Table of Content

    25 October 2020, Volume 42 Issue 10 Previous Issue    Next Issue
    Introduction to the special issue on “Comprehensive Observation System of Natural Resource Elements”
    Zhou Chenghu
    2020, 42 (10):  1837-1838.  doi: 10.18402/resci.2020.10.01
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    Insights: Building a national comprehensive observation system of natural resource elements from the perspective of multidisciplinary integration
    WU Guoxiong, ZHENG Du, YIN Weilun, NAN Zhibiao, FU Bojie, YU Guirui, XIA Jun, LIU Jiongtian, GAO Xuemin, WANG Fengming, SONG Changqing, DUAN Xiaonan, LIU Gang
    2020, 42 (10):  1839-1848.  doi: 10.18402/resci.2020.10.02
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    The construction of a comprehensive observation system for natural resource elements is a foundational and public welfare project of the Ministry of Natural Resources. It is an important measure to fully implement Xi Jinping Thought on Ecological Civilization, to practice the development concept of “a community of shared life” of mountains, waters, forests, croplands, and grasslands, and to fulfill the “two unifications” management responsibilities of natural resources. It provides basic data support for systematic and comprehensive understandings of the law of natural resources movement and predictions of future development trends. Key tasks for constructing the comprehensive observation system mainly include: First, thoroughly improving integration of multiple disciplines and top-level design; Second, inheriting and carrying forward the spirit of the Qinghai-Tibet Scientific Expedition, and building a diligent and stable observation team; Third, considering the coupling of different resources, such as forests and grasslands, and strengthening comprehensive research based on observation systems; drawing on the experience of ecosystem observations both in China and abroad, and using modern methods to build multi-scale networks scientifically; Fourth, breaking barriers to form synergy, exploring the cooperation mechanism between different observation networks and units, and serving major national needs of China; Fifth, clarifying the core tasks, and adhering to the point-line-surface integration principle; Sixth, exploring multi-sector cooperation and conducting pilot demonstrations.

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    Construction of a national natural resources comprehensive observation system and key technologies
    LIU Xiaohuang, LIU Xiaojie, CHENG Shubo, GAO Xuemin, YUN Wenju, FU Yujia
    2020, 42 (10):  1849-1859.  doi: 10.18402/resci.2020.10.03
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    Under the new situation of socioeconomic development in China, natural resource management is being transformed from managed by individual resources and single government departments into a centralized management of “two unifications” guided by the principle of “land, water, forest, agricultural field, lake, and grassland life community” of the earth system science. In this process, not only the impact on and planning of the ecological environment of the territorial space, but also the future state of resources must be considered to ensure the safety of major decisions in the country. Therefore, the construction of a national comprehensive observation system of natural resources is very important for the orderly development of the country’s ecological civilization. The construction of a nation-wide natural resources observation system is meaningful to a nation’s ecological progress. This research examined the traits and shortcomings of the Chinese and international observation networks. Based on the analysis, necessity, basic ideas, and principles of the system were developed. The framework of the observation network includes five parts: factors, technologies, quality control, services, and operation and maintenance. Four types of technologies are used, which include natural resources zoning and observation station layout technique, coupling mechanism of natural resource elements and indicator selection technique, multi-source data integration and data processing technique, and simulation technique and comprehensive evaluation of natural resources. The observation network will provide long-term, stable, and constant comprehensive observations of natural resources, in order to explore the coupling relationships of the factors of natural resources, driving factors and mechanisms of change, and trends. The network serves to protect and manage the environment of the country, provide data support for solving the global climate issues, and finally to contribute to the nation’s centralized management of natural resources and resource-related strategic decisions.

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    Classification system of natural resources for integrated management
    SUN Xingli, LIU Xiaohuang, LIU Xiaojie, GAO Juan, ZHU Zhangliu, ZHENG Wenyi
    2020, 42 (10):  1860-1869.  doi: 10.18402/resci.2020.10.04
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    Exploring the establishment of the classification system under the new institutional arrangements for resource management is important for the integrated management of natural resources. This study analyzed the existing natural resource theories, jurisprudence, and management classifications, which cannot well avoid the overlap of natural resource management and the classification standards are not uniform, which is not conducive to producing a clear inventory of natural resources. It further analyzed the basic connotation of integrated management of natural resources by combining natural resource element management and integrated management, hierarchical management and classified management, and resource supervision and resource asset management. On this basis, the requirements for resource classification in connection with existing laws, effective integration with traditional classification, and integrated management of natural resources are discussed, and unified classification standards, effective connection between new and old classifications, and organic integration of academic, legal, and management classifications are proposed. Based on the classification principles, a natural resource classification system of 3 main categories, 15 sub-categories, and 53 types was constructed for the integrated management of natural resources.

