Arid Central Asia Research Articles

Dipole Pattern of Holocene Hydroclimate Variations Across the Asian Drylands: Critical Evidence From West Asia

AbstractExploring the spatiotemporal differences of hydroclimate variations is crucial for managing future climate change. In the Asian drylands, West Asia (WA) and arid central Asia (ACA) are both climatically dominated by the westerlies and have shown a dipole pattern in precipitation variation during the past several decades. However, it is unclear whether such a difference exists during the Holocene, mainly because the dispute between the δ18O‐based early Holocene hydroclimate optimum and the pollen‐based mid‐Holocene optimum in WA. Here we present a precisely dated record based on lipid biomarkers from Almalou Peatland in the western Iranian Plateau. The chain length of n‐alkanoic acids was interpreted as a hydroclimate indicator based on a proxy validation study. Our record reveals a wetting trend during 9–7.5 cal ka BP, a mid‐Holocene hydroclimate optimum (7.5–3 cal ka BP), and a rapidly drying trend during 3–0 cal ka BP. The hydroclimate variation was supported by a water‐level reconstruction from the same core. The most negative δ18O values during the early Holocene could be partly attributed to the impacts of water vapor sources. Comparing our reconstruction from WA to those from ACA, we found a dipole pattern of hydroclimate variations on the millennial timescale during the Holocene. The simulation results revealed that, unlike the persistent wetting trend in ACA, the pivotal shift of spring insolation led to a transition from wetting to drying conditions in WA, ultimately leading to the generation of dipole pattern. This demonstrates that despite the consistent control by westerlies over the Asian drylands, there are distinct spatial differences in hydroclimate responses to natural forcings.

Reconstructing monthly 0.25° terrestrial evapotranspiration data in a remote arid region using Bayesian-driven ensemble learning method

This study presents a Bayesian-driven ensemble learning framework to minimize errors in evapotranspiration (ET) data assimilation, thereby generating a continuous-scale ET estimation with improved accuracy for the data-scarce arid Central Asia (CA). Five state-of-the-art gridded ET products were extensively tested and utilized to reconstruct new long-term ET data at grid scale, including two Global Land Data Assimilation System (GLDAS)-Land Surface Models (LSM) (Catchment and NOAH), two reanalysis products (European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) and Modern-Era Retrospective Analysis for Research and Applications – ver. 2 (MERRA2)), along with the Global Land Evaporation Amsterdam (GLEAM) satellite ET product ver. 3.6b. Taylor Skill Score was employed to evaluate the input gridded ET datasets, using in situ measurements across four arid biomes — cropland, shrubland, farmland, and grassland —as benchmarks. Bayes-Markov Chain Monte Carlo (Bayes-MCMC)-derived logarithmically transformed predictors from the posterior ensemble anomalies were standardized to resolve the mismatches in the cumulative distribution functions of ET data relating to the in situ observations. We found that the constrained residual errors were more profound between 45th and 95th percentiles for the rescaled total ET anomalies across all the input ET datasets at 95 % confidence interval. Moreover, the weighted ensemble estimates derived from the Bayes-MCMC were instrumental in correcting ET anomalies, leading to the robust reconstruction of a more reliable ensemble mean ET data for Central Asia (CAETens) at monthly temporal and 0.25° spatial resolutions, spanning from 2003 to 2020. Overall, CAETens exhibited superior performance, achieving the highest averaged Kling-Gupta Efficiency of 0.75 and registering the lowest Root Mean Square Error of 6.85 mm/m compared to the standalone gridded ET products. Comparisons of spatial distributions of fine-scale features, and evaluations using standard metrics revealed that all ET products varied significantly (p < 0.05) by biome types. Remarkably, only CAETens exhibited a reasonable low positive bias and pronounced ability to resolve the complex spatiotemporal patterns associated with the input gridded ET products. The study bridges the gap in continuous ET monitoring for sustainable water resources management in CA.

