Arid Regions Of Central Asia Research Articles

Tree ring based drought variability in Northwest Tajikistan since 1895 AD

Determining the mechanisms controlling the changes of wet and dry conditions will improve our understanding of climate change over the past hundred years, which is of great significance to the study of climate and environmental changes in the arid regions of Central Asia. Forest trees are ecologically significant in the local environment, and therefore the tree ring analysis can provide a clear record of regional historical climate. This study analyzed the correlation between the tree ring width chronology of Juniperus turkestanica Komarov and the standardized precipitation evapotranspiration index (SPEI) in Northwest Tajikistan, based on 56 tree ring samples collected from Shahristan in the Pamir region. Climate data including precipitation, temperature and the SPEI were downloaded from the Climate Research Unit (CRU) TS 4.00. The COFECHA program was used for cross-dating, and the ARSTAN program was used to remove the growth trend of the tree itself and the influence of non-climatic factors on the growth of the trees. A significant correlation was found between the radial growth of J. turkestanica trees and the monthly mean SPEI of February–April. The monthly mean SPEI sequence of February–April during the period of 1895–2016 was reconstructed, and the reconstruction equation explained 42.5% of the variance. During the past 122 a (1895–2016), the study area has experienced three wetter periods (precipitation above average): 1901–1919, 1945–1983 and 1995–2010, and four drier periods (precipitation below average): 1895–1900, 1920–1944, 1984–1994 and 2011–2016. The spatial correlation analysis revealed that the monthly mean SPEI reconstruction sequence of February–April could be used to characterize the large-scale dry-wet variations in Northwest Tajikistan during the period of 1895–2016. This study could provide comparative data for validating the projections of climate models and scientific basis for managing water resources in Tajikistan in the context of climate change.

Agricultural water demands in Central Asia under 1.5 °C and 2.0 °C global warming

In the arid region of Central Asia, climate change leads not only to changes in water availability generated by glacier/snow melt in the alpine regions, but also to changes in water consumption. This paper evaluates agricultural water demand and water supply (represented by precipitation) for the five Central Asian countries (Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) under global warming conditions of 1.5 °C and 2.0 °C. As Central Asia is more sensitive to climate change compared to the global average, the temperature is predicted to rise by 1.7 °C and 2.6 °C and precipitation to increase by 9 % and 12 % in global warming scenarios of 1.5 °C and 2.0 °C, respectively. The average crop water requirement (CWR) is expected to increase by 13 mm and 19 mm per year, respectively, under the global warming scenarios of 1.5 °C and 2.0 °C. A widening gap between water supply and water demand is expected compared to the historical period (1976–2005) under global warming scenario of 2.0 °C. Under global warming of 2.0 °C, the anticipated water gaps between precipitation and CWR are projected to increase by 2.8 × 108 m3 and 1.5 × 108 m3 for the rainfed north Kazakhstan region and the irrigated Fergana region while the increase of precipitation could able to meet the increase in CWR under global warming of 1.5 °C. Investigating the water balance for major planting areas in water-limited Central Asia could provide a scientific basis for sustainable development of the entire region.

Water Vapor from Western Eurasia Promotes Precipitation during the Snow Season in Northern Xinjiang, a Typical Arid Region in Central Asia

Atmospheric water vapor plays an important role in the water cycle, especially in arid Central Asia, where precipitation is invaluable to water resources. Understanding and quantifying the relationship between water vapor source regions and precipitation is a key problem in water resource research in typical arid Central Asia, Northern Xinjiang. However, the relationship between precipitation and water vapor sources is still unclear of snow season. This paper aimed at studying the role of water vapor source supply in the Northern Xinjiang precipitation trend, which was investigated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results showed that the total water vapor contributed from Western Eurasia and the North Polar area presented upward trends similar to the precipitation change trend, which indicated that the water vapor contribution from the two previous water vapor source regions supplied abundant water vapor and maintained the upward precipitation trend from 1980 to 2017 in Northern Xinjiang. From the climatology of water vapor transport, the region was controlled by midlatitude westerlies and major water vapor input from the western boundary, and the net water vapor flux of this region also showed an annual increasing trend. Western Eurasia had the largest moisture percentage contribution to Northern Xinjiang (48.11%) over the past 38 years. Northern Xinjiang precipitation was correlated with water vapor from Western Eurasia, the North Polar area, and Siberia, and the correlation coefficients were 0.66, 0.45, and 0.57, respectively. These results could aid in better understanding the water cycle process and climate change in this typical arid region of Central Asia.

