What led to the decline of the Harappan civilization?

Harappan society entered a period of decline about 1900
B.C.E. There is evidence of deforestation as woodlands were cleared to create more
arable land to feed a growing population. This deforestation in turn led to reduced
rainfall and erosion of the topsoil, as a result of which the area soon became a desert.
To this day, it requires considerable irrigation to be farmed. There is further evidence
of some natural catastrophes, possibly earthquakes, which further weakened the society.
It is important to note that there is no evidence of military conflict, so the decline
of the society was not the result of conquest. Also, the decline did not happen
overnight, or even in a single lifetime. It most likely occurred over a period of five
hundred years. By 1500 B.C.E., the society had collapsed. Still, its influence remained
with the people who survived them, including their deities and their cultivation
practices.