Early Southwest Monsoon Trends in 2025

The southwest monsoon covered India nine days earlier than usual. The monsoon arrived in Kerala on May 24. This was eight days ahead of the standard June 1 onset date. Such early onset has occurred only ten times since 1960. Several factors contributed to this anomaly, including the Madden-Julian Oscillation (MJO) and various low-pressure systems.

Factors Influencing Monsoon Onset

The MJO is driver of rainfall. It is a moving system of wind, cloud, and pressure that affects weather patterns. In mid-May and June, the MJO was in its active phase, enhancing rainfall over southern India. This phase allowed moisture to be transported northward by monsoon winds. Low-pressure systems also played important role. In June, five distinct low-pressure systems formed across India. These systems create areas of lower atmospheric pressure, attracting moisture-laden winds from surrounding regions. As these winds move in, they facilitate rainfall and help push the monsoon further inland.

The Role of the Monsoon Trough

The monsoon trough is an elongated area of low pressure. It stretches from northwest India to the Bay of Bengal and influences monsoon behaviour. Recently, the trough remained south of its usual position. This positioning helped draw in more moisture, contributing to the early and widespread coverage of the monsoon.

Climate Phenomena – ENSO and IOD

The El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) are critical climate phenomena affecting monsoon patterns. ENSO has three phases – El Niño, La Niña, and neutral. Recently, ENSO was in a neutral phase, which typically supports normal rainfall. The IOD also has three phases – positive, negative, and neutral. A positive IOD phase usually enhances rainfall, while a negative phase reduces it. In June, the IOD was neutral, indicating minimal impact on rainfall patterns.

Rainfall Performance in June 2025

The all-India average rainfall for June was 180 mm, which is 9% above normal. This marked shift from the deficit trends observed since 2022. Central India recorded an average rainfall of 212.6 mm, exceeding normal levels by 24.8%. However, east and northeast India experienced a continued rainfall deficiency. These regions recorded 272.9 mm, which was 16.9% below normal. Despite this, over 80% of meteorological subdivisions reported normal or above-normal rainfall. Notably, Manipur and Mizoram achieved normal rainfall levels for the first time since 2019.

Questions for UPSC –

1. Discuss the influence of the Madden-Julian Oscillation on monsoon patterns in India.
2. Critically examine the impact of El Niño-Southern Oscillation on global weather phenomena.
3. Explain the significance of low-pressure systems in the context of the southwest monsoon.
4. What is the Indian Ocean Dipole? How does it affect rainfall patterns in the Indian subcontinent?

Answer Hints:

1. Discuss the influence of the Madden-Julian Oscillation on monsoon patterns in India.

1. The Madden-Julian Oscillation (MJO) is driver of tropical weather patterns, including monsoons.
2. It consists of a moving system of wind, cloud, and pressure that influences rainfall distribution.
3. During its active phase, the MJO enhances cloud formation and moisture transport, particularly over southern India.
4. In mid-May and June, the MJO’s active phase contributed to the early onset of the southwest monsoon.
5. The MJO’s influence leads to increased rainfall intensity and coverage across the Indian subcontinent.

2. Critically examine the impact of El Niño-Southern Oscillation on global weather phenomena.

1. ENSO consists of three phases – El Niño, La Niña, and neutral, each affecting global weather differently.
2. El Niño typically leads to warmer sea surface temperatures, suppressing rainfall in India and causing droughts.
3. La Niña often results in cooler ocean temperatures, enhancing rainfall and potentially causing floods in some regions.
4. The neutral phase usually supports normal rainfall patterns, as observed during the recent monsoon season.
5. ENSO influences not only Indian monsoons but also global weather patterns, affecting agriculture and economies worldwide.

3. Explain the significance of low-pressure systems in the context of the southwest monsoon.

1. Low-pressure systems are areas where atmospheric pressure is lower than surrounding areas, crucial for monsoon dynamics.
2. They act as magnets for moisture-laden winds, facilitating rainfall as these winds converge into the low-pressure area.
3. In June, five low-pressure systems developed across India, aiding the early progress of the monsoon.
4. These systems help push the monsoon inland, enhancing rainfall distribution across various regions.
5. Low-pressure systems are vital for breaking dry spells and ensuring adequate rainfall for agricultural activities.

4. What is the Indian Ocean Dipole? How does it affect rainfall patterns in the Indian subcontinent?

1. The Indian Ocean Dipole (IOD) is a climate phenomenon characterized by differences in sea surface temperatures between the eastern and western Indian Ocean.
2. It has three phases – positive, negative, and neutral, each influencing rainfall patterns in different ways.
3. A positive IOD phase typically enhances monsoon rainfall, while a negative phase can lead to reduced rainfall and drought conditions.
4. During neutral phases, like observed recently, the IOD has minimal impact on rainfall, allowing for more stable weather patterns.
5. The IOD is crucial for forecasting monsoon behavior and planning agricultural activities in the Indian subcontinent.