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<title><![CDATA[Journal of Earth Environment -->Early Online Releases]]></title>
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<title><![CDATA[Study on characteristics and influencing factors of phenological changes of qinghai lake ice based on MODIS remote sensing images from 2001 to 2018]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201908300000002&flag=2]]></link>
<description><![CDATA[Background, aim, and scope Qinghai Lake is the largest saltwater lake on the Qinghai-Tibet Plateau. Studying the trend of the lake's freezing and thawing time and its relationship with climate change in this region can provide important insights for predicting future climate changes in the Qinghai Lake water regime.Materials and methods In this study, based on the difference between the brightness temperature value of ice and the brightness temperature value of water, the MODIS MOD02QKM data product and Landsat TM / ETM + remote sensing images from 2001 to 2018 were used to respectively extract Qinghai Lake's starting to freeze, finishing to freeze, starting to melt and finishing to melt, comprehensively analyze the changes in the ice phenology characteristics of Qinghai Lake, and combine the meteorological data to get the response of the lake ice phenology changes to the climate.Results Qinghai Lake enters the glacial period around November every year, and a stable ice sheet begins to form in December, and begins to melt in March or April in the following year. The changes in the length of the lake ice cover and the freezing period are basically the same, showing a trend of shortening as a whole, and the lake ice ablation period is showing a trend of first shortening and then increasing; from 2001 to 2018, the average first-day frozen area was 8.15%, the average freezing rate is 192.02 km2 / d. The dates for starting freezing and completing freezing are slightly delayed.Discussion According to the correlation between the differences in the freezing and thawing time of Qinghai Lake and the climatic factors such as temperature, precipitation, average wind speed, and sunshine hours in the past ten years, the main reason for the inference of the freezing and thawing of Qinghai Lake is calculated and drawn to reflect intuitively.Conclusions Air temperature is the main factor of lake freezing and thawing. The higher the temperature is in winter, the shorter the ice freezing time of Qinghai Lake and the longer the sunshine hours are. The slower the ablation rate is, the greater the average wind speed is and the faster the lake ice melts.Recommendations and perspectives It is preliminarily believed that in the next 1 to 2 years, the temperature of Qinghai Lake in winter will still show an upward trend, and the length of the frozen ice will also appear to shorten.]]></description>
<pubDate>2020/11/23 9:02:28</pubDate>
<category><![CDATA[地理学]]></category>
<author><![CDATA[liuqiuman,Zhanjiang Sha]]></author>
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<title><![CDATA[Surface humidity index in Gansu Province During 1967 to 2016 based on humidity index]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201908080000001&flag=2]]></link>
<description><![CDATA[Abstract: Background, aim, and scope With global warming becoming more and more prominent, water vapor transport is accelerated, in recent years, the rate and magnitude of climate change has increased significantly, and the uncertainty of climate wet and dry change has increased. In this paper, the change of wet index in Gansu in the past 50 years is studied in order to find out the changes of surface wet and wet on the time scale and spatial scale of different wet and dry climate zones and their transformation characteristics under the background of global warming. Materials and methods Based on the data of 32 climate stations in Gansu, this paper selected the World FAO P-M model to calculate the potential evapotranspiration, and then calculate the surface humidity index. We used the methods of B-G segmentation, cumulative distance leveling, IDW and other methods to analyze the climate-change trend and characteristics of humidity index in each dry-wet climate region. Results The humidity index of Gansu province was increasing in the west and decreasing in the east. The EOF spatial distribution mode is mainly the consistent distribution mode of the whole region and the reverse division of the isomorphism of east and west with the Wushaoling as the boundary. The semi-humid region showed a significant downward trend at the rate of -0.018/10a, the mean of the three segmentation stages decreased in turn, the mutation from much to few occurred in 1994. The semi-arid region was on the rise of 0.002/10a, the mean of the four segmentation stages showed a trend of fluctuation, and the surface dried after 1996, but no mutation occurred; The arid region showed an upward trend of 0.003/10a, with the mean of the three segmentation stages increasing in turn, and the surface moisture index increased significantly at 0.006/10a after 1992, but no mutation occurred. Discussion In recent years, the arid region in the west shows a clear trend of transition from warm to warm and humid, which is