The question refers to the 'south-east monsoon,' but in the Indian context, the most significant monsoon is the South-West Monsoon (June to September), which accounts for about 75% of India's annual rainfall. El Niño primarily impacts this South-West Monsoon.

El Niño is a climate pattern characterized by the unusual warming of surface waters in the central and eastern tropical Pacific Ocean. This warming leads to a shift in atmospheric pressure patterns, weakening the trade winds and altering the global atmospheric circulation, including the Walker Circulation.

Relationship with Indian Monsoon: El Niño events are strongly correlated with a weaker Indian South-West Monsoon. The warming in the Pacific suppresses convection (rising air and cloud formation) over the Indian Ocean and enhances it over the Pacific, effectively 'stealing' moisture and energy from the Indian subcontinent. This disruption leads to reduced rainfall, delayed onset of the monsoon, or early withdrawal, resulting in drought-like conditions over large parts of India. While not every El Niño year results in a drought, the probability of below-normal rainfall significantly increases.

Impact on Agriculture: The Indian economy is heavily reliant on agriculture, with a substantial portion of cultivated land being rain-fed. A weak monsoon due to El Niño has severe repercussions:

1. Crop Failure: Reduced rainfall directly leads to crop failures, especially for rain-fed kharif crops like rice, pulses, oilseeds, and cotton, which are sown during the monsoon season.
2. Water Scarcity: Insufficient rainfall depletes reservoirs and groundwater, impacting irrigation for both kharif and subsequent rabi (winter) crops.
3. Reduced Agricultural Output: Overall agricultural production declines, leading to food shortages and price inflation.
4. Farmer Distress: Lower yields and incomes push farmers into debt, leading to economic hardship and, in severe cases, suicides.
5. Rural Economy Impact: The rural economy, heavily dependent on agriculture, suffers significantly, affecting employment and purchasing power.

In summary, El Niño poses a significant threat to India's food security and economic stability by adversely impacting the crucial South-West Monsoon, leading to widespread agricultural distress.