Both the CESM-simulated NNU-2K dataset and proxy reconstructions of Indian Summer Monsoon (ISM) precipitation over the past two millennia reveal a significant centennial-scale period, including periodicities of 105, 150, and 200 years. The 105- and 200-year cycles identified in the NNU-2K all-forcing (AF) experiment closely match those found in the volcanic single-forcing (Vol) experiment, suggesting that volcanic activity is a major driver of these variations. Volcanic forcing induces global cooling, which reduces the land–sea thermal contrast and weakens the monsoon circulation. Furthermore, stronger cooling in the Northern Hemisphere decreases the interhemispheric temperature gradient and weakens the trans-equatorial pressure gradient. This, in turn, suppresses cross-equatorial low-level flow from the Southern Hemisphere, further reducing ISM precipitation. The 105- and 150-year periodicities are also consistent with those in the total solar irradiance (TSI) single-forcing experiment, indicating a substantial response to solar variability. Increased solar irradiance enhances Northern Hemisphere warming, strengthening both the interhemispheric temperature gradient and the cross-equatorial pressure gradient. These changes facilitate stronger northward cross-equatorial flow in the lower troposphere, intensifying the ISM and increasing precipitation. Concurrently, solar forcing amplifies the thermal contrast between the Eurasian continent and the Indian Ocean, further reinforcing monsoon circulation. The 150-year cycle is also evident in the control (Ctrl) experiment, implicating internal climate variability as an additional mechanism. Analysis reveals a quasi-decadal Pacific Decadal Oscillation (PDO)-like sea surface temperature anomaly in the North Pacific. Its negative phase is linked to reduced sea-level pressure over the ISM region, enhanced low-level convergence, and increased precipitation. It also strengthens the Mascarene High over the Indian Ocean, intensifying the Somali Jet and southwesterly monsoon winds, which promote greater moisture transport into the ISM domain.

Graphical In light of the current state of global climate change, this study examined the spatiotemporal variations in seasonal and interannual evapotranspiration and water conditions in the Yangtze River Basin from 1970 to 2014, as well as their underlying causes, and projected future evapotranspiration and water conditions in the basin. This provides valuable insights into the hydrometeorological dynamics of the Yangtze River Basin and its potential future trends. Evapotranspiration, as well as dry–wet conditions, can measure changes of water volume in a region and are important factors affecting atmospheric circulation. With global climate change, the dry–wet conditions in the Yangtze River Basin have undergone profound changes. This study investigates spatiotemporal variations of evapotranspiration and dry–wet conditions in the Yangtze River Basin (1970–2014) using the Penman–Monteith equation and surface moisture index. Results reveal an overall increasing trend in annual evapotranspiration across most stations, with more pronounced increases in spring and autumn compared with winter and summer. Dry conditions dominated the Yangtze River Basin, particularly in spring, autumn, and winter, while summer showed slight wetting trends. Notably, middle-lower reaches exhibited significant aridification. Range/Standard Deviation (R/S) analysis suggests these observed trends in both evapotranspiration and moisture indices are likely to persist. The findings highlight the basin's evolving hydrological patterns under climate change, with implications for water resource management. The seasonal and spatial variations in evapotranspiration and dry–wet conditions provide valuable insights for understanding regional climate dynamics and their potential future trajectories.

During the last glacial, Dansgaard–Oeschger (DO) events are mostly characterized by moderate and shorter fluctuations. Here, we present the three-year-resolution stalagmite isotopic record from Shouyuangong Cave (SYG), southern China, revealing a detailed history of Asian summer monsoon (ASM) and local environmental changes during the middle and late period of DO 14. During this period, the SYG1 δ¹⁸O is characterized by the persistence of centennial-scale oscillations. These centennial δ¹⁸O enrichment excursions are clearly mirrored in the δ¹³C signal. This correlation suggests that changes in soil CO₂ production at this site are closely correlated with centennial-scale ASM variability. Furthermore, power spectrum analysis shows that δ¹⁸O and δ¹³C display the common periodicities consistent with solar activity cycles, implicating a control of solar activity on the ASM and soil humidity. Particularly, weak solar activity generally corresponds to weak ASM and a decline in soil CO₂ production. One possible link between them is that external forcing controls the ASM intensity via the thermal contrast between the ocean and land. Subsequently, the balance of soil moisture co-varies with the hydrological responses. Finally, the soil CO₂ production is further amplified by ecological effect.