Linlin Gao

Living and relict Qilian juniper (Juniperus przewalskii Kom.) trees from the northeastern Tibetan Plateau provide a unique paleoclimate archive spanning centuries to millennia. Various climate signals reflected by Qilian Juniper tree-ring records from different elevations inspire us to investigate the temperature and precipitation covariance along the altitude. Here, we analyses temperature and precipitation measurements from 60 meteorological stations between 1139 and 3663 m asl on the northeastern Tibetan Plateau. We find that summer temperature and precipitation are positively correlated at higher elevations, while they show an inverse relationship at lower elevations. We also observe that anthropogenic warming has led to wetter (drier) conditions at higher (lower) elevations. Not captured by gridded climate data, our results suggest that tree ring-based hydroclimate reconstructions from arid Asian mountain systems are localised representations. We argue that warming-induced convective precipitation is altering the hydrological cycle of Asian ‘Water Towers’ through changes in plant growth, vegetation composition, snow cover, glacier extent, and river runoff.

• Quantitatively study charring progress with multi-indicators; • Analyzing the microstructure changes of wood/charcoal by measuring the thickness of tracheid cell wall and the lumen area during the charring process for the first time; • Comparing the essential indexes of experimental charred wood with archaeological charcoal fossil; • Providing key physical and chemical parameters in the wood charcoalification process.

In the past few decades, the East Asian summer monsoon (EASM) has experienced an unprecedented weakening, exacerbating drought in northern China, especially in the monsoon margin area. Improving our understanding of monsoon variability will benefit agricultural production, ecological construction, and disaster management. Tree-ring is widely used as proxy data for extending the monsoon history. However, in the East Asian monsoon margin, the tree-ring width were mostly formed before the rainy season, thus may have limited ability to indicate the monsoon variability. Intra-annual density fluctuations (IADFs) can provide higher resolution information on tree growth as well as evidence of short-term climate events. Here, we used Chinese pine (Pinus tabuliformis Carr.) samples from the eastern edge of the Chinese Loess Plateau (CLP), where the climate is deeply affected by monsoon, to investigate the response of tree growth and IADFs frequency to climate variation. We show that tree-ring width and IADFs record significantly different climatic signals. The former was mainly affected by moisture conditions at the end of the previous growing season and the current spring. While the latter was common in years when severe droughts occurred in June and July, especially in June. This period coincides with the onset of the EASM, so we further analyzed the relationship between IADFs frequency and the rainy season. Both correlation analysis and the GAM model suggest that the frequent occurrence of IADFs may be related to the late start of the monsoon rainy season, meaning that we have found a new indicator in tree-ring records that can capture monsoon anomalies. Our results provide further insight into drought variation in the eastern CLP, which also implicates the Asian summer monsoon dynamic.

Drought is a recurring challenge, especially in the arid and semi‐arid regions. Therefore, understanding its spatial and temporal variation is important for pre‐disaster planning and sustainable water resource management during drought. However, the sparse and short length of the instrumental records in midlatitude East Asia hampered the full understanding of drought variation, especially at multidecadal and longer timescales. Here, we compiled a tree‐ring network of 364 chronologies in midlatitude East Asia and reconstructed the variation of the averaged May–August Standardized Precipitation Evapotranspiration Index at a spatial resolution of 0.5° × 0.5°, for the period 1501–2000 CE. The reconstruction captured the spatial and temporal variation of actual drought well and has a strong association with a drought atlas that was derived from historical documents. The study area has experienced an expansion of dry areas during the past decades; however, it is still within the natural variability of the past half millennium. According to drought variation during the instrumental period, the study area was divided into four subregions; however, running correlations showed that drought variation in some subregions was similar in past centuries, except in recent decades. This study provides new data for understanding the spatiotemporal variability of drought in midlatitude East Asia, and the vanished correlation between drought variation in some regions during the past decades indicates the complex forcing mechanism of regional drought variation.