Rajasthan IMD Climate Classification GK
PART - 10: India Meteorological Department (IMD) & General Climate Classification
Detailed Index
| Section | Topic | Exam Importance |
|---|---|---|
| 10.1 | Basis & Conceptual Framework | ★★★★ |
| 10.2 | Comparative Master Table | ★★★★★ |
| 10.3 | Arid Climatic Zone | ★★★★★ |
| 10.4 | Semi-Arid Climatic Zone | ★★★★★ |
| 10.5 | Sub-Humid Climatic Zone | ★★★★ |
| 10.6 | Humid Climatic Zone | ★★★★ |
| 10.7 | Very Humid Climatic Zone | ★★★★★ |
| 10.8 | IMD Standards & Criteria | ★★★★★ |
| 10.9 | Key Exam Pointers | ★★★★★ |
| 10.10 | Comparative Study | ★★★ |
📖 10.1 Basis & Conceptual Framework
According to the standard geographical classification of the India Meteorological Department (IMD) and the Rajasthan Granth Academy, the climate of the state has been divided based on the combined analysis of three major climatic variables rather than any single factor:
- Mean Annual Rainfall
- Temperature Profile & Ranges
- Relative Humidity
On this three-dimensional basis, Rajasthan has been classified into 5 Distinct Climatic Zones. This division clearly demonstrates the climatic gradient from the west (arid desert) to the south-east (very humid plateau).
📖 10.2 Comparative Master Table of Five Climatic Zones
| S.No. | Climatic Zone | Mean Annual Rainfall | Summer Temp. | Winter Temp. | Representative Districts | Vegetation |
|---|---|---|---|---|---|---|
| 1. | Arid Zone | 0-20 cm | 34°C-40°C+ | 12°C-16°C | Jaisalmer, Bikaner, Barmer (W), Phalodi | Xerophytes |
| 2. | Semi-Arid Zone | 20-40 cm | 32°C-36°C | 10°C-17°C | Sikar, Jhunjhunu, Churu, Nagaur, Jalore, Pali | Steppe, Thorny Bushes |
| 3. | Sub-Humid Zone | 40-60 cm | 28°C-34°C | 12°C-18°C | Jaipur, Ajmer, Alwar, Dausa, Bhilwara | Deciduous |
| 4. | Humid Zone | 60-80 cm | 30°C-34°C | 14°C-18°C | Bharatpur, Dholpur, Karauli, Sawai Madhopur, Tonk | Dense Monsoon Forests |
| 5. | Very Humid Zone | 80-150 cm+ | 28°C-32°C | 14°C-18°C | Kota, Baran, Jhalawar, Banswara, Mount Abu | Monsoon Deciduous |
📖 10.3 Zone 1: Arid Climatic Zone
This is the extreme western border region of Rajasthan, representing the main part of the Great Thar Desert (Marusthali):
📍 Geographical Extent
Jaisalmer, Phalodi, western part of Bikaner, north-western region of Barmer, and the western edge of rural Jodhpur.🌧️ Rainfall Pattern
| Aspect | Description | |--------|-------------| | **Amount** | 0-20 cm (0-5 cm in Sam village) | | **Rainy Days** | Average only 5-8 days | | **Variability** | More than 50% (highest uncertainty in the state) |🌡️ Temperature Conditions
- Extremely severe heat in summer; afternoon temperature often 45°C to 49°C - In winter, due to intense terrestrial radiation, night temperature drops to 0°C to 3°C - **Daily Temperature Range:** 20°C to 25°C (highest in the state)💧 Relative Humidity
Low, ranging from 10% to 25% in summer.🌱 Soil & Vegetation
- **Soil:** Sandy desert soil (Entisols) - **Vegetation:** Xerophytes — small leaves, modified into thorns, thick bark, and deep roots - **Main Species:** Phog (Calligonum polygonoides), Kair (Capparis decidua), Aakda, Thuhar, Sewan grass (Lasiurus scindicus)📖 10.4 Zone 2: Semi-Arid Climatic Zone
This zone is situated as a 'Transitional Belt' (Rajasthan Bangar) between the arid desert and the Aravalli mountain range:
📍 Geographical Extent
Shekhawati region (Sikar, Jhunjhunu, Churu), Nagaur, Didwana-Kuchaman, Pali, Jalore, Sanchore, and eastern part of Jodhpur.🌧️ Rainfall Pattern
| Aspect | Description | |--------|-------------| | **Amount** | 20-40 cm (25 cm isohyet passes through western border) | | **Rainy Days** | Average 10-15 days |🌡️ Temperature Conditions
- Summer temperature 36°C to 42°C - **Highest annual temperature range in the state** in Churu district - Intense 'Cold Wave' in winter; temperature in Fatehpur (Sikar) often drops below freezing point🌱 Soil & Vegetation
- **Soil:** Sirozem (grey desert soil) and sandy loam (Aridisols) - **Vegetation:** Steppe type - **Main Species:** Khejri (Prosopis cineraria), Rohida (Tecomella undulata), Ber, Babool, Dhaman grass📖 10.5 Zone 3: Sub-Humid Climatic Zone
This zone is mainly spread over the mountainous and foothill slopes of the Aravalli range:
📍 Geographical Extent
Jaipur, Jaipur Rural, Dausa, Alwar, Ajmer, Beawar, Bhilwara, Rajsamand, and northern part of Sirohi.🌧️ Rainfall Pattern
| Aspect | Description | |--------|-------------| | **Amount** | 40-60 cm (50 cm isohyet passes through the middle) | | **Rainy Days** | Average 20-30 days |🌡️ Temperature Conditions