Groundwater Depletion Estimated from GRACE: A Challenge of Sustainable Development in an Arid Region of Central Asia

Under climate change and increasing water demands, groundwater depletion has become regional and global threats for water security, which is an indispensable target to achieving sustainable developments of human society and ecosystems, especially in arid and semiarid regions where groundwater is a major water source. In this study, groundwater depletion of 2003–2016 over Xinjiang in China, a typical arid region of Central Asia, is assessed using the gravity recovery and climate experiment (GRACE) satellite and the global land data assimilation system (GLDAS) datasets. In the transition of a warm-dry to a warm-wet climate in Xinjiang, increases in precipitation, soil moisture and snow water equivalent are detected, while GRACE-based groundwater storage anomalies (GWSA) exhibit significant decreasing trends with rates between-3.61 ± 0.85 mm/a of CSR-GWSA and −3.10 ± 0.91 mm/a of JPL-GWSA. Groundwater depletion is more severe in autumn and winter. The decreases in GRACE-based GWSA are in a good agreement with the groundwater statistics collected from local authorities. However, at the same time, groundwater abstraction in Xinjiang doubled, and the water supplies get more dependent on groundwater. The magnitude of groundwater depletion is about that of annual groundwater abstraction, suggesting that scientific exploitation of groundwater is the key to ensure the sustainability of freshwater withdrawals and supplies. Furthermore, GWSA changes can be well estimated by the partial least square regression (PLSR) method based on inputs of climate data. Therefore, GRACE observations provide a feasible approach for local policy makers to monitor and forecast groundwater changes to control groundwater depletion.

Site- and species-specific climatic responses of two co-occurring shrubs in the temperate Alxa Desert Plateau, northwest China

In the context of global precipitation anomalies and climate warming, the evolution of fragile desert ecosystems, which account for one-third of the world's land area, will become more complex. Studies of regional climate change and ecosystem response are important components of global climate change research, especially in arid desert regions. Zygophyllum xanthoxylum and Ammopiptanthus mongolicus are two dominant but endangered shrub species in the Alxa Desert in the arid region of central Asia. Using dendrochronological methods, we studied the response of radial growth of those two species to climate factors, and the adaptability of the two shrub populations under a regional warming trend. We found that radial growth of both shrubs was mainly affected by precipitation during the growing season. In additionally, along with the decrease of precipitation and the increase of temperature from east to west of Alxa desert Plateau, the limiting effect of drought during the growing season on radial growth increased. The climate response characteristics and changes between dry and wet periods exhibited spatial and temporal heterogeneity due to micro-level geomorphological factors. Under a regional climate warming trend, individual growth and population development of the two endangered shrubs will be adversely affected. In areas where these species are naturally distributed, populations will gradually become concentrated in micro-geomorphic regions with better soil moisture conditions, such as low-lying areas in the gullies that develop in alluvial fans. This finding has important scientific significance for understanding the development of the region's dominant shrub populations and protection of these and other endangered plants in arid desert areas.

Hydro-climatic changes and their impacts on vegetation in Xinjiang, Central Asia

Central Asia is one of the most arid regions in the world. Xinjiang is the core area of the arid region in Central Asia. Climate warming and hydrological changes might affect the vegetation dynamics in the region; however there has been no systematic evaluation of the hydro-climatic changes and their impacts on vegetation in Xinjiang. In this study, the vegetation growth and its response to hydro-climatic changes from 2003 to 2013 were analyzed based on multiple satellite observations. It was found that precipitation increased, with fluctuations, at a rate of 12.07 mm/decade, and evapotranspiration decreased, also with fluctuations, at a rate of −14.79 mm/decade. The change in total water storage, derived from the Gravity Recovery and Climate Experiment satellite, displayed an increasing trend, with a rate of increase of 112.91 mm/decade. The changes in the Global Land Data Assimilation System-derived soil moisture and groundwater estimated by the water budget presented a slight increasing trend from 2003 to 2013. The total water storage, soil moisture, and groundwater all significantly increased after 2008, and the increases in soil moisture and groundwater had positive effects on the increasing total water storage in Xinjiang. There were more obvious time lags in the response of changes in total water storage to precipitation than for the changes in soil moisture. The changes in the normalized difference vegetation index from 2003 to 2013 indicated a slight greening, and the accumulated normalized difference vegetation index anomalies also increased sharply after 2008. There were significant increases in the Tianshan Mountains, Altay Mountains, and around the Tarim Basin, especially along the Tarim River. The results suggested that the changes in total water storage and soil moisture were regarded as better indicators of the vegetation dynamics than other hydro-climatic variables in Xinjiang. Climate warming has led to accelerated glacier shrinkage and snow melt, and the increased runoff is likely to lead to more infiltration of surface water into the soil and ground, resulting in increased total water storage.

