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Northwest China (NWC) is experiencing noticeable climate change accompanied with increasing impacts of climate hazards induced by changes in climate extremes. Towards developing climate adaptation strategies to mitigate the negative climatic impacts on both the ecosystem and socioeconomic system of the region, this study investigates systematically the spatial patterns of climate change and the associated climate hazards across NWC based on high resolution reanalysis climate dataset for the period 1979 to 2018. We find that NWC overall is under a warming and wetting transition in climate with change rate of temperature and precipitation around 0.49 °C/10a and 22.8 mm/10a respectively. Characteristics of climate change over the NWC however vary considerably in space. According to significance of long-term trends in both temperature and aridity index for each 0.1° × 0.1° grids, five types of climate change are identified across NWC, including warm-wetting, warm-drying, warm without wetting, wetting without warming and unchanging. The warm-wetting zone accounts for the largest proportion of the region (41%) and mainly locates in the arid or semi-arid northwestern NWC. Our findings show most region of NWC is under impacts of intensifying heatwave and rainstorm due to significant increases in high temperature extremes and precipitation extremes. The warming but without wetting zone is found under a more severe impact of heatwave, particularly for areas near northern Mount. Qinling and northern Loess Plateau. Areas with stronger wetting trend is suffering more from rainstorm. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) is a region sensitive to global climate change and has been experiencing substantial environmental changes in the past decades. Lake ice phenology (LIP) is a perceptible indicator reflecting changes of lake thermodynamics in response to global warming. Lake ice phenology over the Tibetan Plateau is however rarely observed and recorded. This research presents a dataset containing 39-year (1978–2016) lake ice phenology data of 132 lakes (each with area >40 km2) over the Tibetan Plateau by combining the strengths of both remote sensing (MOD11A2, MOD10A1) and numerical modelling (air2water). Data validation shows that the ice phenology data derived by our method is highly consistent with that based on existing approaches (with R2 > 0.75 for all phenology index and RMSE < 5d). The dataset is valuable to investigate the lake-atmosphere interactions and long-term hydrothermal change of lakes across the Tibetan Plateau. Measurement(s) lake ice phenology Technology Type(s) remote sensing and numerical modeling [ABSTRACT FROM AUTHOR]

Lake surface water temperature (LSWT) is a critical physical property of the aquatic ecosystem and an evident indicator of climate change. By combining the strengths of satellite-based observation and modeling, we have produced an integrated daily LSWT for 160 lakes across the Tibetan Plateau where in situ observation is limited. The MODIS-based lake-wide mean LSWT in the integrated dataset includes the daytime, nighttime, and daily mean for the period 2000–2017. The MODIS-based daily mean LSWT is used to calibrate a simplified physically based model (i.e., modified air2water model), upon which a complete and consistent daily LSWT dataset is reconstructed for the period 1978–2017. The reconstructed LSWT dataset is validated by comparing it with both the satellite-based and in situ observations. The validation shows that the reconstructed LSWT is in good agreement with the observations. According to the reconstructed LSWT dataset, the annual LSWT of lakes in the Tibetan Plateau has increased significantly in the period 1978–2017 with an increase rate ranging from 0.01 to 0.47 ∘ C per 10 years. The warming rate is higher in winter than in summer. The integrated dataset is unique for its relatively large temporospatial span (1978–2017) and high temporal resolution. The dataset together with the methods developed can contribute to research in exploring water and heat balance changes and the consequent ecological effects at the Tibetan Plateau. Data from this study are openly available via the Zenodo portal, with DOI 10.5281/zenodo.6637526 (Guo et al., 2022). [ABSTRACT FROM AUTHOR]

