Southern Tibetan Plateau Research Articles

Indian monsoon precipitation isotopes linked with high level cloud cover at local and regional scales

Precipitation stable isotopes preserve historic changes of evaporation in the source regions and precipitation processes, therefore, they can be used to reveal regional hydrological cycle dynamics and paleoclimate reconstructions. In monsoon regions, strong inverse impacts of convection on precipitation isotope ratios, have created a debate regarding the interpretation of isotope records as local climate proxies. The proportions of stratiform to convective precipitation on water isotopes, together with the influence mechanisms on seasonal and interannual scales remain highly uncertain. To further address the influence of precipitation patterns on water isotopes, we used 10 yrs of precipitation isotope data from the southern Tibetan Plateau (TP) to explore the effects of large-scale cloud cover and local climate on precipitation isotopes. Correlation analysis performed between local precipitation δ18O values and different level cloud data, indicated significant negative correlations between precipitation isotopes and high level cloud cover on both seasonal and interannual time scales. This result suggests that high-level convection in the upper moisture transport stream is a main control on precipitation isotopes in the southern TP. The clear and coherent variations of precipitation isotopes with the Southern Oscillation Index and outgoing longwave radiation confirmed that strong convection activity in the moisture source region and during transport significantly depleted heavy isotopes in vapor, producing substantially decreased precipitation δ18O in the study region. These results agree with earlier findings of tree ring cellulose isotope records that correlate with cloud cover, but we emphasized the important role of larger-scale regional cloud cover. We also delineated different maximum correlation zones for seasonal and interannual time scales, likely due to different mechanisms. These findings further improve the interpretation of paleoisotope records from the Indian summer monsoon region.

Quantifying snow darkening and atmospheric radiative effects of black carbon and dust on the South Asian monsoon and hydrological cycle: experiments using variable-resolution CESM

Abstract. Black carbon (BC) and dust impart significant effects on the South Asian monsoon (SAM), which is responsible for ∼80 % of the region's annual precipitation. This study implements a variable-resolution (VR) version of the Community Earth System Model (CESM) to quantify two radiative effects of absorbing BC and dust on the SAM. Specifically, this study focuses on the snow darkening effect (SDE), as well as how these aerosols interact with incoming and outgoing radiation to facilitate an atmospheric response (i.e., aerosol–radiation interactions, ARIs). By running sensitivity experiments, the individual effects of SDE and ARI are quantified, and a theoretical framework is applied to assess these aerosols' impacts on the SAM. It is found that ARIs of absorbing aerosols warm the atmospheric column in a belt coincident with the May–June averaged location of the subtropical jet, bringing forth anomalous upper-tropospheric (lower-tropospheric) anticyclogenesis (cyclogenesis) and divergence (convergence). This anomalous arrangement in the mass fields brings forth enhanced rising vertical motion across South Asia and a stronger westerly low-level jet, the latter of which furnishes the Indian subcontinent with enhanced Arabian Gulf moisture. Precipitation increases of 2 mm d−1 or more (a 60 % increase in June) result across much of northern India from May through August, with larger anomalies (+5 to +10 mm d−1) in the western Indian mountains and southern Tibetan Plateau (TP) mountain ranges due to orographic and anabatic enhancement. Across the Tibetan Plateau foothills, SDE by BC aerosols drives large precipitation anomalies of > 6 mm d−1 (a 21 %–26 % increase in May and June), comparable to ARI of absorbing aerosols from April through August. Runoff changes accompany BC SDE-induced snow changes across Tibet, while runoff changes across India result predominantly from dust ARI. Finally, there are large differences in the simulated SDE between the VR and traditional 1∘ simulations, the latter of which simulates a much stronger SDE and more effectively modifies the regional circulation.