“Dry gets drier, wet gets wetter”: A case study over the arid regions of central Asia

The “dry gets drier, wet gets wetter” (DGDWGW) paradigm well describes the pattern of precipitation changes over the oceans. However, it has also been usually considered as a simplified pattern of regional changes in wet/dry under global warming, although GCMs mostly do not agree this pattern over land. To examine the validity of this paradigm over land and evaluate how usage of drought indices estimated from different hydrological variables affects detection of regional wet/dry trends, we take the arid regions of central Asia as a case study area and estimate the drying and wetting trends during the period of 1950–2015 based on multiple drought indices. These indices include the standardized precipitation index (SPI), the standardized precipitation evapotranspiration index (SPEI), the Palmer drought severity index (PDSI) and self‐calibrating PDSI (sc_PDSI) with both the Thornthwaite (th) and Penman–Monteith (pm) equations in PDSI calculation (namely, PDSI_th, PDSI_pm, sc_PDSI_th and sc_PDSI_pm). The results show that there is an overall agreement among the indices in terms of inter‐annual variation, especially for the PDSIs. All drought indices except SPI show a drying trend over the five states of central Asia (CAS5: including Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan). The four PDSIs and SPEI reveal a wetting tendency over the northwestern China (NW; including Xinjiang Uygur Autonomous Region and Hexi Corridor). The contrasting trends between CAS5 and NW can also be revealed in soil moisture (SM) variations. The nonlinear wet and dry variations are dominated by the 3–7 years oscillations for the indices. Relationships between the six indices and climate variables show the major drought drivers have regional features: with mean temperature (TMP), precipitation total (PRE) and potential evapotranspiration (PET) for CAS5, and PRE and PET for NW. Finally, our analyses indicate that the dry and wet variations are strongly correlated with the El Niño/Southern Oscillation (ENSO).

Glacier branch lines and glacier ice thickness estimation for debris-covered glaciers in the Central Tien Shan

ABSTRACTInformation about the ice volume stored in glaciers is of high importance for sustainable water management in many arid regions of Central Asia. Several methods to estimate the ice volume exist. However, none of them take the specific characteristics of flat terminus debris-covered glaciers into account. We present a method for deriving spatially-distributed ice thickness for debris-covered dendritic glaciers, which are common not only in Central Tien Shan but also in several other mountain ranges in High Asia. The method relies on automatically generated branch lines, observed surface velocities and surface topographic parameters as basic input. Branch lines were generated using Thiessen polygons and Dijkstra's path algorithm. Ice thicknesses for four debris-covered glaciers – South Inylchek, Kaindy, Tomur and Koxkar glaciers – have been estimated along the branch line network solving the equation of laminar flow. For Koxkar and South Inylchek glaciers, respectively, maximum thicknesses of ~250 and 380 m were estimated. These results differ by ~50 m compared with GPR measurements with an uncertainty for the debris-covered parts of ~40%. Based on geodetic mass balances, we estimate that the investigated glaciers lost between 6 and 28% of their volume from 1975 to the early 2000s.

