Aridification Trend Research Articles

SPATIAL AND TEMPORAL ANALYSIS OF ARIDITY TRENDS USING THE DE MARTONNE INDEX: A GIS-BASED STUDY OF THE TIMGAD BASIN, ALGERIA

Knowledge of drought conditions is necessary for the rational use of water resources, the prevention of the dangers resulting from them, and for explaining landscape and ecology characteristics. To analyze annual, seasonal and monthly aridity trends in the Timgad Basin, North-East Algeria, climate data from 07 meteorological stations within the 1975-2009 period were used. After computing the De Martonne aridity index at each station, a geographic information system (GIS) was utilized to maps this index throughout the region and specify drought trends, visualizing detected annual, seasonal and monthly tendencies. On an annual scale, the De Marton Drought Index shows a semi-arid climate in the entire Timgad Basin. On a seasonal scale, the winter season shows a dry semi-humid climate - from Mediterranean to semi-humid conditions, and the climate of the region in autumn and spring is semi-arid except for some eastern areas, which are characterized by a dry semi-humid climate - from Mediterranean conditions in spring. In contrast, summer shows from very dry to dry. The period extending from May to October is characterized by a semi-arid to dry climate; December and January reveal humid conditions, while November, February, March and April belong to a semi-arid to Mediterranean climate.

Long-Term Monitoring of Trends in Xerothermality and Vegetation Condition of a Northeast Mediterranean Island Using Meteorological and Remote Sensing Data

There is no doubt that global climate change is happening and affecting life on Earth in a variety of ways. It can be seen on the extreme events of natural disasters, prolonged periods of drought, and increased summer and annual temperatures. While climate change affects every place on Earth, the Mediterranean region is considered a hot spot of climate change. Temperature is expected to increase further, precipitation, especially during summer months, is expected to decrease, and extreme rainfall events are projected to increase. These projected changes will affect both continental and insular environments, with small islands being particularly vulnerable due to the lack of space for species to move into more favorable conditions. As a result, these environments need to be studied, the changes quantified, and the consequences monitored. The current study focuses on the island of Fournoi in the central eastern part of the Aegean Sea. We employed data from a local meteorological station, which operates for a limited period, the Climate Research Unit TS data, and remote sensing thermal data to monitor the trends in aridity over a period of almost 40 years. The results show that summer temperature has increased significantly over the last 40 years, and this is confirmed by both meteorological and remote sensing data. At the same time, precipitation seems to remain stable. Despite the increased aridity imposed by the increased temperature and stable precipitation, vegetation seems not to be experiencing extreme stress. On the contrary, it seems to be following a positive trend over the study period. This observation is explained by the extreme resilience of the plant species of the study area and the fact that vegetation has been recovering over the last 50 years after a period of human overexploitation, and this recovery overcomes the stress imposed by increased aridity.

Late Miocene-early Pliocene hydroclimate evolution of the western Altiplano, northern Chile: Implications for aridification trends under warming climate conditions

Late Miocene-early Pliocene hydroclimate evolution of the western Altiplano, northern Chile: Implications for aridification trends under warming climate conditions

Temporal-spatial characteristics of climate drought and its effects on grain yield in Hunan Province, China

The examination of the spatiotemporal characteristics and developmental trends of drought is crucial for enhancing water resource management, bolstering drought resistance, and improving disaster prevention capabilities. This study employs the Standardized Precipitation Evapotranspiration Index (SPEI) and grain yield data across various time scales, in conjunction with methodologies such as Run Theory, Mann-Kendall, and Standardized Yield Residual Series, to conduct an in-depth investigation into the spatiotemporal variation characteristics of meteorological drought in Hunan Province and its impact on grain yield. The findings suggest that: (1) Since 1960, the likelihood of seasonal drought occurrence in Hunan Province has been ranked as autumn > winter > spring > summer, with mild drought occurring most frequently, followed by moderate drought, while the frequency of severe and extreme drought remains low. (2) Meteorological drought in Hunan Province exhibits spatial differences at the seasonal scale, with the overall drought changes in spring and summer displaying a non-significant upward trend; the western and southern regions exhibit a trend of aridification in autumn; and in winter, the Zhangjiajie and Xiangxi regions show an insignificant downward trend. (3) From 1960 to 2022, grain production in Hunan Province has demonstrated a pattern of fluctuation and increase. The meteorological yield of grain crops displays a high-low-high spatial distribution from south to north. Concurrently, there is a positive correlation between short-term climate change and meteorological output, while long-term climate change is not evident. (4) El Niño Southern Oscillation (ENSO) is a significant circulation factor affecting meteorological drought in Hunan Province, and the meteorological drought in autumn and winter in Hunan Province is significantly influenced by ENSO. The research findings can provide reference significance and a scientific basis for drought research and comprehensive management in Hunan Province, and offer data and theoretical support for promoting economic development.