Increased late Holocene dust activity revealed by loess accumulation rates in Central Asia

Dust from the vast arid and semi-arid regions of arid Central Asia (ACA) makes a large contribution to global-scale dust cycles. However, systematic and regional-scale reconstructions of dust activity in ACA are lacking, thus hindering the exploration of its relationship with climate change. Aeolian loess deposits provide valuable records of past dust activity and its linkages to climate. We constructed a stacked, normalized dust mass accumulation rate (MAR) record from 17 loess sections with high-resolution dating, together with a probability density record based on 189 absolute ages from 39 Holocene loess sections. These records were used to reconstruct the temporal pattern of Holocene dust activity in ACA, which shows a pronounced increase during the late Holocene. After evaluating the temporal variation of moisture conditions at different altitudes in ACA, we conclude that while dust activity during the early and middle Holocene was driven predominantly by climate change, this was not the case in the late Holocene. Taking the mountain-basin system of the Yili Basin in Xinjiang as an example, we propose that dust activity on a large spatial scale was not completely controlled by changes in moisture conditions, and that regional factors, such as fluvial geomorphic processes, played an important role in increasing the materials supply to the areas of dust accumulation. We speculate that dust activity may intensify in ACA under future global warming scenarios.

Eurasian drylands are both evolutionary cradles and museums of Nitrariaceae diversity

AbstractAimDrylands cover about 41% of Earth's land surface and are home to fragile biota with high levels of endemism. Two hypothetical models, i.e., cradle and museum, have been proposed to account for present‐day species diversity in an ecoregion or biome. We investigated macroevolutionary patterns to test these two different models in Nitrariaceae, a characteristic component of the Eurasian dryland ecosystem. We also used this family to explore the intercontinental disjunct distribution pattern between the deserts of Eurasia and western North America, known as the Madrean–Tethyan disjunction.LocationDrylands in the Northern Hemisphere.TaxonNitrariaceae (Sapindales, Angiosperms).MethodWe sampled all 16 of the currently recognized extant species of Nitrariaceae and 59 species from the eight other families of Sapindales. A fossil‐calibrated phylogeny was generated using 12 fossil constraints. The ancestral range and climate niche of Nitrariaceae were reconstructed, and diversification rates were estimated.ResultsThe most recent common ancestor of Nitrariaceae likely inhabited arid habitats with low rainfall in the temperate zone in the Late Cretaceous, which geographically corresponds to present‐day Central Asia. The western North American Peganum mexicanum split from its Central Asian sister group at approximately 39 Ma. Net diversification rates of Nitrariaceae experienced a significant increase around 11 Ma. Within Sapindales, at least seven arid species originated markedly prior to the Miocene.Main ConclusionsThe North Atlantic land bridge and global cooling climate in the Late Eocene might have driven the formation of the present‐day disjunct distribution of Nitrariaceae between arid Central Asia and western North America. Nitrariaceae originated in the Late Cretaceous and exhibited long‐term climate niche conservatism, but experienced a rapid diversification in the late Miocene of Eurasia in response to orogenetic and climatic changes. These findings suggest that Eurasian drylands serve as both evolutionary cradles and museums for the diversity of Nitrariaceae and likely for other arid‐adapted lineages.

Time-Transgressive Onset of Holocene Climate Optimum in Arid Central Asia and Its Association with Cultural Exchanges

