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Precipitation variations in arid central Asia over past 2500 years: Possible effects of climate change on development of Silk Road civilization
Abstract
The ecological environment of arid central Asia (ACA) is fragile and sensitive to long-term climate change. Recent palaeoclimatological studies have mainly focused on northwestern China, which is located on the eastern side of the region. Holocene palaeoclimate records from the western region of ACA are scarce, thus hindering the exploration of the relationship between climate change and Silk Road civilization. In this study, we conduct a pollen analysis of Lake Sasikul on the Pamir Plateau in Tajikistan and use pollen data to quantitatively reconstruct the precipitation history over the last 2500 years. The results show that herbaceous pollen is primarily represented by Artemisia and Amaranthaceae, thus suggesting the persistent dominance of grassland in the vicinity of Lake Sasikul. Amaranthaceae, which is the most drought-tolerant pollen type, shows the highest values during the Medieval Warm Period (MWP, 950-1300 CE). The values of Artemisia and cold-wet-adapted Picea pollen are higher during the Little Ice Age (LIA, 1550-1900 CE). The quantitative reconstruction shows that during the MWP, the mean annual precipitation is 120 mm, which is approximately 15% lower than the level of modern precipitation; meanwhile, during the LIA, the average annual precipitation is 160 mm (up to 210 mm), which is approximately 20% higher than the present value. We combine our results with regional temperature records and archaeological data to discuss the possible effects of climate change on the development of Silk Road civilization. The hydrothermal configuration may have altered water resources and thus affect human activities in ACA. From 580 to 900 CE, i.e. during the Sui and Tang Dynasties, ice and snow meltwater increased under warm climate, whereas the amount of precipitation was average. Additionally, human settlements intensified along with urbanization, and the Silk Road civilization was prosperous and well-developed. From 1270 to 1650 CE, i.e. during the Yuan and Ming Dynasties, under overall colder and drier conditions and due to insufficient freshwater input, the intensity of local human settlement weakened, and the Silk Road civilization declined. Therefore, owing to global warming and increasing precipitation, new development opportunities have emerged for the development of agriculture and social economy in ACA.
... A conceptual model describing the relations between the climate, hydrology, and society of an arid mountain-basin system has also improved our understanding of the complex human-environment interactions in arid regions [37]. In the domain of archaeology, the second and third national surveys of cultural relics revealed dozens of archaeological sites in the southern Tarim Basin [38,39], the findings of which have become a primary reference for relevant research [40][41][42][43]. Despite the fact that researchers have dated the activity of Paleolithic human groups in the Kunlun Mountains during the Middle Holocene [44], it is still possible that it was not until the second half of the second millennium BCE that sedentary populations emerged in the oases [45]. ...
... A similar pattern of human activity was also detected in the eastern Tarim Basin, which is especially famous for the decline of the Loulan Kingdom [80]. Inversely, the overall human activity reached a peak, not only in southern Tarim Basin ( Figure 5), but also in the whole region of Xinjiang's Silk Road [43]. Given that land degradation and the shrinkage of the oases and tailwater have been generally validated [3,4,36,81], different hypotheses were developed to explain the collapse of ancient civilizations in the hinterland of the Taklimakan Desert: (1) environmental deterioration due to climate change [43,80,82]; (2) environmental deterioration caused by excessive tillage and irrigation [5,78]; and (3) the impact of geopolitics and frequent warfare (Table S1) and the refined chronology of key archaeological sites labeled as (1) Liushui cemetery; (2) Niya ancient city; (3) Shanpula cemetery; (4) Yuansha ancient city; (5) DDWLK; (6) AKKQKRK. ...
... Inversely, the overall human activity reached a peak, not only in southern Tarim Basin ( Figure 5), but also in the whole region of Xinjiang's Silk Road [43]. Given that land degradation and the shrinkage of the oases and tailwater have been generally validated [3,4,36,81], different hypotheses were developed to explain the collapse of ancient civilizations in the hinterland of the Taklimakan Desert: (1) environmental deterioration due to climate change [43,80,82]; (2) environmental deterioration caused by excessive tillage and irrigation [5,78]; and (3) the impact of geopolitics and frequent warfare (Table S1) and the refined chronology of key archaeological sites labeled as (1) Liushui cemetery; (2) Niya ancient city; (3) Shanpula cemetery; (4) Yuansha ancient city; (5) DDWLK; (6) AKKQKRK. The shadows in grey represent the SPD of each site; crosses in red and black represent the original and calibrated radiocarbon dates, respectively, while the red bars represent the chronology restricted by Bayesian chronological modeling. ...
Famous for Taklimakan, the world’s second largest sandy desert, the Tarim Basin in Xinjiang has long attracted researchers from various fields to investigate its paleoenvironment and antiquity. The southern part of this basin is an ideal region in which to investigate the interactions between humans and the environment due to its fragile habitat and prosperous ancient civilizations. However, the lack of direct radiocarbon dating data has caused the chronologies of some of the archaeological sites to be debatable, which hinders our ability to reconstruct historical patterns of human activity and further understand, in a coherent manner, their interaction with the environment. This study reports 25 new radiocarbon dates acquired from ten undated archaeological sites in the southern Taklimakan Desert in order to refine their chronologies. Based on this, a radiocarbon dataset was established to reveal the trajectory of human activity with the support of Bayesian chronological modeling. The results indicate a two-millennium continuous flourishing of the local society since the beginning of the first millennium BCE, as well as a peak of human activity during the Tang Dynasty (618–907 CE). The distinct trajectory of human activity in the southern Tarim Basin revealed by this study provides a solid foundation for further assessments of human–environment interaction in the Tarim Basin and along the Silk Road.
... In contrast, Li et al. (2020) proposed that glacial meltwater might be the key factor driving Holocene evolution of the glacier-fed lakes on this region. Meanwhile, different levels of hydroclimatic instability at the millennial scale on the QTP have also been noted (Chen et al., 2009;Chen et al., 2023;Ding et al., 2023;Li et al., 2022;Wang et al., 2021). However, high quality paleohydrological records are still scarce on the northern QTP. ...
... The four AMS 14 C dates determined on bulk organic carbon showed a linear correlation that followed the stratigraphic order of the Sumxi Co sediment (Table 1). However, a comparison of the 137 Cs time marker of 1963 CE with AMS 14 C dating of the bulk organic carbon at the same (Lan et al., 2020b); Lake Bosten (Chen et al., 2006); Lake Kalakuli (Aichner et al., 2015;Liu et al., 2014); Lake Sasikul (Ding et al., 2023); Lake Sugan (Chen et al., 2010;Zhou et al., 2007); Lake Ayakum (Wang et al., 2021); Bangong Co Gasse et al., 1996); Guozha Co (Li et al., 2020); Lake Xardai (Chen et al., 2023); Taro Co (Huang et al., 2023a); Serling Co (Hou et al., 2021); Nam Co (Huang et al., 2023b); Sahiya Cave (Sinha et al., 2015) and Dongge Cave (Wang et al., 2005). Arrows indicate the dominant atmospheric circulation systems in the region. ...
... The purple diamonds represent δ 18 O carb variations of ostracod shells. Liu et al., 2014); the hydrogen isotopic record from Lake Karakuli (C, Aichner et al., 2015); reconstructed precipitation based on pollen from Lake Sasikul in Tajikistan (D, Ding et al., 2023); wet events in arid central Asia (E, Liu et al., 2023); and δ 18 O record from Dongge Cave in south China (F, Wang et al., 2005). millennia compare favorably with the high-resolution precipitation changes inferred from the hydrogen isotopic compositions of n-alkanoic acids from Lake Karakuli (Fig. 6C, Aichner et al., 2015). ...
... Since the Neolithic, numerous Neolithic cultures have emerged successively on the NCP, including the Cishan-Beifudi (Duan, 2007(Duan, , 2022, Dawenkou (Wu, 1982;Luan, 2003), Yangshao (Liu and Chen, 2012;Dong et al., 2016), and Longshan (Han, 2003;Dai, 2016) cultures. The relationship between climate change and the development of civilisation has been a focal point in the field of global change research (Fang and Zhang, 2017;Chen et al., 2020;Sun et al., 2022b;Tian et al., 2022;Ding et al., 2023). For example, based on oxygen isotope data from stalagmites in Wanxiang Cave, China, Zhang et al. (2008) found that the transitions between dynasties in China often corresponded to periods of weakened Asian summer monsoons, whereas the strengthening of the monsoon allowed dynasties to prosper and flourish. ...
... Previous studies have indicated that vegetation changes during the Holocene were influenced by climate, evolutionary processes, and human activities (Tarasov et al., 2019;Ding et al., 2022). In particular, as population increased and human activities intensified, human disturbance of vegetation became more pronounced (Mottl et al., 2021;Ding et al., 2022Ding et al., , 2023. Therefore, the influence of human activity should be considered when exploring the evolution of vegetation. ...
... ka BP was a dry-warm period. The prosperous period of the Tang Dynasty coincided with the warm-wet period with high humidity [49]. The warm and humid climate laid the material foundation for population growth, urban prosperity and cultural exchanges along the Silk Road. ...