Glacial and periglacial geomorphology of the eastern flank of the north Patagonian Andes: Quaternary morphoclimatic evolution

The cold climate events of the Upper Cenozoic greatly modified the landscape of Patagonia, where a large number of relicts and active landforms of glacial, periglacial and paraglacial origin is preserved. To assess the regional paleoclimatic record when numerical ages are unavailable, the spatial distribution of local depositional landform sequences was analyzed in six mountain ranges located on the eastern margin of the North Patagonian Andes. The analysis of satellite images and digital elevation model, fieldwork research and its integration into a Geographical Information System were used to develop a detailed inventory of mountain landforms. A total of 67 glacial valleys, 97 glacial cirques, 94 moraines, 75 rock glaciers, 103 protalus ramparts, and more than 145 km2 and 100 km2 of surface affected by solifluction and mass wasting processes respectively were mapped. From the analysis of the spatial and altitudinal distribution of landforms, we defined temporal and spatial sequences of morpho-climate importance. We recognized four major morpho-climate events associated with local paleoclimate conditions and one stage of a recent paraglacial adjustment. The oldest cold climate event recognized might be correlated with the Last Glacial Maximum. The results show the rise in the average air temperature and an aridity trend for the study area since the Late Pleistocene. During this lapse, glacial environments evolved to periglacial environments, although was recognized their coexistence in some areas in the same mountain range.

Stem Growth and Dehydration Responses of Mediterranean Tree Species to Atmospheric and Soil Drought.

Stem growth responses to soil and atmospheric drought are critical to forecasting the tree carbon sink strength. Yet, responses of drought-prone forests remain uncertain despite global aridification trends. Stem diameter variations at an hourly resolution were monitored in five Mediterranean tree species from a mesic and a xeric site for 6 and 12 years. Stem growth and dehydration responses to soil (REW) and atmospheric (VPD) drought were explored at different timescales. Annually, growth was determined by the number of growing days and hours. Seasonally, growth was bimodal (autumn growth ≈ 8%-18% of annual growth), varying among species and sites across the hydrometeorological space, while dehydration consistently responded to REW. Sub-daily, substantial growth occurred during daytime, with nighttime-to-daytime ratios ranging between 1.2 and 3.5 (Arbutus unedo ≈ Quercus faginea < Quercus ilex < Pinus halepensis in the mesic site, and Juniperus thurifera < P. halepensis in the xeric site). Overall, time windows favourable for growth were limited by soil (rather than atmospheric) drought, modulating annual and seasonal growth in Mediterranean species, and stems maintained non-negligible growth during daytime. These patterns contrast with observations from wetter or cooler biomes, demonstrating the growth plasticity of drought-prone species to more arid climate conditions.

Sedimentary Expressions of the Early Jurassic Jenkyns Event in an Inland Lacustrine System in the Yin'gen–Ejinaqi Basin, North China

