Climatic Classification

Climatic classification = Grouping of world regions based on temperature, rainfall, evapotranspiration (ET), and vegetation. It helps in understanding crop distribution, land use, and agro-ecological planning.

1. Köppen’s Climatic Classification (1884, revised 1918 & 1936)

Most widely used system – based on temperature & rainfall and their seasonal distribution.

• Major Groups (with codes):
  1. A – Tropical climates (Rainfall > 1500 mm; all months >18°C) → e.g., Kerala, Assam.
  2. B – Dry climates (Rainfall < Potential Evapotranspiration) → Rajasthan, Gujarat.
  3. C – Warm temperate (mesothermal) → Eastern India, parts of TN.
  4. D – Cold temperate (microthermal) → Not in India (found in Europe, N. America).
  5. E – Polar climates → Not in India.

2. Thornthwaite’s Climatic Classification (1931, revised 1948)

Based on moisture index (MI = (P – PE)/PE ×100) where P = precipitation, PE = potential evapotranspiration.

• Moisture Index Zones:

• 100 = Per-humid

• • 20 to 100 = Humid
  • 0 to 20 = Moist sub-humid
  • –33.3 to 0 = Dry sub-humid
  • –66.7 to –33.3 = Semi-arid
  • –100 to –66.7 = Arid

Relevance to India: Helps classify areas into humid, sub-humid, semi-arid, and arid zones, which directly link to crop planning.

3. Indian Meteorological Department (IMD) Classification

Based on annual rainfall & monsoon.

• Arid Zone: <500 mm (Rajasthan, Gujarat).
• Semi-arid Zone: 500–750 mm (Deccan Plateau, rain shadow regions).
• Sub-humid Zone: 750–1150 mm (Central & Eastern India).
• Humid Zone: >1150 mm (NE India, Western Ghats).

4. Agro-Climatic Zoning by Planning Commission (1989)

• India divided into 15 Agro-Climatic Zones based on soils, rainfall, cropping patterns, and irrigation availability.
• Example: Western Himalayas, Eastern Plateau, Deccan Plateau, etc.

5. Agro-Ecological Zones (NBSS&LUP, 1992)

• Based on length of growing period (LGP), soils & climate.
• India divided into 20 Agro-Ecological Regions (AERs) and 60 sub-regions.

Quick Exam Notes

• Köppen → Temp + Rainfall.
• Thornthwaite → Moisture Index (P/PE).
• IMD → Rainfall-based (arid, semi-arid, sub-humid, humid).
• Planning Commission (1989) → 15 Agro-climatic zones.
• NBSS&LUP (1992) → 20 Agro-ecological regions.

Delineation of Dryland Tracts

1. Basis of Delineation

Dryland tracts in India have been delineated by considering:

• Rainfall amount & distribution
• Length of Growing Period (LGP)
• Moisture Availability Index (MAI)
• Aridity Index (AI)
• Soil type & water-holding capacity
• Temperature regime

2. Major Dryland Tracts in India

India has nearly 72% of cultivated area under dryland farming. The drylands are distributed across arid, semi-arid, and dry sub-humid regions.

(A) Arid Zone (Rainfall < 500 mm; LGP < 90 days)

• Area: ~12% of geographical area
• States: Rajasthan (Thar Desert), Gujarat, parts of Haryana & Punjab
• Features: Sand dunes, saline/alkaline soils, high evapotranspiration
• Crops: Pearl millet, moth bean, cluster bean

(B) Semi-Arid Zone (Rainfall 500–1000 mm; LGP 90–150 days)

• Largest dryland tract (~37% of geographical area)
• States: Deccan Plateau (Maharashtra, Karnataka, Andhra Pradesh, Telangana, Tamil Nadu), Madhya Pradesh, Bundelkhand (UP/MP), Chhattisgarh (parts), Odisha (western parts)
• Features: Vertisols, Alfisols, red sandy loams, recurrent droughts
• Crops: Sorghum, pigeon pea, groundnut, sunflower, soybean, pulses

(C) Dry Sub-Humid Zone (Rainfall 1000–1200 mm; LGP 150–180 days)

• Area: ~15% of geographical area
• States: Eastern Uttar Pradesh, Bihar, West Bengal (western part), Assam (some tracts), Odisha (eastern)
• Features: Higher rainfall but still uncertain distribution, erosion-prone soils
• Crops: Rice, maize, pulses, oilseeds

3. Agro-Ecological Regions & Drylands

NBSS & LUP (ICAR) divided India into 20 agro-ecological zones, out of which 12 zones have significant dryland tracts.

• Examples:
  • Western Dry Region (hot arid) – Rajasthan
  • Central Plateau & Hills – Bundelkhand, Malwa, Satpura
  • Deccan Plateau – Telangana, Karnataka, Maharashtra

Extent of Drylands in India

• Total cultivated area: ~142 million ha
• Rainfed (dryland) area: ~98 million ha (≈ 72%)
• Contribution:
  • 44% of total food grains
  • 75% of pulses
  • 66% of oilseeds
  • 90% of coarse cereals
  • 85% of sorghum & millets

Quick Facts for Exams

• About 2/3rd of India’s population depends on dryland agriculture.
• Semi-arid tropics (SAT) of India are the largest dryland tract in Asia.
• Rajasthan + Deccan Plateau together account for majority of India’s drylands.