Cultural Heritage Sites (CHS) serve as tangible evidence of regional human–environment interactions and spatial representation of historical memory. The research developed a Xinjiang CHS database and integrated geographic information technology and historical geography research methods to examine the spatio-temporal distribution evolution characteristics and geographic influencing factors in the arid region. It utilized the nearest neighbor index, kernel density estimation, the center of gravity model, and standard deviation ellipse to explore the spatio-temporal evolution law. Furthermore, it employed spatial overlay and qualitative text to analyze the geographical influence mechanism of the CHS. The results showed the following: (1) The CHS spatial distribution showed a pattern of “multicore agglomeration-linear extension”, concentrated in 13 key cities and four major areas that extended along the Silk Road routes. (2) The CHS diachronic development fluctuated in a pattern of “three peaks and three valleys”. The spatial center of gravity has shifted from southern Xinjiang to northern Xinjiang, manifesting a concentrated-diffused characteristic along the northeast–southwest axis. (3) The spatial selection followed the rules of “preferring lower terrain” and “proximity to water”. The elevation distribution of CHS has shifted from mid-high elevations to low elevations. The proportion of CHS on low-slope terrain increased from 78.6% in the Pre–Qin period to 93.02% in Modern History. 93.02% of CHS in Modern History were distributed within the 10 km buffer zone of rivers. (4) Climate aridity and human activities formed a dynamic influence mechanism; natural factors constructed the base pattern of CHS distribution, and human activities drove the dynamic adjustment. The findings revealed the historical trajectory and driving logic of the evolution of CHS in Xinjiang and provided a scientific basis for cultural heritage protection and ecological governance. This study had limitations in terms of the limited research scope and the lack of comprehensive quantitative analysis of influencing factors.
... Yu et al., 2021). Environmental issues in the region are closely related to various socioeconomic and developmental changes (Ding et al., 2023;Robinson, 2016). For instance, several studies have confirmed the prevalence of anticipated climate or environmental migration (Blondin, 2019(Blondin, , 2023Hugo & Bardsley, 2014;Rakhmatulina, Samay, & Issova, 2024). ...
... A landscape can be considered to consist of multiple layers, including the atmosphere (e.g., weather and air quality), water (e.g., floods and water shortages), living things, nutrients (e.g., soil and water quality), livelihood (e.g., cultivation and livestock farming), land cover and land use, and society (e.g., tradition, culture, and faith), where each layer has seasonal and annual changes and is interdependent with other layers. Consider an example that demonstrates spatio-temporal changes in society and climate in a landscape at a 100-10,000-year scale (e.g., deMenocal, 2001;Tange, 2010;Nishino, 2019;Inamura et al., 2022;Ding et al., 2023). First, rapid climate change affects the geographical distribution of plants and their species compositions and then alters the geographical distribution of animals (Matthews et al., 2011;Boit et al., 2016;Pecl et al., 2017;Yasuda, 2017;Nishino, 2019;Zemeng et al., 2020;Chust et al., 2023). ...
The relationship between people and the landscape consists of multi-layer components such as the atmosphere, water, living things, nutrients, livelihood, society, and information. To clarify temporal changes in this relationship, previous studies have used conventional approaches based on field work and satellite observation. However, interpretations based on these conventional two approaches are subject to temporal, spatial, representative, and interpretability gaps. In this perspective and review paper, we propose three approaches to bridge these gaps: (1) text mining of historical documents and data (mining for handwritten or printed old documents, books, diaries, field notes, and statistics), (2) video mining (mining for descriptions, interviews, narrations, and background of photos/video), and (3) social sensing (observing real-world events by using digital communication tools such as social networking services, YouTube, and Google Trends). We discuss the utility, limitation, and perspective of each of these proposed approaches by presenting case examples of their application from Northeast Asia. We found that (1) the text mining approach can be useful to remove the temporal, representative, and interpretability gaps but requires immense amounts of time and labor; (2) the video mining approach can be useful to remove the temporal, representative, and interpretability gaps, but uncertainties remain and there are usage limitations with video materials; and (3) the social sensing approach can be useful to reduce the spatial, representative, and interpretability gaps, but it requires careful consideration in terms of data quality and ethical issues. To deepen our understanding of the relationship between people and the landscape during periods of social and climate change on a scale of seasons to centuries from the viewpoint of personal attributes and traits, we conclude that an integrated analysis that combines the conventional approaches such as field work and satellite observation and the proposed approaches should be further developed. Through the development of our proposed integrated analytical approaches, we expect to establish a new transdisciplinary study that integrates anthropology, sociology, informatics, history, and natural sciences.
... Third, a pollen-based quantitative paleoclimatic reconstruction was obtained. Weighted averaging partial least squares (WAPLS), which is one of the most widely used methods based on unimodal species response and with good empirical predictive power and efficient extraction of components (Birks, 1998;Zheng et al., 2016;Herzschuh et al., 2019;Lu et al., 2019;Sun et al., 2020;Ding et al., 2023), was used to establish regression and calibration functions, using the "rioja" library (Juggins, 2022). ...
Variations in East Asian summer monsoon (EASM) precipitation impact the ecological environment, economy, and society of eastern China. However, the nature of precipitation changes and their driving mechanisms in this region during the last millennium remain unclear. We conducted a pollen study of the recent sediments of Moon Lake in Northeast China to quantitatively reconstruct precipitation changes over the past ∼1000 years. The results show that during the Medieval Warm Period (MWP, 1068–1300 CE), the Moon Lake area had a relatively dense vegetation cover and experienced favorable climatic conditions. Precipitation increased during this period, with an average precipitation anomaly percentage (PAP) of 0.1% which reached a peak of 7.2%. However, during the Little Ice Age (LIA, 1400–1900 CE), the climatic conditions in the Moon Lake area deteriorated, and there was a reduction in the cover of forest vegetation and relatively open landscapes developed. Precipitation decreased during this period, with an average PAP of −1.4% which reached a minimum of −9.9%. During the 20th-century warming period (CWP, 1900 CE–present), the regional environmental conditions improved substantially, and the density of the forest vegetation increased. Precipitation increased, with an average PAP of 1.1% and maximum of 11.1%. Additionally, the Moon Lake area exhibited several prominent short-term (centennial- to decadal-scale) climate fluctuations over the last millennium. Drought events, characterized by negative precipitation anomalies, occurred during 1070–1130 CE, 1150–1190 CE, 1370–1420 CE, 1660–1720 CE, and 1870–1930 CE. These climate anomalies also occurred in northern China, with significant impacts on the socioeconomic well-being of the local population. We suggest that changes in EASM intensity, modulated by solar activity, were responsible for these anomalies. Solar activity directly or indirectly drives increases (decreases) in sea surface temperature (SST) in the North Pacific and North Atlantic Oceans, which lead to cold (warm) phases of the El Niño/Southern Oscillation (ENSO) and Pacific decadal oscillation (PDO), as well as to warm (cold) phases of the Atlantic Multidecadal Oscillation (AMO), as occurred during the MWP (LIA). This complex interaction alternately strengthens (weakens) the EASM intensity, resulting in northward (impeded northward) shifts of the monsoon rainbelt, which led to increased (decreased) precipitation in the Moon Lake area during the MWP (LIA). Furthermore, we propose that the anomalous warm PDO phases and anomalous AMO cold phases may act as a driver of the occurrence of extreme drought events on the centennial- to decadal-scale. We suggest that these cold and warm fluctuations of the PDO and AMO should be the focus of research attempts to predict future climate extreme events.
... Bubenzer and Riemer (2007) found that several areas with surface water resources in the eastern Sahara Desert became the locations of hunting and gathering during the humid period of the Holocene, and they were thus the locations of temporary human settlements. A recent study suggested that increased precipitation driven by climatic warming was conducive to cultural development in arid Central Asia (Ding et al., 2023). These results indicate that increased precipitation and a humid climate in arid regions are generally favorable for societal development, although an excessively humid environment may have adverse effects. ...
Spatiotemporal changes in the Holocene climate of the arid region of China were principally caused by shifts in the intensity and location of the East Asian summer monsoon (EASM). However, our knowledge of these EASM variations is limited, especially since the middle Holocene. We investigated two aeolian sedimentary sections (the Linxia/LX and Gulang/GL sections) on the western Chinese Loess Plateau (CLP), to explore the variations in the intensity and location of the EASM and their impact on the regional environment and human cultural development during the middle to late Holocene. The longitudes of these two loess sections are similar, but the GL section is located on the northern edge of the CLP, in the eastern Hexi Corridor, and it is situated further north than the LX section. The chronologies of both sections are based on accelerator mass spectrometry 14 C dating, and environmental magnetic parameters and grain size end-members were used to reconstruct their moisture histories. The results suggest that the climate at the LX section was relatively dry before 3.5 ka, after which it became wetter. In contrast, at the GL section, the climate was also relatively dry before 3.5 ka, with the wettest conditions occurring during 3.5-2 ka, but subsequently there was an abrupt shift to a dry climate. We suggest that these spatiotemporal patterns reflect the westward movement and rapid southward retreat of the EASM and the linked monsoon rainfall belt. TraCE-21 ka climate simulation results support our inference. We also found that, compared with other ancient cultures in the eastern Hexi Corrido, sites of the Shajing culture, dated to ~2.4-2.8 ka, are predominantly located in areas that are arid at the present-day, and relatively distant from rivers. We suggest that this distribution pattern reflected the occurrence of a humid climate during the period of the Shajing culture, thus demonstrating the impact of the EASM on cultural development in this region.