Decomposition of Future Moisture Flux Changes over the Tibetan Plateau Projected by Global and Regional Climate Models

AbstractTo meet the requirement of high-resolution datasets for many applications, a dynamical downscaling approach using a regional climate model (the WRF Model) driven by a global climate model (CCSM4) has been adopted. This study focuses on projections of future moisture flux changes over the Tibetan Plateau (TP). First, the downscaling results for the historical period (1980–2005) are evaluated for precipitation P, evaporation E, and precipitation minus evaporation P − E against Global Land Data Assimilation System (GLDAS) data. The mechanism of P − E changes is analyzed by decomposition into dynamic, thermodynamic, and transient eddy components. Whether the historical period changes and mechanisms continue into the future (2010–2100) is investigated using the WRF and CCSM model projections under the RCP4.5 and RCP8.5 scenarios. Compared with coarse-resolution forcing, downscaling was found to better reproduce the historical spatial patterns and seasonal mean of annual average P, E, and P − E over the TP. WRF projects a diverse spatial variation of P − E changes, with an increase in the northern TP and a decrease in the southern TP, compared with the uniform increase in CCSM. The dynamic component dominates P − E changes for the historical period in both the CCSM and WRF projections. In the future, however, the thermodynamic component in CCSM dominates P − E changes under RCP4.5 and RCP8.5 from the near-term (2010–39) to the long-term (2070–99) future. Unlike the CCSM projections, the WRF projections reproduce the mechanism seen in the historical period—that is, the dynamic component dominates P − E changes. Furthermore, future P − E changes in the dynamical downscaling are less sensitive to warming than its coarse-resolution forcing.

Identifying and contrasting the sources of the water vapor reaching the subregions of the Tibetan Plateau during the wet season

A Lagrangian approach is utilized to identify and compare the sources of water vapor transported to the four subregions of Tibetan Plateau (TP) during the wet season (May–August) of 1980–2016. We focus on the time scale and subseasonal variability of water vapor transport and the relationship between moisture supply and precipitation at the interannual scale. This study finds that: (1) The moisture sources for the four subregions differ significantly in both spatial pattern and magnitude and depend heavily on the combined effects of the summer monsoons, local recycling and the westerlies. (2) The spatial evolution of the moisture sources based on the backward trajectory analysis reveals that, although approximately 80% of the moisture is delivered to the target regions within 1–4 days, the individual subregions feature different transport pathways and associated time scales. (3) The subseasonal migration of the Indian summer monsoon regulates the importance of different moisture sources for the southern TP but not for the northern TP. Additionally, the subseasonal moisture source evolution differs greatly between the southeastern TP and the southwestern TP. (4) The interannual variability of precipitation over the whole TP during summer is negatively correlated with the variation in the moisture transported by the westerlies and is positively related to the moisture conveyed by the Indian summer monsoon for the northern TP and by adjacent moisture transport for the southern TP.

500-year tree-ring reconstruction of Salween River streamflow related to the history of water supply in Southeast Asia

The great rivers that flow from the southern Tibetan Plateau (TP) affect billions of people in the downstream countries of Asia. Understanding of the hydrological variability of these rivers is still limited, however, because of the lack of long-term streamflow records. Tree-ring width chronologies from six sites are applied to reconstruct annual streamflow of the Salween River, the last remaining large free-flowing transboundary river draining the southern TP, and a critical water source for countries of Southeast Asia. Response function analysis shows that precipitation is the main factor limiting the radial growth of the sampled trees. Linear regression of annual (September–June) Salween River streamflow on the first principal component of tree-ring chronologies explains 53.4% of the streamflow variance, 1958–2011, and yields a reconstruction for the interval 1500–2011 CE. A tally of droughts and wet periods emphasizes the severity of droughts before the start of the gauged records, and a tendency toward wetter conditions in recent decades. Regional temperature is negatively associated with the reconstructed streamflow. Cold wet summers controlled by the Asian summer monsoon are responsible for an increasing trend in streamflow over the last decades. Reconstructed hydrological change is linked to the history of mainland Southeast Asia through the impact of water shortages on Burma society. In particular, prolonged periods of low flow of the Salween River coincide with the falls of the Toungoo Empires and the First Anglo-Burmese War. This tree-ring reconstruction provides a long-term perspective on hydrological changes in the Upper Salween River Basin that can give insight for sustainable water management on the TP and in Myanmar.

