The westerly winds and East Asian summer monsoon play a leading role in climate change of southwestern North America and eastern Asia since the Last Glacial Maximum (LGM), respectively. Their convergence in arid and semi-arid regions of the Asian continent (AAC) makes the regional climate change more complicated on the millennial-scale. There are still limitations in applying paleoclimate records and climate simulations of characteristic periods to investigate climate change patterns since the LGM in this region. In this study, we adopt two indexes indicating effective moisture and rely on a continuous simulation, a time slice simulation, and numerous paleoclimate records to comprehensively investigate the climate change modes and their driving mechanisms since the LGM in AAC. Results demonstrate a millennial-scale climate differentiation phenomenon and three climate change modes possibly occurring in AAC since the LGM. The western AAC largely controlled by the westerly winds is featured as wet climates during the LGM but relatively dry climates during the mid-Holocene (MH), coinciding with the climate change mode in southwestern North America. Conversely, dry conditions during the LGM and relatively wet conditions during the MH are reflected in eastern AAC governed by the East Asian summer monsoon, which leans to the climate change mode in eastern Asia. If climate change in central AAC is forced by the interaction of two circulations, it expresses wet conditions in both the LGM and MH, tending to a combination of the southwestern North American and eastern Asian modes. Precipitation and evaporation exert different intensities in influencing three climate modes of different periods. Furthermore, we identify the significant driving effects of greenhouse gases and ice sheets on westerly-dominated zones of AAC, while orbit-driven insolation on monsoon-dominated zones of AAC.
Droughts are the most frequent natural disaster in regions at the margins of the East Asian summer monsoon (EASM), which pose threats to agriculture, the economy, and human lives. However, the limitations of only approximately 60 years of meteorological observations hamper our understanding of the characteristics and mechanisms of local hydroclimate. Trees growing in the marginal region of the EASM are usually sensitive to moisture variations and have played important roles in past hydroclimatic reconstructions. Here, a 303-year tree-ring-width chronology of Pinus tabulaeformis from Mt. Lama, which is located in the junction of the Liaoning Province and Inner Mongolia, China, was used to reconstruct the May-August Palmer drought severity index (PDSI) in the marginal region of the EASM. The transfer function explains 48.0% (or 47.2% after adjusting for the loss of the degrees of freedom) of the variance over the calibration period from 1946 to 2012. A spatial correlation analysis demonstrates that our PDSI reconstruction can represent the drought variability on the northernmost margin of the EASM. The winter Asian polar vortex area index showed a delayed impact on the summer EASM precipitation in the following year.
With the advent of climate change, winter temperatures have been steadily increasing in the middle-to-high latitudes of the world. However, we have not found a corresponding decrease in the number of extremely cold winters. This paper, based on Climatic Research Unit (CRU) re-analysis data, and methods of trend analysis, mutation analysis, correlation analysis, reports on the effects of Arctic warming on winter temperatures in Heilongjiang Province, Northeast China. The results show that: (1) during the period 1961- 2018, winter temperatures in the Arctic increased considerably, that is, 3.5 times those of the Equator, which has led to an increasing temperature gradient between the Arctic and the Equator. An abrupt change in winter temperatures in the Arctic was observed in 2000. (2) Due to the global warming, an extremely significant warming occurred in Heilongjiang in winter, in particular, after the Arctic mutation in 2000, although there were two warm winters, more cold winters were observed and the interannual variability of winter temperature also increased. (3) Affected by the warming trend in the Arctic, the Siberian High has intensified, and both the Arctic Vortex and the Eurasian Zonal Circulation Index has weakened. This explains the decrease in winter temperatures in Heilongjiang, and why cold winters still dominate. Moreover, the increase in temperature difference between the Arctic and the Equator is another reason for the decrease in winter temperatures in Heilongjiang.