Central Asia, located in the innermost part of the Eurasian continent, has experienced “warming and humidification” in recent decades, with potentially important implications for tree growth in alpine forests, which are critical for regional water reserves. We use nested principal component analysis to assess tree radial growth patterns and reveal significant positive trends since the 20th century across Central Asian alpine forests (0.076 per decade during 1900–2021, p = 0.003). Regional hydroclimatic variations affect the greening of these alpine forests, especially with extreme droughts being the most damaging. Growth acceleration is driven by low-latitude warming, which enhances regional temperatures and precipitation. The warming ocean centers alter atmospheric circulation patterns, leading to more moisture being transported to the Central Asian alpine forests, thereby increasing regional precipitation and promoting tree growth. Our model projections indicate that growth rates will continue to rise in the future. However, unprecedented warming may eventually lead to growth deterioration if negative effects, such as insufficient precipitation, occur due to breakdown signs of positive feedback mechanisms, such as moisture transport driven by low-latitude warming. Our study highlights the beneficial, but not unlimited, influences of climate warming on tree growth in Central Asian alpine forests, with implications for the sustainability of water resources. However, as urban and agricultural demands escalate, a holistic, long-term perspective is recommended to mitigate the adverse effects of temperature increases.
The arid Central Asia has long demonstrated a correlation between human activity and climatic fluctuations, particularly during the Holocene. However, Late Holocene palaeoclimate records remain sparse, limiting our understanding of the dynamic relationship between climate variability and human civilization over the past millennium. This study based on peat sediment samples from the Zhaosu Basin on the northern slopes of the Western Tian Shan Mountains, China, reconstructs vegetation and climate changes over the past millennium by employing precise dating techniques and high‐resolution pollen analysis. The results were as follows: (1) grasslands have consistently dominated the northern slopes of the Western Tian Shan over the last millennium, as evidenced by the prevalence of pollen types, such as Artemisia , Chenopodiaceae, and Poaceae. During the Medieval Climate Anomaly (MCA, 1046–1288 ad ), frequently fluctuating Artemisia /Chenopodiaceae (A/C) ratios indicated a transition from warm–arid to warm–humid conditions. This trend shifted during the Little Ice Age (LIA, 1288–1476 ad ), marked by increased Picea pollen and positive principal component analysis axis 2 scores, suggesting a cooler and wetter environment. Pollen concentrations of arborvitae and shrubs peaked during the LIA (1476–1606 ad ), alongside high Picea content, signaling an intensified cold and wet climate. (2) Historical records correlate climate conditions with patterns of human habitation and development. The warm, humid climate during the MCA (1046–1288 ad ) coincided with the Song Dynasty, fostering population growth and cultural development on both slopes of the Tian Shan region. Conversely, during the LIA (1288–1606 ad ), cooling temperatures and frequent conflicts triggered significant migrations, particularly to the northern slopes, (i.e., during the Yuan‐Ming period) where conditions were more favorable. The center of gravity of the population relocated to the northern slopes of the Tian Shan Mountains. This shift promoted agricultural advancements in later periods, despite the challenges posed by the harsher climate.
High-Mountain Asia (HMA) hosts the largest concentration of modern glaciers in middle- and low-latitude regions. The widespread glacial landforms in HMA suggest that these glaciers have experienced significant changes in extent over time. The climate of northern HMA is influenced mainly by the Asian monsoons and the mid-latitude westerlies. Changes in the climate system during glacial-interglacial cycles potentially resulted in a unique pattern of glacial evolution in northern HMA; however, elucidating this pattern requires a comprehensive understanding of the spatiotemporal evolution of the glaciers in this region. To achieve this, we compiled 450 10Be exposure ages from northern HMA, including 84 new and 366 previously reported ages, and we also conducted high-resolution simulations of paleoglacier extent that correspond with glacial geological records. Our findings emphasize the complexity of past glacier evolution throughout HMA. The two climatic domains share similarities in glacial sequences, climatic mechanisms, glacial style, and depression of the equilibrium line altitude (ELA). Landforms created by glacier advances corresponding to Marine Isotope Stages (MIS) 6, 3, and 2 have been identified in both domains, indicating a strong relationship between these advances and cooler climatic conditions. Since the penultimate glaciation, glaciers in northern HMA have gradually evolved from extensive ice fields to piedmont glaciers, to valley glaciers, and then to cirque glaciers. This transformation is reflected in the progressive ascent of the ELA. A key difference in glacial evolution between these two climatic regions is that the timing of the local last glacial maximum (lLGM) was asynchronous compared to the global last glacial maximum (gLGM). The timing of the lLGM varied between the monsoons-westerlies transitional domain and the westerlies domain, occurring during MIS 3 and MIS 4, respectively. This difference was caused by variations in the relative strength of atmospheric circulation systems and changes in moisture supply. In a similarly cool climate, variations in precipitation distribution explain the differing patterns of ELA change observed in these two climate domains during past glacial cycles.
Asian drylands encompass Arid Central Asia (ACA) and West Asia (WA), where water vapor transport is consistently governed by the westerlies. Recent research has identified a dipole pattern in Holocene hydroclimate changes between the ACA and WA, challenging previous assumptions of uniform hydroclimate shifts across the westerlies-dominated mid-latitudes of the Northern Hemisphere. However, the mechanisms behind the dipole pattern remain largely unknown. Our findings demonstrate that PMIP4 models accurately reproduced the dipole pattern, attributing it mainly to contrasting spring precipitation changes. From the middle to late Holocene, strengthened westerlies led to increased precipitation in the ACA. In contrast, rising spring solar insolation intensified the subtropical high, leading to reduced water vapor and increased descending air movement in WA, which decreased precipitation in the region. Our study suggests that WA is a distinctive region within the westerlies-dominated mid-latitudes, where low-latitude processes led to inconsistent precipitation variations from the middle to late Holocene.
The Asian inland arid zone (AIAZ), the largest inland arid region in the world, forms the core area of the Silk Road. Despite its significance, we have limited knowledge about the sediment provenance in the oases and their evolutionary processes. Studying the evolution of oases is crucial for understanding the complex interactions among environmental changes, human history, and survival strategies in the AIAZ. This study provides insights into the interactions between oases and human populations and offers references for future oasis evolution, which is essential for ecological conservation and sustainable development. We investigated three key factors in the peat profile of oasis wetlands in the central Tianshan Mountains of the AIAZ: humification degree, TOC and grain size. Our goal was to identify the sediment provenance of the oases, reconstruct the sedimentary environment and evolutionary processes, and explore the relationship between the oases and human activities. Our results indicate that the sediments in the oasis wetlands of the central Tianshan Mountains primarily originate from the Kurban Tonggute Desert, the Gobi Desert in the intermountain basins, the Baiyang River floodplain, and weathered debris from the mountains brought about by glacial snowmelt. The transport of these sedimentary materials is primarily driven by wind and water. Oasis evolution is largely influenced by warm season temperatures and recharge from glacial snowmelt. Oases expand with increased glacial snowmelt recharge and contract when it decreases. The intensity of human activity has been closely related to the evolution of oases, as they provide crucial survival sites and resources for humans in arid zones. However, the ecology of these oases faces significant challenges due to global warming and intensified human activities. This paper proposes a series of measures based on our understanding of oasis evolution and sediment sources to provide a reference for oasis conservation and sustainable development.
Reconstruction of hydrological fluctuations in arid regions has proven challenging due to a lack of reliable chronologic constraints on sparse geological archives. The aim of this study was to establish an independent record of hydrologic changes in the hyper-arid Tarim Basin (TB; northwest China) with high spatiotemporal resolution. We present comprehensive radiocarbon and tree-ring data sets of subfossilized plant remains in the TB compiled from geomorphological investigations of the paleochannels of the Tarim River (TR), the longest endorheic river in China, crossing the world’s second-largest shifting sand desert. Results show that the late medieval configuration of the TR basin was characterized by enhanced hydrological connectivity, as indicated by the formation of significant riparian forests in the desert regions at ca. 1170 CE. A distinct low-flow interval (ca. 1500−1650 CE) is identified for the first time, refining the period of a wetter-than-present TB. The present-day organization of streams in the lower TR was proto-formed after the dry period, possibly led by episodic flood-induced diversion. Our study describes the centennial-scale dynamics in the TR flow over the past millennium, offering a robust long-term context for hydrological assessment in the extensive drylands of the Asian interior.
Understanding the process and pattern of vegetation succession during the early-to-middle Holocene can yield valuable information for better predicting future vegetation evolution. In this study, we investigated the humidity evolution pattern in the North China Plain (NCP) during the early-to-middle Holocene by employing principal component analysis on 93 fossil spectra. Furthermore, by integrating the Regional Estimates of Vegetation Abundance from Large Sites (REVEALS) model, we quantitatively reconstructed the process of vegetation succession and discussed vegetation response to climate change events. Our results indicate that the sample scores of the first principal component axis (PCA axis 1) exhibited a consistent negative bias, implying a gradual rise in regional humidity. The quantitatively reconstructed tree coverage was found to be lower than the uncorrected pollen proportions, while the coverage of herb plants showed a significant increase compared to their respective pollen percentages. In the early and middle Holocene, the vegetation of the NCP succeeded from meadow steppe (10,000 ~ 8,100 cal yr B.P.) to meadow steppe with pine woodland patches (8,100 ~ 7,100 cal yr B.P.), then to pine forest (7,100 ~ 5,300 cal yr B.P.). The quantitatively reconstructed vegetation exhibited the most pronounced response to 8.2 ka climate event, with Asteraceae emerging as the dominant taxa. Furthermore, we conducted a comprehensive analysis of the impact of the 8.2 ka climate event on vegetation in northern China, identifying four distinct types of vegetation feedback: (1) negligible alterations in vegetation, (2) expansion of steppe or desert steppe, (3) proliferation of temperate tree species, and (4) augmentation of meadow steppe.
