Climatic regions

Introduction

The climate of any region is a reflection of the long-term patterns of temperature and precipitation that prevail over decades, years, seasons, months, or even specific dates. In the case of India, this vast country experiences a diverse range of climatic conditions due to its geographical expanse and varied topography. This diversity ranges from tropical climates in the southern parts to temperate and alpine climates in the Himalayan regions of the north. In this article, we will delve into the climatic regions of India, how they are classified, and how the Köppen Classification System helps in understanding these variations.

Climate

• Climate is determined by the long-term pattern of:
  • Temperature
  • Precipitation
• It can be described for different time intervals, such as:
  • Decades
  • Years
  • Seasons
  • Months
  • Specific dates of the year
• Climate descriptions can refer to areas that are:
  • Local
  • Regional
  • Global

Climate of India

Characteristics

• India comprises a wide range of weather conditions across a vast geographic scale and varied topography.
• India experiences diverse climatic conditions ranging from:
  • Tropical in the south
  • Temperate and alpine in the Himalayan north

India’s Climate

• India is a large tropical country famous for its diverse climatic features.
• The climate can be broadly described as:
  • Tropical monsoon type, with significant regional variations in terms of rainfall and temperature.
  • These regional variations represent sub-types of monsoon climates.

Influencing Factors

• The Himalayas and the Thar Desert strongly influence India’s climate.
• The elevated areas receive sustained snowfall during winters.
• The Himalayas act as a barrier to the frigid katabatic winds blowing down from Central Asia, protecting the plains from extreme cold.
• The Tropic of Cancer passes through the middle of the country, making the climate more tropical.

Classification Criteria

• While classifying the climatic regions of India, most geographers give more importance to rainfall than to temperature.
• This is because variations in rainfall are much more pronounced than those of temperature across India.

What Are Climatic Regions?

• A climatic region refers to a continuous geographic area where similar climate characteristics are observed.
• These characteristics result from a combination of factors, and the geographic area covered may be:
  • Local
  • Regional
  • Global

Classification of Climatic Regions of India

Koeppen’s Classification of Climatic Regions of India

Overview

• One of the most acceptable classifications of world climate is Köppen’s Classification.
• It is suitable for classifying Indian climates due to its empirical nature.

Basis of the Classification

• The classification is based on:
  • Mean annual and monthly temperatures
  • Precipitation
  • Vegetation distribution

Factors Used

• Köppen identified a close relationship between the distribution of vegetation and climate.
• He used three major variables to classify the climatic zones:
  • Temperature
  • Rainfall
  • Vegetation
• Köppen selected certain values for temperature and precipitation and related them to the distribution of vegetation. These values were used for classifying the climates.

Steps in Classification

• According to Köppen, there are two steps to classify the Indian climate:
  • First Step: Identifying the major climatic groups
  • Second Step: Sub-dividing these groups into specific sub-types

Major Climatic Groups Recognized by Köppen

Köppen identified five major climatic groups:

1. Group A – Tropical Climate (Based on temperature)
2. Group C – Warm Temperate Climate (Based on temperature)
3. Group D – Snow Forest Climate (Based on temperature)
4. Group E – Polar Climate (Based on temperature)
5. Group B – Dry Climate (Based on precipitation)

Further Subdivisions

• These five major climatic groups can be further subdivided based on seasonal variations in rainfall and temperature patterns. This includes considering the degree of dryness or coldness.

Seasonal Dryness Indicators

• The seasons of dryness are indicated by small letters:
  • f: No dry season
  • m: Monsoon climate
  • w: Winter dry season
  • s: Summer dry season

Subdivisions of Specific Climates

• Dry Climate (B) is further divided into:
  • S: Semi-arid or Steppe
  • W: Arid or Desert
• Polar Climate (E) is further divided into:
  • T: Tundra
  • F: Ice cap

Application of Köppen’s Classification to India

• India exhibits almost all the types of climates classified by Köppen.
• As the Tropic of Cancer passes nearly through the middle of India:
  • Half of India has a tropical climate.
  • The other half has a subtropical climate.
• India also has:
  • Deserts in the western part
  • Rain shadow zones of the Western Ghats
  • Polar-type climate in the Himalayan region

Stamp’s Classification of Climatic Regions of India

Overview

• Stamp’s classification is very much akin to that suggested by W.G. Kendrew.
• It is considered empirical, arbitrary, and subjective, yet useful for understanding India’s climate.
• This classification uses quantitative limits expressed in easily understood units like:
  • Temperature
  • Rainfall

Major Criteria Used by Stamp

• Temperature
• Topography
• Rainfall

Key Features of Stamp’s Classification

• Stamp used the 18°C isotherm of mean monthly temperature for January to divide the country into two broad climatic regions:
  • Temperate or Continental Zone (in the north) – located north of the 18°C isotherm.
  • Tropical Zone (in the south) – located south of the 18°C isotherm.
• The 18°C isotherm line runs roughly across the root of the Indian peninsula, more or less parallel to the Tropic of Cancer.

