DESERT ECOSYSTEM: The Thar Desert (Marusthali) covers approximately 61% of Rajasthan's area and is the world's most densely populated desert. Unlike the Sahara or Arabian deserts which are largely uninhabited, the Thar supports millions of people, livestock, and a unique ecosystem adapted to extreme aridity. Average rainfall: less than 25 cm. Temperature extremes: summer maxima exceed 50°C (Phalodi recorded 51°C on 19 May 2016 — India's highest ever), winter minima can reach -3°C in Churu/Ganganagar. Sand dunes (dhora) cover much of the landscape: BARCHANS (crescent-shaped, moving dunes), LONGITUDINAL DUNES (parallel to wind direction), TRANSVERSE DUNES (perpendicular to wind). The 25 cm isohyet line roughly marks the desert boundary.

DESERTIFICATION — CAUSES AND CONSEQUENCES: Desertification is the process by which fertile land becomes increasingly arid and unproductive. In Rajasthan, this is both a natural phenomenon (expanding Thar) and human-accelerated (overgrazing, deforestation, over-extraction of groundwater, mining). CAUSES: (a) Overgrazing by livestock (Rajasthan has India's highest livestock population), (b) Deforestation for fuel and agriculture, (c) Over-irrigation leading to waterlogging and salinization (paradoxically, IGNP areas face this), (d) Climate change reducing rainfall further, (e) Mining activities destroying vegetation cover, (f) Invasion of Prosopis Juliflora displacing native species. CONSEQUENCES: Loss of topsoil through wind erosion, declining agricultural productivity, groundwater depletion (water table falling 1-3 metres per year in many districts), migration of rural populations, loss of biodiversity. Rajasthan loses approximately 200,000 hectares to desertification annually.

FOREST COVER AND CONSERVATION: Rajasthan's forest cover is approximately 16,572 sq km (4.84% of state area — among India's lowest, national average ~24%). Udaipur has the highest forest area, followed by Chittorgarh, Alwar, and Baran. Forest types: (a) TROPICAL THORN FOREST — largest area, found in western Rajasthan. Xerophytic vegetation: Khejri, Babool, Ker, Phog, Cactus. (b) DRY DECIDUOUS FOREST — Aravalli region. Teak (Sagwan), Bamboo, Dhak, Tendu. Banswara forest division has the maximum teak area. (c) SUBTROPICAL HILL FOREST — Mount Abu only. Evergreen trees, orchids, ferns. (d) MIXED DECIDUOUS — Hadoti region (Kota-Bundi-Baran). Good rainfall supports dense vegetation. PROTECTED AREAS: 3 National Parks, 27+ Wildlife Sanctuaries, 4 Tiger Reserves, 20 Conservation Reserves. Key legislation: Wildlife Protection Act 1972, Forest Conservation Act 1980, Biodiversity Act 2002, Rajasthan Forestry and Biodiversity Project.

WATER RESOURCES AND CRISIS: Rajasthan possesses only 1.16% of India's surface water and 1.72% of groundwater. Per capita water availability is approximately 780 cubic metres (below the 'water stress' threshold of 1,700 cubic metres). GROUNDWATER DEPLETION: The most critical environmental challenge. Over-extraction through tubewells (over 1 million in the state) has caused water tables to fall dramatically — some areas of Jodhpur, Jaipur, and Nagaur have seen drops of 40-60 metres over 30 years. The Dark Zone declaration by the Central Ground Water Board covers large areas of eastern Rajasthan. FLUORIDE AND ARSENIC contamination of groundwater is widespread — the 'Hump Belt' (Kubad Patti) between Nagaur and Ajmer has high fluoride levels causing skeletal/dental fluorosis. SOLUTIONS: IGNP and ERCP for surface water transfer, rooftop rainwater harvesting (mandatory in some urban areas), community-based watershed management (Rajendra Singh's johad model), revival of traditional water systems (tankas, kunds, baoris), artificial recharge through percolation tanks.

CLIMATE AND CLIMATE CHANGE IMPACT: Rajasthan's climate is becoming MORE EXTREME due to global climate change. Observed trends: (a) Increasing temperatures — heat wave frequency and intensity rising, (b) Erratic rainfall — total rainfall declining in some areas while flash floods increase in others, (c) Glacial melt in Himalayas threatens long-term water supply through rivers like Chambal (fed by snow-melt tributaries). (d) Shifting monsoon patterns — western Rajasthan receiving slightly more rain in some years, eastern getting less. RENEWABLE ENERGY response: Rajasthan has become a SOLAR ENERGY POWERHOUSE — Bhadla Solar Park (Jodhpur, 2,245 MW) is the world's LARGEST solar park. Jaisalmer district leads in wind energy. The state aims for 30+ GW renewable energy capacity. This transforms Rajasthan's liability (extreme sun exposure) into an asset. Solar agriculture livelihood scheme (SAGY) helps farmers earn from solar panels on their fields.

BIODIVERSITY AND THREATS: Despite aridity, Rajasthan hosts unique biodiversity adapted to desert conditions. THREATENED SPECIES: Great Indian Bustard/Godavan (critically endangered — primary threat: collision with high-tension power lines, Supreme Court has ordered underground cabling in GIB habitat), Indian Vulture (critically endangered due to Diclofenac drug), Desert Fox, Spiny-tailed Lizard (Sanda — hunted for supposed medicinal properties), Indian Wolf (one of the rarest canids). CONSERVATION SUCCESS: Crocodile breeding at Jawai Dam area, Gharial conservation in National Chambal Sanctuary, Tiger population recovery in Ranthambore. BISHNOI COMMUNITY: The world's FIRST organized environmental movement. Jambhoji (1451-1536) established 29 principles including non-killing of animals and non-cutting of green trees. The Amrita Devi sacrifice (1730, Khejarli) for Khejri trees predates the Chipko Movement by 243 years. Bishnoi villagers continue to actively protect Blackbuck and Chinkara — the famous Salman Khan blackbuck poaching case (2018 conviction) was filed by Bishnoi community members.

REET EXAM TIPS (5-7 questions): (1) Desertification definition: fertile land → arid/infertile (Q.125 PQR — desert soil is LOW in fertility, NOT high — trap). (2) Forest cover: ~4.84%, Udaipur=highest. (3) Solar: Bhadla=Jodhpur=world's largest solar park. (4) Water: 1.16% of India's surface water. (5) Invasive: Prosopis Juliflora (NOT native). (6) Bishnoi: 29 principles, Amrita Devi 1730 Khejarli, Jambhoji founder. TRAPS: 'Desert soil has high humus' — FALSE. 'Rajasthan has 10% forest cover' — FALSE (~4.84%). 'Bhadla is in Jaisalmer' — FALSE (Jodhpur). Match: NP↔district, sanctuary↔species, dam↔district.