To better understand long-term precipitation changes in arid Central Asia, reconstruction of past precipitation is critical. This paper analyzed the core sediments of Balikun lake in eastern Xinjiang. We analyzed 200 pollen samples, combined with 441 surface pollen samples and a radiocarbon chronology, using the Weighted Averaging Partial Least Sequence (WA-PLS) method, to characterize the Holocene high-resolution precipitation change process in Balikun basin. And, Combined with the vegetation types reconstructed by biome method, we discussed the landscape evolution of Balikun basin. Results show that the mean annual precipitation during the Holocene can be broken into three phases: Early Holocene (11,750–8030 cal yr B.P.), which averaged about 130 mm; Middle Holocene (8030–4420 cal yr B.P.), which averaged about 250 mm; and Late Holocene (4420–0 cal yr B.P.), which averaged about 210 mm. The vegetation changed from desert to steppe during the Holocene, and the wetlands gradually expanded, which was mainly informed by precipitation and glacial melt water.
Xinjiang, China, is a representative arid region in Central Asia that is characterized by a unique mountain–basin structure and fragile mountain–oasis–desert ecosystems. Climate warming directly affects hydrological changes and may threaten water availability and ecological security in Xinjiang (XJ). In this study, we conducted a systematic review of recent climatic changes and their effects on hydrological system changes in XJ. The XJ climate has experienced significant warming and moistening during 1961–2018, and the most dramatic increase has occurred since the mid-1980s. Climate extremes have become increasingly notable in the warming climate, resulting in increases in precipitation and warm extremes and decreases in cold extremes. Moreover, accelerated local precipitation recycling has been triggered by an increasingly warm–wet climate and enhanced evaporation. The accelerated climate warming in XJ has caused significant glacier shrinkage, decreased snow cover and snowfall fraction, aggravated meteorological drought, increased river runoff, and lake expansion. The climate-related changes in the hydrological regimes may have adverse ecological effects, including increased soil moisture loss, reduced growing season vegetation growth, and shrinkage of the desert–oasis ecotone. Despite many achievements in climate and hydrological change research in XJ, we suggest that there is an urgent need to improve the comprehensive ground observation network, reproduce climate variability findings using multiple datasets, reveal the underlying physical mechanisms, and assess the hydro-meteorological disaster risks of a warming climate in the future. In addition, a conceptual framework of the climate and hydrological changes in mountain–basin system proposed, which is expected to contribute to the understanding of arid region hydrology in the future.
A modern pollen dataset with an even distribution of sites is essential for pollen-based past vegetation and climate estimations. As there were geographical gaps in previous datasets covering the central and eastern Tibetan Plateau, lake surface sediment samples (n=117) were collected from the alpine meadow region on the Tibetan Plateau between elevations of 3720 and 5170 m a.s.l. Pollen identification and counting were based on standard approaches, and modern climate data were interpolated from a robust modern meteorological dataset. A series of numerical analyses revealed that precipitation is the main climatic determinant of pollen spatial distribution: Cyperaceae, Ranunculaceae, Rosaceae, and Salix indicate wet climatic conditions, while Poaceae, Artemisia, and Chenopodiaceae represent drought. Model performance of both weighted-averaging partial least squares (WA-PLS) and the random forest (RF) algorithm suggest that this modern pollen dataset has good predictive power in estimating the past precipitation from pollen spectra from the eastern Tibetan Plateau. In addition, a comprehensive modern pollen dataset can be established by combining our modern pollen dataset with previous datasets, which will be essential for the reconstruction of vegetation and climatic signals for fossil pollen spectra on the Tibetan Plateau. Pollen datasets including both pollen counts and percentages for each sample, together with their site location and climatic data, are available at the National Tibetan Plateau Data Center (TPDC; Cao et al., 2021; 10.11888/Paleoenv.tpdc.271191).
The northeastern Qinghai‐Tibet Plateau is strongly influenced by the East Asian summer monsoon (EASM), the Indian summer monsoon (ISM) and the westerlies. However, how these various circulation systems interacted in the region during the Holocene, and the nature of the associated environmental impacts, are unclear and even controversial. Here we present a high‐resolution pollen record from Caodalian Lake since 7.9 ka (1 ka = 1,000 cal yr BP), which is used to reconstruct the regional vegetation history and climatic changes. In addition, we use a novel procedure for pollen‐based quantitative paleoclimatic reconstruction to characterize the evolution of precipitation at Caodalian Lake and nearby Qinghai Lake. The results suggest that mean annual precipitation (Pann) is the most significant factor controlling the fossil pollen record at both sites, and the Pann reconstructions are well correlated with each other (r = 0.72, p < 0.001). A synthesis of the Pann records from the two sites indicates that the precipitation in the region began to increase before 10 ka, reached a maximum during 10–5 ka, and gradually decreased thereafter. We propose that the pattern of precipitation evolution in the Qinghai Lake basin resulted from the combined effects of the ISM and EASM, with a precipitation maximum of 10–7 ka for the ISM and 7–5 ka for the EASM; both systems contributed to the regional precipitation maximum during 10–5 ka. Our well‐dated and unambiguous Pann record also provides the opportunity to reconcile paleoenvironmental reconstructions derived from different paleoenvironmental proxies from the Qinghai Lake basin.
To interpret pollen assemblages in terms of past vegetation, it is important to consider the source of pollen for any given lake profile containing sufficient pollen, and the way it arrives at its preservation site. It is of value to know the proportion of the pollen assemblage derived from the lake catchment and that which was airborne. This has been a long-neglected issue for lakes from arid areas of central Asia. In this study, we used two modified Cour (M-Cour) traps in different biomes (steppe and desert) to collect airborne pollen in the enclosed Balikun Basin during the non-flowering season (late autumn to early winter). The pollen assemblages from the traps are similar with large proportions of herbaceous and (sub-)shrub taxa such as Artemisia and Chenopodioideae. This implies a shared long-distance transport component, in addition to pollen derived from the local vegetation. These xeromorphic species are ubiquitous in the inland desert and/or steppe areas beyond the lake basin, and their pollen is likely to be carried by the wind into lake sediments from a broad area, leading to high percentages of Artemisia and Chenopodioideae pollen in lake surface-sediments. Pollen types from upstream areas (e.g. Picea, Cyperaceae, Leguminosae) are barely found in samples from the river mouth and lake surface-sediments. Thus, we speculate that the transport of pollen by inflow streams makes little contribution to the overall pollen budget in Balikun Lake. This is probably related to the low transport capacity of the surface runoff into the lake, as precipitation is low and there is limited meltwater from snow and glaciers in the surrounding mountains. Pollen assemblages from the near-shore lakebed, which have a high percentage of Chenopodioideae pollen (74.8%), represent only the very local environment, reflecting the expansion of saline-alkali habitats rather than desert. Sedimentary archives from the near-shore lakebed will thus overestimate the desert Chenopodioideae pollen component and hence cause unreliable vegetation or climate reconstructions. We also found the local vegetation composition and pollen depositional processes could significantly bias the ratio of Artemisia/Chenopodioideae (A/C), reducing its effectiveness as an index to distinguish steppe from desert. We suggest using A/C ratios from lake surface-sediments which have a large airborne pollen source area in arid areas, as a better reference for down-core fossil pollen.
Plain Language Summary
Bosten Lake, the largest inland freshwater lake of China, is located in the northeast part of Tarim Basin. The lake is important freshwater resources and plays an important role in sustaining regional social and ecological systems. In this study, we reconstructed the water‐level fluctuations of the lake over the past 2,000 years, based mainly on the Cladoceran microfossil analyses of a sediment core. The results suggest that a lower lake level occurred during the cold, high‐precipitation periods of 280–450 AD and 1570–1850 AD, and that a higher lake level occurred during the warm, low‐precipitation period of 450–1570 AD. The findings show that on the centennial timescale, the water‐level fluctuations of Bosten Lake were modulated mainly by temperature‐driven meltwater input. In addition, historical documents reveal that a large number of ancient cities in the Tarim Basin were abandoned in the third‐sixth centuries and that the trade along the ancient Silk Road was relatively depressed during that time, coinciding with the salinization and the shrinking of Bosten Lake. This suggests that the shortage of freshwater during this cold period may have contributed to the collapse of the ancient cities and the depression of the trade along the Silk Road.
Arid Central Asia (ACA), with its diverse landscapes of high mountains, oases, and deserts, hosted the central routes of the Silk Roads that linked trade centers from East Asia to the eastern Mediterranean. Ecological pockets and ecoclines in ACA are largely determined by local precipitation. However, little research has gone into the effects of hydroclimatic changes on trans-Eurasian cultural exchange. Here, we reconstruct precipitation changes in ACA, covering the mid-late Holocene with a U-Th dated, ~3 a resolution, multi-proxy time series of replicated stalagmites from the southeastern Fergana Valley, Kyrgyzstan. Our data reveal a 640-a megadrought between 5820 and 5180 a BP, which likely impacted cultural development in ACA and impeded the expansion of cultural traits along oasis routes. Instead, it may have diverted the earliest transcontinental exchange along the Eurasian steppe during the 5th millennium BP. With gradually increasing precipitation after the megadrought, settlement of peoples in the oases and river valleys may have facilitated the opening of the oasis routes, “prehistoric Silk Roads”, of trans-Eurasian exchange. By the 4th millennium BP, this process may have reshaped cultures across the two continents, laying the foundation for the organized Silk Roads.