closely related to the increase of precipitation, has a positive impact on the sustainable development of agricultural production and natural environment in the future. As a transitional area of climate transformation, the central semi-arid zone has a weak humidity trend, and with the improvement of surface moisture, the fragile ecological environment of Hexi corridor and Qilian mountain area can be further improved. With the decrease of rainfall, rising temperature, increasing the shortage of surface moisture and increasing the degree of climate drought, the arid area of crops increases, leads to the decline of production and destroys the sustainable and stable development of agriculture. Conclusions Under the background of the transition of climate from warm dry to warm and humid in northwest China, the whole region of climate warm-up change in the study area has consistent, and the warming trend is developing, but the change of surface moisture characteristics has significant spatial difference. The semi-humid zone not only did not change to warm and humid, but also had a clear trend of warm drying in the past half century, especially since 1994, the trend of surface drying was significant, and it was an untransformed area. The semi-arid region showed a weak trend of warm-up and humidity, and the surface moisture index increased and decreased alternately, which was a weak transformation area. The arid zone showed a more obvious trend of warm-up, especially after 1992 the surface at 0.006/10a rate showed a significant upward trend, which is a transformation zone. Recommendations and perspectives On the basis of consistent with the results of previous research, this paper classified the characteristics of climate wet and wet changes in the study area, and made an in-depth study on the specific process of climate wet and wet transformation in northwest China. As a climate dry-wet index which considers the combined effect of various factors, the humidity index is an ideal index for characterizing the change of surface wet and wet in arid areas, and the regional differences of surface wet index in different areas of the study area play an important role in guiding the agricultural development, ecological environment and economic development of the study area.]]></description>
<pubDate>2020/11/19 9:08:27</pubDate>
<category><![CDATA[其他]]></category>
<author><![CDATA[JIAO Liang,TIAN Han-wen,wangxiaodan,ZHANG Yi]]></author>
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<title><![CDATA[Projection of the 21st century sea level change in East China Sea and South China Sea bashed on CMIP5 model results]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=202001170000001&flag=2]]></link>
<description><![CDATA[Background, aim, and scope As an important design indicator and safety parameter for engineering projects, sea levels have significantly risen in the past decades with global warming and increasing impact of human activities. In the context of global warming in the 21st century, the rate of sea level rise is expected to increase further in the future. This situation will pose great challenges to regional environments and the sustainable development of society in the southeast coastal areas of China. Therefore, projecting future sea level changes in the East China Sea and South China Sea has become an important scientific issue with practical significance.  Materials and methods This study uses the results of 34 climate models from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) to select 10 models with good performance in simulating temperature and precipitation trends and patterns worldwide and in central-eastern China, projected trends and distributions of 21st century sea level changes in the East and South China Seas under low (RCP2.6), medium (RCP4.5) and high (RCP8.5) greenhouse gas emission scenarios, and analyzes the contributions of thermosteric, halosteric, and dynamic factors. In addition, the effects of glacial and ice sheet melting and other factors on sea level rise are estimated according to the IPCC Fifth Assessment Report.  Results When only steric sea level (including thermosteric sea level and halosteric sea level) and dynamic sea level changes are considered, the sea level of the East China Sea are projected to rise by 0.07 [-0.01~0.16] m, 0.15 [0.08~0.23] m and 0.24 [0.10~0.38] m in 2081-2100 compared with 2006-2025, and projected rise estimates in the South China Sea are 0.09 [0.03~0.16] m, 0.17 [0.11~0.24] m and 0.25 [0.17~0.33] m, under the RCP2.6, RCP4.5, and RCP8.5 emissions scenarios, respectively (ranges in the square brackets represent the uncertainties). Sea level rise projections due to factors related to glacial and ice sheet melting reach 0.19 [0.01~0.39] m, 0.22 [0.02~0.43] m, and 0.28 [0.05~0.52] m under the three emissions scenarios.  Discussion Thermosteric, halosteric, and dynamic sea levels are all projected to increase throughout the 21st century under the three future emissions scenarios. Melting of glaciers and ice sheets is also an important contributor to sea level rise. Under the medium emissions scenario, the contribution of the steric plus dynamic factors is 41-44.0%, while that of other factors including glacier and ice sheet melt is 55-58%. Their relative contributions seem to change with emission intensity.  