Arid central Asia (ACA) is dominated by mid-latitude westerlies and characterized by a climate optimum (a relatively humid climate that has supported the development of human culture) in clear contrast with the climate of monsoonal Asia during the Holocene. Significantly, whether the onset of the Holocene Climate Optimum (HCO) had an impact on cultural exchanges along the ancient Silk Road remains unknown. In this study, we compared the onset of the HCO in different parts of the vast ACA region by referring to a variety of previously established paleo-moisture/precipitation records. Intriguingly, we found significant differences in the onset of the HCO between the western and eastern parts of ACA. The onset of the HCO in the western part of ACA (i.e., to the west of the Tianshan Mountains) mainly occurred at ~8 ka BP (1 ka = 1000 cal yr BP). In contrast, the onset of the HCO occurred at ~6 ka in northern Xinjiang and even as late as ~5 ka in southern Xinjiang; this is a delay of 2–3 thousand years compared with the western part of ACA. These results likely indicate that the onset of the HCO occurred in a time-transgressive manner in ACA, namely, ‘early in the west but late in the east’. On the other hand, we found that the onset of the HCO in the western part of ACA may have resulted in the inception of wheat planting and the development of agricultural civilization and that the onset of the HCO in northern Xinjiang may have prompted the southward migration of Afanasievo culture after ~5 ka. Additionally, the initiation of the HCO in southern Xinjiang could provide an environmental basis for the spread and planting of wheat and millet in this area after ~4.5 ka. We speculate that the spatial differences in the onset of the HCO in ACA are mainly related to temporal changes in the intensity and position of the mid-latitude westerly jet. Although the increase in insolation and reduction in the global ice volume would have led to an increase in the water vapor feeding the western part of ACA around 8 ka, the climate in the eastern part of ACA (namely, the Xinjiang region) could have only become humid after 6 ka when the westerlies were intensified and became positioned in the south. Moreover, the delayed HCO in southern Xinjiang probably benefited from the stronger westerly winds that appeared around 5 ka, which could have overcome the influence of the tall topography of the Tianshan Mountains. Therefore, in addition to external forcing (i.e., insolation), the ocean–atmospheric teleconnection, the regional topography, and their connection to the climate system are important in determining the spatial differences in the time-transgressive onset of the HCO in ACA. Our findings contribute to understanding the spatio-temporal characteristics of the hydroclimate in regions with complex eco-environmental systems and a diverse history of human activity.

Holocene forcing of aeolian dust activity over the Tibetan Plateau and its surroundings

Aeolian deposits on the Tibetan Plateau (TP) and its surroundings provide crucial source materials for the Asian dust cycle, which significantly affects Asian and global ecosystems and climate. However, it is unclear how the dust dynamics of the TP and its surroundings are linked to Earth's climate system. To address this issue, we examined the grain size and accumulation rate of six Holocene aeolian sections on the southern TP (a new, well-dated high-resolution section, two relatively low-resolution sections, and three published sections) and combined them with equivalent aeolian sedimentary records from eastern arid central Asia. The results suggest that dust activity in both regions decreased during the early to middle Holocene and then increased in the late Holocene. We hypothesize that the primary drivers of Holocene dust activity in both regions are similar. Cold-season insolation, as the primary driving factor, combined with ice volume and atmospheric CO2 concentration, collectively controlled the regional temperature, which determined the near-surface wind intensity via its influence on the TP High and Siberian High, respectively, thus ultimately controlling the regional dust activity. In this context, we project that dust activity on the TP and its neighboring areas will decrease under warm scenarios in the 21st century. Overall, our findings provide an extensive overview of the past, present, and future scenarios of Asian dust activity, especially of the TP dust.

Climatic and anthropogenic impacts on the water balance of Issyk-Kul Lake through its main catchments

Lake Issyk-Kul is an endorheic lake in arid Central Asia that is vital to the region's ecological sustainability and socio-economic development. Climate change and anthropogenic water consumption led to fluctuations in the lake's water level, which affected the water resource. The goal of this study was to examine the impacts of climate change and human activities on the Issyk-Kul water balance by combining the Coupled Model Intercomparison Project Phase 6 (CMIP6) scenarios with hydrological modeling. The Soil and Water Assessment Tool (SWAT) model was used to incorporate signals of future precipitation and temperature changes. According to the scenarios, the total discharge of the three catchments showed an overall increasing trend with a maximum value of 28.02%. The snow and ice-melt water from March to August was revealed, and the increasing trends only occurred from March to May, with the snow and ice melting peak variations ranging from 0.5% to 2%. The high increase in change appeared in northern catchment of the lake. There was an exceptional upward precipitation trend over the northern catchment, with annual increases ranging from 0.7 to 14.5%, and an average annual temperature of 1.72°C. With slight similarities, the total runoff would increase for all catchments, with an average annual value of 10.6%. The northern catchment was significantly more sensitive to precipitation and warming than the southeastern catchments. Under land use land cover change, average annual discharge decreased with agricultural expansion, with discharge differences ranging from −0.005 to −1.06 m3/s. The findings are useful for decision-makers addressing the challenges of climate change mitigation and local water resource management.

