Physical Geography of Rajasthan: Physiography, Drainage, Climate & Soils — RPSC RAS Paper II, Unit III
Weightage: The Rajasthan part of Paper II Unit III (Earth Science) and the Rajasthan geography section of the Prelims. World and Indian geography are covered by the aliased chapters; this chapter carries the state's physical setting, and the next carries its resources and wildlife.
1. The four physiographic regions
Rajasthan is the largest state by area, about 3.42 lakh square kilometres, and the Aravalli range divides it diagonally. The usual four-fold division is:
| Region | Where | Features |
|---|---|---|
| Western sandy plain (Thar) | West of the Aravalli: Jaisalmer, Bikaner, Barmer, Jodhpur | Arid desert with dunes; about three-fifths of the state |
| Aravalli hills | Diagonal belt from Mount Abu to the north-east | Ancient fold mountains, the state's watershed |
| Eastern plains | East of the Aravalli: Jaipur, Bharatpur, Alwar | Fertile alluvium; densely populated |
| South-eastern plateau (Hadoti) | Kota, Bundi, Baran, Jhalawar | Deccan lava, black soil, part of the Malwa plateau |
The Thar has a drier core (the Marusthali) and a semi-arid eastern fringe called the Bagar. Its landforms include barchan dunes and salt-lake basins called playas (dhands).
2. The Aravalli range
The Aravalli is among the oldest fold mountains in the world and now much worn down. The highest peak is Guru Shikhar on Mount Abu (about 1,722 m). Other named hills include Jarga and Raghunathgarh. The range checks the desert's eastward spread, and its gaps and low breaks let dust and sand move east, which is why Aravalli protection is a live environmental issue.
3. Drainage
Rajasthan has three drainage groups, and one is inland.
- Bay of Bengal system: the Chambal and its tributaries (Kali Sindh, Parbati, Banas), which reach the Yamuna.
- Arabian Sea system: the Luni, Mahi and Sabarmati. The Luni rises near Ajmer and ends in the Rann of Kutch, and is saline in its lower course. The Mahi drains the south.
- Inland drainage: streams like the Kantli and the Ghaggar, which vanish into sand or end in playas.
Lakes are a common exam pairing. Sambhar is India's largest inland saline lake and a Ramsar site. Didwana, Pachpadra and Lunkaransar are other salt lakes. Freshwater lakes are mostly artificial: Jaisamand (also called Dhebar) is among the largest artificial freshwater lakes in Asia, and Pichola, Fateh Sagar, Rajsamand and Ana Sagar are well-known city lakes. Pushkar lake is a sacred natural lake.
4. Climate and rainfall
Rajasthan is a semi-arid to arid land with extremes of temperature. In the Köppen scheme, its climates are:
- BWhw: hot desert, in the far west.
- BShw: hot semi-arid steppe, in the central and eastern belt.
- Aw: tropical savanna, in the south-east.
- Cwg: humid subtropical, at Mount Abu.
Rainfall comes mainly from the south-west monsoon, and it falls from the south-east to the north-west. The Aravalli lies parallel to the Arabian Sea branch, so it gives little rain to the west. Mount Abu receives the highest rainfall, while Jaisalmer is among the driest places. Summer heat, hot dry winds called loo and dust storms are typical, and winters bring cold from western disturbances.
5. Soils
| Soil | Region | Notes |
|---|---|---|
| Desert (sandy) soil | West | Low in organic matter; suits bajra and moth |
| Alluvial | East | The most fertile; wheat, mustard |
| Black soil | Hadoti | Moisture-retentive; cotton, soybean |
| Red and yellow soil | South, south-east hills | Maize, pulses |
| Saline-alkaline | Luni basin, salt lakes | Poor for crops without reclamation |
Desertification is a major concern, from wind erosion, overgrazing and salinity, and responses include shelterbelts, the Indira Gandhi Canal, the Desert Development Programme and research at CAZRI, Jodhpur.
6. Traditional water harvesting
Rajasthan's people built systems long before canals: tankas or kunds (underground tanks), johads (earthen check dams), baoris and jhalaras (stepwells), nadis (village ponds) and the khadin system of Jaisalmer, in which a bund captures runoff for a crop. Alwar's revival of johads by voluntary groups became a well-known model of community water management.
Worked example 6.1 (a 10-mark answer, ~150 words). "Describe the physiographic regions of Rajasthan."
Model answer. Rajasthan has four physiographic regions, divided diagonally by the Aravalli range.
The Western sandy plain, or Thar, lies west of the Aravalli and covers about three-fifths of the state, with dunes and salt-lake playas; its drier core is the Marusthali and its semi-arid fringe the Bagar. The Aravalli hills, ancient worn fold mountains rising to Guru Shikhar (about 1,722 m) at Mount Abu, form the watershed. East of the range, the Eastern plains are fertile alluvium supporting dense population and agriculture. In the south-east, the Hadoti plateau of Kota, Bundi, Baran and Jhalawar has Deccan lava and black soil.
The regions differ sharply in rainfall, soil and land use, which explains the contrast between the arid west and the fertile east.
Common traps RPSC sets here
- Placing the Luni in the Bay of Bengal system. It flows to the Rann of Kutch and belongs to the Arabian Sea group.
- Confusing Sambhar with a freshwater lake. It is India's largest inland saline lake.
- Giving Mount Abu's Guru Shikhar as the range's length. It is the highest peak, not a measure of the range.
- Treating Bagar as the desert core. Bagar is the semi-arid eastern fringe.
Memory aids
- "West is Thar, then Aravalli, then plains, then Hadoti": the four regions from west to south-east.
- "Luni is the salty river": the Arabian Sea system's key river.
- "BW, BS, Aw, Cw": the four Köppen types in order from the far west.
Summary
Rajasthan's four regions are the western Thar, the Aravalli hills, the eastern plains and the south-eastern Hadoti plateau. Rivers fall into the Bay of Bengal (Chambal), Arabian Sea (Luni, Mahi, Sabarmati) and inland systems, with Sambhar the great saline lake.
Climate ranges from hot desert to a humid subtropical pocket at Mount Abu, soils track the regions, and traditional water harvesting (tanka, johad, khadin) answers the arid setting.
Exam protocol
- Give physiography answers region by region, west to east.
- Group rivers by drainage system in the first line.
- Pair every lake and soil with its location.