Lake surface water temperature (LSWT) is a critical physical property of the aquatic ecosystem and an evident indicator of climate change. By combining the strengths of satellite-based observation and modelling, we have produced an integrated daily lake surface water temperature for 160 lakes across the Tibetan Plateau where in-situ observation is limited. The satellite-based lake-wide mean LSWT in the integrated dataset includes that for the daytime, night-time and for the daily mean for the period 2000-2017. The dataset is comparable with other satellite-based LSWT products (e.g., LSWT from AVHRR and ARC-Lake) and unique for its tempo-spatial span and resolution. Calibrated and validated against the satellite-based LSWT, complete and consistent daily LSWT dataset have been reconstructed and extended to the period 1978-2017 basing on the modified air2water model. According to the reconstructed LSWT dataset, it is found that annual LSWT of lakes in the Tibetan Plateau has increased significantly in the period 1978-2017 with increase rate ranging at 0.01 to 0.4 °C 10 a−1. The warming trends of the lakes are more evident in winter than in summer. The integrated dataset together with the methods introduced herein can contribute to the research community to explore water and heat balance changes and the consequent ecological effects at the Tibetan Plateau in the future researches. Data from this study are openly available via the Zenodo portal, with DOI https://doi.org/10.5281/zenodo.5111400 (Guo et al., 2021). [ABSTRACT FROM AUTHOR]

Aim: Many studies have found that diazotrophic distribution is mainly determined by soil properties from field to regional scales. However, we lack strong evidence for the relative importance of different drivers controlling broad‐scale biogeography of forest diazotrophs, especially for soil multi‐nutrients. Location: China's forests. Time period: 2012−2013. Major taxa studied: Diazotrophic communities. Methods: We investigated the distribution of soil diazotrophic communities from 146 sites along a 3,900‐km south–north transect by sequencing N‐fixing nifH gene amplicons. The relative contributions of environmental variables were assessed using a combination of stepwise multiple regression, variation partitioning analysis, multiple regression on distance matrices and partial least squares path modelling. Results: Overall, aridity index and temperature were the predominant parameters governing diazotrophic community diversity and structure, mainly through their indirect effects on soil pH, nutrient contents and plant productivity. Although soil multi‐nutrients (Ca, Mg, Fe, Mn, Na, Cu and Zn) were included in the statistical analysis, they still exhibited lower impacts on diazotrophic communities than climate. Intriguingly, the microelement Mo could not explain the diazotrophic community patterns, despite its significance in nitrogenase enzymes. This unexpected phenomenon was attributed to the relatively high Mo supply in our work. Moreover, the distinct responses of diazotroph taxa to climatic factors and large heterogeneity of diazotrophic diversity among forests in different climatic zones further support the dominant role of climatic variation. These results indicate the presence of differentiated climatic niches for diazotrophs, such as warm‐adapted Bradyrhizobium and cool‐adapted Azospirillum. Main conclusions: Our findings suggest for the first time that unlike prior studies, the key roles of soil nutrient limitation (even for Mo) and pH‐dependent mechanisms in small‐scale diazotrophic communities can be surpassed by large‐scale climatic gradients. Future changes in drought severity and temperature might greatly shape diazotrophic distribution and its potential function in forest N2 fixation. [ABSTRACT FROM AUTHOR]

Water storage change of the lakes in the Tibetan Plateau is regarded as one of the most critical regional hydrological consequences owing to climate change. In this study, we investigate the water storage changes in 22 lakes in the Tibetan Plateau based on sequential remote sensed lake area and water level, which are derived from moderate resolution imaging spectroradiometer (MODIS) surface reflectance and Laboratoire D’Etudes en Géophysique et Océanographie Spatiales (LEGOS) altimetry data, respectively. Water storage of the lake is estimated on the basis of the relationship between lake area and water level. The method can be seen as an alternative to the conventional hydrological approaches. The results show that, during 2001–2017, most of the studied lakes in the Tibetan Plateau have shown significant increasing trends in water storage accompanied with larger lake area and higher water level. The changes in lake water storage are found in close relation to variations of climate factors such as precipitation, potential evaporation, and temperature in most lakes. The climate change impacts, however, can be amplified or attenuated by other environmental factors in some lake catchments. [ABSTRACT FROM AUTHOR]