Conclusions In the 21st century, sea levels in the East and South China Seas will continue to rise, although within a slightly smaller range than the global average. Projected increases in the South China Sea are slightly larger than those in the East China Sea. Considering the effects of thermosteric, halosteric, and dynamic sea level changes, as well as glacier and ice sheet melting-induced sea level changes, the total sea level rise in the East China Sea for 2081-2100 compared with 2006-2025 is projected to be 0.26 [0.01~0.55] m, 0.38 [0.10~0.66] m, and 0.52 [0.15~0.89] m, and results for the South China Sea are 0.29 [0.05~0.55] m, 0.40 [0.14~0.67] m, and 0.52 [0.23~0.83] m, under RCP2.6, RCP4.5, and RCP8.5 scenarios, respectively.  Recommendations and perspectives This study uses the multi-model ensemble method to project regional sea level changes to reduce errors from a single model to a certain extent and improve the reliability of the projection results. However, due to the influence of many complex factors, there are still some uncertainties in our projection results. Therefore, further studies are needed in the future.]]></description>
<pubDate>2020/11/19 9:05:44</pubDate>
<category><![CDATA[环境科学]]></category>
<author><![CDATA[LIU Heng,LIU Rui,LIU Xiaodong]]></author>
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<title><![CDATA[The mitigation effect of plateau urban ecological construction on "heat island effect": a case study of Xining city in Qinghai province of China]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201910170000001&flag=2]]></link>
<description><![CDATA[Background, aim, and scope With global accelerating urbanization process and the development of social economy, the urban heat island effect is becoming increasingly acute. After rapid urbanization for past several decades in china, the urban scale and built-up area have grown rapidly, which has intensified the urban heat island effect. Therefore, constantly enhancing the level of ecologicalization and constructing an eco-city, which is fit to dwell for human being, have become the core content during the urban ecological construction. However, the Qinghai-Tibetan Plateau as the most important ecological barrier, its ecological environmental protection and ecological civilization construction are essential foundations for China's sustainable development. Owing to special ecological environment and ecological status, the urban ecological construction of the Qinghai-Tibetan plateau has become a key concern. In this study, Xining city was selected as study area, it located on the Northeastern of the Qinghai-Tibetan Plateau, and is the largest city in this plateau region. Materials and methods Adopting the Landsat remote sensing data during the period of 2000-2019 to analyse surface temperature and vegetation coverage fraction in summer of this study area. Employing the random forest method to interpret land use types. In addition, the corresponding temperature model were obtained by linear fitting, which used to calculating mitigation effect of the heat island effect to the urban ecological construction. Results The results showed that the area of urban heat island in Xining city showed a trend of first increasing and then decreasing during the study period. And the vegetation coverage fraction is on the rise and the water area is expanding. In addition, the regional average cooling effect of forest land, water area ,and grassland in Xining city was 2.12℃, 2.19℃ and 4.29℃, respectively. Thus, the overall ecological construction of Xining city can alleviate the urban heat island effect.  Discussion During the 19 years, the urban heat island area of Xining city showed a trend of first rising and then falling. The overall the vegetation coverage fraction showed an upward trend. The proportion of medium to high vegetation coverage fraction and high vegetation coverage fraction reached its peak in 2010 and 2005, respectively. Ecological construction should adapt to the speed of urban construction, although the process of environmental effect is relatively slow, ecological construction plays an important role in realizing sustainable development of urban environmental friendliness and livability. Conclusions The vegetation coverage fraction and water area of Xining city are continuously expanding. Under the urban development trend of rapid expansion of built-up area, urban heat island effect is obviously controlled and alleviated, which is closely related to urban ecological construction. The results of urban ecological construction between 2000 and 2019 are relatively obvious. Recommendations and perspectives The traditional concentrated greening is transformed into a uniform layout. In the old city reconstruction, a large number of trees should be planted, and should be made to afforestation the roofs and walls of buildings, widen the existing river channels and increase constructed wetlands.]]></description>
<pubDate>2020/10/19 10:32:59</pubDate>
<category><![CDATA[地理学]]></category>
<author><![CDATA[CHEN Qiong,LIU Fei,LIU Fenggui,WU Xue,ZHANG Liang,ZHOU Qiang]]></author>
