In the wake of the #Kerala floods that occurred last month and across other states of India namely, UP, Karnataka, Assam and Bengal and as our country looks back at the appalling death toll of around 900 lives claimed by floods this year, I decided to write on why floods occur and what can be the necessary measures taken.
Believe it or not, floods are the most common natural disaster that occur worldwide claiming more lives and causing major havoc than any other.
The statistics itself speaks volumes – of the causes of floods and the limitation in managing the natural disaster. One may assume places vulnerable to heavy rainfall during a typical monsoon season may be the only ones predisposed to flooding. On the contrary, rain, being one of the major factors, is not the only cause.
What are Floods?
When water enters land (inundates) that is normally dry, this is called a flood. It can be caused by various reasons which we will see shortly. One thing to be noted is that mankind’s activities affect flooding to an alarming level. Floods may vary in its area of extent, its magnitude, duration and may also occur erratically.
Floods can occur suddenly which are known as flash floods or build up gradually. In the present day, however, factors that contribute such as urbanization, land subsidence (sinking of the ground) and climate change will continue to increase chances of flooding at a catastrophic level.
Causes of Floods
The major contributor of flooding is rainfall and is dependent on various factors such as distribution or the area it covers, amount of rain, soil porosity (ability of soil to take up water) and the period of rainfall. Prolonged light showers over a region can also cause the land to overflow with water. And because of its erosive force, it causes much havoc to property and weaken foundations of buildings thereby causing cracks and leading to its collapse.
#2 River Overflows
Regions that are known as lowlands, surrounded by water bodies are prone to flooding. That is because a lowland is usually a plain that may only be within 200 meters above sea level as opposed to uplands which may rise above up to 500 meters above sea level. Constant rainfall may cause the water level to rise and rivers to spill over into the adjacent land.
#3 Lakes & Coastal Flooding
#4 Dam Breaking
#5 Climate Change
#7 Land subsidence
Factors Affecting Flood Management
What Happened in the Kerala Floods
- The south Indian state of Kerala is a strip of land in the peninsula of the subcontinent, situated in the coastal region of the Western Ghats with plenty of backwaters. Starting in the month of July till August this year, Kerala witnessed floods – the worst of its kinds than it has in a century. At least 483 people have died due to the floods with an estimated US$ 3 billion worth of property damage.
- The Central Water Commission of India reported that an unexpected high rainfall and its prolonged period was the main cause of flooding in the state. This along with the lack of reservoirs in the upper reaches of the rivers worsened the flooding thereby severely inundating these regions leading to the worst flooding in central Kerala.
- It is also important to note, as mentioned in the factors above, certain minor but crucial causes of flooding such as inefficient drainage in urbanized cities and the poor planning of residential areas. The floods revealed that many houses were built on inappropriate design and construction especially in flood-prone areas have enormously contributed to the worsening of floods in these areas.
- Furthermore, landslides resulted due to incessant rainfall, maximum retention of soil thereby adding to the instability of the land in hilly regions. Land use and unscientific construction of buildings in these regions have seen the destruction of the property and claim of lives.
 Tollan A. Land-use change and floods: what do we need most, research or management?. Water Science and Technology. 2002 Apr 1;45(8):183-90.