IVC declined after 1900 BCE, however, reasons for the decline are still disputed. There are various theories for its decline such as – (* No need to remember all these names, just glance at it)
| Causes | Historians |
| Drying of Ghaggar river and increasing aridity | D.P Agrawal and Sood |
| Flood | Macay and S R Rao |
| Low Rainfall | Dales, Vatsa and Lambricks |
| Ecological Disturbance | Fairchild |
| Aryan Invasion | Wheeler and Gordon |
| Earthquake | Raikes and Dales |
| Natural Calamity | K.A.R Kennedy |
A recent finding titled ‘Neoglacial climate anomalies and the Harappan Metamorphosis ’, done by an international team of scientists has suggested climate change as the possible reason for the decline of the Indus Valley Civilisation. Changes in temperature and precipitation led to the decline of monsoon and drying up of the Ghaggar-Hakra River. This led to a decline in crop and urban Harappan society turning rural.