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<title><![CDATA[Numerical simulation of photo-transferred phenomenon in 110 oC thermoluminescence (TL) trap]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201910090000002&flag=2]]></link>
<description><![CDATA[Abstract: Background, aim and scope In optically stimulated luminescence (OSL) dating, preheating is widely applied to remove unstable signal without significantly affecting the TL trap at 325 oC. Such depleted signals reappear after optical stimulation, which means that retrapping of OSL electrons is not a negligible process. This phenomenon is photo-transferred thermoluminescence (PTTL). Previous studies focused on experimental results and explanations, but there is a lack of understanding from simulation aspect. Here we present simulation results associated with PTTL and try to understand PTTL in quartz. Materials and methods Coarse quartz is used experimentally to measure a PTTL glow curve. For simulation, our investigation is based on a simple kinetic model with three energy levels (two electron traps and one luminescence center). The simulations are carried out based on R program KMS which is designed to simulate luminescence phenomena in quartz. Results The results show the same qualitative behavior between experimental and simulated PTTL glow curves, but there are differences in magnitude of the signal at peak level. Variations of electron concentration in two traps can be obtained against stimulation time. Electron concentration in 110 oC TL trap first rises and then decreases with stimulation time, and electron concentration in 325 oC TL trap always decreases and can be separated into two phases with different decay rates. In addition, several kinetic parameters are important in photo-transferred process. For parameters such as optical stimulation temperature (ST) and incident photon flux (F), which are associated with experiment condition, PTTL intensity decreases with the increasing ST and F. For parameters of electron trap concentration (N1), retrapping probability (A1) and photoionization cross-section (a1), which are associated with properties of 110 oC TL trap, adding N1 and A1 to a larger extent within a proper range is beneficial for the production of PTTL signal, but enhancing values of a1 imposes negative effects. Discussion Our simulation results suggest that a relatively larger retrapping probability of 110 oC TL trap is of vital importance in simulating PTTL phenomenon. Recombination probability of luminescence center is 2×10-7 cm3?s-1, retrapping probability of 110 oC and 325 oC TL traps are 5×10-8 and 5×10-12 cm3?s-1, respectively. This ensures that most of stimulated electrons recombine at luminescence center and still some are retrapped into 110 oC TL trap and the proportion of electrons which retrapped into 325 oC TL trap is extremely small. Different kinetics were assumed to study the properties of the glow curve by comparing recombination and retrapping coefficients. For process that dominates by recombination, it usually follows first-order kinetics and may change into non-first-order kinetics due to electron concentration change. For process that dominates by retrapping or has equal recombination and retrapping probability coefficients, it follows second-order kinetics. During optical stimulation, electron concentration in 325 oC TL trap follows first-order kinetics at early stage and then decays exponentially, as electron concentration decays to about 1‰ to its initial value, the retrapping rate is larger, the decay rate is slower and follows non-first-order kinetics since then. Electron concentration in 110 oC TL trap first increases and then decreases, which represents the process of electrons retrapping into and escaping from 110 oC TL trap. PTTL intensity could also be affected by experimental and 110 oC TL trap properties. Higher stimulation temperature and larger incident photon flux is beneficial for electrons in 110 oC TL trap to escape, thus experimental procedure could be improved to avoid PTTL phenomenon. By increasing electron trap concentration and retrapping probability, we get higher intensity of PTTL peak, but increasing photoionization cross-section, we get opposite results. Conclusion Energy band model with two electron traps and one recombination center represents key features of PTTL signal. During optical stimulation, electron concentration in 110 oC TL trap first rises and then decreases, and electron concentration in 325 oC TL trap always decreases with stimulation time. Different parameters (not only associated with experiment but also associated with trap properties) contribute differently for the production of PTTL intensity. By increasing electron trap concentration and retrapping probability, we get higher intensity of PTTL peak, but increasing stimulation temperature, incident photon flux and photoionization cross-section, we get opposite results. Recommendations and perspectives It is believed that simulating kinetic models of quartz luminescence system will play a more important role in the future. Establishing complex kinetic models helps to explain phenomenon that obtains during experiments, searches for exact physical mechanisms and sets a fundamental role for putting forward new dating methods with accuracy.]]></description>
