I'm pretty sure that the book and TV series "The Story of India" has a section on the Harappan civilization:

http://en.wikipedia.org/wiki/The_Story_of_India

Michel Danino's "Lost River: On the Trail Of The Saraswati" is a pretty good survey of this view of climate change and eastward migration. http://www.amazon.com/Lost-River-The-Trail-Sarasvati/dp/0143...

Edit: Edited for spelling

Ancient India: A History of Its Culture And Civilization (http://www.amazon.com/o/asin/B000WUC0CY), by D. D. Kosambi (http://en.wikipedia.org/wiki/D.D._Kosambi)