Responses of riparian forests to flood irrigation in the hyper-arid zone of NW China

Knowledge of forest water use is crucial to water resources managers, especially in arid environments. Flood irrigation has sometimes been used to ameliorate forest decline, however, there has only been limited research on vegetation responses to these interventions. We undertook a study to quantify evapotranspiration (ET) and its components, transpiration (T) and evaporation (E), of two Populus euphratica Oliv. stands (MA: middle-aged and OA: old-aged) with and without flood irrigation in the lower Heihe River Basin of NW China. ET and T were measured using eddy covariance and sap flow methods, respectively. Understory E was estimated by difference. Annual ET was 766.4 mm in the MA stand and 532.5 mm in the OA stand with an average of 4.2 and 2.9 mm d−1 during the growing season, respectively. ET of the MA stand was 44% higher than that of the OA stand, with contributions of 28% and 16% from E and T. Despite stand density, leaf area index and canopy cover being higher in the MA than OA stand sapwood area within the two stands was similar (MA 6.04 m2 ha−1 and OA 6.02 m2 ha−1). We hypothesised lower understory E and a lower E to ET ratio in the MA stand than OA stand. However, E was approximately 63% of ET in both stands. Therefore, we conclude that differences in ET, T and E were mainly associated with the flood irrigation. This was further supported by the comparable ET between the OA stand and the other studies in arid regions of Central Asia. In conclusion, flood irrigation has a less significant effect on canopy water use (T) than understory E suggesting alternatives to flood irrigation might be more appropriate in this water-limited ecosystem.

An overview of the influence of atmospheric circulation on the climate in arid and semi-arid region of Central and East Asia

The arid and semi-arid (ASA) region of Asia occupies a large area in the middle latitudes of the Northern Hemisphere, of which the main body is the ASA region of Central and East Asia (CEA). In this region, the climate is fragile and the environment is sensitive. The eastern part of the ASA region of CEA is located in the marginal zone of the East Asian monsoon and is jointly influenced by westerly circulation and the monsoon system, while in the western part of the ASA of CEA, the climate is mainly controlled by westerly circulation. To understand and predict the climate over this region, it is necessary to investigate the influence of general circulation on the climate system over the ASA region of CEA. In this paper, recent progress in understanding the relationship between the general circulation and climate change over the ASA region is systematically reviewed. Previous studies have demonstrated that atmospheric circulation represents a significant factor in climate change over the ASA region of CEA. In the years with a strong East Asian summer monsoon, the water vapor flux increases and precipitation is abundant in the southeastern part of Northwest China. The opposite situation occurs in years when the East Asian summer monsoon is weak. With the weakening of the East Asian summer monsoon, the climate tends to dry over the semi-arid region located in the monsoon marginal zone. Recently, owing to the strengthening of the South Asian monsoon, more water vapor has been transported to the ASA region of Asia. The Plateau summer monsoon intensity and the precipitation in summer exhibit a significant positive correlation in Central Asia but a negative correlation in North China and Mongolia. A significant positive correlation also exists between the westerly index and the temperature over the arid region of CEA. The change in the westerly circulation may be the main factor affecting precipitation over the arid region of Central Asia.

Long-read sequencing and de novo genome assembly of Ammopiptanthus nanus, a desert shrub.

Background Ammopiptanthus nanus is a rare broad-leaved shrub that is found in the desert and arid regions of Central Asia. This plant species exhibits extremely high tolerance to drought and freezing and has been used in abiotic tolerance research in plants. As a relic of the tertiary period, A. nanus is of great significance to plant biogeographic research in the ancient Mediterranean region. Here, we report a draft genome assembly using the Pacific Biosciences (PacBio) platform and gene annotation for A. nanus.FindingsA total of 64.72 Gb of raw PacBio sequel reads were generated from four 20-kb libraries. After filtering, 64.53 Gb of clean reads were obtained, giving 72.59× coverage depth. Assembly using Canu gave an assembly length of 823.74 Mb, with a contig N50 of 2.76 Mb. The final size of the assembled A. nanus genome was close to the 889 Mb estimated by k-mer analysis. The gene annotation completeness was evaluated using Benchmarking Universal Single-Copy Orthologs; 1,327 of the 1,440 conserved genes (92.15%) could be found in the A. nanus assembly. Genome annotation revealed that 74.08% of the A. nanus genome is composed of repetitive elements and 53.44% is composed of long terminal repeat elements. We predicted 37,188 protein-coding genes, of which 96.53% were functionally annotated.ConclusionsThe genomic sequences of A. nanus could be a valuable source for comparative genomic analysis in the legume family and will be useful for understanding the phylogenetic relationships of the Thermopsideae and the evolutionary response of plant species to the Qinghai Tibetan Plateau uplift.

