Flooding in North India [1/3]
✓India is experiencing a series of extreme rainfall events that have caused widespread destruction, landslides, flash floods and deaths in several parts of the country.
✓The rainfall distribution and intensity have been influenced by various factors, such as the monsoon, the western disturbance, the El Nino-Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and climate change.
⁉️What are Causes of Heavy Rainfall in North India?
🔸Interaction between Western Disturbance and the Monsoon Trough:
✓The heavy rainfall in North India is primarily due to the interaction between a western disturbance (a low-pressure system originating from the Mediterranean region) and the monsoon trough (a low-pressure zone along the monsoon wind belt).
✓This interaction leads to intense rainfall over regions like Himachal Pradesh, Uttarakhand, Punjab, and Haryana.
🔸Excess Rainfall and Deficient Distribution:
✓After experiencing a 10% deficiency in rainfall until the end of June, North India has witnessed a surge in monsoon activity, resulting in a 2% excess rainfall over the country.
✓Specifically, there is a 59% excess rainfall over northwest India, while peninsular India and east/northeast India have faced rainfall deficiencies of 23% and 17%, respectively.
🔸Synoptic Conditions and Climate Change:
✓The recent heavy rainfall and flash floods in Himachal Pradesh have been attributed to synoptic conditions similar to the 2013 Uttarakhand floods.
✓These conditions involve an active monsoon with strong low-level easterly winds bringing ample moisture, coupled with upper-level divergence caused by an eastward-moving trough.
✓Climate change also plays a role, as it leads to increased heavy rainfall in hilly areas and surroundings due to extra moisture and orographic lifting.
✓In hilly areas like the Himalayan foothills and the Western Ghats, increased extreme rains occur due to orographic lifting.
✓The hills obstruct the moisture flow, causing it to accumulate and result in heavy downpours.
🔸Flash Floods and Cloudbursts:
✓Flash floods caused by cloudbursts and extreme rainfall events are challenging to predict.
✓Monitoring and forecasting such events require radar systems and close observation of areas prone to flash floods.
✓Land use changes and development activities may aggravate the severity of flash floods.
❓What are the Factors Affecting the Rainfall in India?
🔹Monsoon Affecting Rainfall:
[The monsoon is a seasonal reversal of winds that brings a humid climate and torrential rainfall to India.
✓The monsoon typically lasts from June to September, with peak rainfall occurring in July and August.
✓The Indian Monsoon is caused by a difference in air pressure between the Bay of Bengal and the Arabian Sea.
✓The rainfall distribution in India is impacted by the Thar desert and the Himalayas, as well as temperature and pressure changes over the Indian Ocean, the Arabian Sea, the Bay of Bengal and the southern part of the Pacific Ocean.
🔹Western Disturbance Affecting Rainfall:
✓The western disturbance is a low-pressure system that originates over the Mediterranean Sea or West Asia and moves eastward towards India.
✓It usually affects northwestern India during winter (December to February) and brings snowfall to the Himalayan regions and rainfall to the plains.
✓However, sometimes it can also interact with the monsoon trough during summer (June to September) and bring heavy rainfall to northern India.
✓The western disturbance can enhance or suppress the monsoon activity depending on its location, intensity and timing.
✓When it is located over northwestern India or Pakistan, it can enhance the monsoon activity by providing moisture and instability to the atmosphere.
✓When it is located over central or eastern India, it can suppress the monsoon activity by creating a high-pressure system that blocks the monsoon winds.