<pubDate>2020/9/16 15:56:16</pubDate>
<category><![CDATA[其他]]></category>
<author><![CDATA[pengjun,wangxulong,zhengyue]]></author>
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<title><![CDATA[Study on the Response of the Migration and Subsequent Increase of Income in Southern Shaanxi]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201910110000001&flag=2]]></link>
<description><![CDATA[Abstract: Background aim, and scope Compared with the immigration caused by the traditional push-pull theory, immigrants in South Shaanxi have the characteristics of government behavior, breaking the pattern of matching the laborers formed in the natural evolution with scattered farmland, and the situation of separation between laborers and land may cause unsustainable livelihoods after relocation. Therefore, it is of great theoretical and practical significance to explore the ways to increase the income of immigrants in the future. Materials and methods This article obtains theoretical materials by consulting relevant documents in southern Shaanxi, and conducts field surveys of 584 relocated families in 9 counties, including Hanzhong, Ankang, and Shangluo, as first-hand sample data, and discusses them by means of principal component analysis and correlation analysis. Results Through analysis of the survey data, it is found that: (1) The relocation distance has an impact on the quality of life and income of farmers. (2) The relocation distance will cause a change in the income pattern of farmers. (3) The income level of households, family structure, and employment methods are the main influencing factors on the living standards of farmers. Discussion The relocation distance is within two kilometers as the appropriate distance. The community size is below 500, and the farmers are most satisfied. Conclusions The farther the relocation distance is, the farmers cannot continue to use the original land and other means of production and living, the agricultural production is developing slowly, and the level of agricultural technology is relatively lagging, which reduces the farmers' income from farming, changes the income mode to work and resettles nearby, improves the human capital of immigrants, The resettlement industry and other measures are an alternative way to solve the source of income for resettlement households. Recommendations and perspectives This article has enriched the empirical research on the planning and construction of new villages in southern Shaanxi and the subsequent development of rural industries. Due to the lack of sample data, research period and research content, the follow-up needs further discussion.]]></description>
<pubDate>2020/9/16 15:53:39</pubDate>
<category><![CDATA[区域发展]]></category>
<author><![CDATA[He jiali,Lv Xiao-Lu,xiaoweiwei]]></author>
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<title><![CDATA[A drought event recorded by a stalagmite from northeastern Sichuan in central China]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201908270000002&flag=2]]></link>
<description><![CDATA[Background, aim, and scope With global warming, climatic extremes such as flood, drought and heat wave are becoming increasingly serious and exert more and more threats to human society. Investigations of past climatic extremes help us to understand the variations and controlling mechanisms and to contribute to prediction of these events. In this paper, a drought event which happened ~600 a ago in central China was reported to be recorded by a stalagmite (SI2) collected from NE Sichuan, and its evolution and controlling mechanisms were investigated. Materials and methods The stalagmite SI2 was collected from Shizi Cave (32°24′N, 107°10′E). U-230Th dates and 210Pb dating results indicate that SI2 developed during the last ~2100 years. The stable oxygen isotope (δ18O) of SI2 was determined with a Thermo-Fisher MAT 253 mass spectrometer with analytical errors better than 0.1 ‰. Results The SI2 δ18O record varied from -7.42 ‰ to -9.27 ‰ with an average of -8.67 ‰. A general decreasing trend was observed in the δ18O record prior to AD 200, followed by an apparent and long-lasting increasing trend until AD 1400 when the heaviest δ18O ratio of the whole record, -7.42 ‰ occurred. From AD 1400 to ~AD 1800, an overall negative shift was displayed with the lightest value of the whole record, -9.27 ‰ appeared at the end of this stage. The SI2 δ18O record showed a gradual increasing trend again during the last 200 years. The SI2 δ18O record indicated a drought event happened ~600 a ago, which was supported by the growth of stalagmite SI2. Calcite precipitation in SI2 was relatively more concentrated on the growth center when the event happened, suggesting lower dripping rates under a relatively dryer climate. The SI2 δ18O record suggested that the drought event was episodic, consisting of three dry episodes. Discussion This drought event was also recorded by other stalagmites in central China as well as historical documents. However, changes in hydroclimate in South China did not illustrate an apparent manifestation of this event. The spatial distribution of this event in monsoonal China suggested a possible origin from sea surface temperature in the tropical Pacific Ocean which might be in an El Ni?o-analogue state. However, this explanation was in contradiction with the recent work of Tan et al. (2019) and more investigations were warranted. Conclusions The δ18O ratio and growth of stalagmite SI2 recorded a drought event happened ~600 a ago in NE Sichuan in central China. This event consisted of three dry episodes. Recommendations and perspectives The spatial distribution of this event in monsoonal China suggested a possible tropical origin but further investigations were warranted in future.]]></description>
