As per latest findings by scientists regarding the Indus Valley civilization, climate change led to the rise and fall of the Indus valley civilization. At the beginning rainfall patterns were good enough to sustain life but after a while it became unsuitable for agriculture, causing the region to be largely abandoned.
For further reading check the following articles:
|Major Sites in Indus Valley Civilization||Indus Valley Civilization|
|100 Must-Know Facts about IVC for UPSC||UPSC FAQ|
|NCERT Notes: Arts of the Indus Valley||NCERT notes for History (Modern, Medieval, Ancient), Art and Culture, and Geography|