"It is difficult to point to one single cause that drove the Harappan decline although diverse suggestions from Aryan invasion, to catastrophic flood or droughts, change in monsoon and river dynamics, sea-levels, trade decline to increased societal violence and spread of infectious diseases have been proposed. The continued survival of Harappans at Bhirrana suggests adaptation to at least one detrimental factor that is monsoon change," the research states.
"Our study suggests that the climate was probably not the cause of Harappan decline," the researchers said in a statement. "Increasing evidences suggest that these people shifted their crop patterns from the large-grained cereals like wheat and barley during the early part of intensified monsoon to drought-resistant species of small millets and rice in the later part of declining monsoon and thereby changed their subsistence strategy."
But changing the crop then resulted in "de-urbanisation" as the cities's larger storage facilities were abandoned for smaller personal storage spaces.
"Because these later crops generally have much lower yield, the organised large storage system of mature Harappan period was abandoned giving rise to smaller more individual household based crop processing and storage system and could act as catalyst for the de-urbanisation of the Harappan civilization rather than an abrupt collapse," the report explained.