Precipitation in the arid region of Northwest China (NWC) shows high spatial and temporal variability, in large part because of the region's complex topography and moisture conditions. However, rain gauges in the area are sparse, and most are located at altitudes below 2000 m, which limits our understanding of precipitation at higher altitudes. Interpolated precipitation products and satellite-based datasets with high spatiotemporal resolution can potentially be a substitute for rain gauge data. In this study, the spatial and temporal properties of precipitation in the arid region of NWC were analyzed using two gridded precipitation products: SURF_CLI_CHN_PRE_DAY_GRID_0.5 (CHN) and Tropical Rainfall Measuring Mission (TRMM) 3B43. The CHN and TRMM 3B43 data showed that in summer, precipitation was more concentrated in southern Xinjiang than in northern Xinjiang, and the opposite was true in winter. The largest difference in precipitation between mountainous areas and plains appeared in summer. High-elevation areas with high precipitation showed more stable annual precipitation. Different sub-regions showed distinctive precipitation distributions with elevation, and both datasets showed that the maximum precipitation zone appeared at high altitude.
The glaciers in the Sanjiangyuan Nature Reserve of China (SNRC) are a significant water resource for the Yangtze, Yellow, and Mekong rivers. Based on Landsat Thematic Mapper (TM)/ Operational Land Imager (OLI) images acquired in 2000, 2010, and 2018, the outlines of glaciers in the SNRC were obtained by combining band ratio method with manual interpretation. There were 1714 glaciers in the SNRC in 2018, with an area of 2331.15±54.84 km2, an ice volume of 188.90±6.41 km3, and an average length of 1475.4±15 m. During 2000-2018, the corresponding values of glaciers decreased by 69, 271.95±132.06 km2, 18.59±8.83 km3, and 84.75±34 m, respectively. Glaciers in the Yangtze River source area witnessed the largest area loss (-154.45 km2), whereas glaciers in the Mekong River source area experienced the fastest area loss (-2.02%·a-1) and the maximum reduction of the average length (-125.82 m). Overall, the retreat of glaciers in the SNRC exhibited an accelerating trend. Especially, the loss rate of glacier area in the Yellow River source area in 2010-2018 was more than twice that in 2000-2010. The glacier change is primarily attributed to the significant rise in temperature during the ablation period. Some other factors including the size, orientation and terminus elevation of glaciers also contributed to the heterogeneity of glacier change.
Biologists have considered both winter coldness and temperature seasonality as major determinants of the northern limits of plants and animals in the Northern Hemisphere, which in turn drive the well-known latitudinal diversity gradient. However, few studies have tested which of the two climate variables is the primary determinant. In this study, we assess whether winter coldness or temperature seasonality is more strongly associated with the northern latitudinal limits of tree species and with tree species richness in North America. Tree species were recorded in each of 1198 quadrats of 110 km × 110 km in North America. We used correlation and regression analyses to assess the relationship of the latitude of the northern boundary of each species, and of species richness per quadrat, with winter coldness and temperature seasonality. Species richness was analyzed within 38 longitudinal, i.e., north-south, bands (each being >1100 km long and 110 km wide). The latitudes of the northern range limits of tree species were three times better correlated with minimum temperatures at those latitudes than with temperature seasonality. On average, minimum temperature and temperature seasonality together explained 81.5% of the variation in the northern range limits of the tree species examined, and minimum temperature uniquely explained six-fold (33.7% versus 5.8%) more of this variation than did temperature seasonality. Correlations of tree species richness with minimum temperatures were stronger than correlations with temperature seasonality for most of the longitudinal bands analyzed. Compared to temperature seasonality, winter coldness is more strongly associated with species distributions at high latitudes, and is likely a more important driver of the latitudinal diversity gradient.
With the implementation of the Grain for Green Project, vegetation cover has experienced great changes throughout the Loess Plateau (LP). These changes substantially influence the intensity of evapotranspiration (ET), thereby regulating the local microclimate. In this study, we estimated ET based on the Penman-Monteith (PM) method and Priestley-Taylor Jet Propulsion Laboratory (PT-JPL) model and quantitatively estimated the mass of water vapor and heat absorption on the LP. We analyzed the regulatory effect of vegetation restoration on local microclimate from 2000 to 2015 and found the following: (1) Both the leaf area index (LAI) value and actual ET increased significantly across the region during the study period, and there was a significant positive correlation between them in spatial patterns and temporal trends. (2) Vegetation regulated the local microclimate through ET, which increased the absolute humidity by 2.76-3.29 g m?3, increased the relative humidity by 15.43%-19.31% and reduced the temperature by 5.38-6.43°C per day from June to September. (3) The cooling and humidifying effects of vegetation were also affected by the temperature on the LP. (4) Correlation analysis showed that LAI was significantly correlated with temperature at the monthly scale, and the response of vegetation growth to temperature had no time-lag effect. This paper presents new insights into quantitatively assessing the regulatory effect of vegetation on the local microclimate through ET and helps to objectively evaluate the ecological effects of the Grain for Green Project on the LP.
