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Table of Content

    25 August 2014, Volume 33 Issue 8 Previous Issue    Next Issue
    Orginal Article
    Comprehensive geographic analysis and discussion on strategies for post-earthquake recovery and reconstruction in Ludian, Yunnan Province
    Jie FAN, Chuansheng WANG, Qing TANG, Yong XU, Dong CHEN
    2014, 33 (8):  1011-1018.  doi: 10.11820/dlkxjz.2014.08.001
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    Earthquake area has the most intense interactions between the various spheres of the earth surface and human-environment relationship is under great stress. In-depth comprehensive geographic study has significant implications for the coordination of the human-environment relationship and the promotion of regional sustainable development in such area. This paper analyzes the resource and environmental conditions and regional development of Ludian County before the earthquake. We found that this region has vulnerable ecological environment, high population density, widespread poverty, strong dependence of production and livelihood systems on natural resources, and the resources and environment have been chronically under stress. Accordingly, this paper proposes that an evaluation of the resources and environmental carrying capacity should be carried out imminently for the area, sound recovery and reconstruction plans should be made, regional sustainable development based on innovation of the system and institutions should be promoted, and systematic disaster prevention and reduction research and overall planning at the periphery and in the adjacent mountainous areas of the Qinghai-Tibet Plateau should be initiated.

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    Review on spatial interpolation methods of temperature data from meteorological stations
    Yuechen LI, Zhiming HE, Chunxia LIU
    2014, 33 (8):  1019-1028.  doi: 10.11820/dlkxjz.2014.08.002
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    Spatial interpolation is an important method for creating spatial representation of temperature in geographic and ecological research and is important for supplying fine resolution temperature data for ecological models. This paper reviews existing spatial interpolation research of meteorological factors and compares a number of interpolation methods, including global interpolators (trend surfaces and regression models), local interpolators (inverse distance weighting, gradient plus inverse distance squares method, PRISM, splines, ANUSPLIN), geostatistical methods (Ordinary Kriging, Co-kriging), and mixed methods (combined global, local, and geostatistical methods). These methods are commonly used for the spatial interpolation of temperature data. The aim of this study is to explore the suitability and inadequacies of these methods in order to provide references for future research involving spatial interpolation of temperature data. It also attempts to explore ways to improve the application of the various methods. The comparison of these methods shows that each method has its own strength in particular applications. There is no universal method suitable for all practical applications. In practice, specific geographical characteristics of the study area must be considered and tests should be done to determine the suitability of specific methods. In order to achieve optimal interpolation result of regional temperature, parameters of the methods should be adapted based on actual geographical conditions. Global interpolation and geostatistical methods can be applied to study global trends. Local interpolation based on distance similarity principle does not apply to global trends simulation. Mixed methods are able to combine advantages of global interpolation, local interpolation, and geostatistics, and improve the simulation accuracy. Mixed methods and PRISM and ANUSPLIN are more suitable for application under complex terrain conditions. In future research, integration of various temperature spatial interpolation methods will improve, and more mixed methods combining global, local, and geostatistical methods will be created. Methods based on the physical distribution characteristics of temperature and combined with GIS technology will be prevalent. In order to improve the simulation accuracy of temperature in microscopic details, introduction of additional factors, such as terrain, will be an important future trend.

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    Review of research on anthropogenic heat under climate change
    Wangmin YANG, Chong JIANG, Xiaoyong YU, Xuefeng CUI
    2014, 33 (8):  1029-1038.  doi: 10.11820/dlkxjz.2014.08.003
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    Anthropogenic heat is wasted heat in the form of sensible and latent heat that is released to the urban canopy and planetary boundary layer of cities as a result of human activities, often involving combustion of fuels. It is estimated that nearly 70% of energy produced is consumed within cities that only occupy 2% of the global land area. Buildings, transportation, and human metabolism are the primary sources of heat discharge in cities. For example, in Manchester, the source fractions are 60%, 32% and 8%, respectively. However, the relative contributions of these sources vary greatly in different regions. The magnitude of the anthropogenic heat flux (AHF) in urban areas is very large and shows clear daily and seasonal changes. The peak of anthropogenic heat occurs in the dawn and dust during a day and summer and winter during a year. AHF can be calculated using observation or inventory approaches. Observation methods include surface energy balance and in situ eddy covariance observations. The surface energy balance method is usually based on meteorological and remote sensing data. IMAS (identification of micro-scale anthropogenic sources) filtering on data observed with eddy covariance systems was proposed to identify anthropogenic heat. Currently, inventory approaches (bottom-up and top-down) are widely used. In the top-down approach, energy consumption aggregated at coarse temporal and spatial resolutions is mapped to a finer spatial grid. Unlike the bottom-up method that demands detailed statistics of traffic and building height and floor space to determine the overall growth of the entire urban area from the subsystem scale upward, the top-down approach is suited for estimating anthropogenic heat at large scales. On the regional scale, impacts on regional climate, human health and urban ecology are posed by anthropogenic heat through adding heat and water vapor in thermodynamic energy and water vapor equations. It has been reported that the annual mean warming across western Europe is 0.1 K to 0.5 K due to AHF. On the global scale, the effect of anthropogenic heat release on global temperature is not significant at present. However, with the increasing of energy demand, there will be more anthropogenic heat discharged and accordingly more effect on global climate system. For example, the global average temperature is projected to increase by 0.4 K to 0.9 K from 2004 to 2100 if the elevated rate of energy consumption in 2004 is maintained. AHF may also affect regional precipitation and disrupt global atmospheric circulation patterns. With soaring increscent of global energy demand and population especially in developing countries, there will be a large quantity of anthropogenic heat released into the atmosphere, which will become one of the anthropogenic forcing for regional and global climate change. It is therefore important to estimate a high precise dataset of anthropogenic heat for simulating its climatic effects.