The Interdecadal Pacific Oscillation is responsible for the linkage of decadal changes in precipitation and moisture in arid central Asia and the humid Asian monsoon region during the last millennium

Abstract. Reconstruction and observational studies imply a potential linkage of moisture and precipitation change in arid central Asia and monsoonal East Asia, in which the evolution of moisture and precipitation in central Asia is out of phase with that in northern China but in phase with that in southern China. In order to ascertain whether there is a robust linkage between the changes in climate in Asian arid regions and monsoon regions and to elucidate the underlying dynamic mechanisms, we analyzed the Last Millennium Reanalysis dataset and outputs from the Community Earth System Model Last Millennium Ensemble (CESM-LME). The results indicate a significant decadal linkage between precipitation changes in central Asia's arid region and the Asian monsoon region during the last millennium, which is primarily driven by the Interdecadal Pacific Oscillation (IPO). In spring, the positive IPO could enhance westerlies over the Mediterranean Sea and to its east, which could transport more water vapor and cause increased precipitation over central Asia. In summer, the positive IPO is accompanied by a weakened Asian monsoon and southward Asian subtropical westerly jet, which can lead to increased (decreased) summer precipitation over southern China (over northern China and South Asia). The IPO plays a dominant role in connecting the decadal variations in precipitation between arid central Asia and monsoonal Asia by modulating the precipitation of their respective major rainy seasons. Model results suggest that this decadal linkage stems entirely from the internal variability present in the CESM-LME control and all single-forcing simulations. Changes in external forcing factors do not alter this inherent linkage caused by the IPO. Moreover, based on analyses of the aridity index and soil moisture content, this relationship of precipitation variation also causes a similar decadal linkage of moisture changes in central Asia and monsoonal Asia. The differences in the multi-centennial-scale moisture and precipitation variations in the Asian arid region and the monsoon region between the Medieval Climate Anomaly and Little Ice Age are also likely caused by IPO-like sea surface temperature anomalies.

The Decreased Cloud Cover Dominated the Rapid Spring Temperature Rise in Arid Central Asia Over the Period 1980–2014

AbstractCentral Asia (CA) has experienced a faster temperature rise than the global land over the past decades. However, the role of regional/global drivers and their associated underlying biophysical mechanisms is poorly explored. Here, we combined observations and model simulations to show that the rapid warming in CA was overwhelmingly contributed by rapid spring warming (i.e., 49.23%). The decrease of cloud cover (CLD) was the main driver of spring warming in CA, leading to the surface receiving more solar radiation, consequently heating the surface air temperature, and contributing almost 40.79% to the spring warming. Besides, the strengthening of sea level pressure states results in continuous subsidence of vertical motion over CA, which was unfavorable for cloud formation. Our study will deepen our understanding of the climate evolution in the arid CA.

Climate, human settlement, and migration in South Asia from early historic to medieval period: Evidence from new archaeological excavation at Vadnagar, Western India

Between the second urbanisation of late Iron Age/Early historic and medieval period Indian subcontinent experienced repeated invasion/human migration of central Asian warriors from Greco-Bactrian conquests till Sultanate-Mughals of sixteenth century. Historians often argue whether such invasions/migrations in the past were driven by change in climate and/or social dynamics. We present results of first detailed archaeological excavation and chronology from a multi-cultural site of Vadnagar, Gujarat state, Western India. We document records of seven cultural stages of continuous human settlement from ca. 2754 calibrated (cal) year B.P. (contemporary to Late-Vedic/pre-Buddhist Mahajanapadas or oligarchic republics), Mauryan, Indo-Greek, Indo-Scythian or Shaka-Kshatrapas (AKA ‘Satraps’, descendants of provincial governors of ancient Achaemenid Empires), Hindu-Solankis, Sultanate-Mughal (Islamic) to Gaekwad-British colonial rule (∼318 year B.P.) and recent. We constrain the climate (Indian summer monsoons or ISM) at Vadnagar by both bulk and isotope sclerochronology (seasonality) of molluscan shells and show that each of these periods flourished during a good ISM phase. Conversely the arid/hyper-arid phases witnessed decline in material culture, craftsmanship, and/or increased social instability yet the settlement was never abandoned thus making Vadnagar the oldest living city within a single fortification unearthed so far in India. We also compare the proxy climate data with the coupled General Circulation Climate (Earth system) model-generated precipitation over western India that is in anti-phase with Arid Central Asia (ACA). We suggest that the seven major phases of invasions/migration to India over the past 2200 years occurred during periods when the ACA was hyper-arid and uninhabitable, but the agrarian subcontinent was prosperous with relatively stronger ISM.

