Southeastern Plateau Research Articles

The Late Bronze Age Somló Hill and a new bronze hoard

In January 2023, the National Institute of Archaeology of the Hungarian National Museum launched a new research programme, the aim of which is to explore Somló Hill (Veszprém County), which has been neglected by systematic field research focusing on the Late Bronze Age (LBA) and Early Iron Age (EIA) inhabitation of the site. In the current phase of the research programme, new, preliminary results have been provided on the settlement history of the site, primarily through a systematic metal detector survey. Based on the discovered metal objects, the south-eastern plateau of Somló Hill was inhabited primarily between the Rei Br C and Ha B2 phases, and life on the settlement was probably continuous during the Hallstatt Culture in EIA. In addition to briefly introducing our preliminary results, one of the four hoards, Hoard II from Somló Hill, is introduced. This assemblage was found by Győző Csaba Budai, a volunteer, on the once-inhabited part of the south-eastern plateau. Owing to his discovery, the in situ hoard was documented in excavation. The hoard consists of a handful of objects belonging to a few people, such as a gouge, six Lovasberény-type bracelets, three bracelets with rolled ends, two lumps, and a pseudo-winged axe. The arrangement and grouping of the objects within the assemblage reflect deliberate selection and deposition. The typo-chronological analysis of the objects from the second hoard of Somló Hill suggests that the assemblage was deposited around the younger LBA phase of the settlement in the Ha B1–Ha B2 phases.

Human genetic history on the Tibetan Plateau in the past 5100 years

Using genome-wide data of 89 ancient individuals dated to 5100 to 100 years before the present (B.P.) from 29 sites across the Tibetan Plateau, we found plateau-specific ancestry across plateau populations, with substantial genetic structure indicating high differentiation before 2500 B.P. Northeastern plateau populations rapidly showed admixture associated with millet farmers by 4700 B.P. in the Gonghe Basin. High genetic similarity on the southern and southwestern plateau showed population expansion along the Yarlung Tsangpo River since 3400 years ago. Central and southeastern plateau populations revealed extensive genetic admixture within the plateau historically, with substantial ancestry related to that found in southern and southwestern plateau populations. Over the past ~700 years, substantial gene flow from lowland East Asia further shaped the genetic landscape of present-day plateau populations. The high-altitude adaptive EPAS1 allele was found in plateau populations as early as in a 5100-year-old individual and showed a sharp increase over the past 2800 years.

Threat to the Sustainable Production of Natural Resins: A Case of Rangeeni Strain of Kerria lacca (Kerr) in Eastern Plateau & Hills Region of South East Asia

The study conducted to examine the trends, growth and instability in the production of an insect-based natural resin in India. Study is designed with sampling and Focused Group Discussions (FGDs) based primary data as well as secondary data. District-level time-series data of Jharkhand state for 50 years from 1970-71 to 2019-20 was used. Time series analysis revealed the variation in lac production levels in different levels of geo coordinates. Compound Annual Growth Rate (CAGR) was worked out by fitting the exponential function. The instability indices worked out by using the method suggested by Cuddy and Dell. The growth in lac production and export of lac-based value-added products has decelerated in the post-liberalization period, while yield growth has accelerated. The overall decline in the production level of rangeeni crop ranged from -5.54% in Western Plateau Sub Zone V to -6.98% in South Eastern Plateau Sub Zone VI. Utilization of the existing natural endowment of Butea monosperma in major rangeeni lac-producing districts in Western Plateau Sub Zone V could be a promising strategy to minimize the variation in the production of rangeeni crop. A paradigm shifts from rangeeni lac cultivation during previous decades coupled with climate change issues may be another possible reason for the regional disparity in the level of rangeeni lac production.
 The overall scenario in Jharkhand state depicts the alarming situation for katki crop (Rainy season rangeeni crop) having the highest instability index (49.69), particularly with significant negative growth rates from 2000 to 2020. The magnitude of decline for katki crop was found highest and most significant during the 2001-2010 period. Although, the production of rangeeni strain was affected adversely in Jharkhand (-21.60%) during the Ninth Five Year Plan coupled with shifting from rangeeni to kusmi lac cultivation due to boosting through capacity building and skill development programs which influenced the awareness and knowledge level of the stakeholders. However, COVID-19 could break the momentum, and functionaries including the institutions and facilitators shifted to manage the disrupted supply chains during 2019-20 and 2020-21. Post COVID-19 scenario, emerged with new ICT-enabled interventions with greater scope for extension and awareness programs. However, there is a huge technological gap in the existing lac industry with poor automation and dependency on local labor. Policy interventions including market initiatives like Minimum Support Prices (MSP), Van Dhan Vikas Kendras (VDVKs); and Institutional initiatives like FPOs, SHGs, JLGs, etc. may play a key role in strengthening the sector. New host plants like Flemingia semialata may be promoted to reduce instability indices in the long run.

