Cyclones and floods

Cyclones
The word 'cyclone' is derived from a Greek word meaning 'coil of snake'. In meteorological terms, cyclone is a low pressure from all sides. A cyclone may be elliptical, circular or 'V' shaped. Cyclones can be classified as tropical or temperate based on the location where they occur. The various impacts of cyclone  are listed below:

1. Storm surge causes
1. Flooding in coastal areas
2. Erosion of beach
3. Loss of soil fertility and
4. Damage to structures
2. Winds
1. Damage to structures
2. Loss of power and communication
3. Loss of life
4. Agricultural loss and livestock losses

      3.Torrential rains

1.  Flooding in inland areas
2. Land subsidence
3. Contamination of water supply system
4. Destruction of  crops and livestock

It is difficult to measure the magnitude and intensity of a cyclone. Cyclones are usually accompanied with heavy rains and wind storms. Cyclones paralyse entire public services including communication and transportation. Damages caused by cyclones  to sanitation infrastructure causes a heightened risk of communicable disease outbreak like diarrhea and cholera.

In order to mitigate the effects of cyclones, a rehabilitation plan with geographical focus and prioritization of intervention should be prepared. The plan should contain measurable indicators like infrastructure, livelihood and habitat.

Floods

Floods are a common feature in India occurring in many areas. Floods are a natural phenomena.

Flood is a water related disaster. A flood occurs when the geomorphic equilibrium in the river system is disturbed due to intrinsic or extrinsic factors. or when the system crosses the geomorphic threshold.

1. Flooding in the river bed due to aggradation of river bed (intrinsic threshold)
2. Flooding in the river due to heavy rainfall (extrinsic threshold)

Floods in major cities especially in major cities during rainy season are disastrous not only to the environment but also has serious implications for human life and property
The different types of flood are:

1. Flash floods
2. River floods
3. Coastal flood and
4. Urban flood

According to the duration, floods can be classified as:

1. Slow-onset floods 
2. Rapid-onset floods and
3. Flash floods

Floods can also be classified as:

1. Natural
1. Storm surge
2. Tsunami
3. Glacial melt
4. Landslides
5. Riverine, Estuarine and Marine floods
6. Examples are bursting of landslide and blockades in the catchment areas of rivers
2. Man-made
1. Breach of dam / barrage / embankment
2. Release from reservoir
3. Urban flood
4. Examples are breach of almatti and narayanpur dams in karnataka

Causes of floods

1. Silting of river bed
2. Inadequate capacity within the banks
3. River bank erosion
4. Flow obstruction and change in river course
5. Common floods in the main and tributary rivers
6. Poor natural drainage
7. Cyclones
8. Retardation of flow and backwater flow
9.  Heavy rainfall

Factors influencing floods:

1. Vegetation cover
2. Climate
3. Slopes
4. Rainfall intensity and duration
5. Land use
6. Rock type
7. Lakes and reservoirs
8. Soil depth and type

Impact of floods

1. Human loss
2. Property loss
3. Affects the major roads
4. Disrupts transportation services
5.  Spread of water-borne communicable services
6. Disruption in electricity and communication services
7. Social and economic disruption
8. Pollution of air and water

Flood forecasting - Anticipating floods before they occur helps to take precautions and warn people in order to prepare people in advance for flood conditions.
In order to predict floods accurately, a long-time series of historical data that relates stream flows to measured past rainfall events is required.
Radar estimates of rainfall and general weather forecasting techniques are important components of good flood dorecasting.