AbstractThe Jenkyns Event, more widely known as the Toarcian Oceanic Anoxic Event (T‐OAE), is marked by globally distributed negative carbon‐isotope excursions, widespread oxygen depletion, and large‐scale organic carbon burial, which indicate major climate/environmental perturbations in Earth's surface systems during the Early Jurassic. Although extensive research has been conducted in European continental settings, particularly in the western peri‐Tethys regions, the impacts of this event beyond Europe remains largely unexplored. Here, a multiapproach study including investigations into the spore‐pollen assemblages, pyrite framboids, clay minerals, total organic carbon (TOC) levels, and organic carbon isotope (δ13Corg) levels in a lacustrine borehole section (MED1) from the Yin'gen–Ejinaqi Basin, North China, provides evidence of the occurrence of the Jenkyns Event and its extensive sedimentary responses in the eastern Tethys terrestrial systems. Two distinct spore‐pollen assemblages have been identified in MED1 (drilling depth: 982.4 m to 1267.5 m), with the Cycadopites–Protopinus–Osmundacidites assemblage in the lower part (1267.5 m to 1132.9 m) indicating a middle Early Jurassic age and the Classopollis assemblage in the upper part (1132.9 m to 985.7 m) suggesting a Toarcian age. Framboidal pyrite data suggest more anoxic conditions during the deposition of black mudstone and shale intercalations in the lower part of the Classopollis assemblage (1132.9 m to 1066.9 m), which combined with organic carbon enrichment and negative δ13Corg excursions, are considered the paleoenvironmental response to the Jenkyns Event in the study area. Furthermore, the evolution of vegetation groups changed from plant groups characterized by bisaccate and cycad pollen, as well as fern spores, to vegetation groups represented by Cheirolepidiaceae pollen across the Jenkyns Event, as evidenced by spore‐pollen data, together with the clay mineral assemblage change characterized by a notable increase in illite at the expense of kaolinite, suggests that while a subtropical‐temperate climate persisted, a change toward warmer and drier conditions most likely occurred in the early Toarcian in the study area. In contrast to the humidification evidenced in many coastal settings, this aridification trend in the Yin'gen–Ejinaqi Basin aligns with the conditions in many inland areas. It is hypothesized that the underlying cause of these divergent changes may be linked to certain patterns of spatially variable water availability on land, potentially driven by extremified hydrological conditions.

An exceptional phytoplankton bloom in the southeast Madagascar Sea driven by African dust deposition

Abstract Rising surface temperatures are projected to cause more frequent and intense droughts in the world's drylands. This can lead to land degradation, mobilization of soil particles, and an increase in dust aerosol emissions from arid and semi-arid regions. Dust aerosols are a key source of bio-essential nutrients, can be transported in the atmosphere over large distances, and ultimately deposited onto the ocean's surface, alleviating nutrient limitation and increasing oceanic primary productivity. Currently, the linkages between desertification, dust emissions and ocean fertilization remain poorly understood. Here, we show that dust emitted from Southern Africa was transported and deposited into the nutrient-limited surface waters southeast of Madagascar, which stimulated the strongest phytoplankton bloom of the last two decades during a period of the year when blooms are not expected. The conditions required for triggering blooms of this magnitude are anomalous, but current trends in air temperatures, aridity, and dust emissions in Southern Africa suggest that such events could become more probable in the future. Together with the recent findings on ocean fertilization by drought-induced megafires in Australia, our results point toward a potential link between global warming, drought, aerosol emissions, and ocean blooms.

Paleozoic Equatorial Records of Melting Ice Ages (PERMIA): calibrating the pace of paleotropical environmental and ecological change during Earth's previous icehouse

Abstract. The upper Paleozoic Cutler Group of southern Utah, USA, is a key sedimentary archive for understanding the Earth-life effects of the planet's last pre-Quaternary icehouse–hothouse state change: the Carboniferous–Permian (C–P) transition, between 304 and 290 million years ago. Within the near-paleoequatorial Cutler Group, this transition corresponds to a large-scale aridification trend, loss of aquatic habitats, and ecological shifts toward more terrestrial biota as recorded by its fossil assemblages. However, fundamental questions persist. (1) Did continental drift or shorter-term changes in glacio-eustasy, potentially driven by orbital (Milankovitch) cycles, influence environmental change at near-equatorial latitudes during the C–P climatic transition? (2) What influence did the C–P climatic transition have on the evolution of terrestrial ecosystems and on the diversity and trophic structures of terrestrial vertebrate communities? The Paleozoic Equatorial Records of Melting Ice Ages (PERMIA) project seeks to resolve these issues in part by studying the Elk Ridge no. 1 (ER-1) core, complemented by outcrop studies. This legacy core, collected in 1981 within what is now Bears Ears National Monument, recovered a significant portion of the Hermosa Group and the overlying lower Cutler Group, making it an ideal archive for studying paleoenvironmental change during the C–P transition. As part of this project, the uppermost ∼ 450 m of the core were temporarily transferred from the Austin Core Repository Center to the Continental Scientific Drilling Facility at the University of Minnesota for splitting, imaging, and scanning for geophysical properties and spectrophotometry. Here we (1) review the history of this legacy core, (2) introduce recently obtained geophysical and lithologic datasets based on newly split and imaged core segments to provide a sedimentological and stratigraphic overview of the Elk Ridge no. 1 core that aligns more accurately with the currently recognized regional lithostratigraphic framework, (3) establish the position of the boundary between the lower Cutler beds and the overlying Cedar Mesa Sandstone in the core, and (4) outline our ongoing research goals for the core. In-progress work on the core aims to refine biostratigraphic and chemostratigraphic age constraints, retrieve the polarity stratigraphy, interrogate preserved cyclostratigraphy, analyze sedimentary structures and paleosol facies, investigate stable isotope geochemistry, and evaluate elemental abundance data from X-ray fluorescence (XRF) scanning. Together with outcrop studies throughout Bears Ears National Monument and its vicinity, these cores will allow the rich paleontological and paleoenvironmental archives recorded in the continental Carboniferous–Permian transition of western North America to be confidently placed in a robust chronologic context that will help test hypotheses relating ecosystem evolution to the Carboniferous rainforest collapse, initial decline of the Late Paleozoic Ice Age, and long-wavelength astronomical cycles pacing global environmental change.

