Aravalli Hills Definition: Why Morphological Criteria Fail Ecology

Overview

Delineating the Aravalli Range purely by rigid morphological thresholds fails ecological conservation. A 100-metre elevation cutoff systematically excludes low-lying ridges, piedmont recharge zones, and vital wildlife corridors from statutory environmental protection.

The Aravallis are an ancient, heavily weathered mountain system. Their functional integrity depends on continuous hydrological networks and biodiversity connectivity rather than steep vertical relief.

Defining hills through isolated geometric criteria enables real estate encroachment and commercial mining in ecologically vulnerable foothills. This accelerates groundwater depletion across Delhi-NCR and permits the eastward march of the Thar Desert.

The Supreme Court of India stayed its earlier ruling on 29 December 2025 regarding a uniform definition of the Aravalli Hills. The Court had initially approved an administrative definition on 20 November 2025.

That earlier formula introduced two rigid geometric baselines:

• Elevation Threshold: Classifying landforms rising 100 metres or more above local relief as Aravalli Hills.
• Contiguity Distance: Grouping landforms within 500 metres into unified ranges.

Widespread concern from conservation scientists and civil society prompted judicial reconsideration. Legal experts highlighted that a strict 100-metre elevation benchmark threatened to exclude extensive low-lying hill systems across Haryana, Rajasthan, and Gujarat from legal protection.

The central thesis of the ongoing debate is clear. Protecting ecological integrity requires a landscape-level approach, whereas applying arbitrary geometric metrics opens critical terrain to irreversible degradation.

The Aravalli Range forms one of the planet's oldest fold mountain systems, dating to the Proterozoic Era nearly two billion years ago. The range spans over 690 kilometres, running south-west to north-east across Gujarat, Rajasthan, Haryana, and the National Capital Territory of Delhi.

Millions of years of natural weathering and tectonic stability have eroded these once massive peaks into low rolling hills, pediments, and rocky outcrops.

The range spans four distinct administrative territories along its 690-kilometre corridor:

• Gujarat: Forms the southern anchor of the mountain system.
• Rajasthan: Encompasses the central core and major intermontane wind gaps.
• Haryana: Encompasses extensive piedmont and groundwater recharge zones.
• Delhi (NCR): Represents the northern terminus via the Delhi Ridge.

The geological architecture of the range makes it an indispensable environmental barrier for northern India:

• Desertification Check: The range is a green wall against the eastward expansion of the Thar Desert, protecting fertile agricultural tracts across eastern Rajasthan, Haryana, western Uttar Pradesh, and the Indo-Gangetic plains.
• Regional Groundwater Bank: The fractured quartzite formations and secondary rock porosity allow precipitation to percolate deep underground, yielding an estimated aquifer recharge capacity of up to 2 million litres per hectare annually.
• Climate and Dust Regulation: The hills interrupt western dust storms and moderate regional climate patterns across the densely populated National Capital Region (NCR).

Administrative attempts to demarcate the Aravallis have historically relied on geometric cutoffs rather than continuous ecological mapping.

Current demarcation rules rest on three fragmented administrative mechanisms:

• FSI Morphological Criteria: In earlier assessments submitted to the Supreme Court, the Forest Survey of India (FSI) utilised slope criteria combined with foothill buffer areas and inter-hill contiguity distances to map hillocks.
• Archaic Revenue Classifications: State revenue departments classify these landforms under land records using labels like Gair Mumkin Pahar (uncultivable rocky hill) or Banjar (barren land). Because these classifications govern land-use rights, unnotified parcels face constant targeting for real estate conversion and commercial quarrying.
• State Forest Thresholds: In August 2025, the Haryana government notified criteria for identifying "forest as per dictionary meaning," requiring a minimum 40% canopy density over at least 5 hectares (or 2 hectares if contiguous).

Environmentalists point out that such high canopy thresholds disregard the natural open-scrub and dry thorn vegetation native to the Aravalli landscape.

Uniform morphological standards fail the Aravalli ecosystem. Ecological functions operate across continuous watersheds rather than isolated topographic peaks.

Imposing an arbitrary 100-metre relief threshold discards millions of years of natural denudation. It effectively declares heavily eroded landforms legally invisible.

Morphological criteria create severe conservation vulnerabilities across three core dimensions:

1. Exclusion of Piedmont and Pediment Zones: Low-lying hillocks, pediments (gently sloping rocky surfaces), and piedmont areas (plains lying at the foot of mountains) facilitate maximum rainwater infiltration into regional aquifers. Excluding them leaves vital recharge zones open to paved construction.
2. Creation of Desertification Gaps: Aeolian sand from the Thar Desert enters northern plains primarily through gaps and low saddles between ridges; stripping these low passes of legal protection accelerates land degradation.
3. Severance of Wildlife Corridors: Contiguity thresholds ignore the dispersal requirements of apex predators, fragmenting the critical Northern Aravalli Leopard Corridor that links Sariska Tiger Reserve to the Delhi Ridge.