New paleomagnetic constraints on rift basin evolution in the northern Himalaya mountains

The late Cenozoic sediments in the rift basins in the northern Himalaya Mountains document important information about the uplift and deformation of the most active tectonic region in the Tibetan Plateau. However, these sediments have not been precisely dated, hindering our ability to address the basin development and termination associated with a series of uplifts in the southern Tibetan Plateau. Here, we report a detailed magnetostratigraphic study on the fluvio - lacustrine sedimentary sequence of the Dati Formation bearing abundant Hipparion forstenae fossils in the Dati Basin in the northern frontal region of the Himalaya Mountains. The 195 m – thick section yielded six normal and seven reversed polarity zones that correlate well with Chrons C3An.1r to C4r.2r of the geomagnetic polarity time scale, constraining the section age to ~8.6 – ~6.2 Ma. Together with the magnetostratigraphic results from other rift basins in the region, these results indicate that the horizons bearing the Hipparion fossils were deposited during the age interval of 7.1–6.5 Ma in the northern Himalaya Mountains. The regional tectonic activity and comprehensive magnetostratigraphic and sedimentologic comparisons suggest that the evolution of the rift basins in the northern Himalaya Mountains has involved three major stages since the late Cenozoic, i.e., (1) ~10.0–8.0 Ma, onset of the basins with fan delta facies; (2) ~8.0–3.0 Ma, expansion of the basins with mainly lacustrine facies; (3) ~3.0–1.7 Ma, shrinking and termination of the basins with alluvial fans. The basin evolutionary history indicates an accelerated tectonic uplift of the Himalaya Mountains at ~10.0 Ma, and two deformational events at ~3.0 Ma and at ~1.7 Ma.

Trace elements analysis in hair strand of cooks chronically exposed to indoor air pollution in restaurants of Lhasa, Tibet: preliminary results

Considering the effect of environmental exposure and contamination, six trace elements including arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), and zinc (Zn) in scalp hair samples of cooks at Lhasa city, southern Tibetan Plateau were analyzed by inductively coupled plasma-mass spectrometry. Potential of human hair in indicating the exposure and contamination has been assessed. Concentrations of these elements were found in the rank order of Zn > Cu > Cr > Pb > As > Cd, with concentrations of Zn and Cu exceeding 10 μg/g (Zn = 208.01 μg/g; Cu = 23.60 μg/g). All the elements, especially Cu and Cr concentration in the hair samples were higher than those of the control, indicating higher indoor air pollution posing higher health risk. Cu, Cr, and Zn concentrations were higher than those of other areas (e.g. Turkey, Poland and Italy), implying that these metals might accumulate in the body and affect the health of cooks. No significant difference between genders was observed. Significantly positive correlations for several elements: Cr and As, Cr and Cd, Cu and Pb, As and Pb were obtained, which were different from the control, indicating heavy exposures to these metals through cooking activities. Our observations suggested that human scalp hair could be a useful biomarker to assess the intensity of heavy metals exposure as well as the indoor air pollution to cooks in Tibet.

Feeding solution: Crop-livestock integration via crop-forage rotation in the southern Tibetan Plateau

Separated, specialized crop and forage production has a long history on the Tibetan Plateau. Such isolated pattern has led to current concerns of intensified agriculture, environmental degradation and forage shortage in the increasing pressures of population and livestock growth. To tackle the predicament of feed shortage, an alternative to specialized agriculture is crop-forage rotation for potential crop-livestock integration (CLI). However, its feasibility is understudied and the potential remains unanswered in the southern Tibetan Plateau. Based on the analyses of grazing pressure index and growing degree days (GDD), we examined the practicability and modes of crop-forage rotation for feed solution in the middle reaches of the Yarlung Tsangpo Watershed (YTW). Additionally, cultivated land area suitable for forage rotation after crop harvest was defined. Livestock carrying capacity and grazing pressure indices under forage rotation were compared with those only with rangeland and crop residues. We found that the average number of livestock maintained about 9 million standard sheep unit (SU) in the period 2000–2015, which exceeded the carrying capacity provided by rangeland and crop residues. Growing season length are about 200 days ranging from late April to early November, with daily average temperature ≥ 5 ℃ and over 1500 GDD in the Yarlung Tsangpo River valley. About 158,377 ha, accounting for 74.4% of the cultivated land is suitable for annual forage rotation after crop harvest. The appropriate period for annual forage rotation is ca. 80 days, i.e. from 20th August to 8th November after spring crop harvest and from 1st August to 20th October after winter crop harvest. In addition, the information of GDD also provides elevational thresholds for implementing forage rotation practice in the future. The upper limits for forage rotation are 4000 m after spring crop harvest and 4500 m after winter crop harvest. The grazing pressure indices in most counties can be substantially reduced after filling feed gaps through crop-forage rotation. We demonstrate that crop-forage rotation could be a good solution to forage deficits. These findings also provide insights into promising potential for crop-livestock integration to alleviate grazing pressure in the southern Tibetan agricultural area. However, adoption will depend on farmers’ preference and market factors. Further efforts are needed to encourage farmers’ involvement into the forage rotation by policy guidance.