Most High Mountainous Areas Around the World Present Elevation‐Dependent Aridification After the 1970s

AbstractThe research on the trends of mountainous aridity and the issue of elevation‐dependent aridity (EDA) has long been hindered by limitations in data validity. In this study, we present global monthly merged data sets of Vapor Pressure Deficit and Aridity Index (AI) from 1960 to 2020, aiming to detect and attribute elevation‐dependent patterns of atmospheric and soil aridity in six representative high mountainous areas worldwide. Our findings reveal that most of the mountainous regions experienced significant aridification after the 1970s (p &lt; 0.05). The Rocky Mountains and Ethiopian Highlands are identified as the most vulnerable areas, with both atmospheric and soil aridity increasing by 13% across all elevation gradients. Significant humidification has been observed only in High Asian Regions at 4,000 m above sea level with an approximate decrease of 11% in soil AI. In both temporal and spatial patterns, soil aridity exhibits stronger heterogeneity compared to atmospheric aridity, with certain regions and seasons showing humidification, despite the overall aridification trend. Elevation‐dependent aridity is observed in two‐thirds of the mountains, but whether high altitude alleviates or amplifies aridity depends on the pattern of precipitation changes at different elevations. The rise in air temperature is the primary driving factor for soil and atmospheric aridification, contributing to over 50% of each. In two‐thirds of the regions, changes in precipitation exacerbate soil aridity. Simulations show that human activities are closely related to the ongoing prolonged atmospheric aridification. This study contributes to a comprehensive understanding of global mountainous aridity evolution projected under climate change.

Imprints of Holocene aridity variability in the Aegean Sea and interconnections with north-latitude areas

The analysis of the ASTC1 sediment core from the south Aegean Sea region offers critical insights into the complex interplay of geological and climatic factors over the Holocene period. The data reveals fluctuating climatic conditions during the last 8.7 ka as seen through the elemental concentrations obtained by XRF core scanning combined with a qualitative mineral analysis within a robust chronological framework. Short-term fluctuations in both Ti/Al and Zr/Si ratios suggest brief oscillations of increased aridity which partially coincide with the Holocene “Rapid Climate Change” events (RCCs). Among them, the most pronounced in our record are those centered between 8.5–8 ka, 3–2.5 ka (Greek Dark Ages), and 0.6–0.3 ka (Little Ice Age). The arid and humid events identified in the sediment record align with major archaeological periods in Greece, suggesting a potential influence of climatic conditions on the development and decline of civilizations in the region. Moreover, a general arid trend as of 6 ka toward the present was evidenced in our record and aligns with other high-resolution climatic data from the Northern Hemisphere, suggesting climatic teleconnections. Spectral analysis of the ASTC1 record reveals cyclical climate patterns with periodicities of approximately 2500, 1200, and 550 years, which coincide with the Bond and Hallstatt cycles. The phase relation of these cycles in our record, the Greenland ice record, and the North Atlantic Drift ice indices show that colder conditions in the higher latitudes are expressed as events of enhanced aridity in our record and generally in the lower latitudinal regions.

