Indus Valley Civilisation: Urban Planning and Decline

The Indus Valley Civilisation, at its peak, covered modern-day Pakistan and northwest India. It featured advanced urban planning with gridded streets, multi-storey brick homes, and sophisticated sanitation systems, including flush toilets.

Causes of Decline

• Contrary to the belief that a single catastrophic event led to its downfall, recent studies suggest a series of prolonged droughts over centuries as the primary cause.
• A study published in Communications Earth & Environment used paleoclimate data and computer modeling to analyze climate from 3000 to 1000 BCE.
• The findings indicate that the downfall of Harappa was due to recurring droughts leading to river and soil desiccation.
• These droughts, compounded by diminished food supply and fragile governance, pushed the society towards decline.

Adaptation Strategies

• The civilisation showed resilience by changing agricultural practices, diversifying trade, and relocating settlements closer to reliable water sources like the Indus River.
• This adaptability offers lessons on proactive planning and sustainable systems relevant to today's climate change challenges.

Scientific Analysis

• The study integrated model outputs with environmental indicators such as stalactites, stalagmites, and lake water levels to understand the factors influencing the civilisation’s decline.
• Between 3000 and 2475 BCE, a vigorous monsoon facilitated settlement near rain-abundant areas due to cooler tropical Pacific conditions.
• Warming of the tropical Pacific in subsequent centuries resulted in drier conditions, reduced rainfall, and drought periods.

Key Drought Events

• Four major drought events identified between 2425 and 1400 BCE, each lasting over 85 years.
• The third severe drought around 1733 BCE lasted 164 years, impacting the entire region.
• Overall temperature increased by 0.5°C, and rainfall decreased by 10%-20%, leading to significant hydrological changes.

Research Contributions

• This study advances the understanding of hydroclimate dynamics and their impact on ancient civilisations.
• The methodology offers insights applicable to other river-dependent cultures like Mesopotamia, Egypt, and China.
• Understanding tropical Pacific Ocean temperature fluctuations is crucial for future regional rainfall pattern research.