Early anthropogenic impacts on the Indian summer monsoon induced by land-use and land-cover changes

The impacts of anthropogenic forcing on Indian summer monsoon (ISM) rainfall are obscure, partly due to limited availability of highly resolved hydroclimate proxy records as well as the highly regionalized nature of precipitation. Here, we report an annually-resolved speleothem oxygen isotope record from Xianren Cave, southwestern China, which represents rainfall change over the broad ISM region. We find that the region has endured at least six decadal-scale weak monsoon events in the past three hundred years. One of them, lasting from the early to mid 19th century, shares the similar gradual, persistent trend as the most recent decline in ISM rainfall and both have a magnitude substantially larger than the others dominated by natural variability. This early weak monsoon event occurred during a historical time of intensive deforestation in the region. We conclude that the ISM trend could have been altered by the changes in land-use and land-cover since the early 19th century.Ministry of Education (MOE)National Research Foundation (NRF)Published versionWe are in debt to Dr. Ming Tan who initiated the research in Xianren Cave with a grant from the National Natural Science Foundation of China (NSFC-41272204). This work has been possible thanks to the support by the Earth Observatory of Singapore via its funding from the National Research Foundation Singapore (NRF), the Singapore Ministry of Education (MOE) under the Research Centres of Excellence initiative. X. W. acknowledges the financial support from an MOE Tier 2 grant (MOE2019-T2-1-174) and an NRF grant (NRF2017NRF-NSFC001-047). U-Th dating at the High-Precision Mass Spectrometry and Environment Change Laboratory was supported by grants from the Science Vanguard Research Program of the Ministry of Science and Technology, Taiwan, ROC (109-2123-M-002-001 to C.-C.S.), the Higher Education Sprout Project of the Ministry of Education, Taiwan, ROC (109L901001 to C.-C.S.), and the National Taiwan University (110L8907 to C.-C.S.). K. L. acknowledges the financial support (SKLLQG1815) from State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, China