When did the Harappan Civilization decline?

The Harappan Civilization began to decline around 1900 BCE. The reasons for this decline are not entirely clear, but several factors may have contributed, such as environmental changes, including a shift in the course of rivers and a possible decrease in rainfall. This would have affected agriculture, which was central to the Harappan economy. Additionally, there may have been social, economic, or political changes that led to the gradual abandonment of major cities like Mohenjo-daro and Harappa. Despite the decline, some smaller settlements continued to exist in the region for a while longer.

This question related to Chapter 6 Social Science Class 6th NCERT.
From the Chapter 6. The Beginnings of Indian Civilisation.
Give answer according to your understanding.