Summary: Nam Co Lake is the highest lake in the central Tibetan Plateau, and existing research on water storage and water level variations are lacking. This paper provides a method for estimating the lake water storage based on historical meteorological records from 1976 to 2009, remote sensing images scattered in this period, in situ bathymetric survey, and GIS techniques, and presents a comprehensive 34-year analysis of intra-annual and inter-annual variations of Nam Co Lake water storage. The multi-year mean water storage of Nam Co Lake is 842.36×108 m3, with the maximum water depth of about 98m. During 1976–2009, the lake water storage increased from 786.06×108 m3 to 870.30×108 m3, with a tendency value of 2.67×108 m3/a; the lake area enlarged from 1927.48km2 to 2015.12km2, with a tendency value of 2.71km2/a. The lake area fluctuations annually, increasing from April of each year until late September and early October, then decreasing until March of the next year. Climate change has a significant impact on the water storage variation of the lake. A general pattern of warming temperature is evident with the regional annual mean air temperature increasing significantly by 0.404°C/10a. Preliminary analysis indicates that the enlarging status of Nam Co Lake water storage is closely related to increasing of precipitation and stream runoff especially coming from the input of glacial meltwater. By combining this data with other research, it can be presented that under the trend of global warming, on Tibetan Plateau, the inland lakes which depend on the rainfall and river supply in the basin are shrinking, while the lakes which depend on glacial meltwater supply are enlarging. Climate change is an important factor promoting the lake variation. [ABSTRACT FROM AUTHOR]

Element geochemistry of lake sediments has been widely used to detect climate change because element composition and ratios can reflect the weathering degree in the source area. Given the element composition of lake sediments from Gulug Co Lake, Hoh Xil, Qinghai-Xizang Plateau, chemical index of alteration (CIA), index of composition variability (ICV) and other element ratios have been used to establish the weathering sequence of this area since 1820 AD. The weathering is so weak that the element composition change is more sensitive to climate change and autochthonous processes. From 1820 to 1984 AD, there were two drier periods with a wetter interval from 1870 to 1945 AD. After 1984 the weather showed a tendency of becoming wet. [ABSTRACT FROM AUTHOR]

Abstract: The lightness (L*) and concentrations of Rb, Sr and organic carbon (C org) have been measured in the age-constrained lake sediment cores recovered from Co Ngoin in the central Tibetan Plateau. Dissolved Sr flux is a dominant control on the variation of Rb/Sr ratios in the sediments. Variations in color and geochemical proxies of Co Ngoin sediments display a continuous history of late glacial to mid-Holocene chemical versus physical weathering intensity in response to past climatic changes between approximately 13,500 and 4500 cal yr B.P. A lower chemical weathering under a late glacial climate was followed by a higher weathering during the Holocene Optimum. Weathering intensity in the central Tibetan Plateau catchment also responds to well-known climatic events, such as the Younger Dryas (YD), and possibly the Holocene Event 5 (HE-5). Although there are differences in time or duration of the climatic events, many of the well-known late glacial to mid-Holocene events occurred in high-elevation Co Ngoin where atmospheric circulation might play a hemispherical role in climatic forcing. The sediment hiatus since c. 4200 14C yr B.P. in the Co Ngoin indicates a period of desiccation that was probably associated with a sharp decrease in summer monsoon strength. Our lascustrine results not only imply catchment weathering variations in response to late glacial to mid-Holocene climatic conditions in the central plateau, but also provide further evidence for global connections between regional climates. [Copyright &y& Elsevier]

