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Both the regional earthquake surface wave and seismic ambient noise provide important constraints on the Earth's structure, and yet no study satisfactorily combined them for the best imaging of subsurface seismic structure. In this study, we address this issue by developing a new method to simultaneously determine surface wave phase velocity and earthquake centroid parameters in three steps: (a) preliminary phase velocity inversion based on seismic ambient noise, (b) preliminary earthquake relocation based on earthquake surface wave data, and (c) simultaneous inversion for phase velocity and earthquake centroid parameters with constraints of interstation phase velocity measurements based on seismic ambient noise and event‐station phase velocity measurements based on earthquake surface wave data. Application of the method in the North South Seismic Belt region in China results in high‐resolution Rayleigh wave phase velocity maps and accurate earthquake centroid parameters. The additional earthquake data notably improve resolution of the inverted phase velocity model in west Yunnan and central Tibetan blocks, the regions with sparse seismic station coverage. The inverted phase velocity model exhibits high‐velocity anomalies in cratonic regions and the Emeishan Large Igneous Province, and low‐velocity anomalies in the interior and surrounding regions of the Tibetan Plateau. Relocation places earthquakes in shallow depths with geotherm above the crustal rock's brittle‐ductile transition temperature of ∼400℃ $\sim 400\textdegree$, revealing thermal control on thickness of the seismogenic zone. With earthquake centroid parameters constrained, earthquake data are expected to provide further constraints on the deep seismic structure that is beyond the sampling limit of seismic ambient noise. Plain Language Summary: High‐resolution seismic image of the Earth's interior provides significant physical and structural information inside the Earth. Whereas both the regional earthquake data and seismic ambient noise provide constraints on the seismic imaging, no study yet satisfactorily combined these two types of data for the best results. In this paper, we develop a new method to combine both types of seismic data to better image seismic structure and apply the new method in the North South Seismic Belt region in China. The method consists of three steps to simultaneously determine seismic structure and earthquake source parameters. The resultant seismic images exhibit noted improvement in revealing high‐resolution seismic structure in regions with sparse seismic station coverage, such as the Tibetan Plateau and its adjacent regions. The redetermined earthquake depths reveal thermal control on the maximal depth of earthquake occurrence in the region, with earthquakes occurring at the shallow depths colder than rock's brittle‐ductile transition temperature of ∼400℃ $\sim 400\textdegree$. Key Points: A new method is developed to simultaneously determine surface wave phase velocity and earthquake centroid parametersApplication of the method in the North South Seismic Belt region in China yields high resolution phase velocity maps and event parametersAdditional earthquake data significantly improve the resolution and accuracy of surface wave phase velocity model [ABSTRACT FROM AUTHOR]

In this study, the spatiotemporal changes and driving factors of evapotranspiration (ET) over the Tibetan Plateau (TP) are assessed from 1961 to 2014, based on a revised generalized nonlinear complementary (nonlinear-CR) model. The average annual ET on the TP was 328 mm. The highest ET value (711 mm) was found in the forest region in the southeastern part of the TP, and the lowest value (151 mm) was found in the desert region in the northwestern part of the TP. In terms of the contribution of different subregions to the total amount of ET for the whole plateau, the meadow and steppe regions contributed the most to the total amount of ET of TP, accounting for 30% and 18.5%, respectively. The interannual ET presented a significant increasing trend with a value of 0.26 mm yr−1 from 1961 to 2014, and a significant positive ET trend was found over 35% of the region, mainly in the southeastern part of the plateau. The increasing trend of ET in swamp areas was the largest, while that in the desert areas was the smallest. In terms of the seasonality, the ET over the plateau and different land-cover regions increased the most in summer, followed by spring, while the change in ET in winter was not obvious. The energy factors dominated the long-term change in the annual ET over the plateau. In addition, the available energy is the controlling factor for ET changes in humid areas such as forests and shrublands. Energy and water factors together dominate the ET changes in arid areas. [ABSTRACT FROM AUTHOR]

