1. causes of floods
1.1. NATURAL CAUSES
1.1.1. Excessive rainfall
1.1.1.1. Monsoon winds from the ocean blow over the land and bring heavy and prolonged rains.
1.1.1.2. places in which they experience the tropical monsoon climate, have seasons of heavy rain.
1.1.1.3. The excess rainwater is unable to seep into the ground or when rivers overflow their banks because they can no longer contain them, and thus, flooding occurs.
1.1.2. Storm surges
1.1.2.1. occurs when strong winds raise the waves in the ocean to exceptionally high levels.
1.1.2.2. Tropical storms can cause strong winds to blow over the ocean and create gigantic waves, which crashes onto the coast to flood the land.
1.1.3. Melting snow
1.1.3.1. In places that experience cool temperate climate, the melting of snow in spring releases large amounts of water into rivers and sometimes causes the river to overflow their banks and flood the area.
1.1.4. Global atmospheric processes
1.1.4.1. El Nino and La Nina can cause heavy rains, which can increase the likelihood of flooding in different parts of the world at different times.
1.1.5. Movements of the Earth’s surface
1.1.5.1. Earthquakes can result in landslides, which can cause the loosened soil to be deposited into a river.
1.1.5.2. It may cause the water present in the river to overflow and flood the surrounding areas as the capacity of the river is reduced
1.2. HUMAN CAUSES
1.2.1. Deforestation
1.2.1.1. Removal of vegetation causes an increase in surface runoff, which increases the volume of water flowing into rivers.
1.2.1.2. Deposition of materials on the riverbeds such as mud and soil causes the rivers to become shallower. As a result, flooding occurs.
1.2.2. Urban development
1.2.2.1. Due to the growing population, more land is cleared for the development of housing and industries to meet the needs of the urban population.
1.2.2.2. Tarred roads, concrete pavements and clearing of vegetation reduces the infiltration of water and increases the amount of surface runoff flowing into rivers, which can cause floods.
1.2.3. Enhanced greenhouse effect
1.2.3.1. Global warming will cause climatic changes such as higher rainfall in wetter regions, which may in turn result in higher incidences of floods and severe storms.
1.2.3.2. The increase in the average global temperatures also caused the reduction of ice-cover in the polar regions, resulting in rising sea levels. This increases the possibilities of flooding.
2. impacts of floods
2.1. Flash floods are much more dangerous and flow much faster than regular floods. They result from tropical storms, dam failures, or excessive rain and snow.
2.2. Environmental health hazards
2.3. Densely populated floodplains for crop cultivation
2.4. Fertile soil suitable for farming
2.4.1. Regular flooding of rivers provides the soil along river banks with fertile alluvium
2.4.2. Eg. Nile Delta (fertile alluvium deposited by the River Nile)
2.5. Water is polluted, spreading disease quickly
2.5.1. Makeshift shelters are overcrowded and lack sanitation and clean drinking water.
2.5.2. Cause outbreak of diseases like malaria and cholera
2.6. Saturated ground and overflowing banks and levees
2.7. Severe damages to coastal ecology
2.8. Damages to roads, bridges, and railroads and telephone lines are cut so communication is difficult.
2.9. Submerged village and towns, damages to property
2.9.1. Homes are ruined by the floodwaters and roads become inaccessible
2.9.2. Hurricane Katrina in 2005,
2.10. High economic costs
2.10.1. Flood Damage cost in New Orleans were US$44billion
2.11. Loss of lives
2.11.1. Too many people are crowded at coastal areas for good cultivation of crops, impact of floods become higher
2.11.2. People cannot evacuate in time
2.11.3. Floods occur when people least expect them and hence they are often not prepared
3. causes of droughts
3.1. NATURAL CAUSES
3.1.1. Delayed rain or insufficient rainfall
3.1.1.1. Arid or semi-arid regions such as India and Bangladesh, experience droughts when monsoon winds which bring rain, are delayed and thus, causes a prolonged dry season.
3.1.2. Global atmospheric processes
3.1.2.1. El Nino and La Nina causes change in rainfall patterns.
3.1.2.1.1. El Nino: Abnormal warming of the water surface at the Southeastern part of the Pacific Ocean. It causes extreme weather like heavy rain in Peru, South America, which can increase the likelihood of flooding, and droughts in the Western Pacific, where Indonesia and Australia occur.
3.1.2.1.2. La Nina: Usually follows after an El Nino. This time, places like Peru experience droughts while Indonesia and Australia experience heavy rain, which also increase the likelihood of flooding.
3.2. HUMAN CAUSES
3.2.1. Deforestation
3.2.1.1. When forests are cleared, the reduced vegetation cover lowers the rate of transpiration, leading to less water vapour in the atmosphere. Thus, fewer clouds will be formed and less rain will occur, which in turn leads to droughts.
3.2.2. Enhanced green house effect
3.2.2.1. The increase in greenhouse gases trapped and released in the atmosphere causes a rise in the Earth’s average global temperature, known as global warming.
3.2.2.2. It causes significant changes in the weather conditions in various regions around the world, such as droughts
3.2.2.2.1. in places with drier climates, like the Sahel in Africa.
3.2.3. Overuse of water
3.2.3.1. In places with a growing population, the demand for water in homes, industries and agriculture rapidly increases to meet the needs.
4. impacts of droughts
4.1. Shortage of food and water
4.1.1. lack of water as rivers and lakes dry up
4.1.2. people and animals die of dehydration, crops destroyed
4.1.3. leads to famine
4.1.4. happens mostly in 3rd world countries
4.1.4.1. EG: Africa
4.2. Damage to environment
4.2.1. in arid and semi-arid places, prolonged droughs case desertificationg
4.2.2. spreading of deserts into areas where there is no/ little rain
4.2.2.1. EG: sahara deserts expanded southwards in 1968
4.2.3. soil in region becomes very dry, unable to support vegetation growth
4.2.4. thus blown by wind, leaving barren land
4.3. Forest fires and haze
4.3.1. No rain for long time, vegetation in forest becomes very dry, catches fire easily
4.3.2. Smoke from forest fires is far-reaching. Spread to neighbouring countires, blankets entire city in haze
4.3.3. haze affects environment and health of people. pollutes air, lead to increase in no. of people having breathing difficulties and eye irritations.
4.4. Cost
4.4.1. Expensive to the country as she has to take several measures
4.4.1.1. EG: cloud seeding, high cost and success not always guaranteed