Quantitative source apportionment of water solutes and CO2 consumption of the whole Yarlung Tsangpo River basin in Tibet, China.

The Tibetan Plateau is known as the "Asian water tower," and the Yarlung Tsangpo (YT) River is the largest river that originates in and flows across the southern Tibetan Plateau. Although the solute source of YT River has been extensively and qualitatively analyzed, there is a lack of the quantitative analysis for the whole basin and seasonal variation of hydrochemical characteristics. Here, 212 samples obtained in the mainstream and tributary of YT River in different (wet, normal, and dry) periods were used for the solute apportionment using the mass balance model. The results showed that the solutes in YT River water were mainly derived from the carbonate and silicate rock weathering that accounts 42.2% and 26.9% in the total solute source, respectively, as the complex geological conditions in the basin. A part of the ions (7.5%) was also originated from the atmospheric precipitation as the abundant rainfall in the wet period. Meanwhile, the contribution of solute sources had no significantly seasonal variation in the upstream, whereas it had significantly seasonal variation in the downstream with the tropical climate and heavy rainfall. Importantly, the rock weathering of the basin could consume so much atmospheric CO2 (0.54% of the consumption at global with the only 0.16% of the global surface area) that could mitigate the global warming, which followed an increasing trend from upstream to downstream. The quantitative analysis of the solute source for YT River fills in the gaps in the chemically characteristic cognition of the basin. It is beneficial for the water resource management for the Asian. The proportion of solute sources in the YT River and its tributaries for wet (W), normal (N), and dry (D) periods.

Spatial and Temporal Characteristics of Cirrus Clouds over the Tibetan Plateau Based on CALIPSO and AIRS Observations

The spatial and temporal distribution characteristics of high clouds over the Tibetan Plateau (TP) were studied using the Atmospheric Infrared Sounder (AIRS) and the GCM-Oriented CALIPSO Cloud Product (CALIPSO-GOCCP) monthly mean cloud products from 2007 to 2017. The high clouds over the TP are dominated by cirrus and show seasonal variation characteristics. There were two distinct areas with the high occurrence of cirrus clouds in the area (0°–60°N, 75°–103°E). One was located in the regions from the equator to 25°N, and the other was within the latitude belt from 30° to 40°N. From January to May, cirrus clouds mainly occurred in the central and northern parts of the TP (30° to 40°N), and the cirrus cloud fraction increased from January and reached its maximum (∼0.51) in April. From June to August, cirrus clouds mainly occurred in the southern part of the TP during summer. The cirrus clouds over the southern TP were relatively high (located in 10–17 km) and manifested northward and southward movements. The ice clouds in the southern TP are associated with plateau deep convection activities and abundant vapor transmitted by the Asian monsoon. Cirrus clouds over the northern and central TP may be relevant to the atmospheric lift by an approaching cold front and topographic lifting. Moreover, the high clouds below 11 km are dominated by opaque clouds, while the nonopaque (or thin) and opaque (or thick) clouds above 11 km are comparable.