Temporal variability of precipitation over the Qinghai‐Tibetan Plateau and its surrounding areas in the last 40 years

AbstractThe Qinghai‐Tibet Plateau (QTP) plays a crucial role in regulating the climate and hydrology over Asia, and studies indicate that the QTP tends to be warm and humid as a whole. Although precipitation variability on the QTP has a great impact on floods, soil erosion, and droughts, it is poorly understood owing to sparse meteorological observations. This study has investigated the temporal variability of precipitation on the QTP and its surrounding areas on different time scales over the past 40 years using the standardized variability index (SVI) based on entropy as well as its changing trends. The results show that the variability of precipitation has different spatial patterns on different time scales. In general, the variability of both the precipitation days and amounts are low in the southeast and northwest corners of the plateau and high in the southwest and north. It was found that the number of light precipitation days in the high vegetation coverage area in the southeastern plateau decreased significantly, but increased greatly in the bare land and sparse vegetation coverage areas in the northern part of the plateau. Such changes are believed to be conducive for ecological restoration. Most importantly, in the southern foothills of the Himalayas, many light precipitation days have turned into moderate and heavy precipitation days, and a significant increase in annual precipitation has also been noted, which are likely to cause natural disasters considering the local topographical conditions, such as landslides and mudslides.Highlights In QTP, SVIME in May is closer to summer mode, indicating monsoon beginning have advanced to May. Extreme precipitation significantly influences precipitation variability. Daily SVIAE decreases in grassland/barren/sparsely vegetated land, good for ecology. Light rain days increased in bare land/sparse vegetation areas, benefiting vegetation restoration. In southern Himalayas, light rain changed to moderate/heavy rain, leading to natural disasters.

Unveiling the drivers of nematode community structure and function across rice agroecosystems

Rice agroecosystems has drawn global attention due to its unique transition of flooding to wetland to a terrestrial ecosystem with high biodiversity throughout its growing period. While biodiversity of the aboveground organisms in the rice ecosystem is well studied, understanding the diversity and functions of soil biota, particularly the nematofauna, are often neglected. In the present study, variations in soil nematode community composition in response to edaphic and climatic variables were assessed (n = 501 samples) across three agro-ecological zones of Jharkhand, India. Functional diversity measures were used to estimate the biological soil health of different rice growing areas across the agroecological zones. Relative contribution of edaphic, climatic and spatial structure in shaping nematode community composition was measured using variation partitioning. Among the identified nematode genera (n = 58), Meloidogyne spp. was the most abundant and dominant taxon. Taxonomic diversity measures varied significantly across agro-ecological zones, with highest diversity reported in the central and north-eastern plateau, followed by the south-eastern plateau and western plateau. Average annual temperature, annual precipitation, available nitrogen and organic carbon had significant relationships with taxonomic diversity measures. The spatial variation map of the nematode community composition depicted spatial heterogeneity across agro-ecological zones. Climatic predictors also strongly influenced both the community composition and richness of nematodes, while edaphic factors showed a strong influence on beta diversity, but not on variation partitioning. A moderate level of spatial structure pattern suggested limited dispersal of nematodes. Functional diversity measures based on nematode community composition depicted better soil biological health in the central and north-eastern plateau than rest two zones. This study demonstrates how climatic predictors have a greater influence on nematode community composition than edaphic parameters, presumably as a result of intensively managed rice agroecosystems.