<pubDate>2020/9/16 15:41:15</pubDate>
<category><![CDATA[地理学]]></category>
<author><![CDATA[chengke,liushuhua,liuyuefeng,pengxiaotao,xiehongxia,xieyu,zhouhouyun]]></author>
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<title><![CDATA[Ecological evaluation and obstacle factor analysis of urban green space in Jiayuguan from 2007 to 2016]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201909230000001&flag=2]]></link>
<description><![CDATA[Background, aim, and scope The evaluation of urban green space can provide important support for the scientific planning and management of urban green space and realize the sustainable development of urban green space. The division of health level of green space can provide important information for the management strategy of green space, such as species selection and adjustment of vegetation structure. Etc.; The analysis of greenland vegetation ecological risk sources and the classification of risk levels can alleviate or eliminate stressors for green areas, and on the other hand, formulate corresponding countermeasures for green space health, providing important information for rational planning and management of green space in the next step. By constructing the urban green space ecological evaluation index system, the paper makes a scientific evaluation of the urban green space in Jiayuguan City, and uses certain models to identify the influencing factors affecting the ecological level of the urban green space. It is hoped that people will correctly understand and transform the urban green space construction as a follow-up city. Green space planning and management provide theoretical references. Materials and methods With the urban green space of Jiayuguan city from 2007 to 2016 as the research object, the ecological evaluation index system of urban green space is constructed from three aspects, and the obstacle degree model is adopted to identify the obstacle factors that affect the ecological level of urban green space. Results In the past 10 years, the comprehensive value of urban green space ecological level of Jiayuguan city has gradually increased, and the level has been raised from the lower level to the higher level. However, at present, the ecological level of urban green space belongs to the low level and unstable high level, and the construction pressure of urban green space is still great. From the perspective of criteria, the main threats to the ecological level of urban green space in Jiayuguan are obvious, and the quantity index and structure index are the main obstacles. From the index level, the main obstacle factors are different from year to year, and the biggest obstacle factors have evolved from per capita park green space area, tree species richness to air purification capacity. Discussion Urban green space evaluation initially focused on green space structure and ecological function, then gradually expanded to green space ecological services, ecological health level and ecological risk, and finally developed to sustainability evaluation. Urban green space more attention in the study of urban green space's ecological functions and ecosystem services, and concentrated in the eastern central region, based on "oasis" Jiayuguan city green space as the research object, from the aspects of quantity, structure, function of three comprehensive evaluation of the urban green space ecology level, using the disorder degree model to identify the obstacle factors of the development of urban green space, for the improvement of other urban ecological problems in arid areas provides a certain reference. Recommendations and perspectives The urban green space evaluation initially focused on the green space structure and ecological function, and subsequently expanded to the green space's ecological service, ecological health level and ecological risk, and finally developed to sustainability evaluation. At present, the research on urban green space pays more attention to the ecological function and ecosystem service of urban green space, and concentrates on the eastern and central regions. The article takes the urban green space of Jiayuguan in the “desert oasis” as the research object, and comprehensively evaluates it from three aspects: quantity, structure and function. The ecological level of urban green space, using the obstacle model to identify the obstacle factors that restrict the development of urban green space, provides a reference for the improvement of ecological problems in other cities in the arid region.]]></description>
<pubDate>2020/9/16 15:35:21</pubDate>
<category><![CDATA[地理学]]></category>