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    Theories and technical methods for the comprehensive regionalization of natural resources in China
    ZHANG Haiyan, FAN Jiangwen, HUANG Lin, TANG Yulei, YUE Ying, YANG Yu, LIU Xiaohuang
    2020, 42 (10):  1870-1882.  doi: 10.18402/resci.2020.10.05
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    The comprehensive regionalization of natural resources directly reflects the spatial heterogeneity of complex natural resources of land, minerals, forests, grasslands, wetlands, waters, islands, and so on. It provides an important scientific basis for the construction of the national natural resources observation system and the spatial distribution of scientific field observation stations by zones, categories, and levels. At present, theoretical research on the comprehensive regionalization of natural resources in China is still lacking. Furthermore, a scientific and accurate evaluation paradigm for its technical methods has not been formed. First, based on the spatial pattern and dynamic characteristics of natural resources, and starting with the systematic management of mountain, water, forest, cropland, and grassland systems, this article presented a conceptual framework for the comprehensive regionalization of natural resources. Next, we developed an indicator system and technical methods for the comprehensive regionalization of natural resources according to the basic principles of subjectivity, integrality, multiple scale, hierarchy, and expansibility. Finally, we examined the differences between the comprehensive regionalization of natural resources and natural system and ecological regionalization. This study may help enhance our knowledge of the coupling relationship and differentiation characteristics of natural resources, promote multidisciplinary development, and serve the requirements of the national strategies including the system of natural resource management.

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    Discussion on the indicator system of comprehensive observation of natural resource elements
    ZHANG He, WANG Shaoqiang, WANG Liang, CHENG Shubo, JIANG Zhenglong, ZHANG Zifan
    2020, 42 (10):  1883-1899.  doi: 10.18402/resci.2020.10.06
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    In order to achieve the sustainable management and efficient use of natural resources, long-term, stable, and continuous comprehensive observations are necessary for acquiring basic resource data and information on resource types, quantity, quality, and processes of interactions. It is necessary to construct an indicator system of the comprehensive observation of natural resources. However, due to the lack of a unified indicator system of natural resources observation in China, there exist big gaps in observation and management between different regions, which make it difficult to standardize the management and improve the utilization of natural resources on a national scale. Hence, a scientific, systematic, and normative indicator system of comprehensive observations, which can be applied on a national scale in China, is urgently needed. Based on the primary issues to be addressed and with reference to the existing indicator systems in China and internationally, the authors summarized the basic principles of establishing the indicator system and the selection of indicators. On the basis of the classification of natural resource elements, the authors established a comprehensive observation indicator system that consists of 36 classification modules, 6 comprehensive observation subsystems, and several functional modules, by a combination of forward and inverse inference methods, modularization, and other construction methods. Through the establishment of a multidimensional comprehensive observation network across the atmosphere-surface-subsurface levels and the individual-landscape-regional scales, the data of natural resource elements can be obtained and the management, evaluation, and utilization of natural resources can be achieved.

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    Zonal division of natural resources in the coastal zone of China
    JIANG Zhenglong, WANG Bing, JIANG Lingxiu, CHEN Ying, LIU Jiufen, REN Yongji, ZHANG He
    2020, 42 (10):  1900-1910.  doi: 10.18402/resci.2020.10.07
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    In the coastal zone of China, natural resources are abundant and various, and very important to the coastal economy. To date, a systematic division of natural resources in coastal zone in the world is still lacking, which hinders cross-regional comparison and comprehensive evaluation of natural resources. For the purpose of systematic and scientific evaluation of the natural resources, their types, distributions, and control factors are basic parameters to be observed. This article summarized coastal natural resources distribution characteristics and examined the influencing factors, such as climate, the type of coastal zone, and power, which affect the development and distribution of natural resources. Based on these factors, the hierarchical division of natural resources in the coastal zone of China is discussed. The Chinese coastal zone is divided into four natural resources districts: the Yellow Sea to Bohai Sea coastal district, the East China Sea coastal district, the Southeast coastal district, and the Hainan Island coastal district and 16 coastal natural resources belts. At last, the article described the characteristics of natural resources in each district and belt. The results may be useful for the evaluation and rational development and utilization of natural resources in the coastal zone.

