Climatic Regions

Empirical and genetic approaches to classifying macro and micro climates based on thermal and hydrological thresholds.

• Classification systems use quantitative thresholds of temperature and precipitation rather than qualitative descriptions.
• Macro-climatic divisions reflect the dual control of tropical latitudinal location and subtropical high-pressure continental influences.
• Topographic barriers such as the Western Ghats and the Himalayan arc create abrupt transition zones and rain-shadow pockets.
• Seasonality of rainfall distribution is heavily weighted over absolute annual totals in defining regional types.

• Köppen's classification relies heavily on native vegetation as an integrated climatic index.
• Thornthwaite's schemes incorporate water balance models via Potential Evapotranspiration (PET).

Detailed application of Köppen's letter codes (Am, As, Aw, BSh, BWh, Cwg, Dfc) to Indian sub-regions.

• Am (Tropical Monsoon with short dry season): Malabar Coast, Goa, southern Konkan, and parts of northeast India.
• As (Tropical Wet and Dry with winter dry season): Coromandel Coast of Tamil Nadu, receiving winter rainfall from retreating monsoons.
• Aw (Tropical Savanna): Most of the Peninsular plateau region, excluding the rain-shadow zone and the extreme south.
• BShw (Semi-arid Steppe climate): Interior rain-shadow belt of the Western Ghats, parts of Punjab, Haryana, and western Rajasthan margins.
• BWhw (Hot Desert climate): Extreme western Rajasthan, characterized by high aridity and high diurnal temperature ranges.
• Cwg (Monsoon type with dry winter): Gangetic plain, eastern Rajasthan, northern Madhya Pradesh, and most of North India.
• Dfc (Cold humid winter with short summer): Arunachal Pradesh and high-altitude Himalayan transitional zones.

• The Coromandel coast (As) is a unique exception in India experiencing winter rainfall.
• Cwg is the most extensive climatic type covering the Northern Plains.

Classification based on Precipitation (P) and Potential Evapotranspiration (PET) to determine moisture adequacy.

• Emphasizes the water balance approach, evaluating surplus and deficit water conditions over a annual cycle.
• Identifies distinct moisture regions ranging from Perhumid (A) in Western Ghats and Northeast to Arid (E) in Western Rajasthan.
• Moisture Index (Im) determines the aridity and humidity provinces across the Indian subcontinent.
• Directly correlates with agricultural productivity limits and irrigation water requirements.

• Thornthwaite integrates thermal efficiency with moisture indices.
• Widely applied in modern drought-monitoring and agricultural geography in UGC-NET questions.

Integration of thermal regimes, rainfall seasonality, and vegetation associations across regional belts.

• Tropical Wet zones sustain evergreen and semi-evergreen rainforest ecosystems with high biodiversity.
• Tropical Semi-Arid zones exhibit thorn scrub forests and specialized drought-resistant cropping patterns like millets.
• Subtropical Humid Continental zones (Cwg) feature distinct seasonal rhythms: scorching summers, wet monsoons, and cool winters.
• Montane Alpine zones show rapid vertical zonation of climate and vegetation within short horizontal distances.

• Physiography plays a commanding role in modifying regional temperature and precipitation gradients.
• Monsoonal unpredictability introduces high inter-annual variability in sub-humid and semi-arid zones.