Restricted lithospheric extrusion in the SE Tibetan Plateau: Evidence from anisotropic Rayleigh-wave tomography

Constraining variations of lithospheric structure and deformation across southeastern Tibet and the surrounding region are crucial for understanding the lateral growth of the plateau. Using data from two dense seismic arrays in the SE Tibetan Plateau, we obtained fine-scale Rayleigh-wave phase velocity maps by Eikonal tomography, and further inverted for 3-D shear wave velocity and azimuthal anisotropy of the crust and upper mantle. High velocities and weak lithospheric anisotropy are revealed under Dianzhong Block (DZB), where is covered by the relics of the Emeishan Large Igneous Province, while strong anisotropy is imaged around. We propose that the DZB strengthened by the paleo igneous activity plays an essential role in the evolution along the southeastern plateau margin. On the one hand, the DZB obstructs the migration of plateau material to the southeast. On the other hand, strong deformation is localized along the DZB margins, while the stress due to the plate expansion is transferred further to the Xiaojiang fault, which induced significant deformation within the Yangtze Craton. Furthermore, the lithosphere of DZB deflects the mantle flow driven by the eastward Indian subduction under the northern Indochina block.

Pollen-based biome reconstruction on the Qinghai-Tibetan Plateau during the past 15,000 years

Reconstruction of past vegetation change is critical for better understanding the potential impact of future global change on the fragile alpine ecosystems of the Qinghai-Tibetan Plateau (QTP). In this paper, pollen assemblages comprising 58 records from the QTP, spanning the past 15 kyrs, were collected to reconstruct biome compositions using a standard approach. Six forest biomes were identified mainly on the southeastern plateau, exhibiting a pattern of gradual expansion along the eastern margin during early to mid-Holocene times. The alpine meadow biome was separately identified based on an updated scheme, and showed notable westward expansions towards lower latitudes and higher altitudes during early Holocene times. Consistent patterns of migration could also be identified for the alpine steppe biome, which moved eastward during the late Holocene after 4 ka. As the dominant biome type, temperate steppe was distributed widely over the QTP with minor migration patterns, except for a progressive expansion to lower altitudes in the late Holocene times. The desert biome was inferred mainly as covering the northwestern plateau and the Qaidam Basin, in relatively restricted areas. The spatial distribution of the reconstructed biomes represent the large-scale vegetation gradient on the QTP. Monsoonal precipitation expressed predominant controls on the development of alpine ecosystems, while the variations in desert vegetation responded to regional moisture brought by the mid-latitude Westerlies. Temperature changes played relatively minor roles in the variations of alpine vegetation, but exerted more significant impacts on the forest biomes.

Identifying deep recycled carbonates through Miocene basalts in the Maguan area, SE Tibetan Plateau

Cenozoic mantle-derived magmas are widespread on the Tibetan Plateau, and provide evidence for the evolution of deep mantle and its influence on the Plateau development. Miocene basalts in the Maguan area on the southeastern Plateau have high MgO (9.13–13.10 wt%) and Mg# (0.60–0.70) with high Ce/Pb (10.6–32.5) and Nb/U (43.7–52.9) ratios, similar to those of oceanic basalts. Distinct from Eocene-Oligocene mantle-derived potassic magmas in Western Yunnan and Cenozoic basic volcanic rocks in Tengchong, these Maguan basalts are characterized by high large ion lithophile elements (LILEs) concentrations, positive anomaly in high field strength elements (HFSEs) and depleted SrNd isotopes, consistent with the melt of an asthenospheric mantle origin. The high Ce/Pb and Nb/Y (1.80–2.68) ratios together with low Ba/Y and Ba/Th ratios indicate a significant input of slab-derived melt into the asthenospheric source. Besides, Hf/Hf* and Ti/Ti* ratios are significantly lower than those of ocean island basalt (OIB), which are proportional to the lighter δ26Mg (-0.6‰ to -0.4‰) values. Based on the results of experimental petrology, the SrMg isotope mixing model suggests that the asthenospheric mantle beneath the Maguan area had undergone the significant metasomatism of recycled carbonates prior to the late Miocene. The above petrological and geochemical understanding, together with the geophysical data, allows us to propose that the mantle metasomatism is most probably associated with the Neo-Tethys seafloor subduction, which is further testified by the decoupling between depleted SrNd isotopes and elevated LILE concentrations.

