Adaptation and human migration, and evidence of agriculture coincident with changes in the Indian summer monsoon during the Holocene

Abstract

Human societies have evolved through a complex system of climate and ecological interactions. Known records suggest intimate relationship of adaptations, mitigations and migrations to climate extremes leaving their impacts on human societies. The northwestern part of India provides such an example, where human civilizations flourished in the early Holocene along the major fluvial systems when the Indian summer (southwest) monsoon was much stronger and rainfall was higher over the Indian land mass. Summers were thus wetter, conducive to agriculture and ecodiversity. Changes in the early civilizations in the Indian subcontinent had a close relation to changes in the monsoon climate over the past 10,000 years. The summer monsoon has weakened over the last 7000 years since its peak intensification in the early Holocene (10,000-7000 cal yrs BP). Discrete intervals of dry phases in the summer monsoon are visible in the proxy record of the monsoon winds from the marine sediments of the Arabian Sea, which had significant impact on human settlements in South Asia. The strongest aridity in the Indian subcontinent and extended periods of droughts at ca 5000- 4000 cal yrs BP seems to have triggered eastward human migrations towards the Ganga plain. Other times of monsoon weakening during the Holocene are coincident with the initial development of ponds, reservoirs and other rainwater harvesting structures that may have served as an adaptation to climate change.