Hydrogen isotope records of long-chain alkanes from the monsoon boundary zone over the last 2400 years in North China

The East Asian Summer Monsoon (EASM) plays a key role in the climate dynamics of East Asia, affecting the livelihood of millions of people by contributing to agriculture and water resources. The monsoon boundary zone (MBZ) is particularly sensitive to shifts in climate patterns. However, the complexity of water vapor sources in the region makes it difficult to understand precipitation processes. To address this issue, the records of lipid biomarker abundances and leaf wax stable hydrogen isotope composition of C31–alkanes (δDwax-C31) from a 238 cm sediment core extracted in Lake Dali, located at the northern edge of the EASM, were sampled and examined by 2 cm per sample. Based on analyses of the biogenic molecular indicators(biomarkers), precipitation isotopes, and other indicators of the evolution of the climate environment, we have reconstructed precipitation change history over the past 2400 years. The results show the decrease in alkanes concentrations, along with high A.I. values in Lake Dali sediments indicate an arid trend over the past 2400 years, which have led to a decrease in basin productivity and the development of grasslands. The low temperatures greatly limit the growth of C4 vegetation in this cold region, so the long-chain alkanes in the lake sediments is mainly derived from the leaf wax lipids of C3 vegetation in the grassland. The increase of Paq and the reduction of ACL indicate that the decrease of grass vegetation inputs in the basin and the outbreak of aquatic vegetation. Notably, aquatic vegetation outbreaks may be due to reduced precipitation leading to shrinking lakes and increased nutrients in the lakes. By comparing with the biogenic indicators of Lake Dali and other regional records, the δDwax-C31 value can be used as a proxy for the regional precipitation, with a gradual decrease from about −240 ‰ to about −190 ‰, which indicates a general decreasing trend in the precipitation in the last 2400 years. Specifically, in exception of some significant fluctuations on the centennial to millennial scale, δDwax-C31 value decrease by about 40 ‰ between 1800 and 1600 cal.a BP over a period of only 200 years. As we know, the diminishing solar radiation might lead to a weaker EASM and a reduction in precipitation. Thus, the decrease in regional temperature became the main reason for the anomalous negative precipitation isotope phenomenon due to the lower precipitation from 1800 to 1600 cal.a BP in the monsoon boundary zone (MBZ, this represents only the northern boundary). This study contributes to our understanding of δDwax-C31 within the MBZ and its significance as an indicator of rainfall processes. By analyzing this molecular proxy, the researchers gain insights into the past precipitation patterns and their implications for regional climate. Importantly, the study demonstrates the value of combining biogenic molecular indicators with geochemical indicators, as it leads to improved accuracy in reconstructing regional climate conditions. The findings shed light on long-term climate trends and provide a more comprehensive understanding of the historical impacts of climate change on the EASM region. Moreover, the study's contribution to interpreting the paleoclimate record is crucial for validating climate models used to project future climate scenarios. Overall, this research enhances our knowledge of regional climate dynamics and their implications, offering valuable insights for both historical analysis and future climate projections.

Depositional environments and plant communities in the exceptional context of the Kungurian megacaldera of the Athesian Volcanic Group (Southern Alps, N-Italy)

We used a combined approach (lithofacies and palynology) and multivariate analyses to reconstruct the different depositional environments and changes in the plant communities throughout the middle to late Kungurian in the tropical Pangea. The late Paleozoic terrestrial biotas underwent changes under the pressure of a general aridification trend and a warming event that changed biota composition favoring drought-tolerant taxa during the Artinskian. Few studies integrate the different terrestrial ecosystem components to reconstruct palaeoenvironments and climate changes throughout the Cisuralian (early Permian). We analyzed several sedimentary successions of different stratigraphic positions intercalated in well-dated volcanic units of the megacaldera of the Athesian Volcanic Group (Southern Alps, northern Italy). The obtained palynofacies and quantitative sporomorph records with an exceptional high resolution (∼10 Ma) evidence a palaeoenvironmental/climatic change in the plant communities from the middle to the late Kungurian. The late Kungurian shows a higher diversity in the plant communities with a dominance of seed ferns and a higher relative abundance of xeromorphic-hygromorphic sporomorph taxa. This suggests the presences of more stable and putatively more humid environmental conditions in respect to the middle Kungurian. Furthermore, a direct comparison between lithofacies and all primary components of the palynofacies assemblages permits to characterize lacustrine and alluvial depositional environments since these studies are underrepresented for terrestrial environments.