Characterising Rice (Oryza indica) Ecology in East and Southern Eastern Plateau of Odisha using Multi Source Remote Sensing

Rice is the most important crop of Odisha occupying 41.24% of net sown area in Kharif season and contributing 65.85 % of total food grain production of Odisha state and this is being cultivated in various types environmental and ecological condition. Assessment of rice phenology is prime for management and yield prediction. In view of characterizing rice ecology in East and South Eastern Plateau from 2008 – 2018 to know the time series analysis , remote sensing tools were used . MODIS can0 acquire data over a wide area with high spatial and temporal resolutions easily providing regional scale information .In order to study the seasonal /annual as well as spatial variability of kharif rice vigour and wetness spectral vegetation indices like NDVI(Normalised Difference Vegetation Index),LSWI(Land surface water index) derived from 15 day composite 250 m data were analysed at block level for Odisha state. For studying the start of season variability, SASI index was used. The season maximum NDVI, LSWI were computed for the year 2008-2018 for kharif rice in East and Southern eastern coastal plain zone of Odisha and graphs were generated which shows the variability of the kharif rice vigour and wetness.

Diversity of insect fauna in Rajasthan, India: A Review

Insect diversity is huge and immensely complex with making up an important component of the functional biodiversity of the terrestrial ecosystem. The study of diversity is a systematic approach to assess composition, abundance and comparison of inhabiting species in the various habitats. The Rajasthan state is divided into different climate zones from a western arid desert to a humid region of the south-eastern plateau that represents significant insect diversity. The present review aims to provide baseline information of insect diversity in four eco-geographical regions of the Rajasthan. The exact number of species is still not clear. Although, after perusal of the literature, the study revealed that there were 878 insect species and subspecies recorded belonging to 104 families and 14 orders. Among all, the order Lepidoptera is most diverse representing 234 species followed by Hymenoptera with 208 species and Coleoptera with 129 species. The maximum number of 398 species were recorded from the Aravalli range followed by 283 species in the Thar Desert, 225 species from the eastern plain while the Southeastern plateau is less diverse with 86 species of insects. This review will be helpful to assess the comparison and identify species data of the insect fauna for further study.

Sharp Lateral Moho Variations Across the SE Tibetan Margin and Their Implications for Plateau Growth

AbstractThe tectonic uplift of the Tibetan Plateau is a focus in the geosciences. Middle‐lower crustal flow is a popular model to interpret the geodynamic mechanism on the margin of the Tibetan Plateau. The model predicts different surface and Moho topographies across the plateau boundary due to the different strengths of the surrounding blocks, that is, sharp boundaries on the eastern plateau boundary and gentle variations in the southeastern plateau boundary. Here, we employ receiver function and common conversion point stacking analysis with the seismic waveforms recorded by the dense ChinArray and other local seismic stations to accurately define the Moho topography in southeastern (SE) Tibet. We find that the Moho under the Tibetan Plateau is much deeper than that under the surrounding Yangtze Craton and Indochina block; abrupt Moho changes are found across the southeastern plateau margin, similar to that under the eastern plateau margin. We interpret these sharp Moho variations across the plateau margin to have developed when the Tibetan Plateau was extruded southeastward in the late Miocene. Subsequent gravity collapse resulted in crustal extension and gentle topographic variation, while the sharp Moho slope was preserved.

Episodic Lithospheric Deformation in Eastern Tibet Inferred From Seismic Anisotropy

AbstractMechanisms for uplift and deformation of the Tibetan Plateau remain vigorously debated; hypotheses include stepwise growth, distributed thickening, and crustal channel flow, each with a distinct anisotropic signature. We have developed a new azimuthally anisotropic shear velocity model for the lithosphere beneath eastern Tibet, based on ambient noise tomography from 643 seismic stations. In our model, the Tibetan upper crust is characterized by strong anisotropy with fast axes that correlate with surface geology and mantle anisotropy, suggesting the occurrence of coherent deformation. However, a much different picture emerges in the middle and lower crust, where anisotropy is disordered and weaker beneath the plateau than along its margins, inconsistent with the prediction of large‐scale eastward crust flow in eastern Tibet. Our observations are best explained by heterogeneous crustal thickening beneath the plateau with complex flow in the middle and lower crust, accompanied by asthenospheric upwelling along the southeastern plateau margin.

Phylogeny of spiny frogs Nanorana (Anura: Dicroglossidae) supports a Tibetan origin of a Himalayan species group.

