Abstract
A large part of South Asia receives rainfall mainly during the Indian Summer Monsoon (ISM) season of the year (Jun–Sep). The socioeconomic conditions of most of the developing countries in this region largely depend on the ISM rains. It also played important roles in rise and collapse of ancient civilizations in this region. However, the influence of the ISM on Indian ancient civilizations has not yet been fully explored though there were some attempts to correlate monsoon variation with their rise and fall. For example, in the mid to late Holocene period, Indus Valley or Harappan Civilization flourished in the western part of India from its early development, through its urbanization and eventual transformation into a rural society. Probably a prolonged decrease in the ISM rainfall caused the decline in the urban phase of the Indus Civilization around the 4.2 kyr BP global climate event. Another well-recorded early Holocene global climate event is the 8.2 kyr BP cooling event which also reportedly influenced ISM significantly, but its impact on human settlement is not clear in this region. The present study is a comprehensive review of the archaeological and climatological researches carried out on the role of ISM variability on the rise and fall of ancient Indian civilizations for the most part of the ongoing interglacial period, the Holocene. The review covers the studies on the period of the last 10 kyr as evidence suggests that human settlement and cultural developments in this region started around the beginning of this period. We have noted that the existing studies are mostly restricted to vague qualitative analysis of the weakening/strengthening of the ISM, and researches related to quantitative estimations of changes of the monsoon strengths and durations of drought events that caused collapse of civilizations are limited. Therefore, in the present analysis, emphasis has also been given on the requirement of estimating the absolute changes that might have caused cultural shifts. Some possible ways to quantitatively estimate the changes of some climate parameters are discussed.
Highlights
A Brief History of Ancient Civilizations in the Indian SubcontinentThere is a long history of rise and fall of civilizations in the Indian subcontinent
The existing records indicate that there was human occupation in North India about 30 kyr BP (Singh et al, 1999) though settled life probably started around early Holocene time
For the last 10 kyr, it is clear that the Indian Summer Monsoon (ISM) rainfall was high during the early Holocene (10.0–8.5 kyr) and decreased after 8.5 kyr BP
Summary
There is a long history of rise and fall of civilizations in the Indian subcontinent. Some initial researchers suggested foreign invasions (e.g., Aryan invasions) into India, societal instabilities, and a decline of trade (Possehl, 2002b) as causes, but no strong evidence supporting them exists (Fitzsimons, 1970) Environmental factors such as regional aridification, hydrological changes such as reduction in water flow in the main river channel, the Ghaggar-Hakra system (Kenoyer, 1998; Radhakrishna and Merh 1999; Possehl, 2002a; Fuller and Madella, 2002; Wright et al, 2008; Sengupta et al, 2019), and land degradation due to human activity (Fairservis, 1967; Atkins et al, 1998) were suggested to play major roles in the decline of Harappan Civilization (Kenoyer, 1998; Possehl, 2002b; MacDonald, 2011). There is some speculation that the great war of Mahabharata caused the collapse of Vedic Civilization around 2 kyr BP, though evidence to support this is unreliable
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