Microphysical Properties of Convective Clouds in Summer over the Tibetan Plateau from SNPP/VIIRS Satellite Data

The Tibetan Plateau (TP) plays an important role in formation and development of the East Asian atmospheric circulation, climate variability, and disastrous weathers in China. Among the many topics on TP meteorology, it is critical to understand the microphysical characteristics of clouds over the TP; however, observations of the cloud micro-physics in this area are insufficient mainly due to sparse stations and limited cloud physical data. The Visible Infrared Imaging Radiometer Suite (VIIRS), onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite, has an improved imaging spectroradiometer with 17 channels of 750-m moderate resolution and 5 channels of 375-m image resolution. The high-resolution instrument has an advantage for observing the small or initial convective clouds. Based on the methodologies that we proposed before for retrieving cloud microphysical properties from SNPP, an automated mapping software package named Automatic Mapping of Convective Clouds (AMCC) has been developed at the scale of satellite swath. The properties of convective clouds are retrieved by AMCC and their values are averaged over 0.33° × 0.33° grids based on the SNPP/VIIRS satellite data over the TP during the summers of 2013–17. The results show that: (1) the temperature of lifting condensation level (TLCL) at Naqu meteorological station and the cloud base temperature (Tb) retrieved from VIIRS are linearly correlated, with a correlation coefficient of 0.87 and standard deviation (STD) of 3.0°C; (2) convective clouds over the TP have the following macro- and micro-physical properties. First, the cloud base temperature (Tb) is about −5°C, the cloud base height above the ground (Hb) ranges between 1800 and 2200 m, and the cloud water content is low. Second, the cloud condensation nuclei concentration (NCCN) is between 200 and 400 mg−1 with 0.7% in maximum supersaturation (Smax); consequently, the condensation growth of water cloud droplet with less NCCN and higher Smax is fast. Third, because the precipitation initiation depth (D14) varies within 1500–2000 m and 500–1000 m at the Yarlung Zangbo River basin and southern Tibet, respectively, the clouds over these areas are more prone to precipitation. Fourth, mean height of the cloud top above sea level (Htop) is between 10 and 13 km, but the cloud depth (Dcld) is rather small, which is about 5000 m in southern TP and gradually reduces to 2500 m in northern TP. Fifth, the glaciation temperature (Tg) ranges from −30°C in central and southern TP to −25°C in northern TP, which, combined with the warmer Tg and the Tb less than 0°C, leads to the domination of ice process in the clouds; (3) the macro- and microphysical properties of convective clouds over the TP explain why rainfall there is frequent and lasts over a short time with small amount and large rain drops.

Distinguishing interannual variations and possible impacted factors for the northern and southern mode of South Asia High

Given the large meridional coverage of South Asian High (SAH), the interannual variabilities of SAH and the corresponding impacted factors may differ between mid- to high-latitude and low-latitude components of SAH. This study distinguishes the interannual variations of the mid- to high-latitude and low-latitude components of SAH to obtain further understanding of SAH variations. By means of composite analysis, this study investigates the characteristics of the northern and southern mode of SAH variation (N-SAH, S-SAH). When the SAH is regarded as an entirety (E-SAH) based on numerous previous studies, it strengthens distinctly and expands toward both meridional and zonal directions in strong E-SAH comparing to weak E-SAH. The geopotential height (HGT) and tropospheric temperature (TT) anomalies related to the E-SAH are concurrently observed over the low-latitude and mid- to high-latitude regions. In contrast, when N-SAH and S-SAH are defined in this study, the SAH is distinctly strengthened only over its northern (southern) side and expands northward (southward) in strong N-SAH (S-SAH) comparing to the weak group. The HGT and TT anomalies related to the N-SAH (S-SAH) cases are limited over the mid- to high-latitude (low-latitude) regions. Possible impacted factors related to E-SAH, N-SAH, and S-SAH are further analyzed. The N-SAH is closely associated with precipitation anomalies over Indian Peninsula, meridional circulation over Tibet Plateau (TP), land surface temperature (LST) anomalies over Indian Peninsula and northern TP, meridional LST gradient between Indian Peninsula and northern TP, and circumglobal teleconnection (CGT). For instance, positive rainfall anomalies together with obviously ascending motion over Indian Peninsula contributes to a decreased LST anomalies via cloud-radiation feedback here, which forms a north-to-south LST gradient. The LST gradient will reduce the climatological south-to-north LST gradient here, which in turn contributes to a northward meridional circulation over northern TP, and finally contribute to a strong N-SAH existing over north of 25°N. Furthermore, the positive rainfall anomalies over Indian Peninsula tends to inspire a strong CGT over mid-high latitude through atmospheric response to condensation latent heating source, which in turn contributes to a strong N-SAH. In contrast, the meridional circulation associated with S-SAH is exhibited by southward shifting over southern TP (south of 30°N) due to atmospheric response to heating source generated by significant SST anomalies over Indian Ocean. Obviously warm center is observed in low-upper troposphere from tropical region to southern TP, which finally result in a strong S-SAH, accompanied by shifting southward. However, variation of E-SAH is a result of the combined action of rainfall anomalies over Indian Peninsula and SST anomalies over Indian Ocean. These differences indicate that it is necessary and of scientific significance to distinguish the northern and southern mode of the SAH.