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    Optimization of integrated observation station layout for terrestrial surface natural resources
    GAO Bingbo, WANG Jinfeng, HU Maogui, XU Chengdong, LIU Huilan, ZHOU Chenghu
    2020, 42 (10):  1911-1920.  doi: 10.18402/resci.2020.10.08
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    This study focused on the geographical layout optimization of comprehensive observation stations for terrestrial surface natural resources including land, water, climate, and biology. The study was carried out following three steps according to the spatial statistic trinity. (1) The spatial distribution characteristics of terrestrial surface natural resources were analyzed, and the Eco-geographical Region System for China and the Normalized Difference Vegetation Index (NDVI) of the recent 10 years were adopted to characterize the spatially stratified heterogeneity and their spatial autocorrelation; (2) The point mean of the surface with stratified nonhomogeneity (P-MSN) was chosen as the inference method and its average estimation error variance was set as the objective function for the layout optimization; (3) Spatial simulated annealing was used to minimize the objective function to generate the geographical layout of comprehensive observation stations. The following conclusions were drawn: (1) Average NDVI of multiple years can characterize the spatial distribution characteristics of terrestrial surface natural resources; (2) P-MSN can adapt to the spatial distribution character of terrestrial surface natural resources and place dense stations in areas with large variance and sparse stations in areas with small variance; (3) The sample size-estimation error variance curve can be used to determine the best sample size and 1,000 stations are suggested in this study.

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    Development of an indicator system of wetland resources based on mutidimensional comprehensive observation
    QIAN Jianli, YANG Bin, ZHANG He, YANG Hanwen, ZHENG Linchang, TAN Changhai, DAI Xin
    2020, 42 (10):  1921-1931.  doi: 10.18402/resci.2020.10.09
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    Exploring the development of an indicator system for multidimensional comprehensive observation is of great significance for the integrated management of wetland resources, theoretical research, and related decision making. Starting from the integrated management of resources, this study expounded the characteristics and significance of three-dimensional comprehensive observation of wetland resources and analyzed the current status of wetland resources observation in China. It combined the uniqueness and complexity of wetland resources and characteristics of three-dimensional comprehensive observation, proposed the principles of development of the indicator system, and constructed an atmospheric-surface-underground indicator system of multidimensional comprehensive observation of wetland resources, which is consisted of 5 first-level indicators of climate resources, biological resources, surface water resources, soil resources, and groundwater resources, 18 second-level indicators, and 31 third-level indicators. The system aims to provide long-term, continuous, and stable observations of wetland resources in order to realize the transformation of wetland resource management from empirical to data-driven decision making, from extensive to scientific and precision development and utilization, and from the protection of single resource elements to the protection of all resources of mountains, waters, forests, croplands, and grasslands.

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    Research progress and theoretical framework of multidimensional observation of grassland resources
    FU Jingying, PENG Ting, JIANG Dong, LIN Gang, BIAN Peng, HAN Hao
    2020, 42 (10):  1932-1943.  doi: 10.18402/resci.2020.10.10
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    Acquisition of accurate basic data of grassland resources is not only the foundation for the rational use of grassland, but also an important basis for government decision making. Satellite-aerial-ground based dynamic observation system provides new ways for the multidimensional spatiotemporal observation of the growth process and other parameters of grasslands. Based on the research progress on technologies, indicators, and application services of grassland resources observation, this study provided a technical framework for the multidimensional observation network and its indicators system. We propose that the grassland observation system should strengthen the construction of the three-dimensional monitoring big data platform, and pay more attention to data fusion and data application of satellite- and aerial-based remote sensing monitoring data and ground monitoring data, aiming to improve the ability for automated, all-weather, three-dimensional observation and data acquisition at the national, regional, and local scales. The results of this study may provide a reference for the protection and construction of grasslands and the planning, decision making, and implementation of grassland and grazing industrial development by building a scientific and reasonable grassland management and decision support system.

