to the Black Sea. In China, as in Europe, the months of June and July were very wet.

In Europe, the Danube exceeded the previous highest recorded level by 3 centimetres in Budapest by 22 cm in Komaron and by 30 cm in Esztergom. The Vltava and the Elbe were flooded to levels only expected to occur every 250 to 500 years. In China, the Xiangijang, Xijiang and Yangtze rivers flooded large tracts of land in the southern part of the country. The flooding of Lake Dongting was caused by extremely heavy rain falling on already saturated land. The intensity of the rain in some locations has even been assigned a return period of 1,000 years. The result has been another malor flood descending on the Yangtze River and flowing into Lake Dongting. And just last year in East Africa, floods disrupted life in a number of countries, and waters entered the premises of the United Nations Mission in Ethiopia and Eritrea (see photograph at left taken by a staff member).

We cannot say whether these floods were associated with climate change. We will only be able to do so when we put these events in the overall context of the twentieth and twenty-first centuries. What we can say, however, is that there is already evidence of increasing precipitation in Northern Europe, and the Intergovernmental Panel on Climate Change (IPCC), established in 1983 by WMO and the United Nations Environment Programme, is confident in predicting increased flooding in the future.

Certainly, upstream changes in land use and river improvements, which were made for good economic and social reasons, would have caused some increase in the flood peak and speeded its arrival downstream. But these effects are likely to have been negligible in comparison with the following simple facts:

* the upstream river basins were already saturated from earlier rains;

* there was a series of very heavy storms with large, in some cases record, amounts of rainfall;

* large volumes of water flowed downstream and, with nowhere else to go, occupied or tried to occupy their natural flood plains, and in the case of the Yantze, its natural overflow lake;

* hundreds of years of development have led to the occupation of these banks and flood plains by housing, industrial and commercial properties, and agricultural activities, because they represent a valuable resource of flat land and alluvial soil. …