The decline of the Indus Valley Civilization, one of the world’s oldest and most advanced societies, has baffled historians, archaeologists, and scientists. A recent study led by an international team of researchers suggests that climate change could have been a significant factor in the civilization’s downfall. The research, named ‘Neoglacial climate anomalies and the Harappan metamorphosis’, examined sediments from the Arabian Sea, analyzed marine DNA and undersea fossils, and reconstructed the Indian winter monsoon patterns over the last 6000 years.
Understanding the Indian Monsoon and Its Impact
Indian monsoon, an annual weather phenomenon, collects moisture from the Indian Ocean and distributes it across the Indian subcontinent as rainfall. It plays a pivotal role in shaping climate patterns in the region, with a significant farming population relying on monsoons for their livelihood and survival. The seafloor near the Indus mouth provides ideal conditions for preservation, making it a valuable sample source for the study.
Insight into Harappan Culture
Over 4000 years ago, the Harappan culture flourished in the areas of modern Pakistan and northwestern India, recognized today as the Indus River Valley. The Harappans built sophisticated cities and invented sewage systems even before Ancient Rome. Their long-distance trading ties extended to settlements in Mesopotamia. However, around 1800 BCE, this progressive culture abandoned their urban habitats, choosing instead to inhabit smaller villages in the Himalayan foothills.
Key Findings of the Study
The study proposed that a stronger winter monsoon might have prompted the transition of the urban Harappan society into a rural one, as residents migrated from the summer flood-deficient river valley to the Himalayan plains. Later, a decline in the winter monsoon could have contributed to the decline of these rural late Harappans.
Research data for the last 4500 years suggest lower temperatures than the Holocene thermal maximum. A significant general cooling phase, known as neoglaciation, occurred between 2,500 and 4,500 years ago. This period saw a gradual drying up of summer monsoon rains, making agriculture challenging near Harappan cities.
Impact on Agriculture and River Flow
This shift in temperatures coupled with less severe and unpredictable floods in the Indus and its tributary rivers significantly impacted inundation dependent agriculture. The shift also affected atmospheric temperatures and river flows from the Himalayas, influencing the crops grown in the region.
Furthermore, Ghaggar-Hakra, identified as the probable course of the Saraswati river, dried up during this time. Strong winter monsoons characterized by “Early Neoglacial Anomalies (ENA)” occurred between 4,500 and 3,000 years ago, which affected wind and precipitation patterns across the eastern Northern Hemisphere and tropics.
| Timeline | Climate Change Impact on Harappan Civilization |
|---|---|
| 6000 – 4000 years ago | Harappan culture thrives in urban settlements |
| around 1800 BCE | Urban population starts inhabiting smaller villages |
| 2500 – 4500 years ago | Neoglaciation phase leads to a decline in winter monsoon |
| 4500 – 3000 years ago | ENA leads to changes in wind and precipitation patterns |
Evolution of the Harappan Civilization
The Harappan Civilization, despite the climate challenges, was known for its vivid imagination and artistic sensibility reflected in various artifacts discovered at the excavation sites. The primary urban planning and engineering skills were evident in the planned network of roads, houses, and advanced drainage systems. Some of the critical archaeological findings are from Harappa and Mohenjo–daro in Pakistan, Dholavira and Lothal in Gujarat, Ropar in Punjab, Balathal, and Kalibangan in Rajasthan, Banawali in Haryana, and Alamgirpur in Uttar Pradesh.
Relevance of the Study Today
The Indus story serves as a crucial example of the potential impact of climate change on civilizations. Despite their resourcefulness, the Indus people had to migrate due to severe climate changes. With the increasing protectionism and rigid political boundaries seen today, migration—earlier an effective coping mechanism—becomes an exacerbating issue that can lead to political and social convulsions. These movements are already appearing apparent with migrations out of Syria and African countries, which have roots in climate change. Furthermore, rising sea levels in recent times could trigger massive migrations from low-lying regions such as Bangladesh or hurricane-prone regions in the southern U.S.