The Holocene moisture-temperature correlation on varying spatial-temporal scales in arid Central Asia (ACA) is still controversial. It has been widely reported that ACA experienced multi-centennial alternations between warm/dry and cold/wet climates over the past two millennia. However, less attention has focused on orbital-scale moisture-temperature relationship at a regional scale across ACA. Here, we contribute a framework including a set of quantitative algorithms to acquire reliable pollen-based climatic reconstructions. We apply this methodology to a new pollen record from a wetland in northern Xinjiang (southeastern ACA) for quantitative reconstructions of moisture availability (actual/potential evapotranspiration ratio, AET/PET) and summer temperature (mean temperature of the warmest month, MTWA) over circa the last 10,300 years. We select AET/PET and MTWA because they are evaluated to be most statistically independent and ecologically significant. The effect of differing spatial extents of calibration-sets on model performance is tested to determine the optimal extent. We critically assess the reliability of all reconstructions through calculations of statistical significance, analogue quality and goodness-of-fit statistics. Our final reconstructions are statistically significant with independent features of AET/PET and MTWA, showing an increasing (declining) trend of Holocene moisture (temperature). This anti-phase pattern is consistent with other records and model simulations across southeastern ACA. The data-model consistency postulates that (i) the glacier meltwater from Tien Shan ('Water Tower of Central Asia') is crucial to support major streamflow and watersheds over ACA, and (ii) the Holocene wetting trend may be determined by the interacting effects between decreased summer temperature and increased winter precipitation.
Radiocarbon (C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.
We present a 2000-year high-resolution diatom record from Bosten Lake (Yanqi Basin, Xinjiang), which is the largest inland freshwater lake in China. Our aims were to investigate the influence of climate change and human activity on its aquatic ecology during the late Holocene. During AD 280–480, a low water level and high salinity occurred, based on the dominance of epipelic and brackish diatoms. In addition, the diatom stratigraphy, combined with records of mean grain size and carbonate content, suggests that the lake experienced a high level of eolian input from the surrounding dunes. We hypothesize that during this interval, Loulan Kingdom, an important city of the Han Dynasty, located downstream of Bosten Lake, was abandoned due to the increasing scarcity of water resources and related harsh environmental conditions, including stronger eolian activity, which were the consequences of climate change. The dominance of meso-eutrophic small fragilarioid diatoms coincides with warm and arid intervals which also correspond to intensified human activity. These intervals correspond to the development of the Tang Dynasty (from ~AD 600), the ‘Medieval Warm Period’ (AD 1000–1200), and the last ~200 years. A shift from meso-eutrophic/benthic diatoms to oligotrophic/planktonic diatoms occurred during an interval of enhanced precipitation throughout the humid ‘Little Ice Age’ (AD 1600–1800). A return to markedly eutrophic conditions and a decreasing lake level occurred after the ‘Little Ice Age’, reflecting the more arid regional environment of the last 200 years. The high variability of the proxies suggests that both climate change and human activity were the major drivers of the ecological status of Bosten Lake during the late Holocene. We suggest that both the continuous increase of human activity and ongoing global warming will cause the major eutrophication or salinization of the freshwater lakes in the arid zone of northwest China.
Proxy-based reconstructions and modeling of Holocene spatiotemporal precipitation patterns for China and Mongolia have hitherto yielded contradictory results indicating that the basic mechanisms behind the East Asian Summer Monsoon and its interaction with the westerly jet stream remain poorly understood. We present quantitative reconstructions of Holocene precipitation derived from 101 fossil pollen records and analyse them with the help of a minimal empirical model. We show that the westerly jet-stream axis shifted gradually southward and became less tilted since the middle Holocene. This was tracked by the summer monsoon rain band resulting in an early-Holocene precipitation maximum over most of western China, a mid-Holocene maximum in north-central and northeastern China, and a late-Holocene maximum in southeastern China. Our results suggest that a correct simulation of the orientation and position of the westerly jet stream is crucial to the reliable prediction of precipitation patterns in China and Mongolia.
Open access link https://link.springer.com/book/10.1007%2F978-3-030-00728-7#about
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This open access book discusses socio-environmental interactions in the middle to late Holocene, covering specific areas along the ancient Silk Road regions. Over twenty chapters provide insight into this topic from various disciplinary angles and perspectives, ranging from archaeology, paleoclimatology, antiquity, historical geography, agriculture, carving art and literacy. The Silk Road is a modern concept for an ancient network of trade routes that for centuries facilitated and intensified processes of cultural interaction and goods exchange between West China, Central Asia, the Middle East, and the Mediterranean. Coherent patterns and synchronous events in history suggest possible links between social upheaval, resource utilization and climate or environment forces along the Silk Road and in a broader area. Post-graduates in studying will benefit from this work, as well as it will stimulate young researchers to further explore the role played by the environment in long-term socio-cultural changes.
The social impact of past climate change is one of the key areas of study relating to global climate change, particularly its ability to provide valuable lessons for dealing with ongoing challenges of global climate change. Drawing on the abundant historical literature, many recent studies have examined the social impacts of climate change in China during the past 2000 years. This paper reviews the main progress of these studies in three parts. First, a concept model based on the food security in relation to global climate change has been constructed, which can then be used to interpret impact-response processes of climate change in the history of China. Second, we derive a methodology for quantifying the impact of historical climate change, drawing on a series of 4 key social and economic sequences at a 10-year resolution. These have been reconstructed based on the semantic differential method over the past 2000 years in China. Third, using a variety of statistical analyses, we update the understanding of climate impacts throughout the history of China. The overall impacts of climate were negative in the cold periods and positive in the warm periods, at decadal to centennial scales during Chinese history. However, the impacts seemed a mixed blessing both in the cold or warm periods. The social-economic development and population growth in warm periods would intensify the natural resource shortage and disequilibria in the human-environment system, especially when encountering abrupt climate changes. Adaptation to adverse climate change could not only help people to avoid hardship whilst maximizing profits, but also expanded the capabilities for the continual development of Chinese civilization.
In northwestern China, many historical nomadic kingdoms and Chinese dynasties sought to control the Heihe River basin, an important location on the eastern part of the ancient Silk Road. Archaeologists have argued that changes in material culture are tied to the frequent turnover in polities in the area, but no published evidence supports these claims. In this paper, we evaluate the relative importance of environmental and political factors in determining the spatiotemporal pattern of archaeological sites in the middle and lower reaches of the Heihe River basin by using previously published high-resolution paleoclimate records and a variety of historical documents. Our results indicate that humans intensively exploited the Heihe River basin during Han dynasty (202BC–AD 220). Following the Han dynasty, during the Wei-Jin (AD 222–589) and Sui-Tang (AD 581–907) periods the number of archaeological sites. In the Western Xia-Yuan period (AD 1038–1368), people mainly settled in the lower reaches of the Heihe River basin and only returned to the middle reaches of the Heihe River basin during the Ming and Qing dynasties (AD 1368–1912). Although climate change and the local environment affected human activities in Heihe River basin, geopolitical events, such as forced mass migrations, are more responsible for influencing the distribution of archaeological sites over the past 2000 years.
One of the richest societies along the Silk Road developed in Sogdiana, located in present-day Tajikistan, Uzbekistan, and Kyrgyzstan. This urban civilisation reached its greatest prosperity during the golden age of the Silk Road (sixth to ninth century ce). Rapid political and economic changes, accelerated by climatic variations, were observed during last millennium in this region. The newly developed tree-ring-based reconstruction of precipitation for the past millennium revealed a series of dry andwet stages. During the Medieval Climate Anomaly (MCA), two dry periods occurred (900–1000 and 1200–1250), interrupted by a phase of wetter conditions. During the next centuries distinct dry periods occurred around 1510–1650, 1750–1850, and 1920–1970, respectively. The juniper tree-ring record of moisture changes revealed that major dry and pluvial episodes were consistent with those indicated by other hydroclimatic proxy data from adjacent areas. These climate fluctuations have had long- and short term consequences for human history in the territory of former Sogdiana.
In the context of global warming, the changes in major lakes and their responses to the influence factors in arid and semi-arid regions along the Silk Road are especially important for the sustainable development of local water resources. In this study, the areas of 24 lakes were extracted using MODIS NDVI data, and their spatial-temporal characteristics were analyzed. In addition, the relationship between lake areas and the influence factors, including air temperature, precipitation, evapotranspiration, land use and land cover change (LULCC) and population density in the watersheds, were investigated. The results indicated that the areas of most lakes shrank, and the total area decreased by 22,189.7 km² from 2001 to 2016, except for those of the lakes located on the Qinghai-Tibetan Plateau. The air temperature was the most important factor for all the lakes and increased at a rate of 0.113 °C/a during the past 16 years. LULCC and the increasing population density markedly influenced the lakes located in the middle to western parts of this study area. Therefore, our results connecting lake area changes in the study region highlight the great challenge of water resources and the urgency of implementation of the green policy in the One Belt and One Road Initiative through international collaboration.
