Early Arrival of Monsoon
Kartavya Desk Staff
Syllabus: International Relations
Source:
Context: The India Meteorological Department (IMD) declared the onset of the southwest monsoon over Kerala on May 24, 2025, eight days ahead of the usual June 1 date.
• This marks one of the earliest monsoon arrivals in over a decade, last seen in 2009.
About Early Arrival of Monsoon:
What is the Southwest Monsoon?
• The Southwest Monsoon is a seasonal wind system that brings over 70% of India’s annual rainfall during June–September.
• It plays a critical role in agriculture, water availability, and overall economic activity.
When is Monsoon Onset Declared?
The IMD uses three main criteria to confirm the monsoon’s onset over Kerala:
• Rainfall Trigger: 60% of 14 designated stations must record ≥2.5 mm rainfall for two consecutive days.
• Wind Field Criteria: Westerlies should extend up to 600 hPa (hectoPascals) level with wind speeds of 15–20 knots at 925 hPa.
• Outgoing Longwave Radiation (OLR): OLR must be below 200 W/m², indicating active convection and cloud cover.
Factors Behind Early Monsoon Onset 2025:
• Madden-Julian Oscillation (MJO): Enhanced eastward-moving tropical disturbance boosted convection and rainfall over the Indian Ocean.
E.g. MJO impact observed from May 13 over the south Andaman Sea (IMD).
• Mascarene High Intensification: Strong high-pressure system over the southern Indian Ocean aided in directing moist winds to Indian coastlines.
• Convection Surge: Rising heat and moisture movements increased vertical cloud build-up, bringing early rains.
• Somali Jet Strengthening: Cross-equatorial winds became stronger, accelerating the arrival of monsoon currents over Kerala and Karnataka.
• Heat Low Formation: Persistent low pressure over Pakistan and NW India created suction for moist monsoonal air.
• Monsoon Trough Activation: Elongated low-pressure zone stretching from Arabian Sea to Bay of Bengal activated rainfall over central India and NE India.
Consequences of Early Monsoon Onset
• Agriculture Boost: Early sowing of Kharif crops such as paddy and pulses can begin, improving crop calendar adherence.
• Reservoir Recharge: Helps early water level replenishment in drought-prone states like Tamil Nadu and Karnataka.
• Urban Flooding Risk: Cities unprepared for early rain, e.g., Bengaluru, may see increased urban flooding.
• Altered Weather Patterns: Early monsoon may disrupt normal temperature patterns, seen in cooler summer 2025 trends across south India.
• Forecast Challenges: Early onset may or may not ensure a longer or stronger monsoon season, posing risks for water management planning.
Conclusion:
The early onset of the 2025 monsoon is the result of favourable atmospheric and oceanic conditions including MJO and Somali Jet dynamics. While it brings hope for agriculture and water security, it also demands preparedness against urban flooding and misaligned rainfall patterns.
• Why is the South-West Monsoon called ‘Purvaiya’ (easterly) in the Bhojpur region? How has this directional seasonal wind system influenced the cultural ethos of the region? (10 M)