Over the past week, Delhi’s air quality index has been mostly in the low to mid-20s, even reaching 300 one morning — levels the city routinely records in smoky winters but rarely in summer.
The cause, according to meteorologists, is dust blown up from the deserts and semi-arid regions of Rajasthan by hot, dry winds blowing across northwest India — a weather phenomenon that would not have been of such environmental danger decades ago.
The spike in pollution brings back focus on the destruction of the Aravalli mountain ranges, which have served as a natural buffer for centuries. Since it is oriented almost precisely through the corridor through which northwesterly winds carry the Thar dust towards the capital, the function of the range has been dismantled today.
Decades of mining, quarrying and encroachments — especially in Alwar and Bharatpur districts, the exact geography through which the dust plume traveled this week — have breached the ridgeline. Dust moves unhindered.
“The Aravalli hills – long, continuous ranges plus hundreds of thousands of smaller hills – play a crucial role in controlling the spread of sand from the western Thar deserts,” said Chetan Agarwal, a forest analyst who has studied the region in detail.
“Hills usually slow down winds from the west, which dump their sand loads on the western sides and this sand forms sand dunes. Hills play this role physically, and it is enhanced by the presence of dense vegetation and trees that act as a natural scrubber of sorts,” Agarwal added.
Read also: Why did the new definition of the Aravalli Hills spark a protest? What activists say
A study published in March quantified the scale of the devastation: In just seven years between 2017 and 2024, the region’s built-up areas grew by 53%, or 2,644 square kilometers, replacing primarily agricultural land and pastures.
Mining, especially lead, zinc, marble, sandstone and industrial minerals, puts significant pressure on the landscape, with a high number of active leases causing geomorphological disturbances, the Dean of the Jindal School of Environment and Sustainability (JSES) at OP Jindal Global University said at the time. The research was conducted by JSES and researchers at the Indian Institute of Technology Kharagpur.
The newspaper stated that the future of the Aravalli mountain range is an issue of national importance, noting that the Supreme Court deliberated on redefining the geographical scope of the mountain range, which extends to several states.
The ruling, issued on 20 November 2025, was based on the classification of hills primarily by height, limiting legal protection for sites located above the 100-metre contour line. The court then proposed the establishment of a council of experts to comprehensively examine the issue.
“Comprehensive scientific studies in the region are needed, in light of recent developments, to facilitate informed policy making. This research sought to address some of the policy gaps by developing a scientific understanding of the concerns (soil erosion, land degradation, forest cover) surrounding AMS conservation.”
Agarwal stressed the need to protect the Aravallis and called for maintaining “effective ban on zoning of estates through Natural Conservation Zone (NCZ), and control of mining is essential to reduce desertification and improve air quality in the NCZ”.
Even more worrying is that the deteriorating range may no longer be just a gap in the wall.
Outside of the Thar Desert itself, researchers have identified significant sources of dust along the Indo-Gangetic Plain corridor — dry bodies of water, abandoned farmland, and disturbed terrain associated with human activity in the region.
A 2021 study in the journal Geophysical Research: Atmospheres by researchers at the Indian Institute of Science in Bengaluru, which examined a catastrophic dust event that killed more than 100 people in Delhi, Jaipur and Agra in 2018, noted that when a convective system moves from the northwest to the southeast, “it first picks up dust from the Thar Desert, followed by uplift of dust from anthropogenic sources.”
In urban areas alone, road dust — much of which comes from exposed, disturbed ground surfaces — can contribute more than 20 percent of total PM10 concentrations on a typical day, previous research has found. The bare slopes of the Aravallis, the restricted vegetation stripped away and the soil left loose by quarrying, lie directly in this pass.
