The Thar Desert, also known as the Great Indian Desert, is a vast, arid geographical concept and a subtropical desert ecosystem located in the northwestern part of the Indian subcontinent, primarily in Rajasthan, India, and extending into Pakistan. Covering an area of approximately 200,000 square kilometers in India, it is the world's most densely populated desert, with an average density of over 80 people per square kilometer.
Its origin is linked to ancient geological and climatic processes, including the uplift of the Himalayas around 50 million years ago, which created a basin to the west of the Aravalli Range. The desert's arid climate is maintained by the rain shadow effect of the Aravalli Range, which prevents moisture-laden monsoon winds from reaching the region. Historically, the region was once traversed by the Sarasvati River (or Ghaggar-Hakra River system), which dried up around 4,500 to 5,000 years ago due to climatic shifts and changes in river courses, contributing to the region's desertification.
The desert's mechanism is defined by a tropical desert climate with extreme temperatures, ranging from highs of up to 49°C (120°F) to lows of 0°C (32°F). It receives scant and erratic rainfall, averaging between 100 to 500 mm annually, mostly during the monsoon months from June to September. The landscape features undulating sand dunes, stony hills, and the ephemeral Luni River.
The Thar Desert connects historically to the Indus Valley Civilization, which flourished in its vicinity between 3300 BCE to 1300 BCE. It is also connected to major infrastructure projects like the Indira Gandhi Canal, which has been operational since 1983 and has transformed parts of the northern Thar into agricultural land.
Recently, the Thar Desert has undergone a significant change, becoming 38% greener over the last two decades (2001–2023). This transformation is driven by a 64% rise in precipitation during the summer monsoon season and the expansion of agriculture, facilitated by increased groundwater pumping and canal irrigation. This greening, while increasing vegetation, also raises concerns about the sustainable management of water resources.