Climate warming and concomitant glacier recession in the High Mountain Asia (HMA) have led to widespread development and expansion of glacial lakes, which reserved the freshwater resource, but also may increase risks of glacial lake outburst floods (GLOFs) or debris floods. Using 46 moderate- and high-resolution satellite images, including declassified Keyhole and Landsat missions between 1964 and 2020, we provide a comprehensive area mapping of glaciers and glacial lakes in the Tama Koshi (Rongxer) basin, a highly glacierized China-Nepal transnational catchment in the central Himalayas with high potential risks of glacier-related hazards. Results show that the 329.2 ± 1.9 km2 total area of 271 glaciers in the region has decreased by 26.2 ± 3.2 km2 in the past 56 years. During 2000–2016, remarkable ice mass loss caused the mean glacier surface elevation to decrease with a rate of −0.63 m a−1, and the mean glacier surface velocity slowed by ~25% between 1999 and 2015. The total area of glacial lakes increased by 9.2 ± 0.4 km2 (~180%) from 5.1 ± 0.1 km2 in 1964 to 14.4 ± 0.3 km2 in 2020, while ice-contacted proglacial lakes have a much higher expansion rate (~204%). Large-scale glacial lakes are developed preferentially and experienced rapid expansion on the east side of the basin, suggesting that in addition to climate warming, the glacial geomorphological characters (aspect and slope) are also key controlling factors of the lake growing process. We hypothesize that lake expansion will continue in some cases until critical local topography (i.e., steepening icefall) is reached, but the lake number may not necessarily increase. Further monitoring should be focused on eight rapidly expanding proglacial lakes due to their high potential risks of failure and relatively high lake volumes. [ABSTRACT FROM AUTHOR]

• Bacterial phyla show various distribution patterns with increasing elevation. • Bacterial communities show significant clustering in relation to vegetation. • Soil nutrient and vegetation shape bacterial community along the altitudinal gradient. • Experiment of climate factor manipulation may not predict climate change effects. Alpine zones have a clear climate gradient and are ideal sites for understanding the long-term effects of climate change on ecosystems. As the most sensitive population to environmental changes, the alpine bacterial community is likely to be a microbial indicator of climate change. However, the effects of climate, vegetation and soil factors on the bacterial community are often confounding along an altitudinal gradient. In this work, we utilized alpine zones with similar soil parent material and topography to examine bacterial communities and environmental parameters on Gongga Mountain. We aimed to tease apart the effects of climate, vegetation and soil factors on the bacterial community. The bacterial communities were dominated by Acidobacteria, Proteobacteria, Actinobacteria, Planctomycetes, Bacteroidetes and Chloroflexi, which accounted for 82–92% of all bacterial sequences. Bacterial communities showed different distribution trends with increasing altitude. The bacterial community composition showed significant clustering relative to the vegetation landscape. Our analyses showed that, in terms of direct effects, soil properties played a more important direct role in controlling the distribution pattern of the bacterial community compared with climate and vegetation parameters. A path model based on climate drivers indicated that the climate had the largest effect on the bacterial communities by affecting vegetation and soil properties. This result suggested that the alpine bacterial communities were ultimately shaped by the climate. However, this also suggested that climate change could not alter the bacterial communities if the changes were not great enough to alter vegetation and soil properties. Furthermore, the present study also hints at opportunities and challenges for using microbial changes as indicators of climate change. [ABSTRACT FROM AUTHOR]

• Enzyme activity and stoichiometry were studied along a climate and a vegetation type gradient in subalpine forests. • Climate has little impact on the enzyme activity and stoichiometry. • Vegetation type regulated enzyme activities and stoichiometry by affecting plant-associated microbial communities. Soil extracellular enzymes catalyze the rate limiting steps of organic matter decomposition, and enzyme stoichiometry has been used to reflect microbial resource acquisition strategies. However, the patterns and key driving factors of soil enzyme activities and stoichiometry in subalpine forests, which are areas sensitive to global changes, remain unclear. In this study, rhizosphere and bulk soils along two environmental gradients in the subalpine forests of Gongga Mountain, in the eastern Tibetan Plateau, including (1) a horizontal chronosequence with different vegetation types but a similar climate and (2) a vertical elevation gradient with the same vegetation type but different climates, were sampled during the growing and nongrowing seasons. The activities and stoichiometry of soil enzymes related to the microbial acquisition of carbon (C) (β-1,4-glucosidase, BG), nitrogen (N) (β-1,4-N-acetylglucosaminidase, NAG) and phosphorus (P) (acid phosphomonoesterase, AP) were analyzed to reveal their responses to environmental gradients. The results showed that enzyme activities and stoichiometry varied significantly among vegetation types, but were less affected by climate and root proximity. BG activity and ratios of BG to nutrient-acquiring enzymes were significantly higher in broadleaf forests than in coniferous forests. The differences in enzyme stoichiometry between vegetation types were weakly related to the microbial nutrient status (represented by the ratio of soil to microbial element stoichiometry) but might be explained by the higher proportion of ectomycorrhizal fungi in coniferous forests compared to broadleaf forests. The results of this study indicate that vegetation type was a major factor regulating soil enzyme activities and stoichiometry in the subalpine forests, possibly via its influences on plant-associated microbial communities. [ABSTRACT FROM AUTHOR]