Quantitative evaluation of glacier change and its response to climate change in the Chinese Tien Shan

Glacier melt water is an important water resource in arid regions of central Asia during the dry seasons, and it is very susceptible to climate disturbances. In this paper, based on the glacier datasets of the first and second Chinese Glacier Inventories, the glacier change in the Chinese Tien Shan from 1960s to 2010 was quantify by assessing the Annual Percentages of Area Changes (APAC), Annual Percentages of Volume Changes (APVC), and Equilibrium Line Altitude (ELA). The results indicated that the mean glacier area and mean glacier volume decreased by 0.7% ± 0.6% per year and 0.83% ± 0.73% per year in the Chinese Tien Shan during the period of 1960–2010, respectively. The mean ELA increased by 24.87 ± 126.84 m during the study period. In addition, we also found that the glacier retreat in the Bogda Mountains was the fastest, mainly due to the sensitivity of small glaciers to climate change, with an APAC of −0.86% ± 0.49% per year and APVC of −1.04% ± 0.55% per year, and the mean ELA increased by 44.35 ± 55.07 m. Moreover, increases in both air temperature (in terms of Thawing Degree-Day (TDD) and Freezing Degree-Day (FDD)) and precipitation were found over the study area during the past five decades. However, such increases in precipitation did not result in any significant changes in the ratio of annual snowfall to total precipitation (S/P) across the Chinese Tien Shan Mountains. Hence, the glacier shrinkage mainly resulted from the significant increase in TDD and FDD in the study region.

Analysis of Hydrochemical Characteristics and Three-Dimensional Fluorescence Spectra in the Semi-Arid Ebinur Lake Watershed, Xinjiang, China

Hydrochemical characteristics and three-dimensional fluorescence spectra for Lake Ebinur and its major inflow tributaries have been analyzed. The results indicate that Jing and Bortala River ions differ very little. Anions are composed of HCO3− > SO42− > Cl−, while cations have the following composition: Ca2+ > Mg2+ > Na+ > K+. The Jing and Bortala Rivers include mainly SO42− and HCO3− anions; these cations are primarily Ca2+. Hydrochemical components of the Jing and Bortala Rivers are of the HCO3−-Ca2+ type. Ion compositions of the Jing and Bortala Rivers are derived primarily from the weathering of rocks. In addition, a parallel factor method (PARAFAC) analysis of three-dimensional fluorescence spectra (EEM) of the Jing and Bortala Rivers shows that all the sampled water bodies contain C1 (260/420 nm) humic organic matter, C2 (240, 240/490 nm), C3 (220/280, 300/450 nm) protein-like C4 (260, 270/530 nm), and humic substances. To further understand characteristics of dissolved organic matter (DOM) components, we base our research on regional standards related to water quality and fluorescence. A fluorescence regional integration (FRI) analysis of the Jing and Bortala Rivers shows that protein organic matter levels are the highest, whereas fulvic acid levels are the lowest. Of the correlation coefficients of hydrochemical factors and fluorescence indices, the biological index (BIX), TDS, HCO3−, and K+ are stronger in major inflow tributaries of Ebinur Lake with correlation coefficients of 0.577, 0.708, and 0.764, respectively, at the p < 0.01 significance level; correlations between the humification index (HIX) and HCO3− concentrations amount to 0.568 at the p < 0.05 significance level. Hydrochemical factors and fluorescence indices show the presence of three fitting relationships. While the HIX and HCO3− fitting effect is strongest with a correlation coefficient of 0.789, the second strongest is that of BIX and K+ with a correlation coefficient of 0.814. The results of this work offer scientific support for water quality monitoring and restoration in arid regions of Central Asia.

Water use strategies of Populus euphratica seedlings under groundwater fluctuation in the Tarim River Basin of Central Asia