Recent advances in the understanding of the evolution of the Asian continent challenge the long‐held belief of a faunal immigration into the Himalaya. Spiny frogs of the genus Nanorana are a characteristic faunal group of the Himalaya–Tibet orogen (HTO). We examine the phylogeny of these frogs to explore alternative biogeographic scenarios for their origin in the Greater Himalaya, namely, immigration, South Tibetan origin, strict vicariance. We sequenced 150 Nanorana samples from 62 localities for three mitochondrial (1,524 bp) and three nuclear markers (2,043 bp) and complemented the data with sequence data available from GenBank. We reconstructed a gene tree, phylogenetic networks, and ancestral areas. Based on the nuDNA, we also generated a time‐calibrated species tree. The results revealed two major clades (Nanorana and Quasipaa), which originated in the Lower Miocene from eastern China and subsequently spread into the HTO (Nanorana). Five well‐supported subclades are found within Nanorana: from the East, Central, and Northwest Himalaya, the Tibetan Plateau, and the southeastern Plateau margin. The latter subclade represents the most basal group (subgenus Chaparana), the Plateau group (Nanorana) represents the sister clade to all species of the Greater Himalaya (Paa). We found no evidence for an east–west range expansion of Paa along the Himalaya, nor clear support for a strict vicariance model. Diversification in each of the three Himalayan subclades has probably occurred in distinct areas. Specimens from the NW Himalaya are placed basally relative to the highly diverse Central Himalayan group, while the lineage from the Tibetan Plateau is placed within a more terminal clade. Our data indicate a Tibetan origin of Himalayan Nanorana and support a previous hypothesis, which implies that a significant part of the Himalayan biodiversity results from primary diversification of the species groups in South Tibet before this part of the HTO was uplifted to its recent heights.

Quantifying Trends of Land Change in Qinghai-Tibet Plateau during 2001–2015

The Qinghai-Tibet Plateau (QTP) is among the most sensitive ecosystems to changes in global climate and human activities, and quantifying its consequent change in land-cover land-use (LCLU) is vital for assessing the responses and feedbacks of alpine ecosystems to global climate changes. In this study, we first classified annual LCLU maps from 2001–2015 in QTP from MODIS satellite images, then analyzed the patterns of regional hotspots with significant land changes across QTP, and finally, associated these trends in land change with climate forcing and human activities. The pattern of land changes suggested that forests and closed shrublands experienced substantial expansions in the southeastern mountainous region during 2001–2015 with the expansion of massive meadow loss. Agricultural land abandonment and the conversion by conservation policies existed in QTP, and the newly-reclaimed agricultural land partially offset the loss with the resulting net change of −5.1%. Although the urban area only expanded 586 km2, mainly at the expense of agricultural land, its rate of change was the largest (41.2%). Surface water exhibited a large expansion of 5866 km2 (10.2%) in the endorheic basins, while mountain glaciers retreated 8894 km2 (−3.4%) mainly in the southern and southeastern QTP. Warming and the implementation of conservation policies might promote the shrub encroachment into grasslands and forest recovery in the southeastern plateau. While increased precipitation might contribute to the expansion of surface water in the endorheic basins, warming melts the glaciers in the south and southeast and complicates the hydrological service in the region. The substantial changes in land-cover reveal the high sensitivity of QTP to changes in climate and human activities. Rational policies for conservation might mitigate the adverse impacts to maintain essential services provided by the important alpine ecosystems.

Spatial and Temporal Variations in the Rainy Season Onset over the Qinghai–Tibet Plateau

Precipitation on the Qinghai–Tibet Plateau (TP) in southwestern China is subject to interactions between the complex and variable terrain and the sensitive climate. The regional climate is mainly affected by three circulations: westerlies, the South Asian monsoon, and the East Asian monsoon. Spatial and temporal variations in the rainy season onset were characterised based on daily precipitation from 106 meteorological stations on the TP from 1971 to 2015. Using the Theil–Sen Median trend analysis, Mann–Kendall test and mutation detection, the characteristics and reasons for the variations during the rainy season over the plateau over the past 45 years were investigated. The following results were obtained from the analysis: (1) There were obvious regional differences in the rainy season onset over the TP, and the rainy season began on the southeastern plateau and moved northwestward. (2) The TP rainy season underwent a significant mutation in approximately 1997, and following this mutation, the area affected by the delayed rainy season increased. (3) Against the background of global warming, the rainy season trend over the TP was advanced; however, there were still several multiple contiguous concentrated areas on the plateau. (4) Before the rainy season mutation, there were two centres of delayed precipitation on the plateau, which existed primarily due to their location at the end of the plateau water vapour transport channel. After the mutation, the number of delayed precipitation centres on the plateau increased to three and presented a spatially expanding trend, which may be related to the weakening trend in atmospheric circulation.