The scientific community has widely reported the impacts of climate change on the Central Himalaya. To qualify and quantify these effects, long-term land surface temperature observations in both the daytime and nighttime, acquired by the Moderate Resolution Imaging Spectroradiometer from 2000 to 2017, were used in this study to investigate the spatiotemporal variations and their changing mechanism. Two periodic parameters, the mean annual surface temperature (MAST) and the annual maximum temperature (MAXT), were derived based on an annual temperature cycle model to reduce the influences from the cloud cover and were used to analyze their trend during the period. The general thermal environment represented by the average MAST indicated a significant spatial distribution pattern along with the elevation gradient. Behind the clear differences in the daytime and nighttime temperatures at different physiographical regions, the trend test conducted with the Mann-Kendall (MK) method showed that most of the areas with significant changes showed an increasing trend, and the nighttime temperatures exhibited a more significant increasing trend than the daytime temperatures, for both the MAST and MAXT, according to the changing areas. The nighttime changing areas were more widely distributed (more than 28%) than the daytime changing areas (around 10%). The average change rates of the MAST and MAXT in the daytime are 0.102 °C/yr and 0.190 °C/yr, and they are generally faster than those in the nighttime (0.048 °C/yr and 0.091 °C/yr, respectively). The driving force analysis suggested that urban expansion, shifts in the courses of lowland rivers, and the retreat of both the snow and glacier cover presented strong effects on the local thermal environment, in addition to the climatic warming effect. Moreover, the strong topographic gradient greatly influenced the change rate and evidenced a significant elevation-dependent warming effect, especially for the nighttime LST. Generally, this study suggested that the nighttime temperature was more sensitive to climate change than the daytime temperature, and this general warming trend clearly observed in the central Himalayan region could have important influences on local geophysical, hydrological, and ecological processes. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) is a region sensitive to global climate change, and could trigger climate variation worldwide. Numerous lakes in the TP play important roles in the climate system. And the formation and ablation of lake ice is one of the unique properties of lakes in the TP highly related to temperature variation. Thus lake ice phenology are considered as a sensitive indicator of global warming. And it also have substantial ecological impacts. In the Tibetan Plateau, remote sensing has been used as an effective tool to detect the changes of lake ice phenology, as there is limited ground observation of lake ice phenology. Because of the difference of both the sources of remote sensing and the current available algorithms, differences exist in identifying lake ice phenology. In this study, four results of lake ice phenology based on different sources of remote sensed data (MODIS reflectance data, snow product, land surface temperature data, and microwave data) are used to identify the lake ice phenology of 18 lakes in the Tibetan Plateau for the period 2002–2015. Compared the results of the four methods, it can be seen that the highest consistency is occurred in the monitoring of the completely ice-covering duration (CID), and the lake ice duration in Tibetan Plateau becomes longer from the south to the north. And we also analyzed the main climatic-environmental elements affecting the lake ice phenology. The results show that the factors, especially the temperature, play a greater role in the freezing and thawing process of the lake. The inter-annual variation trend of lake ice period of northeastern part was delayed. In the middle and northern of the plateau, the lake ice period is mainly extended. [ABSTRACT FROM AUTHOR]

