Why was the monsoon season so important to farmers in the Indian River Basin?

Monsoon season provided rainfall for crops and supplied irrigation in the dry season.

Describe the irrigation systems that were used in the basin. 

Northern India has the Gangas River that allows great irrigation system. Southern India was very populated therefor irrigation systems such as wells, dams, and canals increased greatly in numbers 

Why was India's population able to grow throughout the postclassical era? 

It was the result from a increase in agriculture production