Immobilization of relic anthropogenic dissolved organic matter from alpine rivers in the Himalayan-Tibetan Plateau in winter

The Tibetan Plateau is a critical ecosystem that sensitively responds to ongoing glacier shrinkage and permafrost thaw. Dissolved organic matter (DOM) in Tibetan Alpine rivers plays pivotal roles in the biogeochemical cycling of elements and nutrients at regional and even global scales, impacting water quality, downstream environments, and climate. However, little is known about the characteristics and dynamics of DOM in these watersheds. We investigated five major Himalayan rivers in the southern Tibetan Plateau, utilizing bulk dissolved organic carbon (DOC), optical properties, and molecular formulas. We found extremely low DOC and fluorescent DOM (FDOM) levels in the rivers (average DOC: 0.25–0.87 mg L−1, FDOM: 0.02–0.05 RU) with a highly degraded molecular signature, which was enriched with heteroatomic molecular formulas (S-containing: 58–72%, N-containing: 61–86%) and condensed aromatics (31–39% vs. ∼11% in world major rivers). Further, 81–99% of the condensed aromatics was identified as dissolved black nitrogen (DBN) with multiple nitrogen atoms, typical for grassy biomass combustion. The findings highlighted potentially fast DOM remineralization leading to the release of CO2 and enriched apparently anthropogenic condensed aromatics and heteroatomic formulas in what have been considered pristine Tibetan rivers. These findings should be considered in future biogeochemical models and ecosystem management.

Formation of Snow Cover Anomalies Over the Tibetan Plateau in Cold Seasons

AbstractThe present study investigates relationship between interannual variations of snow cover and local surface and atmospheric variables, and the formation of interannual snow cover anomalies over the Tibetan Plateau in the cold seasons (autumn, winter, and spring). It is shown that the snow‐related surface heat flux and atmospheric heat source anomalies increase from autumn to spring, whereas precipitation anomalies are most prominent in autumn. This suggests that snow cover anomalies over the central eastern Tibetan Plateau are mainly formed in autumn and their impacts are most prominent in spring. The central eastern Tibetan Plateau snow cover anomalies have high month‐to‐month persistence during October through April, indicative of a large contribution of persistence to snow cover anomalies in winter and spring. The Tibetan Plateau snow cover anomalies in cold seasons are influenced by large‐scale atmospheric circulation anomaly pattern of different paths. In autumn, a wave pattern from the North Pacific to the Tibetan Plateau via the North Atlantic, induced by eastern North Pacific and western North Atlantic sea surface temperature anomalies, plays an important role in the formation of snow cover anomalies. In winter, a North Atlantic Oscillation related wave pattern from the North Atlantic to East Asia may contribute to snow cover anomalies. In spring, a midlatitude wave pattern originating over the western North Atlantic and propagating through the Mediterranean Sea to southern Tibetan Plateau may have a supplementary contribution to snow cover anomalies.