Intraseasonal Variations of Summer Convection over the Tibetan Plateau Revealed by Geostationary Satellite FY-2E in 2010–14

Based on the infrared black body temperature (TBB) observed by the geostationary meteorological satellite FY-2E from 2010 to 2014, the seasonal migration, occurrence frequency, and intraseasonal variability of summer convection over the Tibetan Plateau (TP) and its surrounding areas are analyzed. The results show that in May, convection mainly occurs over the eastern edge of the TP; in June, following the onset of the Asian summer monsoon, the strongest (severe) convection occurs in the southeastern part of the TP; and in July–August, strong southwesterly winds transport abundant moisture to the eastern and central areas of the TP, leading to formation of an active convection belt over southeastern TP. The results also show that in the western TP, the area with convection frequency greater than 6% occupies the southern plateau around the 37th pentad, and gradually moves northward until the end of July; in the central plateau, convection (severe convection) becomes active since early (mid) June, and maintains through the entire late summer with three major northward movements until reaching 34°N; and in the eastern TP, the convection is relatively active since the beginning of May and its northward stretching is slightly later than that over the central plateau. Overall, summer convective activities are unevenly distributed over the TP, with frequency of convection decreasing from south to north; and they also exhibit considerable intraseasonal variability, the maximum of which is found over the middle reach of the Yarlung Zangbo River and the southeastern plateau. EOF analysis of summer convection frequency over the TP reveals two leading modes, with the first mode being a dipole variation pattern between the Indian monsoon region and the southeastern TP, and the second mode a tripole pattern over the western TP, the Indian continent west of 80°E, and the South Asian continent east of 80°E.

CLM4.5 Model Simulation of Soil Moisture over the Qinghai-Xizang Plateau and Its Performance Evaluation

The Community Land Model version 4.5 (CLM4.5) driven by atmospheric forcing data (CRUNCEP) is used to simulate spatial and temporal characteristics of soil moisture in the Qinghai-Xizang Plateau for the period 1981-2016. Compared with station data, two reanalysis products (i.e.,the ERA-Interim and GLDAS-CLM) and the microwave remote sensing FY-3B/MWRI data, it is found that CLM4.5 can well reproduce the spatial and temporal variations of soil moisture in the Qinghai-Xizang Plateau. The microwave data with high spatial resolution (0.1°×0.1°), which is derived from various satellite remote sensing in the Qinghai-Xizang Plateau, provides detailed description of the spatial features of soil moisture. The results show that the spatial and temporal distributions of simulated soil moisture are consistent with station observations.The simulation is significantly correlated with observations in all soil layers but with high systematic deviations. And the consistency between simulation and observations gradually decreases from the surface downward. The spatial distribution of soil moisture in the Qinghai-Xizang Plateau is characterized by gradual increase from northwest to southeast. The high-value areas are found in the Sanjiangyuan Wetland and the southeastern Plateau, while the dry regions are located in the Qaidam Basin and the Tarim Basin. Soil moisture generally increases from surface downward. Temporal variation of soil moisture presents an alternate dry and wet pattern. There is little difference in soil moisture variation in different layers. The simulation also reasonably reproducesmonthly changes in soil moisture in the summer. Soil moisture in most of the southwestern region including the southern periphery of the plateau obviously increases in the summer. The dry area in the northern Qaidam Basin also markedly shrinks to the north. The simulated soil moisture provides more detailed description of spatial distribution and monthly changes of soil moisture in the summer compared with reanalysis data and microwave remote sensing data.