Riparian vegetation in arid regions is subject to frequent water environmental fluctuations and plays an important role in maintaining the riparian ecosystem. In recent decades, Populus euphratica (P. euphratica) has been threatened by decreasing groundwater levels, and large areas of P. euphratica seedlings are withered. To better understand the adaptive mechanism underlying hydrological process alterations, we designed an experiment to identify the water sources of P. euphratica seedlings using δ18O values (plant stem xylem, soil water and groundwater) under different groundwater scenarios by simulating the wild habitats conditions in the Tarim River bank of Central Asia. Seedlings were grown in lysimeters (2.0 m tall × 0.4 m inner diameter) under varying hydrological conditions. P. euphratica seedlings generally took up water from the shallow soil layer (0–80 cm). Under the T. ramosissima disturbance, the water source depths of the P. euphratica seedlings moved down as the groundwater depth increased. With increasing groundwater depth, the proportions of groundwater used by P. euphratica seedling monocultures (only P. euphratica seedlings) and P. euphratica seedling mixtures (P. euphratica and T. ramosissima seedlings) were reduced. Under shallow groundwater treatment (W1: 25 cm), the plant height growth of the P. euphratica seedlings slowed, and their biomass accumulation decreased. The aboveground and total biomasses of the non-coexistence seedlings under W2 (75 cm) treatment were maximized, while the maximum value for coexistence seedlings occurred under W3 (125 cm) treatment. Thus, we suggest that shallow groundwater depth is not beneficial to P. euphratica seedling growth, and appropriately decreasing the groundwater depth may promote their growth. Such information will be valuable to provide the configuration of water resources for a typical river basin in an arid region of Central Asia based on the ecological water requirements of desert riparian vegetation.

К вопросу о древнем земледелии на аридных территориях Центральной Азии: земледелие в Убсунурской котловине

К вопросу о древнем земледелии на аридных территориях Центральной Азии: земледелие в Убсунурской котловине

Observational characteristics of cloud radiative effects over three arid regions in the Northern Hemisphere

Cloud–radiation processes play an important role in regional energy budgets and surface temperature changes over arid regions. Cloud radiative effects (CREs) are used to quantitatively measure the aforementioned climatic role. This study investigates the characteristics of CREs and their temporal variations over three arid regions in central Asia (CA), East Asia (EA), and North America (NA), based on recent satellite datasets. Our results show that the annual mean shortwave (SW) and net CREs (SWCRE and NCRE) over the three arid regions are weaker than those in the same latitudinal zone of the Northern Hemisphere. In most cold months (November–March), the longwave (LW) CRE is stronger than the SWCRE over the three arid regions, leading to a positive NCRE and radiative warming in the regional atmosphere–land surface system. The cold-season mean NCRE at the top of the atmosphere (TOA) averaged over EA is 4.1 W m–2, with a positive NCRE from November to March, and the intensity and duration of the positive NCRE is larger than that over CA and NA. The CREs over the arid regions of EA exhibit remarkable annual cycles due to the influence of the monsoon in the south. The TOA LWCRE over arid regions is closely related to the high-cloud fraction, and the SWCRE relates well to the total cloud fraction. In addition, the relationship between the SWCRE and the low-cloud fraction is good over NA because of the considerable occurrence of low cloud. Further results show that the interannual variation of TOA CREs is small over the arid regions of CA and EA, but their surface LWCREs show certain decreasing trends that correspond well to their decreasing total cloud fraction. It is suggested that combined studies of more observational cloud properties and meteorological elements are needed for in-depth understanding of cloud–radiation processes over arid regions of the Northern Hemisphere.

Monitoring lake level changes by altimetry in the arid region of Central Asia

The study of lake level changes in arid region of Central Asia not only has important significance for the management and sustainable development of inland water resources, but also provides the basis for further study on the response of lakes to climate change and human activities. Therefore, in this paper, eleven typical lakes in Central Asia were observed. The lake edges were obtained through image interpretation using the quasi-synchronous MODIS image, and then water level information with long period (2002-2015) was acquired using ENVISAT/RA-2 and Cryosat-2 satellite borne radar altimeter data. The results show that these 11 lakes all have obvious seasonal changes of water level in a year with a high peak at different month. During 2002 – 2015, their water levels present decreased trend generally except Sarygamysh Lake, Alakol Lake and North Aral Sea. The alpine lakes are most stables, while open lakes’ levels change the most violently and closed lakes change diversely among different lakes.

