Harappan civilisation end. 2018 study 1-2

A shift in temperatures and weather patterns over the Indus valley starting about 2500 BC may have driven the Harappans to resettle far away from the floodplains of the Indus, a study has found. 

said researchers from the Woods Hole Oceanographic Institution (WHOI) in the US. (2018)

Yet by 1800 BC, this advanced culture had abandoned their cities, moving instead to smaller villages in the Himalayan foothills. Beginning in roughly 2500 BC, a shift in temperatures and weather patterns over the Indus valley caused summer monsoon rains to gradually dry up, making agriculture difficult or impossible near Harappan cities, said Liviu Giosan, a geologist at WHOI. 

Although fickle summer monsoons made agriculture difficult along the Indus, up in the foothills, moisture and rain would come more regularly,” said Giosan, lead author of the study published in ‘Climate of the Past’. 

We don’t know whether Harappan caravans moved toward the foothills in a matter of months or this massive migration took place over centuries. What we do know is that when it concluded, their urban way of life ended

2019 'Cell' rakhigarhi Haryana study shows that did not have DNA of Iranian settlers and transition from local hunter gatherer towards Indus Valley civilization.