State revenue classifications often diverge sharply from the functional hydrological and ecological realities of the Aravalli landscape.

The Supreme Court of India has repeatedly intervened through landmark environmental rulings to halt uncontrolled mining across the fragile Aravalli terrain.

Key judicial milestones governing the Aravalli Range include:

• The Godavarman Precedent (1996): In the historic T.N. Godavarman Thirumulpad v. Union of India (1996) ruling, the Court held that the word "forest" under Section 2 of the Forest (Conservation) Act, 1980 must be interpreted according to its dictionary meaning. This established that statutory protection extends to all forested tracts regardless of land ownership or formal revenue notification.
• Curbing Illegal Quarrying (2002–2009): In the M.C. Mehta line of cases between 2002 and 2009, the Court clamped down on extensive illegal stone crushing and mining across Faridabad, Gurugram, and Mewat.
• Vanishing Hills Documentation: A detailed report by the Supreme Court-appointed Central Empowered Committee (CEC) revealed that 31 out of 128 sampled hills in Rajasthan had completely vanished over five decades due to unregulated quarrying.

To prevent piecemeal exploitation, the Supreme Court mandated that no new mining leases shall be granted across the entire range until the Ministry of Environment, Forest and Climate Change finalises a comprehensive Management Plan for Sustainable Mining (MPSM) via the Indian Council of Forestry Research and Education (ICFRE).

The ongoing degradation of the Aravalli Range causes compounding environmental stress across northwest India:

• Accelerated Desertification: Unregulated mining and urbanisation destroy the natural topography that holds back airborne sand from Rajasthan, threatening agricultural productivity across Haryana and the Indo-Gangetic plains.
• Severe Groundwater Depletion: Groundwater tables across southern Haryana and Delhi have registered alarming declines due to the destruction of fractured quartzite recharge zones.
• Habitat Fragmentation and Conflict: The fragmentation of forested tracts between Sariska Tiger Reserve in Rajasthan and the Asola Bhatti Wildlife Sanctuary in Delhi causes frequent human-wildlife conflict and isolates resident leopard populations.

Environmental governance in the Aravalli belt reflects an intense ethical clash between constitutional intergenerational equity and rapid commercial exploitation. Sustainable governance is anchored in constitutional obligations:

• Article 21: The fundamental right to life, which the higher judiciary has consistently interpreted to include the right to a clean, healthy, and pollution-free environment.
• Article 48A: A non-justiciable Directive Principle instructing the State to protect and improve the natural environment and safeguard forests and wildlife.
• Article 51A(g): A Fundamental Duty obliging every citizen to preserve the natural environment, including forests, lakes, rivers, and wildlife.

In M.C. Mehta v. Kamal Nath (1997), the Supreme Court enunciated the Public Trust Doctrine, holding that certain common environmental resources are held by the state in sacred trust for the public and future generations. Sacrificing ancient mountain catchments for immediate real estate revenues directly violates this doctrine by imposing severe ecological deficits on future generations.

Conserving the Aravalli belt requires shifting from arbitrary geometric boundaries toward remote-sensing-backed landscape governance and unified regional planning. The Union Government has initiated the Aravalli Green Wall Project, aiming to establish a green buffer zone across 29 districts in Gujarat, Rajasthan, Haryana, and Delhi.

To ensure lasting conservation, policymaking must implement concrete institutional measures:

1. Landscape-Level Delineation: Define protected boundaries using integrated watershed hydrology, high-resolution satellite remote sensing, and ecological connectivity mapping rather than single elevation points.
2. Protection of Open Scrub Forests: Realign state forest criteria to include open scrub and dry-deciduous thorn vegetation under the dictionary meaning mandated in the Godavarman judgment.
3. Strict Buffer Zone Management: Maintain a zero-tolerance policy against mining and real estate conversions in identified piedmont recharge zones and wildlife corridors.
4. Inter-State Coordination: Empower the NCR Planning Board and regional bodies to enforce uniform land-use controls across state borders.

• The Supreme Court stayed its November 2025 order that used a 100-metre elevation criterion to define the Aravallis, calling for comprehensive reconsideration to avoid excluding vulnerable foothill ecosystems.
• The Aravalli Range is an ancient Proterozoic fold mountain system spanning over 690 kilometres across Gujarat, Rajasthan, Haryana, and Delhi.
• Morphological thresholds like height and steep slope fail because they ignore critical piedmont zones, fractured quartzite aquifer recharge points, and intermontane desertification gaps.
• The T.N. Godavarman (1996) ruling established that forests must be identified by their dictionary meaning irrespective of statutory revenue records, protecting natural open scrub vegetation.
• Mining and real estate conversion have already caused the disappearance of 31 out of 128 sampled hills in Rajasthan, as documented by the Supreme Court-appointed Central Empowered Committee.
• Sustainable management requires implementing the Aravalli Green Wall Project and enforcing the Public Trust Doctrine across state boundaries.