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    Construction of the quality management system for comprehensive observation of natural resources
    LIU Jiufen, GAO Yang, FENG Xin, XUE Yanping, HE Haiyang, LAI Ming, DAI Xin
    2020, 42 (10):  1944-1952.  doi: 10.18402/resci.2020.10.11
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    The comprehensive observation system of natural resources has many characteristics, such as multiple objects, indicators, and technical means. In order to ensure the quality of observation data, it is necessary to build a quality management system covering the entire process from collection to publication of data products. Based on the new requirements for a quality management system by the comprehensive observation of natural resources and the analysis of the current situation of quality management systems in the field of observation in China and abroad, this study established a comprehensive observation quality management system framework according to the ISO9001 international standards. The system consists of five parts: target layer, organization layer, regulation layer, control layer, and evaluation layer. Using a modular integration design, this study built a vertical and horizontal multi-level quality control system; established a four-level external inspection process in the vertical direction including the comprehensive center, first level station, second level station, and third level station; and established an observation, proofreading, and review three-level internal inspection process in the horizontal direction. With regard to the quality control technologies, the system focuses on the quality control modules of different observational processes, established four quality control modules: QC0 (sample test quality control module), QC1 (observation data internal quality control module), QC2 (observation data external quality control module), and QC3 (data quality assessment and evaluation module). These modules improve the quality control relevance and effectiveness. By building a comprehensive quality management system and developing scientific quality control methods, this study promotes the long-term and stable development of the comprehensive observation of natural resources.

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    Soil fertility assessment indicators from the perspective of natural resources comprehensive observation
    PEI Xiaolong, HAN Xiaolong, QIAN Jianli, CHEN Wen, QIN Tian, LI Xuan
    2020, 42 (10):  1953-1964.  doi: 10.18402/resci.2020.10.12
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    Soil fertility is the basic property and qualitative characteristic of soil, and the establishment of its assessment indicators system is an important support for the comprehensive observation and unified management of natural resources. Based on the bibliometric method, this paper made a statistical analysis of the relevant literature in the CNKI database, summarized the main indicators used by domestic scholars in assessing soil fertility, and discussed three different properties of soil chemistry, soil physics, and soil biology. The results showed that organic matter, total nitrogen and available kalium were important indicators of soil chemical properties, bulk density, soil moisture content and texture were important indicators of soil physical properties, urease, invertase and metabolic quotient were important indicators of soil biological properties. On this basis, guided by the requirements of natural resources comprehensive observation in China, and following the principles of comprehensive, stability, independence and accessibility, the preliminary construction scheme of the soil fertility quality assessment indicators system was proposed, aiming at providing scientific basis for long-term soil resource positioning observation and quality evaluation.

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    Construction of a comprehensive observation platform for natural resource elements based on Internet of Things and Open Data Processing Service technologies
    SUN Yi, FANG Mengyang, HE Jianning, LIU Jiufen, ZHANG Siyuan, YANG Wantao, GAO Tiansheng
    2020, 42 (10):  1965-1974.  doi: 10.18402/resci.2020.10.13
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    The characteristics of the comprehensive observation data of natural resource elements are multiple sources, complex types and huge data volume. It is necessary to establish a comprehensive observation platform for natural resource elements (COPN) for the unified management and utilization of data. This article builds a comprehensive observation platform for natural resource elements (COPN) based on Internet of Things (IoT) and Open Data Processing Service (ODPS) technology, it mainly includes three modules: a natural resource element data center, an Internet of Things center, and a model cloud center. The platform enables the processes of data transmission, processing, and analysis from sensors to model clouds. The COPN serves the integrated management of natural resources across China and provides decision support for macro-control. The platform designed in this study will explore the design of various natural resource element related models and modularize them for scientific research and practical applications.

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    Operation and maintenance and data quality control of the Heihe integrated observatory network
    XU Ziwei, LIU Shaomin, CHE Tao, ZHANG Yang, REN Zhiguo, WU Adan, TAN Junlei, ZHU Zhongli, XU Tongren, MA Tao
    2020, 42 (10):  1975-1986.  doi: 10.18402/resci.2020.10.14
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    Distributed observatory network connects global and regional field sites, which is one of the prerequisites in earth surface processes observation. It is a priori to keep proper operation and maintenance, and perform strict data quality control for obtaining high-quality observation data. The current study took the Heihe River Basin (HRB), the second largest endorheic basin in China, as an example to introduce the research progress of the site maintenance and data quality control of the Heihe integrated observatory networks. The introduction of the operation and maintenance procedure covers daily, 10-day, monthly, and annual time intervals; while the data quality control process consists of instrument comparison and calibration, data processing, screening and checking, among others. Taking three superstations as an example, the observation data in 2018 are presented. Finally, the achievements of the Heihe integrated observatory network are introduced. The results can serve as a reference for the field observation and data quality control of the endorheic basins along the “Silk Road Economic Belt”.

