Over the past decade, the number of droughts and floods have increased dramatically, as environmental conditions have deteriorated and the global climate continues to change due to accelerated greenhouse gas emissions.

Nearly all of the world's river systems have been altered by human activities. River modifications and excessive water withdrawals have contributed to and aggravated drought conditions in dry lands throughout the world. This has been exacerbated by loss of tree cover in watersheds, since trees and other vegetation help to soak up and store water during the wet season, making more available during the dry season.

Many rivers no longer reach their deltas during dry periods. Rivers such as the Colorado, Huang-He (Yellow River), Ganges, Nile, Syr Darya and Amu Darya run dry in their lower reaches during the dry season - some of these are dried up for half of the year or more. The conversion of wetlands to agricultural and urban land also have impoverished the capacity of these natural sponges to soak up and store excess water during the rainy season.

What this means, according to the World Resources Institute, is that droughts are now becoming more frequent and more severe in drylands, while floods have also increased in intensity and frequency, particularly in flood prone regions throughout the world.

 Floods throughout Asia in 1998 killed 7,000 people, damaged more than 6 million houses and destroyed 25 million hectares of cropland in Bangladesh, China, India and Vietnam.
 In September, 2000 flooding and landslides killed seven people in Japan and forced the evacuation of 45,000 people caught by flood waters; the rainfall was the most in a 24-hour period ever recorded since records began in 1891.
 In September 2000, heavy rains in Southeast Asia resulted in unprecedented flooding along the Mekong River and its tributaries. Damage was widespread:
 
- Flood waters inundated parts of northern Thailand, damaging more than half a million hectares of cropland
 
- Nearly half a million people in the Mekong Delta (in Cambodia and Vietnam) had to abandon their homes
 
- In Cambodia, rising flood waters submerged close to 400,000 hectares of cropland; emergency supplies were distributed to 1.4 million people
 
- In Laos, over 18,000 families had to be evacuated from flood plains and the rampaging waters severely damaged just under 50,000 hectares of cropland

The UN's Economic and Social Commission for Asia and the Pacific (ESCAP) blamed the floods (and droughts) in the region on widespread deforestation in watershed areas, poor soil management practices, reclamation of flood plains and wetlands and the rapid expansion of urban areas.

The see-saw effect of droughts followed by floods is becoming more severe according to the UN. Destruction of forests and wetlands is the main reason. But as climate change sets in, these increasingly destructive cycles are expected to become even worse.

Source: People and the Planet