I know very little about the Kerala flood, but have spent portions of my career addressing their effects. If you are familiar with the term envelop curve (i.e., a curve that represents the greatest floods by drainage size in history, sometimes by physiographic area). Some areas have a substantial rainfall and flood level history, others not. There are some geomorphologists that have developed techniques in defining paleofloods, to expand the flood indicators through greater time periods. One must remember that coastal areas subject to hurricanes, typhones, monsoons and tsunamis may be subject to extremes that are difficult to predict. Urbanization and human modification of stream and river systems, including dams can alter severity of flooding. Dams with careful management can help reduce flooding, but extreme events and excessive dam releases and especially dam failure may add severity.

Poor management of higher gradient headwaters with unstable slopes may contribute landslides that will fill lower gradient channels downstream, resulting in increased flooding as river channels loose capacity.

Predicting extreme flooding effects in the future needs to take into account not only the potential for extreme rainfall and streamflow, but also dam and other hydromodifications, land use including urbanization and the unstable lands, areas burned severely, etc. Recognize there is uncertainty in predictions, and early flood warning and various compensations in management needed. There seem to be many other issues besides life and property damage to consider.

Continuing, man can contribute to flood severity. But flood events are often a natural occurance, so severity except in natural watersheds may be a mix. Developing flood and storm emergency plans and responses may help. Various coastal cities have these plans for examples. Utilizing skills of meteorologists, hydrologists, geomorphologists, civil engineers, city and watershed planners may help develop comprehensive plans. Mapping floodplains and evacuation routes helpful. What to do with all the cattle, animals and snakes may need some wildlife biology considerations. By better understanding and managing the network of dams would probably help reduce severity. But expect some coastal areas to have circumstances over time with extreme rainfall, streamflow, tidal conditions that deserve attention and planning for responsible notification and hopefully response and evacuation as needed.

To begin with one has to recognise the fact that the flood event and destruction due to water logging/flooding which took place in Kerala State in India was UN-PRECEDENTED and not known for the last 100 years. Any flood management plan would not have worked for this magnitude.

Reasons: The severity of the floods in Kerala is due to the combined effect of extreme events like excess rainfall; improper dam release operations; Urbanization and human modification of stream and river systems; Failure in predicting extreme flooding effects; lack of preparations and machineries to fight the extreme events; Public not taking the warning signals from the Government seriously and not moving to safer places; etc. The event was a typical example of severity of natural devastation due to the combined effect of natural and man made causes.

Lessons: Do not under estimate the natural disasters. Do not encroach the river banks or sea shores. Dam release operation policies should be re-visited taking into consideration the recent un-precedented rainfall & flood event. Do the urbanization planning in flood prone areas with extra care and concern, if it can not be avoided. Public should consider the warning signals from the Government with much more seriousness, and move to the safer places, as the natural disaster can take place any time and the severity/damages can not be predicted. This event is a lesson for all - Government & Public.

Thanks for the answers.

Beware of climate change-Join effective world actions!

The flood in Kerala is combined effect of both human intervention and natural causes. The anthropological impacts are due to the building of large size dams and the natural cause is excessive rainfall this year. The large size dam can store huge amount of water, which is very effective for control of small or medium floods, which resulted in reduction of flood occurrence. Due to control of small and medium flooding, we started thinking that the flood prone area is no more flood prone and the large area of river catchment is actually occupied by human settlement. This year, the normal rainfall occurred for longer duration and almost all dams of Kerala filled at is highest capacity. Thereafter, the state witnessed the heavy rainfall for more than ten days and there was no more space for water storing in dams, which lead to the opening of dam’s gate. Thus, this combo effect of runoff from the rainfall and opening of dam’s gate leads to this devastating flood in Kerala and the flood prone rivers catchment areas is affected badly.

The floods in kerala are partially man made, the Madhav Gadgill committee reported that Kerala as ecologically sensitive zone and indicated to stop the human disturbance. But the government of Kerala rejected the report. The deforestation, illegal mining and urbanization are the main reason for the flood.

Ram Kishor Fagodiya

So the Big Dams may be disastrous if not managed scientifically !!

We are worried as Big dams are planned in the North East to usher in development(!) of the region through generation of huge energy.

Yes, partially it is true. The big dams could be a reason of the mass destruction, if not maintained properly.

@Subrata chakraborty

Big or small, if a dam is not properly operated and maintained, it will be disastrous to the people and the property in the downstream region. We have noticed the destruction of a plantation area, eroding the precious soil layer along with the cardamom plants and making the whole region into a bald hillock (without any soil layer in Idukki region in Kerala) due to the collapse of a small check dam constructed across a small stream for agricultural purpose. Big / medium or small dams are built based on various parameters including the purpose & possibilities. By building a dam there will be losses and gains, and that's why EIA (Environmental Impact Analysis) will be conducted and cost-benefit ratios will be determined before finalizing a project. The operation policy of a dam is designed taking into consideration the long term rainfall pattern in the region.

What happened this year in Kerala was an unprecedented rainfall with respect to intensity and duration which led to water logging/flooding in the low lying areas. But the magnitude of the flooding got multiplied, when the water was released from many dams simultaneously. Off course, all other factors like urbanization, deforestation, etc., have also contributed in their own way to the destruction due to flooding.

nice explanation by @prasad. Thanks

Reasons and lessons explained nicely by @N B Narashima Prasad and @William F. Hansen. Thanks a lot. Even though natural disasters like floods are inevitable yet the severity can be minimised by proper forecasting and efficient flood management plans.

It is very sad to learn from others' sufferings, but unfortunately this flood together with many other disasters around the globe are:

1. the tangible evidence of climate change that many politicians around the world still are not convinced to admit.

2. the proof that global events require global responses

My prayers go to the dead, the lost the foodless and homeless left after the flood!

Nice Explanations by @N B Narashima Prasad and @William F. Hansen and I wish to write the following. 1. Irrespective of size the operation of dams must be based on scientific guidelines and it should be made mandatory while planning and executing the projects. 2. There should be comprehensive study by experts of that domain to suggest policies to the decision makers. 3. Since climate change is playing it should also be looked into while formulating. 4. We can not avoid development and agriculture but care should be taken on the impact of environmental issues particularly critical hilly areas.

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