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    Precipitation observation network and its data application in the alpine region of Qilian Mountains
    HAN Chuntan, WANG Lei, CHEN Rensheng, LIU Zhangwen, LIU Junfeng, YANG Yong, LV Hanqin
    2020, 42 (10):  1987-1997.  doi: 10.18402/resci.2020.10.15
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    Precipitation is the fundamental replenishment source of surface and groundwater resources, which directly affects the spatial and temporal distribution of water resources and the distribution and development of mountainous cryosphere. The alpine region of the Qilian Mountains is an area of large amounts of precipitation and runoff. The characteristics of precipitation are greatly affected by topography. However, the existing precipitation observation network cannot reasonably reflect the changes of precipitation on the vertical topographic gradient. To determine how the spatial and temporal change of precipitation affects the hydrological and ecological processes of the alpine mountains, it is necessary to observe the changes of precipitation pattern and type from the vertical gradient of the catchment. This article summarized the gridded, stepped, and automated precipitation observation network in the alpine region of the Qilian Mountains. The network is formed by the Geonor T-200BM3 weighing-type all weather precipitation gauges. A precipitation calibration system is also built in the Aug-one Glacier periglacial area, which is based on the Double Fenced Intercomparison Reference (DFIR) recommended by the World Meteorological Organization (WMO). In the Aug-one Glacier region, a preliminary analysis of precipitation datasets was conducted, and the applicability of GPM and TRMM precipitation datasets in the Qilian Mountains was evaluated using observational data. The development of this network is important for an in-depth understanding of the changes of rain, snow, and water vapor at different elevations, and minute division of the evaluation of precipitation resources in the alpine mountains. This network provides methods and data products for the comprehensive observation and evaluation of precipitation resources across China.

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    Retrieval of daily net surface shortwave radiation climatic resources based on machine learning
    YING Wangmin, LIU Xiaojie, FANG Shifeng, LI Xiujuan, LAI Ming, ZHANG Xuzhen, WU Hua
    2020, 42 (10):  1998-2009.  doi: 10.18402/resci.2020.10.16
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    Daily net surface shortwave radiation (DNSSR) is one of the most important parameters in various global land process and hydrological models and is required in climate change, energy balance, ecological, and atmospheric circulation research. This study constructed a daily net surface shortwave radiation model using the random forest (RF) method and MODIS twin-satellite products. 15531 pairs of samples containing 18 independent variables were extracted by matching MODIS twin-satellite products and FLUXNET daily observations. The Bias, RMSE (root mean square error), and R2 for the proposed DNSSR model using the RF method are -0.1W/m2, 27.8 W/m2, and 0.90, respectively. Based on the process, MODIS-DNSSR global distribution in different seasons were presented. Verification with field observations shows that the results are similar to the ERA5 reanalysis data, which are closely related to the seasonal distribution of solar energy. To further verify the results, ERA5-DNSSR were compared with the FLUXNET-DNSSR. The result shows that the proposed DNSSR model has also better accuracy and higher resolution than the ERA5 data. The RF-based DNSSR model has a good retrieval accuracy, high spatial resolution, and good temporal continuity. It can be effectively transplanted to the retrieval of other climatic resources.

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    Improving ecological security pattern based on the integrated observation of multiple source data: A case study of Wannian County, Jiangxi Province
    GAO Yang, LIU Yuexin, Qian Jianli, GUO You, HU Yingshan
    2020, 42 (10):  2010-2021.  doi: 10.18402/resci.2020.10.17
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    In recent years, the lack of ecological efficiency has restricted the sustainable development of the economy and society to a certain extent. Therefore, determining the current status of natural resources and optimizing the ecological security pattern based on this is of great significance for the comprehensive development and overall spatial configuration of natural and socioeconomic factors. Taking Wannian County, Jiangxi Province as an example, this study observed the status of regional resources through land use type, digital elevation model, road, and nature reserve data. The study determined ecological sources based on the InVEST model, granularity inversion method, and current regional conditions. Land use types and terrain and road factors were used to construct a comprehensive resistance surface. The circuit theory was then applied to determine ecological corridors and identify key points for ecological restoration. The results show that: (1) The total area of the 16 ecological sources are 95.93 km2, of which forest is the main land-use type, which is crucial for the stability of the regional ecological network. The length of ecological corridors is 217.89 km, of which 33 key corridors throughout the region need to be given priority for protection. These corridors can be used as a key area for comprehensive observation and monitoring of natural resources. (2) We identified 11 “pinch points” that are mainly ecological land distributed around high resistance areas, and 74 “barrier points” that appear in areas of intensive activities. There is much room for regional habitat connectivity improvement. (3) Based on the circuit theory, we integrated the natural resources of mountains, waters, forests, croplands, and grasslands through the point-line-surface construction process and proposed resource optimization strategies for different regions according to the ecological security pattern, which has positive practical significance for improving the structural supply capacity of regional resources.

