How did the climate of Indus river valley change between 6000 BC and 2500 BC?

6000-5000 BC: Warm and Wet-

♦ Wet, tropical summer monsoon dominated the entire plain along with heavy seasonal monsoon rainfall

♦ Thick evergreen forests were present across most of the plain with dense vegetation throughout, especially near river valleys

5000-4000 BC: Gradual Drying-

♦ Monsoons weakened slowly with decreasing water levels in streams

♦ Forest area reduction along with reduced flow and volume in tributaries

4000-3300 BC: Drier & Seasonal

♦ Continued decline in water levels led to rivers concentrating in main courses of river Indus

♦ Increased aridity leading to seasonal rainfall patterns that shifted towards west leading to desert development in northwest part

♦ Forests mainly near the larger waterways; sparse growth elsewhere

3300- 2500 BC: More Arid and Monsoon Retreats-

♦ Monsoons shifted further westwards creating monsoon shadow on eastern side leading to reduced moisture carrying systems

♦ This led to less rain, forest degradation leading to the gradual development of semiarid conditions on western and eastern borders

As temperatures increased and the climate gradually became drier, some Indus sites were abandoned by their inhabitants who likely migrated either west to the relatively milder areas along the Sutlej River or to areas east (present-day India and Nepal) in pursuit of more favourable and less arid environments.