In this study, the spatiotemporal changes in net primary production (NPP) and drivers, including climate change, atmospheric CO2 concentration and land use change, over the Tibetan Plateau from 1979 to 2016 were investigated using the version 4.5 of the Community Land Model. Based on high-resolution atmospheric forcing data, six numerical experiments were designed to assess the relative contribution of different environmental factors on NPP. Our simulation results suggest that NPP over the Tibetan Plateau has increased significantly at a rate of 2.25 TgC/year² since 1979. At the plateau scale, changes in precipitation, CO2 concentration, and land use change contributed approximately 63.3%, 16.7%, and 9.5% to the interannual variation ofNPP, respectively. Temperature did not exert a significant effect on the trends ofNPP,which results from the increasing temperature enhancing the autotrophic respiration (AR) more than the gross primary production.We also divided the alpine grasslands into four types, including alpine meadow of permafrost, alpine steppe of permafrost, alpinemeadow of seasonal frost, and alpine steppe of seasonal frost. Wefound that the increasing rate of NPP in permafrost regions was significantly higher than that in seasonal frost regions. Compared with other factors, precipitation change played a dominant role in the NPP over the four different types of grasslands. Temperature-induced change on NPP and AR was larger in the alpine meadow regions compared to in the alpine steppe regions. In addition, NPP and AR showed a more remarkable response to temperature change over alpine meadow of permafrost than other regions. [ABSTRACT FROM AUTHOR]

The Lhasa River, one of the tributaries of the Yarlung Zangbo River on the Tibetan Plateau, provides water for the vast majority of residents in Tibet. The main purpose of this study is to identify regional environmental risk factors that may be affecting the Lhasa River basin. The minimum cumulative resistance (MCR) model was used to determine the "source-sink" risk pattern of the Lhasa River by identifying the sources of metal ions and trace elements in the basin. The results show that loss of soil ions, climate conditions and environmental factors contribute to the hydrochemical characteristics of the Lhasa River basin. The distribution of soil type greatly overlaps with the likelihood of soil ions loss. The low-risk and high-risk zones mainly consist of calcic soils and litho soils, respectively. In terms of the climate and environmental risk factors, rainfall erosivity poses the greatest risk during the low-flow season, vegetation coverage during the high-flow season, and freeze-thaw erosivity during the normal-flow season. High-risk sources and low-risk sources were identified by the MCR model. The high-risk sources were the vegetated and unused lands, which are vulnerable to weathering of Ca and Mg rich sedimentary and mixed rocks, while low-risk sources were the urban, construction, industrial and mining areas and forest land. This study can contribute to the development of policies for the sustainable management of water resources and the protection of the water environment in the Lhasa River Basin. • Source analysis of main ions and trace elements was performed by Pearson correlation analysis and PCA. • Resistance surface was constructed by the MCR model to identify the regional environmental risk factors. • Source-sink risk characteristics were analyzed by combining the hydrochemical factor source and spatial source. • High-risk sources were the weathering effects caused by Ca, Mg and their sedimentary and mixed rocks. • Low-risk sources were human activities such as urban construction, industrial activities and mining. [ABSTRACT FROM AUTHOR]

To address pasture degradation on the Tibetan Plateau, the Chinese government has launched the ecological restoration project Grazing Withdrawal Program (GWP) since 2004. However, few studies have evaluated the impact of the GWP on grassland recovery. Based on monthly remote-sensed vegetation index and meteorological data from 2000 to 2012, we assessed the dynamics of annual net primary productivity (NPP) in alpine grasslands and quantified the effects of climatic factors and anthropogenic activities on NPP change by using the climate-driven NPP and the Carnegie-Ames-Stanford Approach (CASA) models. We found that there existed two distinct periods with an accelerating trend in NPP increase before and after 2004. The area percentage of NPP change induced by climatic factors increased from 41.55% to 83.75%, but that percentage caused by human activities decreased from 58.45% to 16.25% in the two periods of 2000–2004 and 2004–2012. Between 2000 and 2004, overgrazing reduced the positive effect of climate change on NPP variability, resulting in wide-scale grassland degradation. Between 2004 and 2012, grassland ecosystems gradually recovered from heavy grazing pressure, and the human-induced degradation was reversed after the implementation of the GWP. Thus, temperature and solar radiation became dominant factors in driving NPP change. Our results indicated that the GWP produces a significant positive effect on the restoration of alpine grasslands by controlling livestock numbers and decreasing grazing intensity. This study provides an objective assessment of restoration actuation on grassland ecosystems, having important implications for demonstrating the effectiveness of the GWP on grassland restoration on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]