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    Changes of spatial distribution and ecosystem service value of oasis wetlands in arid areas: Taking three typical inland river basins as examples
    MENG Yangyang, HE Zhibin, LIU Bing, CHEN Longfei, LIU Bei
    2020, 42 (10):  2022-2034.  doi: 10.18402/resci.2020.10.18
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    Wetlands play an important role in maintaining the structure, function, and hydrological cycle of oasis ecosystems in arid areas. The comprehensive monitoring and evaluation of oasis wetlands is the basis for accurately understanding the effectiveness of wetland protection policies and strengthening the restoration and protection of wetland ecological environment. Based on the multi-period remote sensing image interpretation from 1975 to 2015 and the benefit transfer method, this study quantitatively analyzed the spatial pattern and ecosystem service value change characteristics of the typical oasis wetlands in the upper reaches of the main stream of the Tarim River, the middle reaches of the Heihe River, and the middle and lower reaches of the Shiyang River in recent 40 years before and after the implementation of wetland protection policy in 2000, and put forward the corresponding management countermeasures of oasis wetlands. The study pointed out that due to people’s pursuit of short-term economic benefits in oases before 2000, the area of oasis wetlands was greatly reduced, and the wetlands landscape was gradually fragmented, resulting in more loss of wetland ecological benefits. Under the implementation of wetland protection policy after 2000, the area of oasis wetlands in the upper reaches of the main stream of the Tarim River and the middle reaches of the Heihe River and their ecological benefits have basically increased, but wetland loss in the Shiyang River oasis was serious and the protection and restoration of its wetlands needed to be further strengthened. The total value of ecosystem services of wetlands was mainly from its regulating service function (accounting for 74%-81% of the total). The wetland area of oases was very small, but the contribution rate of wetlands to the change of total ecosystem service value of oases was large. Therefore, the protection and restoration of wetlands are very important to the stability of oasis ecosystem and the improvement of ecosystem service value.

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    Verification and comparison of three high-resolution surface evapotranspiration products in North China
    HE Shaoyang, TIAN Jing, ZHANG Yongqiang
    2020, 42 (10):  2035-2046.  doi: 10.18402/resci.2020.10.19
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    The North China Plain is a critical agricultural region in China and one of the most severe water deficient areas in the world. Surface evapotranspiration (ET) is the largest component of water resource consumption, therefore obtaining accurate ET data is an important basis for water resource management on the North China Plain. In this study, accuracy verification and spatiotemporal comparison of three global high-resolution ET products were conducted in North China in order to provide a reference for the selection of a high-resolution ET data product that is more suitable for the North China Plain and can better serve the purpose of water resource research and management. Through the comparison with the eddy correlation measurement, the research showed that the PML_V2 product had the highest accuracy in North China, followed by SSEBop_V4 and MOD16A2, with correlation coefficients of 0.81, 0.74, and 0.52, respectively. The root mean square errors were 0.87, 1.52, and 1.44 (mm/d), respectively. PML_V2 showed the highest consistency with the fluctuation trend observed at the site. The correlation between the estimated and observed ET of the three products in the growing season of wheat was higher than that of maize. SSEBop_V4 ET and PML_V2 ET estimates had the highest correlation with the observed ET in wheat season and maize season, respectively. Comparatively, PML_V2 and SSEBop_V4 are more similar in spatial distribution, with the highest correlation coefficient of 0.76. The spatial distribution of MOD16A2 is very different from that of the other two products. The biggest difference of the three products appears in the cultivated land area. In 2003-2018, MOD16A2 showed a clear trend of increase for three land use types, while SSEBop_V4 and PML_V2 showed no obvious change.

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