Recent geophysical research suggests that the Ghaggar-Hakra system was a system of monsoon-fed rivers and that the Indus Valley Civilisation may have declined as a result of climatic change, when the monsoons that fed the rivers diminished at around the time civilisation diminished some 4,000 years ago. Yet, another study suggests that between 9,000 and 4,500 years ago the Ghaggar was perennial, receiving sediments from the Higher and Lesser Himalayas, which likely facilitated development of the early Harappan settlements along its banks..