<author><![CDATA[Da xiaojun,Dong Jianhong,Ma yaxiong,Zhang zhibin,Zheng lan]]></author>
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<title><![CDATA[Combining Remote Sensing and Tree Ring Techniques to Investigate Forest Vegetation Dynamics and its Response to Climate Change in Yimeng Mountainous Area from the Early 20th Century]]></title>
<link><![CDATA[http://jee.ieecas.cn/dqhjxben/ch/reader/view_abstract.aspx?file_no=201909150000001&flag=2]]></link>
<description><![CDATA[Background, aim, and scope: Remote sensing is an effective approach of vegetation monitoring, and remote sensing-based vegetation indices can well capture vegetation growth curve. However, the longest remote sensing observations are only available for about 40 years, which limits their use in research on long-term vegetation dynamics. Tree ring data usually have longer records, which overcomes the limitations of remote sensing observations, but there is no direct link between tree ring and vegetation properties (e.g., gross primary productivity, biomass). Previous studies combine tree ring width and satellite-based vegetation index to reconstruct vegetation dynamics for a long period. However, the selection of indicators depends much on correlation, and thus different indicators might be chosen for different regions, which is not suitable for comparison spatially. Here, we took Yimeng Mountainous area as the study area, reconstructed long-term accumulative NDVI values of the growing season, an effective indicator of annual gross primary productivity, from the earlier 20th century, and characterized their temporal changes. Materials and methods: (1) 225 tree ring cores were collected from three sites within our study area: Meng Mountain, Ta Mountain and Yi Mountain. The ring widths of all the cores were measured using MeasureJ2X professional measurement software under the LINTAB tree ring width meter (measuring accuracy 0.01 mm), and then COFECHA program was used to test the cross-dating quality. Finally, the standardized chronology (STD), difference chronology (RES) and autoregressive standardized chronology (ARS) were established by the ARSTAN program. (2) To derive the time series of accumulative NDVI of the growing season, we extracted NDVI time series at 15-day interval for each sampling site, used the TIMESAT software to determine the start, end, and length of the growing season, and finally get the sum of NDVI values within the range of the growing season. (3) The Bootstrap method was used to establish the empirical relationships between tree ring width and accumulative NDVI, and reconstruct the time series of accumulative NDVI from early 20th century. (4) Wavelet analysis was utilized to identify the underlying periods within the long-term time series of climate variables and accumulative NDVI. Results: The mean accumulative NDVI of growing season for Yi Mountain area is 7.36, which was lower than that in Meng and Ta Mountain areas. Vegetation productivity in Meng Mountain area showed an increasing trend, and the magnificence of increase was particularly large after 1980s, but there was no significant trend in Ta and Yi Mountain areas. There were 2 years, 4 years and 8 years of period underlying the time series of accumulative NDVI for three sites. Variations in mean wavelet power between 2 to 8 years for accumulative NDVI was more consistent with those for PDSI than temperature. Discussion: Our research found that tree ring width significantly correlated with accumulative NDVI of growing season, an effective indicator of vegetation productivity. Meanwhile, our used nonparametric method, Bootstrap regression, was more robust than traditional statistical method, which could address the situations when the sample size was small or the distribution of samples was not normal. Therefore, our research provides a framework which accurately reconstructs vegetation dynamics for a long time period. We also found that vegetation dynamics within our study area were determined by combined water and temperature, as indicated by the highly consistence between variations in accumulative NDVI and PDSI.  Conclusions: We concluded that integrating remote sensing and tree ring techniques could effective reconstruct long-term vegetation dynamics, and accumulative NDVI of growing season was useful indicator to be chosen for reconstruction given its high correlation with tree ring width and its close link with vegetation productivity. Vegetation dynamics in the Yimeng Mountainous areas were determined by water and temperature factors. Recommendations and perspectives: We develop a framework to accurately reconstruct vegetation dynamics by combined remotely sensed data and tree ring materials, which could be extended to other research areas. Our findings that both water and temperatures are important to determine vegetation productivity are useful for explaining and predicting vegetation dynamics under climate change especially in the warm temperate Yimeng Mountainous regions.]]></description>
<pubDate>2020/9/16 15:32:43</pubDate>
<category><![CDATA[地理学]]></category>
<author><![CDATA[Bu,Xiangfeng,Guo,Yuanyuan,Li,Wenjing,Qu, Xiaoqian,Ren, Jiaxuan,Tian, Jinmei,Wang,Shuxin,Zhao,Xingyun,Zhu,Likai]]></author>
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