In the Tibetan Plateau (TP), the changes of lake ice phenology not only reflect regional climate change, but also impose substantial ecohydrological impacts on the local environment. Due to the limitation of ground observation, remote sensing has been used as an alternative tool to investigate recent changes of lake ice phenology. However, uncertainties exist in the remotely sensed lake ice phenology owing to both the data and methods used. In this paper, three different remotely sensed datasets are used to investigate the lake ice phenology variation in the past decade across the Tibetan Plateau, with the consideration of the underlying uncertainties. The remotely sensed data used include reflectance data, snow product, and land surface temperature (LST) data of moderate resolution imaging spectroradiometer (MODIS). The uncertainties of the three methods based on the corresponding data are assessed using the triple collocation approach. Comparatively, it is found that the method based on reflectance data outperforms the other two methods. The three methods are more consistent in determining the thawing dates rather than the freezing dates of lake ice. It is consistently shown by the three methods that the ice-covering duration in the northern part of the TP lasts longer than that in the south. Though there is no general trend of lake ice phenology across the TP for the period of 2000–2015, the warmer climate and stronger wind have led to the earlier break-up of lake ice. [ABSTRACT FROM AUTHOR]

Lakes and vegetation are important factors of the Earth's hydrological cycle and can be called an “indicator” of climate change. In this study, long-term changes of lakes' area and vegetation coverage in the Qinghai-Tibetan Plateau (QTP) and their relations to the climate change were analyzed by using Mann-Kendall method during the past 30 years. Results showed that: 1) the lakes' area of the QTP increased significantly during the past 30 years as a whole, and the increasing rates have been dramatically sped up since the year of 2000. Among them, the area of Ayakekumu Lake has the fastest growing rate of 51.35%, which increased from 618 km 2 in the 1980s to 983 km 2 in the 2010s; 2) overall, the Normalized Difference Vegetation Index (NDVI) increased in the QTP during the past 30 years. Above 79% of the area in the QTP showed increasing trend of NDVI before the year of 2000; 3) the air temperature increased significantly, the precipitation increased slightly, and the pan evaporation decreased significantly during the past 30 years. The lake area and vegetation coverage changes might be related to the climate change. The shifts in the temporal climate trend occurred around the year 2000 had led the lake area and vegetation coverage increasing. This study is of importance in further understanding the environmental changes under global warming over the QTP. [ABSTRACT FROM AUTHOR]

Carbon sequestration by terrestrial ecosystems can offset emissions and thereby offers an alternative way of achieving the target of reducing the concentration of CO 2 in the atmosphere. Net primary production (NPP) is the first step in the sequestration of carbon by terrestrial ecosystems. This study quantifies moderate-resolution imaging spectroradiometer (MODIS) NPP from 2000 to 2014 at the country level along with its response to drought and land cover change. Our results indicate that the combined NPP for 53 countries represents > 90% of global NPP. From 2000 to 2014, 29 of these 53 countries had increasing NPP trends, most notably the Central African Republic (23 g C/m 2 /y). The top three and top 12 countries accounted for 30% and 60% of total global NPP, respectively, whereas the mean national NPP per unit area in the countries with the 12 lowest values was only around ~ 300 g C/m 2 /y - the exception to this was Brazil, which had an NPP of 850 g C/m 2 /y. Large areas of Russia, Argentina, Peru and several countries in southeast Asia showed a marked decrease in NPP (~ 15 g C/m 2 /y). About 37% of the NPP decrease was caused by drought while ~ 55% of NPP variability was attributed to changes in water availability. Land cover change explained about 20% of the NPP variability. Our findings support the idea that government policies should aim primarily to improve water management in drought-afflicted countries; land use/land cover change policy could also be used as an alternative method of increasing NPP. [ABSTRACT FROM AUTHOR]