Hydroclimatic variability and corresponding vegetation response in the Darjeeling Himalaya, India over the past ~2400 years

Abstract

To understand the present day climate change impacts on ecosystem, knowledge of the rapid climatic events occurred within the last few thousand years is crucial. Indian summer monsoon (ISM) dominated eastern Himalayan vegetation is sensitive to even a minor change in climate parameters, hence suitable for studying climate-plant interactions. We reconstruct a ~2400 years climatic history of the Darjeeling area, eastern Himalaya combining pollen, phytoliths, non-pollen palynomorphs (NPPs), δ13C signatures, sediment texture and total organic carbon (TOC) records from a lacustrine deposit to explore ecosystem response to climate change and to understand the possible forcing mechanisms behind it. This study is centred on two northern hemispheric late Holocene climatic events namely Medieval Warm Period (MWP) and Little Ice Age (LIA). Although considerable variations exist globally for these warm (moist) and cool (dry) periods with respect to their timing, duration, and hydroclimatic dynamics, our results identify a humid climatic phase at the beginning of the last millennium, a pre-MWP less humid phase, while MWP was wetter than the former phase and a wet LIA in the Darjeeling Himalaya. Our results indicate that this climatic variability also induced changes in the regional vegetation. During 364 BCE to 131 CE, the region was humid harbouring a dense broad-leaved evergreen forest; a comparatively drier condition prevailed between 131 CE and 624 might be the reason behind the thinning in the forest cover. A wet phase is observed during 1118 CE. A further increase in monsoonal strength is apparent between 1367 CE and 1802. Considering the available records from the eastern Himalaya and peninsular India it is inferred that centennial scale variations in frequencies of “active dominated” and “break-dominated” periods govern the internal dynamics of the ISM, and considered to be the key forcing mechanism behind the differential behaviour of the ISM over these regions.