Why in News?

Delhi experienced an intense pre-monsoon weather event due to a rare combination of high atmospheric moisture, clashing wind patterns, and strong vertical air movement (dynamic lift).

What began as mild drizzle soon turned into a severe downpour. It became the second-highest single-day rainfall for May since 1901, with the heaviest being 119.3 mm in 2021.

The heavy rain overwhelmed the city's infrastructure, causing waterlogging, power cuts, flight delays, and resulting in five deaths.

What’s in Today’s Article?

• What Happened Over Delhi on Friday
• 5 Key Reasons Behind Delhi’s Intense Rainfall

What Happened Over Delhi on Friday

• Dual Moisture Plumes Over Delhi:
  • On May 2 morning, Delhi was positioned beneath two major moisture-laden wind systems — easterlies from the Bay of Bengal and southerlies from the Arabian Sea.
    • Easterlies are winds that blow from the east toward the west.
    • In India, they often originate from the Bay of Bengal, carrying moisture inland.
    • These winds can significantly influence weather patterns, especially during the pre-monsoon and monsoon seasons.
• Formation of a Convergence Zone
• These wind systems collided over Delhi-NCR, creating a strong low-level convergence zone where moist air was forced to rise.
• Atmospheric Lifting
  • As the converging moist air was squeezed upwards, it triggered intense cloud formation and precipitation.
• Transitional Weather Phase
  • May is a transition period for northern India, making such weather phenomena more likely, though their intensity depends on additional factors.
• Role of Troughs
  • The presence of troughs — elongated low-pressure zones — further intensified the convergence and rainfall in the region.
    • A trough is an elongated region of relatively low atmospheric pressure, often associated with unsettled weather.
    • It helps channel moisture and lift air, contributing to cloud formation, rainfall, and thunderstorms.

5 Key Reasons Behind Delhi’s Intense Rainfall

• Western Disturbance and Cyclonic Circulations
  • A Western Disturbance, seen as a cyclonic circulation over south Punjab, north Rajasthan, and west Haryana, interacted with multiple upper-air cyclonic circulations across southwest and northeast Rajasthan.
  • This intensified regional instability.
• Shifting Upper-Air Systems
  • A cyclonic system moved from southeast Rajasthan to northeast Rajasthan and northwest Madhya Pradesh, altering wind patterns and contributing to strong vertical air movement.
• Active Monsoon Trough
  • The presence of a monsoon trough from west Madhya Pradesh to north Kerala helped channel moist air from the southern peninsula into the northern plains, feeding the storm system.
• Strong Surface Winds Over Delhi
  • Delhi experienced strong westerly surface winds (20–25 kmph, gusting up to 54 kmph) that enhanced the vertical lift by interacting with incoming moist air, promoting convection.
• Powerful Convective Activity and Himalayan Influence
  • Intense upward motion of heat and moisture (convection) led to the formation of towering cumulonimbus clouds (up to 13 km high), indicated by satellite visuals of overshooting tops.
    • Cumulonimbus clouds are large, towering clouds associated with thunderstorms and heavy rainfall.
    • They form due to intense upward motion of warm, moist air and can reach heights over 13 km, often producing lightning, strong winds, and hail.
  • Cool winds descending from the Himalayas since midnight also contributed to thunderstorm formation.