Positive correlation between dust activity and humidity in arid Central Asia during the Holocene

A long-standing view of the paleoclimatology of arid and semiarid regions is that humid conditions inhibit dust lofting. Here, we combine proxy climate records from four loess sections in Central Asia (CA) with a transient Earth system model simulation to examine the controls on dust activity in CA during the Holocene. Dust activity and regional humidity were in-phase and there was a trend of gradual wetting and increasing dust storm intensity from the early through late Holocene. This intensified Holocene dust storm activity in CA was caused by dry conditions and the strengthening of regional wind/cyclone activity in spring, in response to winter snow depth memory. However, summer cooling and increased precipitation in the late Holocene led to increased summer and even annual wetting and hence to an increase in soil water content. Our results emphasize the importance of insolation and changes in humidity seasonality in driving the positive correlation between dust storm activity and humidity.

Climate overtakes vegetation greening in regulating spatiotemporal patterns of soil moisture in arid Central Asia in recent 35 years

ABSTRACTSatellite datasets have revealed significant greening and soil drying in arid Central Asia. However, the influence mechanism of vegetation and climate on soil moisture dynamics is still unclear. In this study, we investigated the spatiotemporal consistency of vegetation and soil moisture changes, examined the controlling factors of soil moisture under different vegetation indices (normalized differential vegetation index, NDVI; leaf area index, LAI), and explored the time lag and accumulation effects of vegetation greening on the soil moisture in arid Central Asia in the period of 1985 to 2020. The results showed that the co-occurrence of vegetation greening and soil drying in 30.4% (NDVI) and 19.4% (LAI) of the study area spatially. Temporally, the soil moisture increased from 1985 to 1989, but decreased from 1989 or 1990 to 2020. In contrast, vegetation activity increased continuously during 1985–2020. Precipitation accounted for the most variance of the soil moisture. The vegetation greenness demonstrated positive correlations with soil moisture, representing 20.7% (for NDVI) and 39.3% (for LAI) of vegetated areas (areas with long-term mean NDVI ≥ 0.1 and LAI > 0), while negative correlations were observed in only 5.4% (for NDVI) and 3.3% (for LAI) of vegetated areas, respectively. Soil moisture exhibited varying time lag and accumulation effects in response to different vegetation indices, precipitation, and temperature. The main temporal effects of NDVI and temperature were simultaneous changes with no time lag or accumulation effects on soil moisture. In contrast, the main temporal effects of LAI and precipitation included 1-month lag in their influence on soil moisture. Considering the inconsistencies in spatiotemporal patterns between vegetation and soil moisture, as well as the dominance and time lag effects of precipitation on soil moisture variations, we concluded that climate, especially precipitation, rather than vegetation greening, regulates soil moisture in Central Asia. These findings provide a scientific basis for vegetation restoration or regional water resource management in drylands.

