Middle Holocene Indian summer monsoon variability and its impact on cultural changes in the Indian subcontinent

Abstract

Agriculture is a major contributor to the economic development of modern as well as ancient India and largely depends on the rainfall in the monsoon season. In order to understand the impact of climate variability on cultural changes in the Indian subcontinent, high resolution centennial to millennial scale middle Holocene Indian summer monsoon (ISM) variability was reconstructed from Bednikund lake, located in an alpine meadow of the Pindar basin, Chamoli, Central Himalaya. Increased ISM precipitations were found during ∼5930-3950 (mid-Holocene climate optimum), ∼3380–2830 (Minoan Warm Period), ∼2610–1860 (Roman Warm Period), ∼1050–760 (Medieval Climate Anomaly), and ∼320 cal yr BP to Present (Current Warm Period). The decreased ISM strengths were found during ∼3950-3380, ∼2830–2610, ∼1860–1050 (Dark Ages Cold Period), ∼760–580, and ∼500-320 cal yr BP (Little Ice Age). The covariance between our records of precipitation change and total solar irradiance for the middle to late Holocene and with Northern hemisphere (NH) temperature for the past two millennia suggested solar insolation as a primary forcing mechanism of ISM variability. The reconstructed paleoclimate combined with archaeology and historical records indicated that ancient Indian civilizations e.g., the Indus Valley (∼5200-3300 cal yr BP) and Vedic (∼3400-2400 cal yr BP) had established and thrived during periods of strengthened ISM precipitation, whereas their collapse closely corresponded to the decreased strength in ISM. From ∼2400 to 200 cal yr BP, the Indian subcontinent witnessed the rise and fall of various Kingdoms/dynasties. This period saw an exponential expansion/growth in agriculture, economy, population, languages, architecture, and religions in the Indian subcontinent. The agrarian-based economy showed little or no impact of monsoon weakening after ∼2400 cal yr BP possibly due to development and reforms in administrative policies, construction of irrigation systems such as dams, lakes and canals, use of technology for irrigation such as waterwheel, knowledge of double cropping, production of cash crops. The ancient civilizations of India were directly impacted by the strengthening and weakening of ISM, whereas for the later periods, civilizations were able to adapt to climate change.