Mountainous landscapes are particularly vulnerable and sensitive to climate change and human activities, and a clear understanding of how ecosystem services (ES) and their relationships continuously change over time, across space, and along altitude is therefore essential for ecosystem management. Chongqing, a typical mountainous region, was selected to assess the long-term changes in its key ES and their relationships. From 1992 to 2018, the temporal variation in water yield (WY) revealed that the maximum and minimum WYs occurred in 1998 and 2006, which coincided with El Niño-Southern Oscillation and severe drought events, respectively. Soil export (SE) and WY were consistent with precipitation, which reached their highest values in 1998. During this period, carbon storage (CS) and habitat quality (HQ) both decreased significantly. ES in Chongqing showed large variations in altitude. Generally, WY and SE decreased with increasing altitude, while CS and HQ increased. For spatial distribution, WY and SE showed positive trends in the west and negative trends in the east. In regard to CS and HQ, negative trends dominated the area. Persistent tradeoffs between WY and soil conservation (SC) were found at all altitude gradients. The strong synergies between CS and HQ were maintained over time.
Investigating topographic and climatic controls on erosion at variable spatial and temporal scales is essential to our understanding of the topographic evolution of the orogen. In this work, we quantified millennial-scale erosion rates deduced from cosmogenic 10Be and 26Al concentrations in 15 fluvial sediments from the mainstream and major tributaries of the Yarlung Zangbo River draining the southern Tibetan Plateau (TP). The measured ratios of 26Al/10Be range from 6.33 ± 0.29 to 8.96 ± 0.37, suggesting steady-state erosion processes. The resulted erosion rates vary from 20.60 ± 1.79 to 154.00 ± 13.60 m Myr-1, being spatially low in the upstream areas of the Gyaca knickpoint and high in the downstream areas. By examining the relationships between the erosion rate and topographic or climatic indices, we found that both topography and climate play significant roles in the erosion process for basins in the upstream areas of the Gyaca knickpoint. However, topography dominantly controls the erosion processes in the downstream areas of the Gyaca knickpoint, whereas variations in precipitation have only a second-order control. The marginal Himalayas and the Yarlung Zangbo River Basin (YZRB) yielded significantly higher erosion rates than the central plateau, which indicated that the landscape of the central plateau surface is remarkably stable and is being intensively consumed at its boundaries through river headward erosion. In addition, our 10Be erosion rates are comparable to present-day hydrologic erosion rates in most cases, suggesting either weak human activities or long-term steady-state erosion in this area.
The Qinling Mountain Range (QMR) spans a large region in China and is an important area of hominin activities. Many Paleolithic sites are found in Bahe, South Luohe, and Hanjiang river valleys in the northern, eastern, and southern part of the range, respectively. The Danjiang River valley acts as a channel connecting these valleys and stretches from the north to the south of the QMR. The previous dating of the Paleolithic sites in the Danjiang valley mainly relied on geomorphologic comparison, stratigraphic correlation, fossil characteristics, and Paleolithic artifacts, indicating a lack of absolute data. In this study, we conducted a detailed geochronological investigation of the entire valley, and selected an ideal site—the Miaokou profile. Based on the identification of the loess-paleosol sequences, optically stimulated luminescence, and magnetostratigraphy, the Paleolithic artifacts of the Miaokou site located within the S5 and S6 layers of the profile belong to ~0.6-0.7 Ma. This suggests that the Paleolithic site is an old site in the Danjiang River valley, and this period also witnessed a rapid increase in the number of hominin sites during the Middle Pleistocene. Combining our results with previous reports across the QMR, we propose that the Danjiang River valley might have been a corridor for hominin migration, and is worthy of further investigation.
