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Lakes can be effective indicators of climate change, and this is especially so for the lakes over the Qinghai-Tibet Plateau (QTP), the highest plateau in the world, which undergo little direct human influence. The QTP has warmed at twice as the mean global rate, and the lakes there respond rapidly to climate and cryosphere changes. The QTP has ~1200 lakes larger than 1 km² with a total area of ~46000 km², accounting for approximately half the number and area of lakes in China. The lakes over the QTP have been selected as an essential example for global lakes or water bodies studies. However, concerning lake data over the QTP are limited to the Landsat era and/or available at sparse intervals. Here, we extend the record to provide the comprehensive lake evolution data sets covering the past 100 years (from 1920 to 2020). Lake mapping in 1920 was derived from an early map of the Republic of China, and in 1960 from the topographic map of China. The densest lake inventories produced so far between 1970 and 2020 (covering all lakes larger than 1 km² in 14 epochs) are mapped from Landsat MSS, TM, ETM+ and OLI images. The lake evolution shows remarkable transitions between four phases: significant shrinkage in 1920-1995, rapid linear increase in 1995-2010, relative stability in 2010-2015, and further increase in 2015-2020. The spatial pattern indicates that the majority of lakes shrank in 1920-1995, and expanded in 1995-2020, with a dominant enlargement for central-north lakes in contrast to contraction for southern lakes in 1976-2020. The time series of precipitation between 1920 and 2017 indirectly supports the evolution trends of lakes identified in this study. The lake data set is freely available at http://doi.org/10.5281/zenodo.4678104 (Zhang et al., 2021). [ABSTRACT FROM AUTHOR]

Monitoring of the thermal state of permafrost is important in environmental science and engineering applications. However, such data are generally unavailable mainly due to the lack of ground observations and the uncertainty of traditional physical models. This study produces novel permafrost datasets for the Northern Hemisphere (NH), including predictions of the mean annual ground temperature (MAGT) at the zero annual amplitude depth and active layer thickness (ALT) with a 1- km resolution for the period of 2000–2016, as well as estimates of the probability of permafrost occurrence and permafrost zonation based on hydrothermal conditions. These datasets integrate unprecedentedly large amounts of field data (1,002 boreholes for MAGT and 452 sites for ALT) and multisource geospatial data, especially remote sensing data, using statistical learning modelling with an ensemble strategy. Thus, these data are more accurate than those of previous circumpolar maps (bias=0.02±0.16 °C, RMSE=1.32±0.13 °C for MAGT; bias=2.71±16.46 cm, RMSE=86.93±19.61 cm for ALT). The datasets suggest that the areal extent of permafrost (MAGT≤0 °C) in the NH, excluding glaciers and lakes, is approximately 15.03 (13.84–19.29) ×106 km², and the areal extent of permafrost regions (permafrost probability>0) is approximately 20.14×106 km². The areal fractions of humid, semiarid/subhumid, and arid permafrost regions are 51.84%, 44.83%, and 3.33%, respectively. The areal fractions of cold (≤-3.0 °C), cool (-3.0 °C to -1.5 °C), and warm (>-1.5 °C) permafrost regions are 37.93%, 14.35%, and 47.72%, respectively. These new datasets based on the most comprehensive field data to date contribute to an updated understanding of the thermal state and zonation of permafrost in the NH. They are potentially useful for various fields, such as in climatology, hydrology, ecology, agriculture, public health, and engineering planning. As a baseline, these datasets are also of great importance for evaluating future changes in MAGT, ALT, permafrost extent, and other spatial features of permafrost in the NH. All of the datasets are published through the National Tibetan Plateau Data Center (TPDC), and the link is https://data.tpdc.ac.cn/en/data/5093d9ff-a5fc-4f10-a53f-c01e7b781368 or https://doi.org/10.11888/Geocry.tpdc.271190 (Ran et al., 2021b). [ABSTRACT FROM AUTHOR]

The soil freeze-thaw cycle in the permafrost regions has a significant impact on regional surface energy and water balance. Although increasing efforts have been made to understand the responses of spring thawing to climate change, the mechanisms controlling the global interannual variability of the start date of permafrost frozen (SOF) remain unclear. Using long-term SOF from the combinations of multiple satellite microwave sensors between 1979 and 2020, and analytical techniques, including partial correlation, ridge regression, path analysis, and machine learning, we explored the responses of SOF to multiple climate change factors, including warming (surface and air temperature), start date of permafrost thawing (SOT), soil properties (soil temperature and volume of water), and the snow depth water equivalent (SDWE). Overall, climate warming exhibited the maximum control on SOF, but SOT in spring was also an important driver of SOF variability; among the 65.9% significant SOT and SOF correlations, 79.3% were positive, indicating an overall earlier thawing would contribute to an earlier frozen in winter. The machine learning analysis also suggested that apart from warming, SOT ranked as the second most important determinant of SOF. Therefore, we identified the mechanism responsible for the SOT-SOF relationship using the SEM analysis, which revealed that soil temperature change exhibited the maximum effect on this relationship, irrespective of the permafrost type. Finally, we analyzed the temporal changes in these responses using the moving window approach and found increased effect of soil warming on SOF. In conclusion, these results provide important insights into understanding and predicting SOF variations with future climate change. [ABSTRACT FROM AUTHOR]

Lakes in the permafrost zone have been proposed to serve as key outlets for methane and carbon dioxide emissions. However, there has been no geological record of the hydrological and biogeochemical responses of lakes throughout the thawing of surrounding permafrost. We use multiple biomarker and isotopic proxies to reconstruct hydrological and biogeochemical changes in Lake Wudalianchi in northeastern China during regional thawing of the permafrost. We show permafrost thawing, as indicated by lignin degradation, initiated rapid lake water freshening as a result of the opening of groundwater conduits, and negative organic δ13C excursion due to increased inorganic and organic carbon fluxes. These hydrological changes were followed, with an ∼5-7 yr delay, by abrupt and persistent increases in microbial lake methanotrophy and methanogenesis, indicating enhanced anaerobic organic decomposition and methane emissions from lakes as permafrost thaws. Our data provide a detailed assessment of the processes involved during permafrost thaw, and highlight the importance of lakes in ventilating greenhouse gases to the atmosphere. [ABSTRACT FROM AUTHOR]

The Shule River Basin is an ecologically fragile area in arid zone. To understand the state of land eco-security, the Environment-Economic-Society model was applied to build a land eco-security evaluation index system in the Shule River Basin. An entropy-weighted and matter-element model was built for eco-security evaluation from 2005 to 2014. Principal component analysis was used to quantitatively study the limiting factors of land ecological security. The result showed: the direction of development of the state of land eco-security in the Shule River Basin from 2005 to 2014 was characterized by “unsafe (No4) → safe (No1),” and presented an upward trend. The land eco-security status during 2005–2007 was in the “Unsafe” state and the state changed to “Critical Safe” in 2008–2009, “Safer” in 2010–2011, but “Safe” in 2012–2014. The key factors that affected land eco-security in the Shule River Basin were Per Capita Arable Land, Forest Cover Rate, Per Capita Water Resources, Water Production Modulus, the Tertiary Industry Output Value, and GDP Ratio and Water Consumption. Among them, Forest Cover Rate and Water Production Modulus had the greatest impact, with principal component loads of up to 0.973 and 0.968, respectively. The result of this study is expected to serve as reference and support for the conservation and management of Shule River Basin to ensure sustainable development. [ABSTRACT FROM AUTHOR]

A major research plan entitled "Integrated research on the eco-hydrological process of the Heihe River Basin" was launched by the National Natural Science Foundation of China in 2010. One of the key aims of this research plan is to establish a research platform that integrates observation, data management, and model simulation to foster twenty-first-century watershed science in China. Based on the diverse needs of inter-disciplinary studies within this research plan, a program called the Heihe Watershed Allied Telemetry Experimental Research (HiWATER) was implemented. The overall objective of HiWATER is to improve the observability of hydrological and ecological processes, to build a world-class watershed observing system, and to enhance the applicability of remote sensing in integrated eco-hydrological studies and water resource management at the basin scale. This paper introduces the background, scientific objectives, and experimental design of HiWATER. The instrumental setting and airborne mission plans are also outlined. The highlights are the use of a flux observing matrix and an eco-hydrological wireless sensor network to capture multiscale heterogeneities and to address complex problems, such as heterogeneity, scaling, uncertainty, and closing water cycle at the watershed scale. HiWATER was formally initialized in May 2012 and will last four years until 2015. Data will be made available to the scientific community via the Environmental and Ecological Science Data Center for West China. International scientists are welcome to participate in the field campaign and use the data in their analyses. [ABSTRACT FROM AUTHOR]