As debate intensifies over the Supreme Court’s December 20, 2025 verdict on the Aravalli hill range, environmental experts have warned that redefining the ancient landscape could weaken a critical natural shield protecting Delhi and large parts of the fertile Indo-Gangetic Plain from the expanding influence of the Thar Desert.
The Aravallis, among the oldest hill ranges on Earth, were formed through nearly two billion years of tectonic activity and geological upheaval. Despite enduring lava flows, submergence, uplift and erosion over geological time, the range has survived as a vital ecological and climatic barrier. However, over the last four decades, illegal mining, deforestation and real estate expansion have severely degraded the hills, leaving them vulnerable to further loss.
Environmentalists argue that the Supreme Court’s acceptance of the Union environment ministry’s elevation-based definition of the Aravallis could accelerate this decline. Under the new criterion, only landforms rising at least 100 metres above the local relief, or clusters of such hills within 500 metres, will qualify as part of the range. Critics fear this narrow definition could exclude large stretches of low-lying ridges, opening them up for commercial exploitation.
The concern is rooted in long-standing scientific evidence. A 2017 study by the Wildlife Institute of India found that the Aravallis once functioned as a continuous green barrier that prevented desertification and checked the eastward spread of the Thar Desert into eastern Rajasthan, Haryana, western Uttar Pradesh and the Indo-Gangetic plains. Today, the study noted, the Aravalli forests are among the most degraded in the country, with many indigenous plant species already lost.
The depletion of forest cover has weakened the range’s ability to block sand migration. The study identified twelve major gaps in the hills, stretching from the Magra hills in Ajmer district to the Khetri-Madhogarh hills in Jhunjhunu and the northernmost hillocks in Haryana’s Mahendragarh district. These gaps, researchers warned, act as corridors through which desert winds and sand can move eastward.
Some researchers point out that parts of the Thar Desert are witnessing increased rainfall and surface vegetation. Scientists from the Indian Council of Agricultural Research’s Central Arid Zone Research Institute have observed significant changes in rainfall patterns and land use across western Rajasthan, suggesting a partial “greening” of the desert.
However, experts caution that this greening is fragile and misleading. Sachin Pernacca Sashidhar, senior policy analyst at the Ashoka Trust for Research in Ecology and the Environment, said the apparent increase in vegetation is driven largely by irrigation, shifting monsoon patterns, groundwater extraction and the spread of invasive species such as Prosopis juliflora. These factors, he explained, mask deeper risks of land degradation.
While irrigation and rainfall have boosted surface biomass, they have also caused salinisation and waterlogging, threatening long-term soil productivity. Heavy groundwater use risks collapse if extraction exceeds recharge, and invasive species drain deep soil moisture while harming native biodiversity. If water availability declines, the green cover could disappear, leaving behind landscapes even more vulnerable than the original desert terrain.
Sashidhar added that the threat facing Haryana and the National Capital Region is not just the slow movement of sand dunes but a more dangerous atmospheric form of desertification. This manifests as dust storms, high particulate matter and heat transfer driven by wind patterns. Containing this requires a continuous physical wind barrier, a role historically played by the Aravallis.
If the range is structurally weakened, low-lying ridges and natural gaps could become channels for dust-laden winds to move eastward. Even if the core desert remains green, the loss of this geological shield would allow atmospheric desertification to spread through newly opened breaches.
Ecologist Ghazala Shahabuddin, Visiting Professor at Ashoka University, stressed that the Aravallis provide far more than a single protective function. As an ancient landscape, she said, the range supports biodiversity, regulates climate, recharges groundwater and sustains human livelihoods. Reducing its value to an elevation-based definition, she warned, risks erasing its ecological importance altogether.
“The Aravallis are an ancient topographical feature with multi-dimensional functions for both biodiversity and humans,” Shahabuddin said. “We cannot see them merely as a physical barrier, and we certainly cannot allow them to be blasted out of existence.”