Evaluation of SWAT Model performance on glaciated and non-glaciated subbasins of Nam Co Lake, Southern Tibetan Plateau, China

This paper presents an assessment of the Soil and Water Assessment Tool (SWAT) on a glaciated (Qugaqie) and a non-glaciated (Niyaqu) subbasin of the Nam Co Lake. The Nam Co Lake is located in the southern Tibetan Plateau, two subbasins having catchment areas of 59 km2 and 388 km2, respectively. The scores of examined evaluation indices (i.e., R2, NSE, and PBIAS) established that the performance of the SWAT model was better on the monthly scale compared to the daily scale. The respective monthly values of R2, NSE, and PBIAS were 0.94, 0.97, and 0.50 for the calibration period while 0.92, 0.88, and −8.80 for the validation period. Glacier melt contribution in the study domain was simulated by using the SWAT model in conjunction with the Degree Day Melt (DDM) approach. The conjunction of DDM with the SWAT Model ensued improved results during both calibration (R2=0.96, NSE=0.95, and PBIAS=−13.49) and validation (R2=0.97, NSE=0.96, and PBIAS=−2.87) periods on the monthly time scale. Average contribution (in percentage) of water balance components to the total streamflow of Niyaqu and Qugaqie subbasins was evaluated. We found that the major portion (99.45%) of the streamflow in the Niyaqu subbasin was generated by snowmelt or rainfall surface runoff (SURF_Q), followed by groundwater (GW_Q, 0.47%), and lateral (LAT_Q, 0.06%) flows. Conversely, in the Qugaqie subbasin, major contributor to the streamflow (79.63%) was glacier melt (GLC_Q), followed by SURF_Q (20.14%), GW_Q (0.13%), and LAT_Q (0.089%). The contribution of GLC_Q was the highest (86.79%) in July and lowest (69.95%) in September. This study concludes that the performance of the SWAT model in glaciated catchment is weak without considering glacier component in modeling; however, it performs reasonably well in non-glaciated catchment. Furthermore, the temperature index approach with elevation bands is viable in those catchments where streamflows are driven by snowmelt. Therefore, it is recommended to use the SWAT Model in conjunction with DDM or energy base model to simulate the glacier melt contribution to the total streamflow. This study might be helpful in quantification and better management of water resources in data scarce glaciated regions.

Complex subduction beneath the Tibetan plateau: A slab warping model

Morphology of the subducting Indian lithosphere beneath Tibet is the key to understanding the tectonic evolution of the Tibetan plateau. In the present study we determine three-dimensional P-wave velocity images of the mantle under the entire Tibetan plateau and its adjacent areas by inverting ~200,000 teleseismic relative travel-time residuals recorded at 893 stations belonging to >32 portable seismic networks deployed in and around the plateau. An east-west varying high-velocity anomaly with a large dip angle down to the mantle transition zone is revealed clearly, which represents the subducting Indian slab. On the basis of the tomographic results, we propose a slab warping model to describe the complex subduction of the Indian plate beneath the plateau, which is characterized by lateral bending in addition to downward subduction. The complex geometry of the present Indian slab is possibly caused by non-uniform pulling of an earlier subducted slab in a process with the Indian slab detachment propagating laterally. As a result, a warping arc has formed beneath the Himalaya block to keep the Indian lithosphere intact. This slab warping model agrees well with many observations, such as magmatism and surface deformations in the western and southern Tibetan plateau.

Delayed impacts of the IOD: cross-seasonal relationships between the IOD, Tibetan Plateau snow, and summer precipitation over the Yangtze–Huaihe River region

Significant anomalous signals are found during the ensuing summer after the Indian Ocean Dipole (IOD) forcing mode dissipates over the tropical Indian Ocean. These signals manifest as increased summer precipitation over the Yangtze–Huaihe River (YHR) region associated with abnormal water vapor convergence contributed mainly by southerly water vapor input along the western flank of an anomalous anticyclone over the subtropical western North Pacific (WNP). The mechanism of these delayed impacts of the IOD is investigated and summarized as a relationship between the IOD, Tibetan Plateau (TP) snow, and summer precipitation. The evolution of the moisture circulation response to the IOD reveals that the IOD can modulate the precipitation over the TP during winter and deepen the snow distribution over the southern TP. Anomalous snow conditions over the TP are a likely capacitor of the delayed effect of the IOD in that they can exert further influence on the ensuing summer monsoon. The influence of deeper snow over the southern edge of the TP on summer precipitation is confirmed: (1) the melting of excessive snow over the TP can lead to a weakened thermal land-sea contrast and weakened Asian summer monsoon westerlies; (2) easterly anomalies can further induce divergence over the WNP, meanwhile stimulating a Pacific-Japan teleconnection pattern; and (3) the anomalous anticyclone over the WNP strengthens the subtropical high and benefits southerly water vapor input to the YHR, while the anomalous cyclone dominates Japan. In between, the subtropical upper-level westerly jet accelerates, and the divergence at its right entrance can enhance the ascending vertical motion over the YHR, which is also favourable for precipitation.