Projecting how the East Asian summer monsoon (EASM) rainfall will change with global warming is essential for human sustainability. Reconstructing Holocene climate can provide critical insight into its forcing and future variability. However, quantitative reconstructions of Holocene summer precipitation are lacking for tropical and subtropical China, which is the core region of the EASM influence. Here we present high-resolution annual and summer rainfall reconstructions covering the whole Holocene based on the pollen record at Xinjie site from the lower Yangtze region. Summer rainfall was less seasonal and ~ 30% higher than modern values at ~ 10–6 cal kyr BP and gradually declined thereafter, which broadly followed the Northern Hemisphere summer insolation. Over the last two millennia, however, the summer rainfall has deviated from the downward trend of summer insolation. We argue that greenhouse gas forcing might have offset summer insolation forcing and contributed to the late Holocene rainfall anomaly, which is supported by the TraCE-21 ka transient simulation. Besides, tropical sea-surface temperatures could modulate summer rainfall by affecting evaporation of seawater. The rainfall pattern concurs with stalagmite and other proxy records from southern China but differs from mid-Holocene rainfall maximum recorded in arid/semiarid northern China. Summer rainfall in northern China was strongly suppressed by high-northern-latitude ice volume forcing during the early Holocene in spite of high summer insolation. In addition, the El Niño/Southern Oscillation might be responsible for droughts of northern China and floods of southern China during the late Holocene. Furthermore, quantitative rainfall reconstructions indicate that the Paleoclimate Modeling Intercomparison Project (PMIP) simulations underestimate the magnitude of Holocene precipitation changes. Our results highlight the spatial and temporal variability of the Holocene EASM precipitation and potential forcing mechanisms, which are very helpful for calibration of paleoclimate models and prediction of future precipitation changes in East Asia in the scenario of global warming.
The vast Indo-Gangetic Plain in South Asia has been home to some of the world’s oldest civilizations, whose fortunes ebbed and flowed with time—plausibly driven in part by shifts in the spatiotemporal patterns of the Indian summer monsoon rainfall. We use speleothem oxygen isotope records from North India to reconstruct the monsoon’s variability on socially relevant time scales, allowing us to examine the history of civilization changes in the context of varying hydroclimatic conditions over the past 5700 years. Our data suggest that significant shifts in monsoon rainfall have occurred in concert with changes in the Northern Hemisphere temperatures and the discharges of the Himalayan rivers. The close temporal relationship between these large-scale hydroclimatic changes and the intervals marking the significant sociopolitical developments of the Indus Valley and Vedic civilizations suggests a plausible role of climate change in shaping the important chapters of the history of human civilization in the Indian subcontinent.
The rise and fall of ancient cultures and civilizations is a hotly debated topic that has generated disagreements and disputes. In this paper we summarize some case studies on the abandonment of ancient sites, the prosperity and collapse of ancient cultures, and demographic changes, as well as the influence of environment and technology during the prehistoric and historic periods. We then suggest that the dominant influencing factors for the evolution of ancient societies vary by spatial scale. At the local scale, sudden disasters are critical factors leading to the destruction and abandonment of large settlements. On a regional scale, climatic variations (e.g., droughts or cold events lasting for decades or centuries) are important factors that induce the collapse of ancient civilizations and mass migrations, while an enduring and stable optimal climate facilitated the prosperity of ancient civilizations. On a global scale, major technological innovations and their dispersion lasting for centuries and even millennia are major catalysts for population growth and social development. Lastly, we illustrate a possible mechanism under which environmental and technological factors played a critical role in ancient human survival and social evolution on different spatial scales.
Traditionally, the evaluation of pollen-based quantitative paleoclimate reconstructions focuses on the ability of calibration sets to infer present climatic conditions and/or the similarity between fossil and modern assemblages. Objective criteria for choosing the most appropriate climate parameter(s) to be reconstructed at a specific site are thus lacking. Using a novel approach for testing the statistical significance of a quantitative reconstruction using random environmental data, in combination with the advantageous large environmental gradients, abundant vegetation types and comprehensive modern pollen databases in China, we describe a new procedure for pollen-based quantitative paleoclimatic reconstructions. First, the most significant environmental variable controlling the fossil pollen assemblage changes is identified. Second, a calibration set to infer changes in this targeted variable is built up, by limiting the modern ranges of other environmental variables. Finally, the pollen-based quantitative reconstruction is obtained and its statistical significance assessed. This novel procedure was used to reconstruct the mean annual precipitation (Pann) from Gonghai Lake in the Lvliang Mountains, and Tianchi Lake in the Liupan Mountains, on the eastern and western fringe of the Chinese Loess Plateau, respectively. Both Pann reconstructions are statistically significant (p<0.001), and a sound and stable correlation relationship exists in their common period, showing a rapid precipitation decrease since 3300 cal yr BP. Thus, we propose that this procedure has great potential for reducing the uncertainties associated with pollen-based quantitative paleoclimatic reconstructions in China.
We created a new dataset of spatially interpolated monthly climate data for global land areas at a very high spatial resolution (approximately 1 km 2). We included monthly temperature (minimum, maximum and average), precipitation, solar radiation, vapour pressure and wind speed, aggregated across a target temporal range of 1970–2000, using data from between 9000 and 60 000 weather stations. Weather station data were interpolated using thin-plate splines with covariates including elevation, distance to the coast and three satellite-derived covariates: maximum and minimum land surface temperature as well as cloud cover, obtained with the MODIS satellite platform. Interpolation was done for 23 regions of varying size depending on station density. Satellite data improved prediction accuracy for temperature variables 5–15% (0.07–0.17 ∘ C), particularly for areas with a low station density, although prediction error remained high in such regions for all climate variables. Contributions of satellite covariates were mostly negligible for the other variables, although their importance varied by region. In contrast to the common approach to use a single model formulation for the entire world, we constructed the final product by selecting the best performing model for each region and variable. Global cross-validation correlations were ≥ 0.99 for temperature and humidity, 0.86 for precipitation and 0.76 for wind speed. The fact that most of our climate surface estimates were only marginally improved by use of satellite covariates highlights the importance having a dense, high-quality network of climate station data.
Remnants of cities and farmlands in China’s hyperarid Tarim Basin indicate that environmental conditions were significantly wetter two millennia ago in a region which is barren desert today. Historical documents and age data of organic remains show that the Loulan Kingdom flourished during the Han Dynasty (206 BCE–220 CE) but was abandoned between its end and 645 CE. Previous archaeological, geomorphological and geological studies suggest that deteriorating climate conditions led to the abandonment of the ancient desert cities. Based on analyses of lake sediments from Lop Nur in the eastern Tarim Basin and a review of published records, we show that the Loulan Kingdom decline resulted from a man-made environmental disaster comparable to the recent Aral Sea crisis rather than from changing climate. Lop Nur and other lakes within the Han Dynasty realm experienced rapidly declining water levels or even desiccation whilst lakes in adjacent regions recorded rising levels and relatively wet conditions during the time of the Loulan Kingdom decline. Water withdrawal for irrigation farming in the middle reaches of rivers likely caused water shortage downstream and eventually the widespread deterioration of desert oases a long time before man initiated the Aral Sea disaster in the 1960s.
The extent to which climate variability in Central Asia is causally linked to large-scale changes in the Asian monsoon on varying timescales remains a longstanding question. Here we present precisely dated high-resolution speleothem oxygen-carbon isotope and trace element records of Central Asia's hydroclimate variability from Tonnel'naya cave, Uzbekistan, and Kesang cave, western China. On orbital timescales, the supra-regional climate variance, inferred from our oxygen isotope records, exhibits a precessional rhythm, punctuated by millennial-scale abrupt climate events, suggesting a close coupling with the Asian monsoon. However, the local hydroclimatic variability at both cave sites, inferred from carbon isotope and trace element records, shows climate variations that are distinctly different from their supra-regional modes. Particularly, hydroclimatic changes in both Tonnel'naya and Kesang areas during the Holocene lag behind the supra-regional climate variability by several thousand years. These observations may reconcile the apparent out-of-phase hydroclimatic variability, inferred from the Holocene lake proxy records, between Westerly Central Asia and Monsoon Asia.
Global drylands encompassing hyper-arid, arid, semiarid, and dry subhumid areas cover about 41 percent of the earth's terrestrial surface and are home to more than a third of the world's population. By analyzing observations for 1948–2008 and climate model simulations for 1948–2100, we show that global drylands have expanded in the last sixty years and will continue to expand in the 21st~century. By the end of this century, the world's drylands (under a high greenhouse gas emission scenario) are projected to be 5.8 × 106 km2 (or 10%) larger than in the 1961–1990 climatology. The major expansion of arid regions will occur over southwest North America, the northern fringe of Africa, southern Africa, and Australia, while major expansions of semiarid regions will occur over the north side of the Mediterranean, southern Africa, and North and South America. The global dryland expansions will increase the population affected by water scarcity and land degradations.
When and how humans permanently colonized high altitude areas of the Tibetan Plateau are widely discussed issues. The Nuomuhong Culture was the sole Bronze Age group living higher than 2700 m above sea level in the Qaidam Basin on the northern Tibetan Plateau. Here we report the results of an archaeological investigation comprising radiocarbon dating as well as archaeobotanical and zooarchaeological analyses from five typical Nuomuhong sites, to explore the chronology and subsistence strategy of the culture. Abundant plant and animal remains were identified, including charred grains of barley, wheat, broomcorn millet, and foxtail millet; and bones of sheep, cattle, yak, horse, dog, and deer. Resident relics were also found in these investigated sites, together with dating results, indicating Nuomuhong groups permanently settled on the Qaidam Basin during 3400–2450 Cal BP. People adapted to the harsh environment by establishment of resident facilities, and adoption of a cold-tolerant mixed agro-pastoral economy. This work provides valuable dataset for understanding the exact chronology and livelihoods of Bronze societies on high altitude areas of the Tibetan Plateau.
