Abstract: Southwestern China is a high-risk area of drought. However, hydroclimate behavior and its mechanism on various timescales in southwestern China are still unclear, largely due to scarce long-term high-resolution hydrological reconstructions. Moreover, the speleothem-based oxygen isotope record shows an ambiguous relationship between Asian summer monsoon variation and regional hydrological change. Here, we present a nearly 800-yr-long (1180-1969 AD) annually resolved and accurately dated regional hydroclimate record based on annual laminae thickness data from a stalagmite (NO. DX1) in Dongge Cave, Guizhou Province. The regional climatic conditions are dominantly influenced by the Asian summer monsoon and the Intertropical Convergence Zone (ITCZ). In the continuously-growing section (from 0-58.2 mm), regular laminations can be observed under a microscope. The microscopic features of the lamina resemble those from Shihua and Hulu caves in the monsoonal regions of China. Therefore, we obtain a layer-counting timescale and an annual laminae thickness record from 1180 to 1969 AD. The close similarity between the annual laminae thickness and δ13C records suggests that annual laminae thickness of stalagmite DX1 can serve as a proxy for regional hydroclimate. Centennial-scale hydroclimate changes are broadly similar to the Northern Hemisphere (NH) temperature variations, with a significant drought event (-1540-1630 AD) during the Little Ice Age (LIA), supporting that the NH temperature has an important influence on low-latitude hydrological changes, via meridional shifts of the ITCZ. The mathematical analyses reveal that the regional hydrological changes display significant -3-year and -7-year periodicities (accounting for -44% of the total variance), likely related to the interannual El Niño-Southern Oscillation (ENSO) variations. In addition, the 31-yr running biweight variance for the regional hydroclimate gradually decreased from the Medieval Warm Period to the LIA, reached the minimum during the coldest LIA interval (-1540-1630 AD), then gradually increased, and became unusually high during the Current Warm Period. This hydroclimate variance is largely consistent with the reconstructed ENSO variance and further modulated by secular NH temperature background states. Our observation implies that the ENSO and low-latitude hydrological variance will increase, and the frequency and amplitude of extreme climate events will increase under the scenario of continuous global warming.

Key words: Southwestern China, stalagmite, annual layer thickness, hydroclimate, Northern Hemisphere temperature, ENSO