The Two Major Climatic Regions and Their Subdivisions

The two primary climatic regions identified by Stamp are further divided into eleven smaller regions based on temperature and rainfall.

Temperate or Continental Zone

1. The Himalayan Region
   • West Himalayan Region: Low rainfall
   • East Himalayan Region: Very high rainfall (more than 200 cm)
2. The North-Western Region
   • Moderate rainfall (less than 200 cm)
   • Includes parts of Punjab, southern Jammu, and Kashmir.
3. The Arid Low Land
   • Rainfall: less than 40 cm
   • Includes the desert region of Rajasthan and the Kachchh region of Gujarat.
4. The Region of Moderate Rainfall
   • Rainfall: between 40 to 80 cm
   • Covers parts of Punjab, Haryana, Western Uttar Pradesh, and Madhya Pradesh.
5. The Transitional Zone
   • Rainfall: between 100 to 200 cm
   • Includes Eastern Uttar Pradesh and Bihar.

Tropical Zone

1. Region of Very Heavy Rainfall
   • Rainfall: more than 200 cm
   • Includes Meghalaya, Assam, Nagaland, Tripura, and Mizoram.
2. Region of Heavy Rainfall
   • Rainfall: 100 to 200 cm
   • Includes Jharkhand, Chhattisgarh, and Andhra Pradesh.
3. Region of Moderate Rainfall
   • Rainfall: 50 to 100 cm
   • Located between the Western and Eastern Ghats.
4. The Konkan Coast
   • Rainfall: more than 200 cm
   • Stretches from Mumbai to Goa.
5. The Malabar Coast
   • Rainfall: more than 250 cm
   • Extends from Goa to Kanyakumari.
6. Tamil Nadu
   • Rainfall: 100 to 200 cm
   • Receives rainfall in winter from the northeast monsoon.

Thornthwaite’s Classification of Climatic Regions of India

Overview

• Thornthwaite presented his climate classification in 1931 and made significant refinements in 1933 and 1948.
• His classification is known for its emphasis on precipitation effectiveness and temperature effectiveness.

Precipitation Effectiveness Index (P/E Index)

• The P/E index is calculated as the sum of the 12-month P/E ratio (total monthly precipitation divided by evapotranspiration).
• Based on this index, Thornthwaite classified humidity regions into five types:
• A (Wet/Rainforest)
  • P/E Index > 127
• B (Humid/Forest)
  • P/E Index between 64 to 127
• C (Sub-humid/Grassland)
  • P/E Index between 32 to 63
• D (Semi-Arid/Steppe)
  • P/E Index between 16 to 31
• E (Arid/Desert)
  • P/E Index less than 16

Temperature Effectiveness Index (T/E Index)

• The T/E index measures the temperature effectiveness and divides the climatic regions into:
• A’ (Tropical) – T/E Index > 128
• B’ (Subtropical) – T/E Index between 64 to 127
• C’ (Temperate) – T/E Index between 32 to 63
• D’ (Taiga) – T/E Index between 16 to 31
• E’ (Tundra) – T/E Index between 1 to 15
• F’ (Frost) – T/E Index = 0

Rainfall Variation Classification

• Thornthwaite also classified climatic regions based on rainfall variation:
  • r: Rainfall all year
  • s: Rainfall deficient in summer
  • w: Rainfall deficient in winter
  • d: Rainfall deficient throughout the year

Thornthwaite’s Simplification in 1948

• Thornthwaite introduced the potential evapotranspiration (PET) concept, which combines evaporation from the soil and transpiration from vegetation.
• Based on water balance, he identified the monthly values of water surplus and water deficit.

Thornthwaite’s Climatic Regions Identified in India

1. Per-Humid (A)
   • Includes: Western Ghats, Most parts of the North-Eastern States
2. Humid (B)
   • Includes regions adjacent to the Per-Humid region.
3. Moist Sub-Humid (C1)
   • Includes: Narrow belt adjoining the humid region of the Western Ghats, Eastern India (West Bengal and Odisha)
4. Dry Sub-Humid (C2)
   • Includes: Northern narrow belt of the Ganga basin, parts of Uttar Pradesh, Bihar, Madhya Pradesh, Chhattisgarh, Jharkhand, Western Maharashtra, and Southern Gujarat
5. Semi-Arid (D)
   • Includes parts of Punjab, Haryana, Eastern Rajasthan, Maharashtra, Karnataka, Telangana, and western parts of Tamil Nadu.
6. Arid (E)
   • Includes Western Rajasthan, Western Himalayan Region, and the rain shadow zone of the Western Ghats.