Climate change in complex mountain regions has an impact on the change of water resources, especially in
arid areas. Here, we use long-term meteorological and hydrological station observation data to analyze the
time series of climate indices and runoff to study the variability of climate in the Kaidu River Basin. The analysis results are as follows: 1) the variability rate of low temperature indices are of greater magnitude than high temperature indices; 2) overall, for the river basin, frost days and ice days all exhibited decreasing trends, and growing season lengths increased considerably; 3) during the past 50 years, overall precipitation has increased in the river basin, but there are some differences in some seasons, and precipitation from June to August accounts for approximately 66% of the annual precipitation; and 4) temperature lapse rate and precipitation of the mountain region are major factors influencing the change of runoff for the Kaidu River Basin, temperature
lapse rates are the main factor influencing the run off change in the spring and fall, and precipitation in the
mountain region is the major factor influencing the runoff change in the summer. Generally, climate change in complex mountain regions will be expected to seriously affect water resources in arid regions.
Although the Pamir Plateau is an ideal place to investigate paleo-environmental changes in the westerlies-dominated high Central Asia, there are only few Holocene records from this region. We present a sub-centennially resolved lacustrine record of moisture variations from Sasikul Lake, central Pamir Plateau, based on geochemical, sedimentological, and mineralogical proxies. Our results show that generally dry conditions at Sasikul Lake during the past 2540 years were interrupted by a pronounced wet period between ad 1550 and 1900, corresponding to the ‘Little Ice Age’ (LIA). More negative values of carbonate δ18O, lower total inorganic carbon (TIC) and sand content during the LIA all indicate a relatively wet period with higher lake level. Higher TIC during the ‘Medieval Warm Period’ (MWP; ad 950–1200) reveals a lower lake level relative to the LIA. Low δ18O during this time is probably attributed to changes in the isotopic composition of input water and/or upstream moisture sources. The significant increase in detrital minerals and decrease in carbonate during the LIA provide further evidence for higher allochthonous input during the wet period at Sasikul Lake. The inferred moisture variations are consistent with existing records from regions of the northern Tibetan Plateau and Central Asia that are also influenced by the westerlies, but out-of-phase with those records from the Asian monsoon region, indicating that moisture variations at Sasikul Lake were mainly influenced by the strength and trajectories of the westerlies. The inferred water level at Sasikul Lake decreased significantly during the first half of the 20th century, and then increased in recent decades. This is consistent with the increase in lake area derived from satellite images and the monitoring data of large lake-level changes in Central Asia.
Late Holocene glacier variations in westernmost Tibetan Plateau were studied based on the analysis of grainsize, magnetic susceptibility, and elements from an 8.3-m long distal glaciolacustrine sediment core of Kalakuli Lake. Our results show that there are four glacier expansion episodes occurring in 4200–3700 cal yr BP, 2950–2300 cal yr BP, 1700–1070 cal yr BP, and 570–100 cal yr BP, and four glacier retreat periods of 3700–2950 cal yr BP, 2300–1700 cal yr BP, 1070–570 cal yr BP, and 50 cal yr BP-present. The four glacier expansion episodes are generally in agreement with the glacier activities indicted by the moraines at Muztag Ata and Kongur Shan, as well as with the Late Holocene ice-rafting events in the North Atlantic. Over the last 2000 years, our reconstructed glacier variations are in temporal agreement with reconstructed temperature from China and the Northern Hemisphere, indicating that glacier variations at centennial time scales are very sensitive to temperature in western Tibetan Plateau.
The innovations of agricultural production and their extensive dispersal promoted the transformation of human livelihoods and profoundly influenced the evolution of human-land relationships in late prehistoric Eurasia. The Steppe and Silk Roads (SSRs) played important roles in the transcontinental exchange and dispersal of cereal crops and livestock related to agricultural innovation across Eurasia before the Han Dynasty (202 BC to AD 220), while the geographical-temporal variations in prehistoric subsistence in relation to the spread and exchange of cereal crops and livestock originating from different areas of Eurasia still remain unclear. In this paper, we explore these issues based on the review and analysis of published archaeobotanical, zooarchaeological, and carbon-stable isotope data from human bones from Neolithic-Early Iron Age sites in areas along the SSRs, with a comparison to updated results based on radiocarbon dating and ancient DNA analyses. Our results suggest that humans engaged in hunting game, while foxtail/broomcorn millet cultivation gradually became the primary subsistence strategy in Eastern SSRs from 10,500 to 6000 a BP. In contemporaneous Western SSRs, humans mainly cultivated wheat/barley and raised sheep/goats, cattle, and pigs. Trans-Eurasian exchange, which is reflected by the mixed utilization of wheat/barley and millet, emerged in the south-central Steppe during 6000–4000 a BP, while millet cultivation and pig husbandry became the dominant livelihoods in most areas of Eastern SSRs. During 4000–2200 a BP, Silk Roads became the major passageway for trans-Eurasian exchange, the interactive development of oasis agriculture and pastoralism facilitated intensive human settlement in the Central Silk Roads, and subsistence strategies substantially changed with significant geographical differences in Eastern SSRs, while subsistence in some areas of Western SSRs was evidently affected by the introduction and adoption of millet crops after 3000 a BP. The geographical-temporal variations in subsistence in the SSRs from the Neolithic to Early Iron Age were primarily affected by the prehistoric dispersal of farming groups across Eurasia, which was accompanied by the spread of cereal crops/livestock, while the impacts of climate change still need to be further evaluated.
Precipitation fluctuation has been suggested as a crucial influencing factor in the evolution of ancient civilizations across the world. Nuomuhong culture (~3400–2450 BP) and Tuyuhun (313–663 CE) were unique ancient civilizations that developed in the eastern Qaidam Basin of the north Tibetan Plateau. However, how precipitation variation in the mountain–basin system has affected the rise and fall of these two ancient civilizations is not well understood. Based on analyses of grain size, magnetic susceptibility, Rb/Sr ratio, loss on ignition, and optically stimulated luminescence dates from an aeolian deposit sequence, lowland climate change in the Qaidam Basin during the late Holocene is reconstructed. The Rb/Sr ratio varies from 0.31 to 0.33 during ~2500–2300 BP, it increases from 0.33 to 0.44 during ~2300–1600 BP, and decreases from 0.44 to 0.29 during ~1600–1400 BP, suggesting the climate was relatively dry during ~2500–2300 BP and ~1600–1400 BP and relatively wet during ~2300–1600 BP in the lowlands of the eastern Qaidam Basin, which corresponded well to the gap between the Nuomuhong and Tuyuhun periods. However, the prosperous periods of the Nuomuhong and Tuyuhun were synchronous with high precipitation in the surrounding mountains. Therefore, high precipitation in the surrounding mountains nourished the expansion of oases and then facilitated the development of Nuomuhong and Tuyuhun, which was inconsistent with precipitation variation in the lowlands of eastern Qaidam Basin. The spatiotemporal pattern of precipitation in the mountain–basin system of the Qaidam Basin during the late Holocene was likely affected by solar activity through uplifting–subsiding air flow mechanism, with more precipitation in the mountain and less precipitation in the basin under higher solar activity. A cognitive model is provided to illustrate how solar activity affected the spatiotemporal patterns of precipitation in the mountain–basin structure of the eastern Qaidam, and then human settlement and civilization evolution during the late Holocene.
It is unclear whether the Holocene climatic optimum (HCO) occurred synchronously throughout the East Asian summer monsoon (EASM) region, and if it did, whether it occurred in the early Holocene (EH, 11.7–8.0 ka, ka = 1000 years before present, where the “present” is defined as the year CE 1950), or in the middle Holocene (MH, 8.0–4.0 ka). This is because the definition of the HCO in previous paleoclimatic studies was mainly based on the criterion of maximum temperature or some “optimum” combination of temperature and precipitation. Since the development of prehistoric societies and human welfare are closely linked to climatic variability, it may be more meaningful to define the HCO from the perspective of climatic stability, which may provide fresh insight into the debate on the timing of the HCO. Here we use calculations of squared chord distance (SCD), an effective method for quantifying temporal dissimilarity of the variance of samples in a time series, to quantitatively compare the climatic stability of the EH and the MH, based on a diverse range of the EASM-associated paleoclimatic records from the EASM region. The results show that the SCD values decreased significantly from the EH to the MH, indicating a more stable climate which occurred synchronously during the MH in the EASM region. We suggest that the stable climate of the MH provided an optimum environment for the development of agriculture and animal husbandry, which contributed to rapid population growth and the flourishing of the Yangshao culture which was the most prosperous Neolithic culture in the EASM region of China during the Holocene. Thus we propose that the stable MH climate can be used to define a synchronous HCO of the EASM which was more supportive of societal development and population growth than that during the EH. The results of TraCE-21 ka climatic modeling reveal that, with the retreat of the Northern Hemisphere ice sheets, the variability of the westerly jet (WJ), which was previously perturbed by large ice sheets, was significantly reduced from the EH to the MH. This reduced WJ variability during the MH enhanced the stability of the climate of the EASM region, via the interactions of the EASM and the WJ.
