Flash Floods – the causes, prevention and future?
On Wednesday, the flash flood in West Bengal’s Jalpaiguri took away the lives of at least eight people and caused several others missing. Meanwhile, the India Meteorological Department has predicted moderate to heavy rainfall in several states for the upcoming three days, even as the south-west monsoon is forecasted to start withdrawal on Friday. Moreover, heavy rainfall is predicted in several parts of the country, including Uttarakhand, Himachal Pradesh and Uttar Pradesh, while light rains are expected in the capital.
In the past few years, the occurrence of natural disaster like flash floods has increased in India. This can be attributed to climate change. For instance, the 2018 Kerala floods, 2021 Uttarakhand floods, 2021 Maharashtra floods, 2017 Gujarat flood and many other.
What is a flash flood?
In simple words, a flash flood is a sudden flood of water caused by heavy rain. This specific type of flooding occurs within a short frame of time after a precipitation event, which is generally less than six hours. It takes place in areas near rivers or lakes. However, it can also take occur at places with no water bodies nearby.
These are characterized by very fast rise and recession of flow of small volume and high discharge, which causes high damages because of suddenness.
Causes of flash floods?
A flash flood is often the result of a heavy or excessive rainfall. Whenever it rains, the soil acts as an absorber, and absorbs the precipitation. However, in cases of heavy rain, the soil may be saturated to capacity and unable to absorb any more water.
Flooding can also occur after a drought, when the soil is too dry and hardened to absorb the precipitation. This is why, flash floods are a common scene in desert landscapes after heavy rainfalls. The other reason of flash floods are cloudburst or thunderstorm. It is common in places such as hilly, not too hilly regions and sloping lands.
Depression and cyclonic storms in the coastal areas of Orissa, West Bengal, Andhra Pradesh, Karnataka, and Tamil Nadu also cause flash floods. Further, the states of Arunachal Pradesh, Assam, Orissa, Himachal Pradesh, Uttarakhand, the Western Ghats in Maharashtra and Kerala are more vulnerable to flash floods caused by cloud bursts.
In addition to these, sudden release of waters from upstream reservoirs, breaches in landslide dams and embankments on the banks of the rivers can also lead to disastrous floods. The severe floods in Himachal Pradesh in August 2000 and June 2005, and in Arunachal Pradesh in 2000 are a few examples of flash floods caused by breaches in landslide dams.
Floods in Assam, Bihar, Uttar Pradesh, Orissa and Andhra Pradesh are generally caused by breaches in embankments. Incidents of high intensity rainfall over short durations, which cause flash floods even in the area where rains are rare phenomena, are on the rise and the problem needs to be tackled in a scientific manner.
Has the number of their occurrence increased?
According to the ‘Climate change and India: A 4X4 assessment a sectoral and regional analysis for 2030s floods report’, temperature rise in India would increase the frequency of flood events in India during the end of the 21st century (2071-2100). Further, the Himalayan belt is also projected to witness a significant rise in temperature up to 2.6 degrees Celsius. By the 2030s, the intensity is expected to increase by 2-12%.
The report further stated that the temperature rise will result in multiplication of flash flood incidents leading to extensive landslides, which would bring extreme damage to the agricultural area thereby threatening the food security of the country.
How can be safe in such a situation?
Flash floods are dangerous as its occurrences are sudden with less time to respond. It is advisable to listen to weather bulletins to avoid visiting places with chances of a flash flood.
On the Authorities front, the NDMA also advices the inhabitation of low-lying areas along the rivers, nullah and drains to be regulated by the state governments/State Disaster Management Authorities (SDMAs)/ District Disaster Management Authorities (DDMAs) as a preventive measure.
Central Water Commission (CWC)/ National Remote Sensing Agency (NRSA)/ state governments/ SDMAs also check for landslides and blockages in rivers with the help of satellite imageries. In case of their occurrence, warning systems are set up to reduce losses. It is also advised to take appropriate structural measures to eliminate the damage in case of sudden collapse of the blockages.
Furthermore, the India Meteorological Department (IMD) has been using Doppler radars, a flash floods forecasting and warning systems to predict the occurrence of flash floods.