Contrasting patterns of Last-deglacial and Holocene precipitation between the southern and northern portions of Arid Central Asia

The north-south migration of prevailing westerly system shapes the seasonality of modern precipitation in Arid Central Asia (ACA). The temperate continental climate with warm-season precipitation dominates the northern ACA and the Mediterranean climate with cold-season precipitation dominates the southern ACA. However, the north-south contrasts of precipitation/moisture for longer time scales remain unknown. In this study, we quantitatively reconstructed the precipitation sequence covering the past ~14.4 cal. kyr BP based on pollen data obtained from Shayan loess section in southern ACA using MAT (Modern Analogue Technique) method. Our reconstruction shows that the precipitation had an increasing trend from ~14.4 to ~8.2 cal. kyr BP and a decreasing trend from ~8.2 to ~1.5 cal. kyr BP with the past 1500 years being characterized by an averagely high precipitation. The precipitation trend in southern ACA was rather different from that in northern ACA where the precipitation has increased more or less constantly since the late deglaciation. The contrast between southern and northern ACA appears to have been associated with the south-north migration of westerlies that was accompanied with alterations of NAO (North Atlantic Oscillation) phases and also with changes in strengths of Siberian High and ENSO (El Nino-southern Oscillation).

Decreased Westerly moisture transport leads to abrupt vegetation change in northern Central Asia during late MIS3: Evidence from Zeketai Loess, Ili Basin

Moisture transportation to (semi-)arid Central Asia is influenced by the interplay of multiple atmospheric circulation patterns. The mechanism underlying the hydroclimate evolution in CA has recently received increasing attention. In northeastern CA, most of the precipitation falls in summer, counter to other westerly-dominated regions of CA where precipitation maximizes in boreal winter. The marine isotope stage (MIS) 3 offers a unique opportunity to examine the mechanisms driving hydroclimate variations during warm periods of the ice age in the CA. However, due in part to reliable proxies for reconstruction, the hydroclimate and vegetation change during MIS3 in northeastern CA have not been well studied. Here, we use grain size and magnetic susceptibility data from the Zeketai loess profile to reconstruct historical shifts in precipitation patterns during MIS3 in the Ili Basin from arid Central Asia (ACA). Notably, abrupt changes around 35 ka are evident in the grain size and magnetic susceptibility records, reflecting a transition to reduced wind intensity and increased aridity. Subsequent analysis of plant leaf waxes (n-alkanes), hydrogen isotopic composition of n-alkanes (δDn-alkane), and stable carbon isotope ratios of total organic carbon (δ13Corg) within the loess profile indicates a concurrent shift towards more shrubs, aligning with reduced moisture availability. The δ13Corg record further elucidates that during MIS3, the Ili Basin predominantly harbored C3 vegetation. However, the alteration in δ13Corg and δDn-alkane to more positive values at approximately 35 ka substantiates the transition to more drought-resistant vegetation. Furthermore, we link the paleo-hydroclimate variations to the decrease in solar radiation and the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) and Siberian High during late MIS3. This joint influence weakens the Westerly winds and subsequently diminishes the conveyance of moisture to CA.

Late Bronze Age agriculture and the early westward transmission of rice at Luanzagangzi, Northern Xinjiang, China

The Dzungar Basin of northern Xinjiang has previously been considered a marginal environment with little evidence for the development of prehistoric agriculture. Recent archaeobotanical studies have indicated the region as being a route for the transmission of domesticated plants, technologies and ideas between East and West Eurasia during prehistory, as early as 5000 BP. These interactions are still poorly understood and most evidence for early plant food production and consumption in the region comes from limited mortuary contexts. In this study we present plant macrofossil analysis from the settlement site of Luanzagangzi on the southern side of the Dzungar Basin. From ca. 3130 BP an agricultural package of east and west Asian cereals and chaff is present, comprising wheat, barley, foxtail millet, broomcorn millet, and significantly a single grain of japonica type rice. AMS dating indicates this is the oldest directly dated rice in Xinjiang and the broader region, ranging 3069–2881 cal. BP. Cereal morphometrics and material culture from the site further indicate a connection with the Gansu region to the east. The spread of agriculture into the site environment may be linked to the onset of wetter conditions relating to strengthened westerly systems across arid Central Asia in the Late-Holocene. A declining abundance of West Asian cultivars over the period of the site’s occupation possibly reflect a shift away from intensive agriculture to low-level management of millets.