High resolution palaeoecological records for climatic and environmental changes during the last 1350 years from Manzherok Lake, western foothills of the Altai Mountains, Russia

Compilation of spore-pollen, diatom and biochemical analyses of samples from the top 80-cm sediments of Manzherok Lake, located on the western foothills of the Altai Mountains (51°49′15.5″N, 85°48′35.7″E, 400 m a.s.l.), revealed influence of regional climate changes during the past 1350 years on the hydrological budget of the lake and the dynamics of the surrounding vegetation. Based on indicator species of diatom complexes in the lake sediments, the reconstructed lake level and pH can be deciphered as (1) shallow pond with relatively high pH prior to the Medieval Warm Period (MWP), (2) dramatic flooding with freshwater in the MWP, (3) lowering of the lake level during the Little Ice Age (LIA), and (4) contemporary rise of the lake level after the LIA. Increased concentrations of the detrital elements and severe degradation of diatom assemblages in the lake sediments took place during the dramatic flooding stage. The reconstructed lake level based on the diatom assemblages is in good agreement with the palynological data which indicate changes from birch forest-steppe to pine and cedar forests in the beginning of MWP, and then to birch-pine anthropogenically transformed forest-steppe in the LIA. Sharp maxima of non pollen palynomorphs Anabaena and Bryales/Algae at the 43–46 cm depth (∼900 a BP) possibly mark ecological crises in lake's biotope. Cold and dry conditions during the LIA were clearly expressed in pollen diagram of Manzherok Lake by decline of maxima of Siberian pine pollen and increase of Artemisia pollen. This study provides evidence to support a dry episode in the 9th century, wet climatic conditions in the MWP and a dry LIA in the Russian Altai Mountains in contrast to the opposite pattern revealed for arid regions of Central Asia and NW China during the same periods (Chen et al., 2010; Eichler et al., 2011; Chen et al., 2015). Our study indicates that, as a small and shallow lake located in the forest-steppe western foothills of the Altai Mountains, Manzherok Lake is more sensitive to high-resolution (less than centennial scale) climatic and environmental variations, in comparison with the large and deep Teletskoye Lake located in the mountain taiga zone of the northern Altai.

Response of vegetation NDVI to climatic extremes in the arid region of Central Asia: a case study in Xinjiang, China

Observed data showed the climatic transition from warm-dry to warm-wet in Xinjiang during the past 30 years and will probably affect vegetation dynamics. Here, we analyze the interannual change of vegetation index based on the satellite-derived normalized difference vegetation index (NDVI) with temperature and precipitation extreme over the Xinjiang, using the 8-km NDVI third-generation (NDVI3g) from the Global Inventory Modelling and Mapping Studies (GIMMS) from 1982 to 2010. Few previous studies analyzed the link between climate extremes and vegetation response. From the satellite-based results, annual NDVI significantly increased in the first two decades (1981–1998) and then decreased after 1998. We show that the NDVI decrease over the past decade may conjointly be triggered by the increases of temperature and precipitation extremes. The correlation analyses demonstrated that the trends of NDVI was close to the trend of extreme precipitation; that is, consecutive dry days (CDD) and torrential rainfall days (R24) positively correlated with NDVI during 1998–2010. For the temperature extreme, while the decreases of NDVI correlate positively with warmer mean minimum temperature (Tnav), it correlates negatively with the number of warmest night days (Rwn). The results suggest that the climatic extremes have possible negative effects on the ecosystem.

On the teleconnection patterns to precipitation in the eastern Tianshan Mountains, China

The Tianshan Mountains are known as the “water tower” in the arid region of Central Asia. Change in precipitation amount and pattern can have a profound impact on regional civilization and life supporting ecosystems. For this study, a systematic analysis of long-term precipitation data for the eastern Tianshan Mountains was conducted to investigate the influence of climate teleconnections on annual and intra-annual precipitation using data collected between 1951 and 2014 from 39 meteorological stations. Annual precipitation has increased during the past six decades at an average rate of 6.7 mm/10 years largely due to the increase in precipitation during the intra-annual wet period (May–October). The annual precipitation and its rate of increase were higher in the northwestern region. Annual precipitation was found to be most strongly correlated with index of Indian Summer Monsoon (ISM), and partially correlated with indices of Pacific Decadal Oscillation (PDO), Pacific North American Teleconnection Pattern (PNA), Arctic Oscillation (AO), El Nino–Southern Oscillation (ENSO), and North Atlantic Oscillation (NAO). ISM was positively correlated with the precipitation in almost the entire region during the intra-annual wet period, while it showed positive correlations in the northern slope and the alpine region, and negative correlations in the southern slope during the intra-annual dry period (November to April). PDO had much weaker influence both in spatial scale and strength and primarily affected low elevations on the southern slopes of the middle and western regions. The impacts of PNA and AO on precipitation were weak and localized. ENSO and NAO indices were almost not correlated with annual precipitation observation in the eastern Tianshan Mountains.