Extreme Rainfall events

Extreme Rainfall events

News: Several states in North India are witnessing extreme rains which has caused loss of lives, damage to infrastructure etc.

What is extremely heavy rainfall event?
• An extremely heavy rainfall event in India is defined as a rainfall event that exceeds 204.4 mm in 24 hours. Such events are rare but have become more frequent and intense in recent years due to the effects of climate change.
• India saw 125 extremely heavy rainfall events in September and October 2021, the highest in five years, according to the India Meteorological Department (IMD).

What are the reasons for Extreme rainfall?
• Rains post the impact of Biparjoy cyclone - By the first two weeks of the monsoon, India had accumulated a rainfall deficit of more than 50%. However, this deficit had come down to 8% by the end of June.
• Western disturbances - IMD has attributed this spell to an interaction between the monsoon winds and western disturbances that converged over northern India.
• The recent heavy rainfall and flash floods in Himachal Pradesh have been attributed to synoptic conditions similar to the 2013 Uttarakhand floods. Such conditions involve an active monsoon with strong low-level easterly winds bringing ample moisture, coupled with upper-level divergence caused by an eastwardmoving trough.
• Flash Floods caused by cloudbursts and extreme rains are difficult to predict.
• Such events are routinely attributed to climate change, but without a proper attribution assessment, scientists are reluctant to describe them as such.
• Warming of the Arabian Sea - Excess rainfall over northwest India is consistent with the Arabian Sea having warmed by about 1.5 degrees Celsius since January.
• Overall rainfall during the monsoon has remained more or less constant over the last two decades, but the intra-seasonal variation has increased. That means that fewer days are producing a bulk of the seasonal rainfall, while the rest of the days remain dry.

What are government initiatives to tackle Flood management?
• Structural measures - These include the construction of embankments, flood walls, river training and bank protection works, anti-erosion and town protection works, river channelization, drainage improvement, sluices, dams, reservoirs, barrages, etc. These measures aim to regulate the flow of water and reduce the risk of flooding.
• Non-structural measures - These include flood forecasting and warning, flood zoning, flood insurance, flood relief and rehabilitation, flood plain management, watershed management, afforestation, etc. These measures aim to enhance the preparedness and resilience of the people and the environment to cope with floods.
• Institutional measures such as National Flood Risk Mitigation Project, National Disaster Management Plan, Central Water Commission (monitoring water levels of major rivers and reservoirs and issues flood forecasts).
Source – Hindustan Times, The Hindu, Indian Express