Historical Evolution and Future Trends of Precipitation Based on Integrated Datasets and Model Simulations of Arid Central Asia

Earth system models (ESMs) are important tools for assessing the historical characteristics and predicting the future characteristics of precipitation, yet the quantitative understanding of how these land–atmospheric coupling models perform in simulating precipitation characteristics remains limited. This study conducts a comprehensive evaluation of precipitation changes simulated by 43 ESMs in CMIP5 and 32 ESMs in CMIP6 in Arid Central Asia (ALL) and its two sub-regions for 1959–2005 with reference to Climate Research Unit (CRU) data, and predicts precipitation changes for 2054–2100. Our analyses suggest the following: (a) no single model consistently outperformed the others in all aspects of simulated precipitation variability (annual averages, long-term trends, and climatological monthly patterns); (b) the CMIP5 and CMIP6 model simulations tended to overestimate average annual precipitation for most of the ALL region, especially in the Xinjiang Uygur Autonomous Region of China (XJ); (c) most model simulations projected a stronger increasing trend in average annual precipitation; (d) although all the model simulations reasonably captured the climatological monthly precipitation, there was an underestimation; (e) compared to CMIP5, most CMIP6 model simulations exhibited an enhanced capacity to simulate precipitation across all aspects, although discrepancies persisted in individual sub-regions; (f) it was confirmed that the multi-model ensemble mean (MME) provides a more accurate representation of the three aspects of precipitation compared to the majority of single-model simulations. Lastly, the values of precipitation predicted by the more efficient models across the ALL region and its sub-regions under the different scenarios showed an increasing trend in most seasons. Notably, the strongest increasing trend in precipitation was seen under the high-emission scenarios.

External Forcings Caused the Tripole Trend of Asian Precipitation During the Holocene

AbstractTo investigate the evolution of precipitation over Asian continent in the Holocene and the associated mechanisms, we used a set of simulations of the transient climate evolution over the past 21,000 years (TraCE‐21ka), multimodel results from the Paleoclimate Modeling Intercomparison Project Phase 4 (PMIP4), and proxy records in Asia. The TraCE‐21ka results showed a tripole pattern in suborbital‐scale precipitation trends over the Asian continent during the Holocene, with a trend of increase over southern parts of the monsoon regions and arid Central Asia (ACA), and a trend of decline over northern parts of the monsoon regions and their areas of transition with ACA. This tripole pattern was corroborated by proxy records from multiple regions and multimodel results from the PMIP4. Further analysis based on single‐forcing simulations of TraCE‐21ka indicated that influences from different external forcings were different on the Asian precipitation in the main rainy seasons in the Holocene and that their combined effects shaped the tripole pattern. In summer, orbital forcing, by reducing solar radiation in mid‐to‐high latitudes and weakening the land‐sea thermal contrast, has been the dominant factor in the long‐term evolution of precipitation in the monsoon region and West Asia. In winter and spring, changes in meltwater flux played dominant roles in intensifying local water cycle and horizontal moisture advection, which drove the trend of increase in precipitation in ACA. Additionally, changes in greenhouse gas concentration and continental ice sheet forcings both also contribute to the increase in precipitation in ACA.

A copula-based parametric composite drought index for drought monitoring and applicability in arid Central Asia

Due to the complexity of meteorological and hydrological conditions in a changing environment, previous drought indices for monitoring a specific drought type do not reflect the overall regional situation of water scarcity. Therefore, in order to obtain accurate and reliable drought monitoring, a more integrated drought index should be developed to identify drought events comprehensively. In this paper, a non-linear trivariate drought index (NTDI) was constructed based on the joint probability distribution of parametric copulas, combining precipitation (P), potential evapotranspiration (PET), and root zone soil moisture (SM) variables. Subsequently, it was respectively compared with four drought indices, SPEI, SSMI, SC-PDSI and TVDI, and cross-validated with actual recorded drought events and annual crop yield to evaluate its applicability in arid Central Asia (ACA). The results indicated that: (1) Frank copula (1-,3-month scale) and Gumbel copula (6-,12-month scale) were considered to be the best-fitted copula functions for constructing joint probability distributions in the ACA. (2) The NTDI integrated the P-PET and SM drought signals to sensitively capture drought onset and duration, reflecting the combined characteristics of meteorological and agricultural drought. (3) The drought information expressed by NTDI was generally consistent with recorded drought events, and the monitoring results are accurate. (4)The NTDI performed better in agricultural drought monitoring than other drought indices. This study provides a reliable multivariate composite indicator which is significant for drought monitoring, prevention and risk assessment in ACA.