The interpretation of trace element/calcium ratios of speleothems as indicators of local hydroclimatic variability in the vicinity of caves has led to controversy in reconstructing the evolution of moisture conditions in arid central Asia (ACA) during the Holocene. Here we present records of Mg/Ca, Sr/Ca, Ba/Ca, and U/Ca from precisely dated stalagmites from Baluk cave in Xinjiang (northwest China), spanning the past 9370 years. The co-variations of the trace element ratios, together with the slopes of the regression lines of the corresponding logarithmically transformed data, suggest that they are dominated by prior calcite precipitation (PCP) and thus can be used as reliable proxies of changes in moisture/precipitation. The trace element ratios are relatively high during ~9 to 5 ka and lower from 5 ka to the present, indicating a trend of increasing mid–late Holocene moisture in ACA. The long-term trend of variation of the trace element ratios is correlative with two other records of speleothem trace element ratios from caves in ACA: Kesang cave (western Xinjiang) and Ton cave (Uzbekistan). This spatial coherency of the trend of inferred moisture conditions from three caves that are separated by hundreds of kilometers demonstrates that speleothem trace element ratios are indicative of large spatial scale rather than local hydroclimatic variability in ACA during the Holocene. However, the long-term trend of variation of the trace element ratios is the inverse of the corresponding oxygen isotope (δ ¹⁸ O) records from the same cave sites, which implies that Holocene speleothem δ ¹⁸ O records do not represent changes in the precipitation amount in ACA; rather, they most likely reflect moisture sources and related water vapor transport controlled by Northern Hemisphere summer insolation (NHSI). Our findings provide new evidence for a ‘westerlies-dominated climatic regime’, which influenced hydroclimatic changes in ACA during the Holocene.
This study investigated the contributions of snow/glacier meltwater to river runoff in the northern and central Tianshan Mountains (Central Asia). Based on end- member mixing analysis (EMMA), the hydrograph separation was carried out in six benchmark catchments with different glacier area ratios (GARs) and snow area ratios (SARs) during a typical snow melt period (TSMP) and a typical glacier melt period (TGMP). The results indicate that the contribution of snow/glacier meltwater to river runoff is positively correlated with GARs or maximum SARs. The contribution ratios of snowmelt water vary from 22% to 49% in TSMP. The contribution ratios of glacier meltwater vary from 12% to 59% in TGMP. The contribution ratios of snow meltwater in the northern Tianshan Mountains (36%) are higher than central Tianshan Mountains (31%), while the contribution ratios of glacier meltwater in the northern Tianshan Mountains (36%) are lower than central Tianshan Mountains (42%). The contribution of rainfall to river runoff is higher in TGMP (9%–23%) than in TSMP (5%–9%). Baseflow is the most important recharge source to river runoff, with the contribution ratios vary from 44% to 73% in TSMP, and vary from 30% to 75% in TGMP. The spatial and temporal variations in tracer concentrations in streamflow components were found to be responsible to the uncertainties in hydrograph separation.
It is often mentioned that the "Silk Road" was a trade route between theEast and the West. Conceptually, it represents the history of communicationbetween China and the West: goods and merchants frequently travelledalong this route. The meaning of the Silk Road and its formation processand scope of influence has been documented in different records, and hadan impact on academic research in several countries: in the field of researchon the history of China, the study of the Silk Road is a subject that manyresearchers have tackled and discussed. Early historical chronicles have beenanalyzed and discussed as well as documents and unearthed artefacts foundalong the Silk Road; these studies involve political, cultural, and economicaspects. Research has not been limited to China, but has also interested thecountries which were along the Silk Road and those which were affected bythe Silk Road culture. The Silk Road acted as a cultural bridge between Eastand West: it did not only promote commerce but also cultural exchanges.For example, Buddhism, as one of the religions of the Kushan kingdom,reached China thanks to this route.
Rich ancient societies of central Asia developed on the basis of trade between East and West; their existence was dependent on natural resources that favoured agriculture. The branches of the Silk Road in central Asia clearly coincide with loess areas, where many settlements were erected based on the presence of fertile loess soil and water. The aim of the study was to analyse the environmental factors that led to the growth and decline of one of the most important Silk Road “loess towns,” ancient Panjikent, as an example of human and climatic impacts on landscape changes. The town, established in the fifth century, quickly became one of the most important cities of Sogdiana. Local loess material was used for the production of the sun-dried bricks. Rapid population growth led to deforestation and consequently increased the intensity of erosion rates and reductions in cultivation area. A period of drought near the end of the first millennium AD influenced the final abandonment of the ancient town and its relocation to the lower terrace of the Zarafshan River. A decline in natural and agricultural resources and subsequently climatic forces caused a decline in the number of cities in semiarid regions of central Asia.
Based on environmental records, archaeological findings, and isotopic data, the environmental changes and cultural exchange between East and West along the Silk Road in arid Central Asia during the Holocene have been studied. The results show that the cultural exchange is definitely influenced by geographic setting and environmental changes. Hexi Corridor is located at the marginal area of monsoonal Asia, characterized by monsoon-westerly transitional model. From Xinjiang to Central Asia, the environmental change demonstrated uniform trends during the Holocene: the early Holocene witnessed dry environment conditions and desert vegetation, while during the mid and late Holocene, steppe vegetation expanded when moisture increased. The cultural exchange between East and West along the Silk Road took advantage of moisture conditions during the mid to late Holocene. Benefited from the improvement of environmental conditions, the cultural exchange between East and West accelerated after 2000 BC. During 2500-2000 BC, Eastern and Western agriculture met and integrated along the Silk Road, representing the beginning of prehistoric "Silk Road" along the Tianshan Mountains. Furthermore, during 2000-1000 BC, a mixed economy characterized by wheat/barley-millet-husbandry appeared in the oases along the Silk Road, and expanded to the Eurasia steppe after 1500BC, being a sharp contrast to the surrounding animal husbandry and continuing to the historic periods. Such spatial differentiation is the result of integrated geographic setting and cultural exchange between East and West. During the prehistoric period, Eastern and Western agriculture oppositely spread along the oases in a leapfrogging forward way. While during the historic periods, political factors were the primary controlling upon the Silk Road, but environmental change was still a factor that cannot be ignored.
Quantitative information regarding the long-term variability of precipitation and vegetation during the period covering both the Lateglacial and the Holocene on the Qinghai–Tibetan Plateau (QTP) is scarce. Herein, we provide new and numerical reconstructions for annual mean precipitation (PANN) and vegetation history over the last 18,000 years using high-resolution pollen data from Lakes Dalianhai and Qinghai on the northeastern QTP. Hitherto, five calibration techniques including weighted averaging (WA), weighted average-partial least squares regression (WA-PLS), modern analogue technique (MAT), locally weighted weighted averaging regression (LWWA) and maximum likelihood (ML), were firstly employed to construct robust inference models and to produce reliable PANN estimates on the QTP. The biomization method was applied for reconstructing the vegetation dynamics. The study area was dominated by steppe and characterized with a highly variable, relatively dry climate at ~18,000–11,000 cal a B.P. PANN increased since the early Holocene, obtained a maximum at ~8000–3000 cal a B.P. with coniferous–temperate mixed forest as the dominant biome, and thereafter declined to present. The PANN reconstructions are broadly consistent with other proxy-based paleoclimatic records from the northeastern QTP and the northern region of monsoonal China. The possible mechanisms behind the precipitation changes may be tentatively attributed to the internal feedback processes of higher-latitude (e.g., North Atlantic) and lower-latitude (e.g., subtropical monsoon) competing climatic regimes, which are primarily modulated by solar energy output as the external driving force. These findings may provide important insights into understanding the future Asian precipitation dynamics under the projected global warming.
The lack of a precisely-dated, unequivocal climate proxy from northern China, where precipitation variability is traditionally considered as an East Asian summer monsoon (EASM) indicator, impedes our understanding of the behaviour and dynamics of the EASM. Here we present a well-dated, pollen-based, ~20-yr-resolution quantitative precipitation reconstruction (derived using a transfer function) from an alpine lake in North China, which provides for the first time a direct record of EASM evolution since 14.7 ka (ka = thousands of years before present, where the “present” is defined as the year AD 1950). Our record reveals a gradually intensifying monsoon from 14.7–7.0 ka, a maximum monsoon (30% higher precipitation than present) from ~7.8–5.3 ka, and a rapid decline since ~3.3 ka. These insolation-driven EASM trends were punctuated by two millennial-scale weakening events which occurred synchronously to the cold Younger Dryas and at ~9.5–8.5 ka, and by two centennialscale intervals of enhanced (weakened) monsoon during the Medieval Warm Period (Little Ice Age). Our precipitation reconstruction, consistent with temperature changes but quite different from the prevailing view of EASM evolution, points to strong internal feedback processes driving the EASM, and may aid our understanding of future monsoon behaviour under ongoing anthropogenic climate change.
Streamflow simulation is often challenging in mountainous watersheds because of incomplete hydrological models, irregular topography, immeasurable snowpack or glacier, and low data resolution. In this study, a semi-distributed conceptual hydrological model (SWAT-Soil Water Assessment Tool) coupled with a glacier melting algorithm was applied to investigate the sensitivity of streamflow to climatic and glacial changes in the upstream Heihe River Basin. The glacier mass balance was calculated at daily time-step using a distributed temperature-index melting and accumulation algorithm embedded in the SWAT model. Specifically, the model was calibrated and validated using daily streamflow data measured at Yingluoxia Hydrological Station and decadal ice volume changes derived from survey maps and remote sensing images between 1960 and 2010. This study highlights the effects of glacier melting on streamflow and their future changes in the mountainous watersheds. We simulate the contribution of glacier melting to streamflow change under different scenarios of climate changes in terms of temperature and precipitation dynamics. The rising temperature positively contributed to streamflow due to the increase of snowmelt and glacier melting. The rising precipitation directly contributes to streamflow and it contributed more to streamflow than the rising temperature. The results show that glacial meltwater has contributed about 3.25 billion m3 to streamflow during 1960-2010. However, the depth of runoff within the watershed increased by about 2.3 mm due to the release of water from glacial storage to supply the intensified evapotranspiration and infiltration. The simulation results indicate that the glacier made about 8.9% contribution to streamflow in 2010. The research approach used in this study is feasible to estimate the glacial contribution to streamflow in other similar mountainous watersheds elsewhere.