India needs region-specific plans to improve climate resilience
The 150th anniversary of the India Meteorological Department (IMD) is commemorated, having been initially conceived during the colonial era to comprehend the influence of the southwest monsoon on agricultural yields.
GS-01 (Physical Geography)
- A Council on Energy, Environment and Water (CEEW) analysis of IMD data reveals that 55% of India’s tehsils have experienced increasing monsoon rainfall, while 11% witnessed a decrease, primarily affecting the Indo-Gangetic plains, northeastern India, and the Indian Himalayan region.
- Approximately 30% of India’s districts faced multiple years of deficient rainfall, and 38% encountered excessive rainfall, indicating varied precipitation patterns across the country.
- Regions historically dry, such as some tehsils in Rajasthan, Gujarat, central Maharashtra, and parts of Tamil Nadu, are experiencing increased rainfall.
- Changes in the northeast monsoon, impacting peninsular India, show an over 10% increase in rainfall in the past decade in Tamil Nadu, Telangana, and Andhra Pradesh, emphasizing the need for region-specific climate resilience plans.
India’s Monsoon Climate:
- India experiences a monsoon climate, primarily in the southern and southeastern regions.
- The country is divided into four seasonal divisions, with monsoons occupying two crucial segments.
Monsoon Seasons in India:
- Southwest Monsoon Season: A seasonal rainfall occurrence transpiring between June and September, driven by southwest monsoons.
- Retreating Monsoon Season: Marked by retreating monsoons, prevailing in October and November.
Factors Influencing Southwest Monsoon Formation:
- Differential heating and cooling of land and water create low pressure on the Indian landmass.
- Shifting position of the Inter Tropical Convergence Zone (ITCZ) during the summer over the Ganga plain.
- Presence of a high-pressure area east of Madagascar in the Indian Ocean.
- Intense heating of the Tibetan plateau, causing low pressure at high altitudes.
- Movement of the westerly jet stream north of the Himalayas and the presence of the tropical easterly jet stream over the Indian peninsula during summer.
- Southern Oscillation (SO) affecting pressure conditions in the Pacific Ocean.
- El Nino Phenomenon: El Nino refers to the periodic warming of ocean currents along the coast of Peru, impacting global weather patterns. It leads to increased sea-surface temperatures and weakened trade winds.
Onset Mechanism of Southwest Monsoon:
- ITCZ’s northward shift in June due to the sun’s vertical position over the Tropic of Cancer.
- Southeast trade winds from the southern hemisphere cross the equator and blow in a southwest-northeast direction.
- Collection of moisture from the warm Indian Ocean.
- ITCZ’s shift to 20°-25° N latitude in July, known as the Monsoon Trough.
- The easterly jet stream’s onset at 15°N latitude responsible for the monsoon burst in India.
- Two branches of the monsoon: Arabian Sea branch and Bay of Bengal branch.
Retreating Southwest Monsoon:
- Marked by clear skies and rising temperatures.
- Moist land leads to oppressive conditions known as the ‘October heat.’
- Subsequent temperature drop in northern India by late October.
- Dry weather in northern India but rainy conditions in the eastern Peninsula, especially during October and November.
- Rain associated with cyclonic depressions originating in the Andaman Sea, crossing the eastern coast and causing destructive tropical cyclones.
- The retreating monsoon is vital for farming and water security in the southern region.