Causes of floods and tropical cyclones

CAUSES OF FLOODS

Floods are experienced all over the world for a variety of reasons both natural and man made or human-induced. Some of the reasons are natural while many others are human induced or man-made. Some of the reasons are listed below:

1. Heavy rains - The simplest explanation for floods is heavy rains. Human beings designed infrastructure and systems designed to move rainwater into appropriate basins and reservoirs. However, incessant and heavy rains cause these systems to be overwhelmed causing rainwater to back-up and causes the water level to rise and flood residential and commercial buildings. This normally happens due to heavy rainfall over a short period of time.                                                 
2. Overflowing rivers - When rivers experience heavy rains, it could cause an overflow in the river and it may overflow the banks. Therefore overflowing rivers may also cause floods.                   
3. Broken dams - Due to heavy rains, old dams may fail, and unleash torrents of water on households. Levees may fail aggravating the effects of a flood. Dams may fail structurally releasing the water behind as a flood                                                                                                           
4. Urban drainage basins - Urban areas are primarily made of concrete and other impermeable material. This prevents water from being absorbed into the soil. This causes the drainage basins to fill-up quickly resulting in flooding of low lying areas                                                                             
5. Storm surges and tsunamis - Storm surges related to hurricanes and other storms can result in  flooding like tsunamis caused due to underwater earthquakes.Sometimes storm surges and tsunamis give little warning before coming ashore                                                                                    
6. Channels with steep sides - Flooding often occurs when there is fast run-off into lakes, rivers and other reservoirs. This occurs mainly where channels have steep sides.                                              
7. Lack of vegetation - Vegetation can help slow run-off and prevent flooding. Where there is sparse to no vegetation, there is no obstruction to the flow of water and this is aggravated by drought like conditions. Lack of vegetation after a drought can cause flash flooding. This can happen if heavy rains are followed by long periods of drought                                                          
8. Melting snow and ice - Heavy snow and precipitation in winter can cause flooding. This can aggravate flood like conditions in low-lying areas around the mountains. 

CAUSES OF TROPICAL CYCLONE

1. A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain.
2. "Tropical" refers to the geographical origin of these systems, which form almost exclusively over tropical seas. "Cyclone" refers to their winds moving in a circle
3. Winds in a cyclonic cyclone blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
4. Tropical cyclones typically form over large bodies of relatively warm water
5. They derive their energy through the evaporation of water from the ocean surface, which ultimately recondenses into clouds and rain when moist air rises and cools to saturation
6. Coastal regions are particularly vulnerable to the impact of a tropical cyclone
7. The primary energy source for these storms is warm ocean waters
8. Though their effects on human populations are often devastating, tropical cyclones can relieve drought conditions
9. They also carry heat energy away from the tropics and transport it toward temperate latitudes, which may play an important role in modulating regional and global climate