- Summer relatively less oppressive; average temperature 30°C to 36°C - Winter pleasant and temperate; average temperature 10°C to 15°C🌱 Soil & Vegetation
- **Soil:** Red-yellow soil, mountain soil (Inceptisols), and alluvial loam - **Vegetation:** Tropical dry deciduous/mixed deciduous forests - **Main Trees:** Dhokra (Anogeissus pendula), Salar, Khair, Neem, Shisham, Baheda📖 10.6 Zone 4: Humid Climatic Zone
This zone covers the fertile alluvial plain basin (Banas and Banganga basin) located east of the Aravalli:
📍 Geographical Extent
Bharatpur, Dholpur, Karauli, Sawai Madhopur, Tonk, northern part of Chittorgarh.🌧️ Rainfall Pattern
| Aspect | Description | |--------|-------------| | **Amount** | 60-80 cm (by 'Purvaiya' of Bay of Bengal) | | **Rainy Days** | Average 30-35 days |🌡️ Temperature Conditions
- Summer temperature 32°C to 38°C - Winter temperature 12°C to 16°C - Mawath and dense fog (Radiation Fog) in winter🌱 Soil & Vegetation
- **Soil:** Alluvial / Kamp / Loam soil (Alfisols) - **Vegetation:** Dense deciduous forests - **Main Trees:** Bad (Banyan), Peepal, Gular, Dhak/Palash ('Flame of the Forest'), Jamun, MahuaPer-Humid Climatic Zone
This is the zone receiving the highest rainfall, with maximum humidity and densest vegetation cover in Rajasthan:
📍 Geographical Extent
1. **Hadoti Plateau:** Jhalawar, Baran, southern part of Kota 2. **Southern Vagad Region:** Banswara, Dungarpur, Pratapgarh 3. **Special Mountain Segment:** Mount Abu area of Sirohi district🌧️ Rainfall Pattern
| Aspect | Description | |--------|-------------| | **Amount** | 80-100 cm+ (up to 150 cm in Mount Abu) | | **Rainy Days** | Average 35-45 days (Jhalawar 40, Mount Abu 48) |🌡️ Temperature Conditions
- Summer temperature 30°C to 35°C; humidity causes sultriness - Winter extremely pleasant and temperate (14°C to 18°C) - In Mount Abu, temperature drops below zero due to altitude🌱 Soil & Vegetation
- **Soil:** Medium black soil (Vertisols) and Red Loam in southern part - **Vegetation:** - Savanna-like dense forests and **Tropical Dry Teak Forests** (Banswara, Dungarpur) - **Main Species:** Teak (Tectona grandis), Bamboo (Dendrocalamus), Mahua, Tendu, Mango - **Sub-tropical Evergreen Vegetation** in Mount Abu📖 10.8 IMD Standards & Criteria
Major technical standards used by the India Meteorological Department (IMD) in the context of Rajasthan:
| Standard Phenomenon | Scientific Scale Determined by IMD |
|---|---|
| Rainy Day | A day on which at least 2.5 mm or more rainfall is recorded |
| Heat Wave | When maximum temperature of a plains station is ≥ 40°C and is 4.5°C to 6.4°C above normal (Severe: >6.4°C above normal) |
| Cold Wave | When minimum temperature in plains is ≤ 10°C and is 4.5°C to 6.4°C below normal |
| Normal Drought | Seasonal rainfall 26% to 50% below normal |
| Severe Drought | Rainfall deficit more than 50% below normal |
📖 10.9 Key Exam Pointers
- Basis of Classification: The main basis of IMD/general classification is rainfall amount, temperature, and relative humidity (whereas Koppen's basis is mainly vegetation).
- Dividing Isohyets:
- 20-25 cm line: Separates Arid and Semi-Arid zones
- 40 cm line: Separates Semi-Arid from Sub-Humid
- 60 cm line: Separates Sub-Humid from Humid
- 80 cm line: Separates Humid from Very Humid
- Largest Zone by Area: Arid and Semi-Arid zones (Western Rajasthan) — about 61% of total area
- Teak Forests Region: Very Humid Climatic Zone (Banswara, Dungarpur, Jhalawar)
- Palash (Flame of the Forest): Found in Humid and Sub-Humid zones (Rajsamand, Chittorgarh, Sawai Madhopur)
📖 10.10 Comparative Study
Quick Comparison of Five Zones
| Aspect | Arid | Semi-Arid | Sub-Humid | Humid | Very Humid |
|---|---|---|---|---|---|
| Rainfall | 0-20 cm | 20-40 cm | 40-60 cm | 60-80 cm | 80-150+ cm |
| Rainy Days | 5-8 | 10-15 | 20-30 | 30-35 | 35-45 |
| Summer Temp | 34-40°C+ | 32-36°C | 28-34°C | 30-34°C | 28-32°C |
| Winter Temp | 12-16°C | 10-17°C | 12-18°C | 14-18°C | 14-18°C |
| Main Districts | Jaisalmer, Bikaner | Sikar, Churu | Jaipur, Ajmer | Bharatpur, Tonk | Kota, Banswara |
| Vegetation | Xerophytes | Steppe | Deciduous | Dense deciduous | Teak/Evergreen |
IMD vs Koppen Classification
| Aspect | IMD Classification | Koppen Classification |
|---|---|---|
| Basis | Rainfall, temperature, humidity | Vegetation, temperature, rainfall |
| Zones | 5 | BWh, BSh, Cwa |
| Main Use | Rajasthan government | Global |
| Extent | State level | Global |
Exam Revision
Rainfall + temperature + humidity -> 5 climatic zones -> 20/40/60/80 cm isohyets -> arid to very humid sequence -> IMD criteria -> heat wave, cold wave and drought
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