Stratospheric Aerosol Injection Geoengineering Would Mitigate Greenhouse Gas‐Induced Drying and Affect Global Drought Patterns

AbstractStratospheric aerosol injection (SAI) is suggested as a potential measure for alleviating global warming. The potential effects of SAI on global temperature and precipitation have been extensively discussed, but its impact on drought has received little attention. Based on the simulations from the G6sulfur experiment that employs SAI to reduce the global mean surface temperature from the level of high‐tier forcing (Shared Socioeconomic Pathways SSP5‐8.5) scenario to that of medium‐tier forcing (SSP2‐4.5) scenario, we investigate the drought response to SAI via the standardized precipitation evapotranspiration index. During 2081–2100, SAI effectively offsets the greenhouse gas‐induced aridity trend by increasing the climate water balance at the global scale. Drought duration and severity decrease but drought frequency increases under SAI forcing. Robust wetting responses occur over most regions, especially the Sahara, South America, southern Africa and Australia, while Alaska, Greenland, Southeast Asia, and tropical Africa face enhanced drought due to SAI. Relative to the SSP2‐4.5 scenario, the regional drying and wetting patterns in G6sulfur are remarkably different. Notably, in tropical Africa, SAI reverses the wetting caused by greenhouse gases and induces severer drought. The drought pattern changes are largely due to evaporative demand alterations caused by the vapor pressure deficit response.

Drought and aridity trends on the Algerian steppe

Drought and aridity trends on the Algerian steppe

Analysis of Drought Characteristics and Causes in Yunnan Province in the Last 60 Years (1961–2020)

Abstract Droughts are becoming more frequent and severe in southwest China, with Yunnan being the most affected region. Most of the current studies on droughts in Yunnan are limited to individual cases and lack a common determination of the causes of historical drought events. In this study, we analyzed drought characteristics and causes over the last 60 years (1961–2020) in Yunnan Province in two seasons: dry and rainy. There was a clear trend of aridity in Yunnan Province in terms of both temporal and spatial changes, and there was a long-term drought period in approximately 2010; in particular, the frequency of drought in the dry season significantly increased. Due to its unique geographical location, precipitation in Yunnan Province is influenced by various factors, and the main influencing factors differed in different periods. SST variation is the most important factor affecting Yunnan drought. Precipitation in Yunnan Province is affected by the warm pool of the Indian Ocean throughout the year, and thermal anomalies in different locations of the Pacific Ocean have different effects on Yunnan Province and often overlap with the effects of SST anomalies in the Indian Ocean. Significance Statement In this study, we analyzed drought characteristics and causes over the last 60 years (1961–2020) in Yunnan Province in two seasons: dry and rainy. The causes of historical drought events in Yunnan Province in terms of common characteristics were determined, and SST variation was the most influential factor, with the Indian Ocean and the Pacific Ocean having the greatest influence. Increased temperature may be a more important cause of dry season drought in Yunnan Province, while drought in the rainy season is mainly due to reduced water vapor transport. These results point the way toward better understanding of the occurrence of drought in Yunnan Province.

A multiproxy approach to reconstruct the Late Holocene environmental dynamics of the semiarid Andes of central Chile (29°S)

Mountain ecosystems located in the Andes cordillera of central Chile (29–35°S) have been strongly affected by the ongoing Mega Drought since 2010, impacting the snow cover, the surficial water resources (and thereby water storage), as well as the mountain biota and ecosystem services. Paleoenvironmental records in this part of the semiarid Andes are key to estimating the effects of past climate changes on local communities helping to forecast the ecological and biological responses under the aridification trend projected during the 21st century. Here we present a 2400-year multiproxy paleoenvironmental reconstruction based on pollen, diatoms, chironomids, sedimentological and geochemical data (XRF and ICP-MS data) of Laguna El Calvario (29°S; 3994 m a.s.l), a small and shallow Andean lake. Four main hydrological phases were established based on changes in the lithogenic and geochemical results associated with allochthonous runoff input and the subsequent response of the biological proxies. Between 2400 and 1400 cal yrs BP, wetter than present conditions occurred based on the intense weathering of the lake basin and the dominance of upper Andean vegetation. A decrease in moisture along with sub-centennial discrete wet pulses and lake-level changes occurred until ~800 cal yrs BP followed long-term stable climate conditions between 1850 and 1950 AD as suggested by a drop in vegetation productivity and low lake levels. From 1950 AD to the present, a decline in moisture with a severe trend to drier conditions occurring in the last decades occurred as reflected by an upward vegetation belt displacement around Laguna El Calvario along with a turnover of diatom assemblages and high productivity in the water column.