Effect of topography and protecting barriers on revegetation of sandy land, Southern Tibetan Plateau

Revegetation on sandy land has attracted worldwide attention, especially on the extremely fragile alpine eco-region of the Tibetan Plateau. However, the effectiveness of revegetation and its controlling factors have rarely been reported. We collected plant growths and species composition from seven field sites in 2011 and conducted a follow-up random investigation in 2016. The indicators, including richness and diversity, were used to compare the differences among these sites based on redundancy and cluster analyses. The results indicated that plant growth has different characteristics in different land types. The distribution and growth of Artemisia sphaerocephala, Artemisia younghusbandii and Heteropappus gouldii varied with topography, and the crown widths of A. sphaerocephala were 100.6 cm × 87.2 cm on barchan dune and 26.0 cm × 25.4 cm on moving sandy land at valley slopes. These species are likely the pioneer plants for revegetation on sandy land. It seems that sand-protecting barriers play an important role in revegetation. The stone and plastic checkerboard barriers increase plant diversity, while straw barrier promotes the plant growth. These findings provide useful guidance to the ongoing vegetation recovery on sandy land, an important component of the Project on Construction and Protection of Ecological Security Barriers on the Tibetan Plateau.

Coupling the Common Land Model to ECHAM5 Atmospheric General Circulation Model

The ECHAM5 model is coupled with the widely used Common Land Model (CoLM). ECHAM5 is a state-of-the-art atmospheric general circulation model incorporated into the integrated weather and climate model of the Chinese Academy of Meteorological Sciences (CAMS-CSM). Land surface schemes in ECHAM5 are simple and do not provide an adequate representation of the vegetation canopy and snow/frozen soil processes. Two AMIP (Atmosph-eric Model Intercomparison Project)-type experiments using ECHAM5 and ECHAM5-CoLM are run over 30 yr and the results are compared with reanalysis and observational data. It is found that the pattern of land surface temperature simulated by ECHAM5-CoLM is significantly improved relative to ECHAM5. Specifically, the cold bias over Eurasia is removed and the root-mean-square error is reduced in most regions. The seasonal variation in the zonal mean land surface temperature and the in situ soil temperature at 20- and 80-cm depths are both better simulated by ECHAM5-CoLM. ECHAM5-CoLM produces a more reasonable spatial pattern in the soil moisture content, whereas ECHAM5 predicts much drier soils. The seasonal cycle of soil moisture content from ECHAM5-CoLM is a better match to the observational data in six specific regions. ECHAM5-CoLM reproduces the observed spatial patterns of both sensible and latent heat fluxes. The strong positive bias in precipitation over land is reduced in ECHAM5-CoLM, especially over the southern Tibetan Plateau and middle–lower reaches of the Yangtze River during the summer monsoon rainy season.

Differential crustal deformation across the Cona-Oiga rift, southern Tibetan Plateau

The Cona-Oiga rift (COR) is the easternmost member of a series of ∼N-S trending Cenozoic rifts in the southern Tibetan Plateau. The Yarlung River flows from west to east, across the COR and exhibits diverse river morphology along strike. We analyze tributary fluvial longitudinal profiles in the Yarlung drainage and the published strain rate field on both sides of the rift in order to gain knowledge about its development and crustal deformation patterns within the plateau interior. Tributaries on the western side of the rift have relatively low normalized steepness index (ksn). Concave curves in χ-elevation plots and cross-divide contrasts in χ, mean relief, and mean gradient, indicate ongoing river reorganization in this region. In contrast, high topographic relief and steep stream channels developed on the eastern side. In addition, spatial variations in negative dilatational strain rates indicate diverse crustal shortening and regional uplift across the COR. We suggest that the Cona-Oiga rift plays an important role in accommodating deformation associated with the continuing indentation of the eastern Himalayan syntaxis. Tectonic forcing might be the dominant factor controlling landscape evolution across the COR.