Like all living organisms, human beings need water to survive. It is used for washing, drinking, and watering crops, to name just a few things. The amount of water that is available usually depends on the amount of rain and snow that falls. Unfortunately, precipitation is not distributed equally around the world. Some areas barely see rain while others get more than their share. Over time, most people in an area get used to too little or too much. The problems start when dramatic changes occur when they are least expected. Droughts occur when an abnormally long dry period uses up available water resources. Floods happen when watercourses or rain swallow up land that is usually uncovered. These natural disasters are often made worse by human action. Paved roads and cities full of asphalt prevent water from sinking into the ground. As it builds up on the surface, the water ends up causing widespread damage.
An overflowing river, long periods of rain, uncontrollable seas, or a break in a dam can all cause flooding. Swelling rivers cause the most floods. Abundant rains and rapidly melting ice may raise water levels in rivers until they overflow their banks. Storms sometimes cause unexpected flooding, along with the extremely heavy rains that accompany cyclones and hurricanes. Besides destroying everything in their path, floods sometimes contaminate underground reserves of drinking water with all kinds of waste. The dirty water becomes more than undrinkable: It also helps spread disease that can infect thousands of people.
A heavy rain falls on the town and the surrounding countryside. The sudden downpour is too much for the ground and the nearby river to soak up in a short amount of time. The river starts to rise, and then overflows its banks. Confusion and destruction follow as the town begins to flood. During severe floods, furniture, trees, rocks, and even vehicles are carried away by the rushing waters. Drivers are caught inside their cars, houses fill with mud, and the town’s drinking water becomes too dirty for people to use. Every year, more damage is caused and more lives are lost because of floods than because of lightning, hurricanes, or tornadoes.
Very heavy rains falling in the mountains often cause landslides. Under the pressure from all the water hitting the ground, tons of mud and rocks may fall down the mountainsides with amazing speed. Landslides can bury roads under debris, uproot trees, and destroy houses.
Floods along the Chang River (also called Yangtze) are dreadful. In 1931, this river in China swallowed up the surrounding land after weeks of uninterrupted rain. The flooding and famine that followed led to the deaths of more than 3 million people. Following the disaster, the Chinese built almost 20,000 miles (32,000 km) of dikes along the river and its tributaries. As effective as they were, however, these barriers were still unable to prevent the Chang from overflowing its banks again a few times.
Many countries that receive very little rain count on small downpours to water their crops. If the absence of rain lasts a few years, it can result in poor harvests and soil that can never recover its nutrients. In regions where the survival of inhabitants depends on agriculture, a lack of rain can be dramatic. Famine may occur, causing many deaths. In the last 50 years, the longest-lasting droughts and the most frequent famines have been in Africa. The drought that ravaged countries like Chad and Ethiopia from 1968 to 1988 killed thousands of people and forced millions of others to move to more humid regions.
In the Visual Dictionary: "Earth" section
In the encyclopedic capsules :
In the ikonet games: