Significant changes and driving mechanism of Bosten Lake in Xinjiang, China

As nodes in the interaction of land surface systems such as the atmosphere, biosphere, lithosphere, hydrosphere, and terrestrial hydrosphere, lakes are extremely sensitive to global climate change, especially inland lakes in arid areas, which are indicators of climate change and environmental variability in the basin (Zheng 2017). Freshwater lakes in arid regions are important freshwater resources in their location and have regional economic, ecological, and environmental functions. The region's large freshwater lakes are generally recharged by precipitation and alpine snow and ice melt, making it one of the most sensitive geographic units in terms of response to climate fluctuations (Kaplan & Avdan 2017; Rodell et al. 2018; Zhang et al. 2019). Both too-low and too-high water levels in lakes can have adverse impacts (Yao et al. 2018), in which too low a drop in water level will lead to shrinking wetland areas, degradation of vegetation, and reduction of biodiversity. While too high a water level and expansion of water surface area will exacerbate soil salinization and agricultural losses, increasing food risks, and exceeding a certain ecological water level, will also produce a series of flood disasters, causing certain socio-economic losses (Wan et al. 2006; Bai et al. 2011; Guo et al. 2015). Located in the northeastern Tarim Basin, Bosten Lake is a typical arid zone lake in Xinjiang. As the largest inland freshwater lake in China, it is an important water resource in the basin, and for the arid climate zone with low precipitation, the lake plays a role in supporting the ecosystem of the region (Yang 2020). Although Bosten Lake plays a critical role in regional water resource management, the extent to which climate change and human activities have contributed to its hydrological variations over the past two decades remains unclear. This study aims to address these gaps by providing comprehensive, long-term monitoring of Bosten Lake's water dynamics.

The study of the lake watershed area is the basis of the lake hydrology research (Schultz & Engman 2000). The development of satellite remote sensing technology provides strong support for real-time dynamic monitoring of lake changes, especially the application of high-resolution remote sensing satellites that provide effective data for the study of changes in lake areas. Landsat, with its advantages of long time-series observation, relatively high accuracy, and convenient download, has become a widely used remote sensing data source for scientific research. Landsat is of great significance for monitoring the continuous change of the lake area, which can be used to reflect the rise and fall of lakes within a short period and the trend of multi-year changes (Sokolov et al. 2022). Traditional monitoring of lake water levels relies on field measurements at hydrological stations, which requires a large amount of human and material inputs despite its high accuracy. Due to the limitations of natural conditions and spatial distribution, it is difficult to obtain long-term continuous observation data for remote inland lakes. Moreover, traditional water level monitoring has a low sharing degree, which further increases the difficulty of data collection (He et al. 2020). In contrast, satellite radar altimetry has a wide monitoring range and the ability to make periodic observations to capture multiple dynamic changes in terrestrial water bodies (Sun et al. 2022). The results of several studies have demonstrated the excellence of satellite altimetry in effectively monitoring the dynamics of lake water levels (Crétaux et al. 2005; Cooley et al. 2021). Radar altimetry satellites (e.g., TOPEX/Poseidon, Jason-1, Jason-2, Jason-3) have the characteristics of real-time and all-weather (Birkett 1995), especially for rivers and lakes distributed in high mountains, plateaus, or remote areas lacking surface hydrological observation stations; real-time monitoring of water level changes can greatly make up for the shortage of water level observation data in these lakes (Zhang et al. 2014). At the same time, time-series water level databases of large lakes, reservoirs, and rivers around the world based on these satellite altimeter data have been established, such as Hydroweb (Crétaux et al. 2011), DAHITI (Schwatke et al. 2015), and G-REALM (Birkett et al. 2011). The establishment of a lake water level database will help to continue many aspects of lake research, such as the use of algorithms to explore the far-reaching impact of lake water level fluctuations on key water quality parameters (Li et al. 2019). Current studies on the changes in water levels and surface areas of inland lakes often rely on existing global lake datasets or single-sensor, low-resolution remote sensing data (Chen et al. 2020). While these data sources are useful for large-scale analyses, they fall short in providing the precision needed for finer-scale monitoring, particularly for long-term assessments of specific lakes of interest. Accurate monitoring of water volume changes in individual lakes remains relatively scarce. To address this limitation, newer, higher-resolution satellite altimetry datasets offer promising opportunities for more detailed lake studies. Among these, Jason-series satellite data stand out due to their higher spatial resolution, improved accuracy, and the advantage of long-term continuity compared to most previous altimetry missions. The higher resolution and continuity of Jason's data offer significant advantages for precise, long-term hydrological monitoring at local scales (Peng et al. 2024; Ross et al. 2024).

Earlier altimetry data, with limited spatial and temporal resolution, have constrained the systematic study of small lake dynamics (Yapiyev et al. 2019). The precision of these studies often fails to meet the accuracy required for water resource analysis in arid regions, particularly for lakes like Bosten Lake, which exhibit significant spatiotemporal variability. Additionally, many existing studies primarily focus on singular aspects such as water level or surface area, without integrating a comprehensive analysis of water level, surface area, and volume. This lack of a holistic approach restricts our understanding of the substantial changes in Bosten Lake and their implications for future development (Li et al. 2021; Peng et al. 2021). Although some recent efforts have combined multi-source remote sensing data for long-term lake analysis (Fu et al. 2024), a more integrated use of diverse remote sensing datasets is urgently needed to improve our understanding of inland lake dynamics, particularly in arid regions. To address these gaps, this study focuses on nearly two decades of detailed monitoring of Bosten Lake. This study integrates Jason-1/2/3 altimetry data with Landsat imagery to establish a framework for long-term monitoring of water dynamics. This methodology not only compensates for the limitations of previous large-scale monitoring studies, which often lacked sufficient data for small lakes and were constrained by the availability of long-term time series, but also provides valuable insights for monitoring similar lakes globally. Furthermore, the climate in the Xinjiang region has experienced significant shifts since the 20th century, transitioning from warm-dry to warm-wet conditions. This climatic change has had a pronounced impact on the runoff patterns of major tributaries feeding Bosten Lake, such as the Kaidu and Peacock Rivers, further destabilizing the lake's water resources. Bosten Lake plays a pivotal role in sustaining the region's economic development and ecological balance, as fluctuations in its water resources and the efficiency of their use have become key indicators of sustainable development in the region. The changes in Bosten Lake's water levels and resources have become a focal point in climate and environmental research, making in-depth monitoring crucial for understanding the behavior of freshwater lakes in arid regions and their role in regional water systems under the influence of global warming. Given the continuous availability of remote sensing and altimetry data, this research focuses on a comprehensive analysis of the water level, area, and volume variations in Bosten Lake over the two-decade period from 2002 to 2022. In addition, it explores the relative contributions of climate factors (e.g., precipitation and evaporation) and human activities (e.g., water resource management and industrial production) to these changes. This research offers valuable insights for future management strategies in the Bosten Lake basin and serves as a reference for studies of similar freshwater lakes in arid regions around the world.

Since 1972, the Landsat series of Earth observation missions, co-sponsored by the National Aeronautics and Space Administration (NASA) and the US Geological Survey, has successfully launched seven satellites, of which Landsat 1–5 have been retired, Landsat 6 has not been successfully orbited, and the satellites that are still able to provide images are Landsat-7. Currently, the satellites that can still provide images are Landsat-7, Landsat-8, and Landsat-9 (Cohen & Goward 2004; Wulder et al. 2012). The Landsat data have a resolution of 30 m and a revisit period of 16 days, which provides a dense time-series image that is sufficient to reflect the short-term upward and downward movement of the lake within a year and the multi-year trend. The multi-source and multi-temporal Landsat remote sensing data can be used to identify the extent of the lake and extract the area after geometric correction, geographic alignment, radiometric correction, and atmospheric correction. Specifically, surface reflectance data from Landsat-5 TM covering the period from 2002 to 2011, Landsat-7 ETM+ for 2012, and Landsat-8 OLI for 2013 to 2022 were utilized. The imagery was obtained through the Google Earth Engine (GEE) platform, which provides convenient access to pre-processed Landsat data. The data were analyzed to extract the lake area and assess the trend in lake surface change over time.

In this study, time series water level data for Bosten Lake were obtained from several well-established global databases, including DAHITI (available: https://da-hiti.dgfi.tum.de/en/), Hydroweb (available: https://hydroweb.next.theialand.fr/), and G-REALM (available: https://ipad.fas.usda.gov/cropexplorer/global_reserve-oir/#datasets). The Inland Waters Hydrographic Time Series Database (DAHITI), developed by the German Institute of Technology (DGFI-TUM) in 2013, provides a time series of water levels in lakes, reservoirs, rivers, and wetlands measured by multi-mission satellite altimeters for hydrological applications. The Hydroweb database was developed by the Space Laboratory of Geophysics and Oceanography. To estimate the time series of lake and river water levels, a multi-mission approach using satellite altimeter data from TOPEX/Poseidon, ERS-1, ERS-2, ENVISAT, Jason-1/2/3, SARAL, and GFO was used. The Global Reservoir and Lake Monitor (G-REALM) is jointly maintained by the US Department of Agriculture's Foreign Agricultural Service (USDA/FAS) and NASA. The water level time series of lakes and reservoirs is estimated by using a single altimeter task on the target under study. The product consists of combining data from different continuous altimeter missions monitored on the same target, updated weekly, with no simultaneous altimetry for the same target during the same period. These global water level databases regularly track water level changes in large lakes and reservoirs worldwide. In this study, data from these databases were used to assess the accuracy of lake levels derived from Jason series satellite altimeter data.

Meteorological data were obtained from the Resources and Environment Science and Data Center of the Chinese Academy of Sciences (available: https://www.resdc.cn/DOI/). These data, subjected to stringent quality control procedures, are suitable for supporting climate change research. Two conventional meteorological stations, Heshuo (42°15′N, 86°48′E, 1,085.4 m a.s.l) and Yanqi (42°4′N, 86°34′E, 1,055.3 m a.s.l), both located in the plains near Bosten Lake, were selected for this study. Monthly data from these stations covering the period from 2002 to 2022 were used. The meteorological variables include monthly mean air temperature, monthly mean precipitation, and monthly evaporation, which serve as essential supporting data to analyze the climatic conditions in the lake basin and to assess the response of lake level and area to climate change. In addition, glacier distribution data were derived from two key sources: the ‘GAMDAM Glacier Inventory for High Mountain Asia: Central Asia’ dataset and the second Glacier Inventory of China (available: http://www.ncdc.ac.cn) (Liu et al. 2012; Sakai 2019). These datasets provided glacier data for the Bosten Lake basin in 2000 and 2010, respectively. Furthermore, based on Landsat OLI remote sensing images from 2020, a band synthesis approach was applied to enhance the visualization of glacier surface features. Glacier distribution data were extracted using the maximum likelihood method for supervised classification, combined with visual interpretation, to improve accuracy in mapping glacier distribution in the Bosten Lake basin.

With millions of servers around the world and powerful cloud computing and storage capabilities, the GEE platform currently calls on a vast amount of Earth observation data and provides scientific research with an inherently parallel approach to processing massive amounts of imagery (Dong et al. 2016; Tan et al. 2019). Based on the GEE platform, this paper calls Landsat-5/7/8 images from 2002 to 2022 through JavaScript language. To ensure image quality, Landsat-5/7/8 images with less than 10% of the total cloud cover and clearly visible in the study area were used. In the GEE platform, the cloud removal process is carried out on the called image data to retain clear surface reflectivity. The water body index NDWI was added, and the water body was screened and extracted according to the set threshold value. The area of the water body is calculated using the extracted water body range, the minimum area threshold is set to 100 m², and the small area of the water body is removed. The area data of Bosten Lake were visualized and exported. The Landsat images of Bosten Lake with a few clouds during the abundant water period of September 2002–2022 were selected for visual interpretation to calculate the area of water bodies and verify the processing results of the GEE platform.

Figure S2 shows the relationship between the level and area of Bosten Lake, indicating a high correlation (R² = 0.8472). In this paper, the observed lake level and area values of the same period were used to calculate the changes in water quantity of Bosten Lake in different observation periods from 2002 to 2022 according to the water balance formula (Figure S3). The water quantity of the lake fluctuates greatly and changes frequently. Table 2 shows that the water volume of Bosten Lake will decrease by 2.715 km³ during 2002–2022. From 2002 to 2013, the lake water volume decreased significantly, and the total water volume decreased by 3.993 km³. From 2013 to 2020, the amount of lake water increased by 2.473 km³. In 2020–2022, the lake shrank again, and the water volume decreased by 1.175 km³, showing a downward trend. In conclusion, the variation in lake water volume is consistent with the variation trend of lake level and area.

The decreasing precipitation at the Heshuo meteorological station and the continuously rising air temperatures at both stations are closely related to the overall decreasing trend in the lake level and area. In 2016, for instance, while precipitation sharply increased, the lake also expanded. In the three stages of lake change, from 2002 to 2013, the data from the Yanqi and Heshuo meteorological stations showed an increase in evaporation (18.029 and 9.367 mm/a), while precipitation exhibited a decreasing trend (−3.061, and −4.121 mm/a), leading to a shrinking trend in the lake during this period. From 2013 to 2020, the evaporation at the Yanqi meteorological station showed a rapid decrease (−32.036 mm/a), while precipitation continued to increase, resulting in an expanding trend for the lake. After 2020, there was a slight increase in evaporation and a decrease in precipitation, leading to another period of lake shrinking. Regarding seasonal changes in the lake, the water volume of the lake rapidly increases from March onwards due to warming air temperatures and the supply of meltwater from ice and snow. Precipitation increases rapidly from March to May, followed by a rapid increase in the lake level and area. Despite sufficient water supply to the lake, the summer, being the period of strongest evaporation, results in relatively low lake levels and areas. This indicates a close relationship between climate factors and the expansion and contraction of the lake.

According to grey system theory, the correlation between temperature, precipitation, and evaporation from the Heshuo and Yanqi meteorological stations and the level and area changes of Bosten Lake is determined by Equations (5) and (6). As shown in Table 3(a), the annual evaporation from the Heshuo meteorological station exhibits the highest correlation with the annual average lake area (0.83). Additionally, Table 3(b) demonstrates that the evaporation from the Heshuo meteorological station also shows the highest correlation with the lake's area in terms of monthly average variation (0.66).

The water resources system of the Bosten Lake basin in the arid region is fragile, and the uncertainty of the unstable water resources is aggravated by the frequent extreme climate. However, the influence of man-made water use factors on Bosten Lake is also especially important. At present, although human activities are still smaller than the impact of climate change on the lake level change, the impact on the water level change of Bosten Lake shows an increasing trend, which is mainly reflected in the main runoff consumption area of the plain and basin below the alluvial fan where human activities are frequent.

Hydropower is one of the main indicators of economic development in the Bosten Lake basin. The Kaidu River, the largest river in the Yanqi Basin, flows through Dashankou Hydropower Station and empties into Bosten Lake. Dashankou Hydropower Station is the largest hydropower station on the Kaidu River, which is mainly used for power generation and flood control during flood season. The project provides energy applications and brings significant economic benefits to the Yanqi Basin, but also changes the natural runoff injected into Bosten Lake, which plays an important role in the water control of the lake. In addition, with the growth of population and the development of the agricultural economy in the surrounding areas, the change of cultivated land has played a positive role in promoting the change of cultivated land. The cultivated land area of Yanqi Basin has been expanding continuously, from about 42% in 2000 to more than half of the total area of the basin in 2012 (Ghalip et al. 2015). The increase in cultivated land area also means the increase in irrigation area, and the agricultural irrigation water mainly comes from surface water diversion in different reaches of the Kaidu River and groundwater extraction in different irrigation areas. Therefore, the water diversion and consumption of agricultural irrigation increased year by year, increasing the water pressure of the runoff of Bosten Lake Basin and accelerating the continuous reduction of the water volume of Bosten Lake to a certain extent (Wang et al. 2008). On the other hand, the state began to implement the western development strategy in 2000. The western development requires it to take comprehensive measures, adhere to comprehensive management, and achieve sustainable development. In the process of treatment and conditioning, Bosten Lake undertook the task of emergency water transmission to the green ecological corridor of the lower reaches of the Tarim River, and the west pumping station was always running at full capacity. By November 2011, 11 ecological water transfers had been completed from Bosten Lake to the lower reaches of the Tarim River, with a total ecological water transfer volume of about 30 × 108 m³ (Zou et al. 2021), which affects the distribution and utilization of lake water resources. Such changes in water resource allocation and utilization patterns put the water volume of Bosten Lake in a continuous downward trend, resulting in the continuous shrinking of the water body of Bosten Lake.

Statistics show that since 2010, 13 central investment projects have been implemented in Bazhou to improve the ecological environment of rivers and lakes. These include ecological protection projects, pollution prevention and control projects of industrial enterprises, pollution source control projects, and environmental monitoring and supervision capacity building. Major measures include the implementation of an ecological water replenishment project in Bosten Lake. Since 2018, the Bayingoleng Management Bureau of the Tarim River Basin has organized the implementation of the ‘Diversion of the Kaidu River and the Huangshui Ditch’ project, focusing on the Huangshui Ditch. By 2022, the total amount of ecological water replenishment to Bosten Lake will reach 7.26 × 108 m³ (Zhao 2017). In 2010, Xinjiang Bohu Reed Industry Co., Ltd built a natural wetland conservation and ecological restoration technology research demonstration area in the Tianhe Reed Area (a small lake area southwest of Bosten Lake) to promote the restoration of water bodies here. Strengthening the unified management of water resources and developing water-saving agriculture, the state government has imposed a quota water supply target for the Kaidu-Peacock River Basin, and since 2016, it has been vigorously developing highly efficient water conservation in agriculture and conventional water conservation. To manage the ecological environment, Bazhou has stepped up efforts to manage the ecological environment of the source of the Kaidu River and the Bayinbuluk Grassland and to enhance its ability to conserve water (Yaermaimaiti et al. 2024). Since 2021, the water conservancy department of the government has implemented the ‘lake chief system’ of rivers. In the face of increasing ecological risks such as continuous discharge, water intercepting, and water transfer downstream of Bosten Lake, multiple measures have been implemented in parallel to continuously strengthen ecological construction, and the artesian flow from Bosten Lake to Peacock River has been realized for the first time in more than two decades.

This paper qualitatively discusses the driving effect of various factors on the dynamic changes of Bosten Lake in different periods and reveals the complexity of the hydrological changes of the lake. Although the study focused on the local area of Bosten Lake, the multi-source remote sensing monitoring method used has broad applicability and can be extended to the long-term water resources management of inland lakes in other arid regions. The research results not only provide a basis for the in-depth understanding of the changes in Bosten Lake but also have important implications for water resources regulation in arid areas around the world, especially in coping with hydrological instability caused by climate change. Certainly, we plan to perform a quantitative analysis in the future. This will involve utilizing the cutting-edge cryosphere – hydrology lake – dam model as described by Wang et al. (2022). By employing model-based numerical simulations, the hydrological processes of the lake-river network will be reproduced. Simultaneously, spatial information such as Digital Elevation Model (DEM), soil type, and land cover will be integrated to quantify the factors influencing lake changes.

Lakes are monitors of climate and ecological change in arid/semi-arid regions and are important links in the water cycle of the basin. In this paper, Bosten Lake, a lake in the arid region of central Asia, which is a sensitive region of global climate change, is selected as the research object. (1) Using Jason-1/2/3 data, a time series of lake water levels in Bosten Lake from 2002 to 2022 is constructed. Through comparative analysis with DAHITI, Hydroweb, and G-REALM lake water level products, it is proved that the lake level time series extracted in this study is long, highly precise, and reliable. The research results show that the level of Bosten Lake in 2013 and 2020 as nodes presents three change processes of rising and then falling. The decrease of lake level from 2002 to 2013 and the rise of lake level from 2013 to 2020 are consistent with the results of previous studies. The annual level of the lake shows a certain seasonal change. Lake levels are highest in the spring and relatively high in the summer. (2) Using Geographic Information System (GIS) and Remote Sensing (RS) technology, the GEE platform, and comprehensive utilization of Landsat-5/7/8 images from 2002 to 2022, the changing trend of the Bosten Lake area in the past two decades was obtained. The general trend of the area is in good agreement with that of the lake level. (3) Based on the time series data of lake level and area, the lake water balance formula was used to estimate the change in lake water volume from 2002 to 2022. In the past 20 years, the lake water volume decreased by 2.715 km³, which showed a decreasing trend from 2002 to 2013, an increasing trend from 2013 to 2020, and a decrease again from 2020 to 2022. (4) According to the above results, the driving mechanism behind the dynamic change of Bosten Lake is discussed by using the climate data of meteorological stations, glacial data, and human activity factors. During the study period, the dynamic changes of Bosten Lake were jointly affected by climate change and human activities, among which the main factors were evaporation, glacier melting, industrial and agricultural water use in human activities, and ecological regulation of water resources in the region, among which the effects of human activities became more and more significant in the process of lake change. Indeed, the future water security of Lake Bosten may depend heavily on the impact of human activities.

The above research conclusions have important reference significance for Bosten Lake wetland ecological environment protection, rational ecological water transfer, comprehensive utilization and development of water resources, local people's life stability and socially sustainable development, and can provide scientific basis and data support for future policy formulation of Bosten Lake water resources comprehensive development and utilization. At the same time, the results of this study show that Bosten Lake will show a certain shrinking trend after 2020. Therefore, the focus of the next step is to continue to track and study the temporal and spatial dynamic changes of Bosten Lake and explore the optimal water control interval of the lake to achieve the maximum optimization of the interests of all parties in the region, and ensure the stable and healthy development of the ecosystem of Bosten Lake while delivering water to the downstream ecology.

The Jason altimeter data used in the study came from AVISO, and the Landsat image data came from NASA. We would like to express our sincere thanks!

The manuscript was funded by The Major Science and Technology Project of the Qinghai Provincial Science and Technology Department (No. 2021-SF-A6). The funder supported this research primarily in the following aspects: Data collection and analysis and general research funding.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.