Temporal and Spatial Variations in the Climate Controls of Vegetation Dynamics on the Tibetan Plateau during 1982–2011

The ecosystem of the Tibetan Plateau is highly susceptible to climate change. Currently, there is little discussion on the temporal changes in the link between climatic factors and vegetation dynamics in this region under the changing climate. By employing Normalized Difference Vegetation Index data, the Climatic Research Unit temperature and precipitation data, and the in-situ meteorological observations, we report the temporal and spatial variations in the relationships between the vegetation dynamics and climatic factors on the Plateau over the past three decades. The results show that from the early 1980s to the mid-1990s, vegetation dynamics in the central and southeastern part of the Plateau appears to show a closer relationship with precipitation prior to the growing season than that of temperature. From the mid-1990s, the temperature rise seems to be the key climatic factor correlating vegetation growth in this region. The effects of increasing temperature on vegetation are spatially variable across the Plateau: it has negative impacts on vegetation activity in the southwestern and northeastern part of the Plateau, and positive impacts in the central and southeastern Plateau. In the context of global warming, the changing climate condition (increasing precipitation and significant rising temperature) might be the potential contributor to the shift in the climatic controls on vegetation dynamics in the central and southeastern Plateau.

Spatiotemporal variability of snow cover on Tibet, China using MODIS remote-sensing data

ABSTRACTSnow cover is an important component of the cryosphere, and the study on spatial and temporal variations of snow cover is essential for understanding the consequences and impacts of climate change and water resources management. In this study, the temporal variation of snow-covered area (SCA) and spatial variability of snow-cover frequency (SCF) on Tibet is analysed based on the Moderate Resolution Imaging Spectroradiometer (MODIS)/Terra snow cover product (MOD10A2) from 2000 to 2015, and relationships with main climate variables are investigated. Results are as follows: (1) there is a very weak decreasing trend in annual mean SCA, and a slight increasing trend in autumn and winter and a slight decreasing trend in spring and more robust decreasing trend in summer for SCA are found. (2) The temporal variation of SCA is negatively correlated with temperature, whereas it is little correlated with corresponding precipitation. (3) The general trend of spatial SCF variation on Tibet, predominated by snow-cover variations in spring and autumn, tends to decrease in spring while it tends to increase in autumn. (4) The spatial variability of SCF is attributed to snow-cover variations in autumn and spring, which is more obvious in higher latitudes in autumn while it is more noticeable in lower-latitude southeastern plateau in spring. (5) The regions with higher variability of snow cover are main pastoral land and more prone to snow-related disaster in Tibet, becoming key zone of snow-cover monitoring and disaster prevention and mitigation.

The Model for Dilution Process of Landslide Triggered Debris Flow —A Case of Guanba River in Tibet Southeastern Plateau

Understanding and modeling the downstream dilution process of a landslide triggered debris flow is the foundation for recognizing the boundary condition and dilution mechanism of this type of debris flow, and this serves as the theoretical basis for the categorized control of viscous debris flows, diluted debris flows, hyperconcentration flows and flash floods in a drainage basin. In this study, taking as an example a typical debris flow that occurred in the Guanba River on Tibet’s southeastern plateau on July 6th, 1998, empirical models are used to calculate the density, water flow discharge, debris flow discharge, average depth of loose materials and channel gradient at 11 cross-sections upstream to downstream in the debris flow. On this basis, the dilution characteristics and debris flow dilution process are analyzed in this study. According to the correlation between the debris flow density and the water-soil ratio and channel gradient, we have established the density evaluation model for the debris flow dilution process, which can predict the dilution process of a landslide triggered debris flow. The study results include the following four aspects: (1) The key factors in the dilution process of landslide triggered debris flows are the water flow discharge, average depth of loose materials and channel gradient. (2) The debris flow dilution characteristics in the Guanba River in 1998 include the occurrence of the debris flow dilution process after a significant increase in the water-soil ratio; an increase in the proportion of fine particles after dilution of the debris flow; and the size distribution of grain is “narrowed.” (3) In accordance with the density and dilution characteristics, the debris flow dilution process in the Guanba River can be divided into the upstream viscous debris flow section, midstream and downstream transitional debris flow section and downstream diluted debris flow section. (4) The density evaluation model for the debris flow dilution process is expressed by the Lorentz equation, and this model can reflect the debris flow dilution process such that the debris flow density will decrease gradually with an increase in the water-soil ratio and decrease in channel gradient. The density evaluation model for the debris flow dilution process has been verified by three debris flow cases, which include Gaoqiao Gully, Haizi Valley, and Aizi Valley