Continuing the theme of desertification in recent posts see www.sciencedaily.com/releases/2012/05/120528154943.htm … we have climate change directly involved in the collapse of the Indus civilisation, around 4000 years ago.
The Indus civilisation once sprawled across one million square km over what is now Pakistan, NW Indias, and eastern Afghanistan. The cities and towns were mostly located near rivers and their tributaries, which parallels the situation in contemporary Egypt and Babylonia, and flourished between 3200 and 2000BC. Thereafter it slowly disintegrated until around 1000BC when it finally dispersed altogether (people moving south into the Ganges Plain or in the opposite direction). All we have left behind in the modern world are the ruins buried in a vast desert far from flowing water.
The mouth of the Indus was within easy sailing distance of the Gulf, and therefore of Sumeria and Akkad, and Dynasty One Babylon. A team specialising in geology, geomorphology, archaeology and mathematics explored the region between 2003 and 2008 and made use of satellite photography and topographical details collected by the Shuttle Radar Topography Mission. What has become clear is that formerly, the monsoon rains had been reliable and it was the decline in monsoon that weakened river systems (possibly in tandem with tectonic changes as a result of earthquakes), leading to agricultural yields falling.
One feature found was more than a little interesting, a raised elevation 10 to 20 m high and over 100km wide running 1000km, a ridge built by a river as it carried sediment downs to its lower course. Remains of settlements lie along the ridge and others are buried in the sand, indicating the silt had been used in fields. It seems the people of the Indus civilisation may have taken advantage of a unique window of opportunity that existed between 3200 and 1200BC, and it was finally abandoned at the end of the Bronze ages. It doesn't mention the fact but this was contemporary the abandonment and collapse of civilisations elsewhere in the world, especially in western Asia and the Aegean. The Mycenaeans, Hittites, Mitanni, the Middle Assyrian empire, and the aridity that was a feature of dynasty 20 Egypt all coincide with 1200BC and immediate centuries that followed.
The Indus civilisation had thrived from the Arabian Sea right up to the foothills of the Himalayas. Prior to 3200BC the centre of human settlement appears to have been in ancient Baluchistan, where Pakistan borders Iran. People appear to have abandoned that region and moved virtually enmasse to the Indus flood plain.