Physical Mechanism of Winter Temperature Multidecadal Variations in Arid Central Asia: The Role of the Atlantic Multidecadal Oscillation (AMO)

Abstract This study investigates the influence of the Atlantic multidecadal oscillation (AMO) on the multidecadal variability of winter surface air temperature in arid central Asia (ACASAT). Apart from a long-term warming trend, the observational analysis shows that the winter ACASAT exhibits a significant multidecadal variability, which is characterized by antiphase fluctuations with the AMO. The mechanism for this negative correlation between the AMO and the winter ACASAT is explored from the aspect of wave teleconnection. The AMO provides energy for the Scandinavian teleconnection pattern at middle and low altitudes by regulating the high-altitude wave train over the middle and high latitudes of Eurasia, and thus has an impact on the remote climate in arid central Asia. Results from the linear baroclinic model (LBM) provide evidence for the linkage between the AMO and the Scandinavian teleconnection pattern. When the AMO is in its warm periods, the Scandinavian teleconnection pattern is in a positive phase, which further makes the cold air from the northeast strengthen, leading to the anomalously colder surface air temperature in arid central Asia. Based on the relationship that the North Atlantic Oscillation (NAO) leads the AMO by 15–20 years, it is further found that there is a leading relationship between the NAO and the winter ACASAT via the AMO. On this basis, an empirical model using the NAO as a predictor was established to predict the ACASAT, and the empirical model shows good hindcast performance. Results from the model show that the winter ACASAT will continue to rise in the next 10 years and decline after 2030.

Soil bacterial communities in alpine wetlands in arid Central Asia remain stable during the seasonal freeze–thaw period

Under the background of climate change, freeze–thaw patterns tend to be turbulent: ecosystem function processes and their mutual feedback mechanisms with microorganisms in sensitive areas around the world are currently a hot topic of research. We studied changes of soil properties in alpine wetlands located in arid areas of Central Asia during the seasonal freeze–thaw period (which included an initial freezing period, a deep freezing period, and a thawing period), and analyzed changes in soil bacterial community diversity, structure, network in different stages with the help of high-throughput sequencing technology. The results showed that the α diversity of the soil bacterial community showed a continuous decreasing trend during the seasonal freeze–thaw period. The relative abundance of dominant bacterial groups (Proteobacteria (39.04%–41.28%) and Bacteroidota (14.61%–20.12%)) did not change significantly during the freeze–thaw period. At the genus level, different genera belonging to the same phylum dominated in different stages, or there were clusters of genera belonging to different phylum. For example, g_Ellin6067, g_unclassified_f_Geobacteraceae, g_unclassified_f_Gemmatimonadaceae coexisted in the same cluster, belonging to Proteobacteria, Desulfobacterota and Gemmatimonadota respectively, and their abundance increased significantly during the freezing period. This “adaptive freeze–thaw” phylogenetic model suggests a heterogeneous stress resistance of bacteria during the freeze–thaw period. In addition, network analysis showed that, although the bacterial network was affected to some extent by environmental changes during the initial freezing period and its recovery in the thawing period lagged behind, the network complexity and stability did not change much as a whole. Our results prove that soil bacterial communities in alpine wetlands are highly resistant and adaptive to seasonal freeze–thaw conditions. As far as we know, compared with short-term freeze–thaw cycles research, this is the first study examining the influence of seasonal freeze–thaw on soil bacterial communities in alpine wetlands. Overall, our findings provide a solid base for further investigations of biogeochemical cycle processes under future climate change.