Decreasing monsoon precipitation in southwest China during the last 240 years associated with the warming of tropical ocean

Based on an absolutely dated stalagmite δ¹⁸O record from Yunnan province, China, we reconstructed monsoon precipitation variations in southwest China since 1760 AD with a resolution of about 2 years. Combining the speleothem δ¹⁸O and observed rainfall records, we find an overall decreasing trend in monsoon precipitation in this region and suggest that the recent drought in 2009–2012 AD has been the driest since 1760 AD. Our speleothem record is consistent with the monsoon precipitation records reconstructed from tree rings in the Nepal Himalaya and southeastern Tibetan Plateau. However, it is anti-correlated with a speleothem record from central India, which confirms the observed anti-phase variations of Indian monsoon precipitation with moistures from the Bay of Bengal and Arabian Sea on multi-decadal to centennial timescales during historical time. The long-term warming of tropical ocean may have caused the decrease of the land-sea thermal gradient and the amount of moisture transported from the Bay of Bengal, which may reduce precipitations in southwest China during the last 240 years. On decadal scale, El Nińo-like conditions of tropical Pacific sea surface temperature may cause drought in this region. Climate model simulations suggest El Niño-like conditions exist in tropical Pacific under global warming scenarios. As a result, it is crucial to have adaptive strategies to overcome future declines in precipitation and/or drought events in southwest China.