Trewartha’s Classification of Climatic Regions of India

Overview of Trewartha’s Classification

• Trewartha identified four major climatic groups, which are further subdivided based on temperature, rainfall, and seasonal variations.
• This classification offers more accuracy in understanding India’s climatic patterns in relation to vegetation, agriculture, and geography.

Major Climatic Groups Identified by Trewartha

Group A: Tropical Climate

Characteristics

• The tropical climate experiences temperatures that do not fall below 18°C throughout the year.
• This group is further divided into two distinct types:

1. Tropical Humid Climate (Am)

• Annual temperature: Around 27°C
• Annual rainfall: Over 250 cm
• Regions included:
  • Western coastal plains
  • Tripura

2. Tropical Wet and Dry Savanna (Aw)

• Annual rainfall: Approximately 100 cm
• Receives summer rainfall only
• Regions included:
  • Peninsular plateau
  • North Eastern Mizoram

Group B: Dry Climate

Characteristics

• In this climate, the rate of evaporation exceeds the moisture received from precipitation.
• This group is divided into three types:

1. Semi-Arid or Steppe Climate (BS)

• Suitable for:
  • Dry farming
  • Livestock rearing
• Temperature: Varies from 20°C to 23.8°C (December) and up to 32.8°C (May)
• Regions included:
  • The rain shadow zone of the Western Ghats
  • Extends southwards from Central Maharashtra to Tamil Nadu on the leeward side of:
    • The Western Ghats
    • Cardamom Hills

2. Tropical and Sub-Tropical Desert Climate (Bsh)

• Temperature: Ranges from 12°C (January) to 35°C (June), with maximum temperatures reaching up to 49°C
• Regions included:
  • Gujarat
  • Rajasthan
  • Haryana

3. Sub-Tropical Desert (Bwh)

• Mean monthly temperature: Uniformly high at around 34.5°C
• Regions included:
  • West Rajasthan
  • Kutch region

Group C: Humid Sub-Tropical Climate

Characteristics

• Also referred to as the Humid Mesothermal Climate.
• Regions included:
  • Northern plains including:
    • Punjab foothills
    • Uttar Pradesh
    • Bihar
    • West Bengal
    • Assam
    • Arunachal Pradesh

Sub-Type Caw: Sub-Tropical Humid (Dry Winters)

• Rainfall in summer with dry winters.
• Annual rainfall varies from 62.5 cm in the plains to 250 cm in the east.

Group H: Mountain Climate (Highlands)

Characteristics

• Characterized by low temperatures and heavy snowfall in winters.
• Regions included:
  • The Himalayan region, stretching from Jammu and Kashmir to Arunachal Pradesh.

Rainfall and Temperature

• Northern slopes receive low rainfall (8-10 cm annually) due to the rain-shadow effect.
• Southern slopes receive up to 250 cm of rainfall.
• Mean maximum temperatures range between 10°C and 15°C, while mean minimum temperatures drop below zero.

Subdivisions of Major Climatic Groups

Trewartha further subdivided the major climatic groups into seven climatic types using specific letters to indicate different climatic conditions:

Sub-Divisions Explained

• a: Indicates hot summers where the warmest month has temperatures over 22°C.
• h: Used when the mean annual temperature exceeds 18°C.
• m: Stands for heavy but seasonal monsoon rainfall, with a very short dry period.
• s: Indicates a steppe or semi-arid climate.
• w: Refers to a desert climate.

Conclusion

India’s climatic diversity is shaped by its vast geographical expanse, varied topography, and influences from factors like the Himalayas and the Tropic of Cancer. Different classification systems, such as Köppen’s, Stamp’s, Thornthwaite’s, and Trewartha’s, have provided comprehensive frameworks to understand this complexity. These classifications highlight India’s range of climatic regions, from tropical and arid to temperate and mountain climates, reflecting diverse patterns of temperature, precipitation, and vegetation. By considering factors like rainfall, temperature, vegetation, and evapotranspiration, these systems offer valuable insights into India’s unique and varied climatic conditions, essential for agricultural planning, environmental management, and regional development.

1. How does the Köppen Classification System categorize India’s diverse climate, and what factors contribute to the presence of almost all climatic types within the country? (250 words)
2. How do Stamp’s and Thornthwaite’s classifications differ in their approach to understanding India’s climatic regions, and what advantages does each system offer? (250 words)
3. Explain the significance of the different subdivisions (a, h, m, s, w) in Trewartha’s classification for understanding India’s climate diversity. (250 words)