Obliquity forcing of Late Pliocene–Early Pleistocene aridification in the Qaidam Basin, NE Tibetan Plateau

Knowledge of the variations of aridification during past warm periods can help predict future aridification trends. However, the variation of aridity during the warm Pliocene epoch, a potential analog for the future climate, has not been sufficiently studied due to the lack of high-resolution records. Here, we present high-resolution (∼7 kyr) oxygen and carbon isotope records spanning the Late Pliocene–Early Pleistocene from the Qaidam Basin, northwestern China. We interpret enriched carbonate δ18O value as indicating stronger evaporation, based on the general correlation between the enrichment of carbonate δ18O and an increased sedimentary halite content. Our results reveal that the Qaidam Basin was already an extremely arid environment no later than ∼3.9 Ma, and that aridification was further intensified at ∼2.6 Ma. Interestingly, the Qaidam Basin experienced decreased aridity or climate wetting during the high insolation intervals within the middle Piacenzian warm period, in contrast with the intensified aridity in the semi-arid Chinese Loess Plateau. Strikingly, the Qaidam Basin experienced intensified aridification during high-obliquity intervals, with smaller global ice sheets, during 3.6–2.5 Ma. We attribute this obliquity signal of Asian aridification to the effects of insolation and possibly glacial forcing, via their impacts on regional evaporation and reduced monsoon precipitation. Using the Late Pliocene as an analogue, our findings suggest that future aridification variations in Central Asia during the next ∼100 kyr may be dominated by 40-kyr cycles, under natural climatic forcing.

An improved methodology for quantifying the impact of human activities on hydrological drought change

Study regionUpper Shiyang River in the eastern Qilian Mountains, China. Study focusQuantifying the impacts of anthropogenic and climate change on wet and dry hydrological variability was done by improving the Slope Change Ratio of Cumulative Quantities (ISCRCQ) method. New hydrological insights for the regionThe scientific method is critical to quantify the driving factors of dry-wet hydrological changes. In this study, the slope change ratio of cumulative quantity (SCRCQ) method was improved to quantify the impacts of human activities and climate change on dry-wet hydrological changes. The results show a hydrological aridification trend at an annual scale from 1961 to 2016 in the upper reaches of the Shiyang River. However, the dry-wet hydrological change trends of the six tributaries differed: the hydrological humidification of the four western tributaries was apparent, while the remaining tributaries showed hydrological aridification. The influences of human activities and climate change on dry-wet hydrological changes were also evidently distinct in the different tributaries. Changing in climate is a vital factor triggering the dry-wet hydrological changes in the western tributaries, while human activities have completely changed the direction of the dry-wet hydrological changes and intensified the hydrological aridification in the eastern tributaries. Human activities have resulted in an increase both in the frequency of droughts and in the risk of socio-economic droughts. Thus, human activities in the region of eastern tributaries should be controlled within reasonable limits.

Hominin Response to Oscillations in Climate and Local Environments During the Mid‐Pleistocene Climate Transition in Northern China

AbstractArcheological evidence from loess sediments from Shangchen on the southeastern Chinese Loess Plateau indicates a suspension of hominin occupation around the time of the early mid‐Pleistocene climate transition, prompting a re‐assessment of climate‐vegetation‐hominin interactions. Loess deposits with in situ lithic records cover the period of hominin occupation and reveal four distinct climate‐vegetation periods (2.1–1.8, 1.8–1.26, 1.26–0.9, and 0.9–0.6 Ma). Major oscillations in climate superimposed upon an aridification trend and an expansion of C4 herbaceous vegetation from about 1.26 Ma may have driven early humans to move to more hospitable locations in the region. Comparison with the record at Nihewan indicates that large‐scale climate oscillations induced disparate hominin responses due to distinctive local environmental conditions.