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    Advances in study of reconstruction of regional forest net primary productivity based on tree rings
    Ouya FANG, Yang WANG, Xuemei SHAO
    2014, 33 (8):  1039-1046.  doi: 10.11820/dlkxjz.2014.08.004
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    Forest net primary productivity (NPP) shows the capacity of forest vegetation to convert or fix CO2 into compounds. As a reflection of forest carbon sequestration capacity, NPP is one of the main indicators of forest succession and carrying capacity of terrestrial ecosystems. Methods based on remote sensing or inventory data are limited by observation time, which makes the estimation of NPP over a long time period very difficult. However, tree ring data effectively reflect the history of forest growth year by year at decadal and centennial scales, and thus have great advantages in retrieving NPP of forest populations or communities in the past. It can be used to carry out long-term, dynamic, and continuous estimation and prediction of forest biomass, NPP, and dynamic status of carbon cycle. This article summarizes the main scientific research for reconstruction of regional NPP based on tree ring data. The results show that current studies mainly focus on two types of methods for reconstructing the NPP of forests: the first is to obtain forest growth volume in historical periods directly by measuring the radial growth and diameter at breast height of trees; the second is using correlation between vegetation index and tree ring index to infer the evolution of regional NPP in the past. The first approach can be further divided into two applications. Combined with survey data from sampling plots, NPP of the ecosystem can be evaluated by calculating total biomass and productivity of all single trees on the plot. In addition, models that contain tree ring data as an argument that can refer to the vegetation growth can be used to derive NPP of the ecosystems. Measuring forest annual biomass with tree ring data at plot level generates high precision results and the method is suitable for reflecting NPP change of small-area forest stands. For large-scale applications, however, as a result of widely spaced sampling sites this method produces low precision estimates of NPP. The second method is capable of dealing with high heterogeneity in NPP and vegetation indices, and has irreplaceable advantage in estimating forest biomass and NPP at large scales. In some areas, however, the method has limitations because of low correlation between tree ring index and vegetation indices. Accuracy of the results is also limited by the accuracy of remote sensing vegetation indices. Most of the results show that climate factors have conspicuous correlation with NPP in most places. Since the industrial revolution, the warming of the global climate and increasing CO2 concentration led to the increase of NPP of forest in most areas, especially in high latitudes in the northern hemisphere. These results are beneficial to ecosystem carbon sink and carbon balance evaluation in the climate change scenarios. However, assumptions and limiting factors are involved in the two methods. The spatiotemporal accuracy of NPP estimation using tree rings can still be improved in future research.

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    Effect of city administrative division adjustment on urbanization: a case study of Zhongshan City
    Yungang LIU, Jie JIN
    2014, 33 (8):  1047-1057.  doi: 10.11820/dlkxjz.2014.08.005
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    China has experienced a rapid urbanization period since the adoption of the opening-up policy and the economic reform from the late 1970s. The urbanization rate of China has reached 52.57% in 2012. According to the statistics, urban population of China increased from 373 million in 1996 to 712 million in 2012. Urban area also expanded from 13000 km2 to 45750.7 km2, which represents a 252% increase. How China achieves this tremendous rate of urban population growth and how this process occurs in such a short period of time became important questions in urban transition research. To understand the process and mechanism of urban making and urbanization in China, the role of local governments needs to be examined. Previous studies show that the rapid functional change of land use brings about a series of urban problems, such as pseudo-urbanization and passive urbanization. This paper explores the change of administration division of Zhongshan City, Guangdong Province, and found that the development of the South Area and the West Area of Zhongshan City has undergone a pseudo-urbanization to real urbanization process. The focus of the study is on the adjustment of administrative regions (AAR) implemented in Zhongshan City, Guangdong Province. Using an ethnographic examination of the AAR process and the role played by various stakeholders, we investigate the effects of the AAR, specifically, does it create "passive" or "fake" urbanization? In the conclusion, we further discuss the theory of urbanization in China and link it to the concept of government-led administrative unit adjusting urbanization. We argue that government-led adjusting urbanization is characterized by a transformation from passive and fake urbanization at the beginning of the process to proactive and real urbanization at later stages. Accordingly, rural land, populations, industry, and lifestyles are all converted into city property. The study used participatory observation and questionnaire survey methods. The result shows that the local government indeed pushed the urbanization by adjusting different administration districts, that is, engaged in the "government-led adjusting urbanization". It suggests that a long term and more inclusive examination method of Chinese urbanization mechanism is required, which should be more suitable in China than the western definition of urbanization. The "government-led adjusting urbanization" might be a special phenomenon only occurred in China. Whether it serves the purpose of the government remains a question that needs to be answered by further case study and research.

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    An allometric analysis of the scaling relations between population and urban area of Xinyang
    Yanguang CHEN, Li ZHANG
    2014, 33 (8):  1058-1067.  doi: 10.11820/dlkxjz.2014.08.006
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    The relationship between urban population and construction land area is supposed to follow the law of allometric growth, which is based on exponential growth or distribution. However, if we apply the allometric scaling law to Chinese cities using data from the statistical yearbooks of China, the relationship is often unclear or unconvincing, possibly due to the quality of the statistical data used. In this study, the ordinary least square method and log-linear regression analysis are employed to make a longitudinal allometric analysis of urban evolution of Xinyang, a medium-sized city of Henan Province, China. Population of the urban area (which is greater than the non-agricultural population of the same city) was estimated by using the census data from multiple years; the area of urban construction land was estimated using the land-use maps. The quality of these data is clearly higher than those provided in the statistical yearbooks. The result of the analysis shows that from 1949 to 2004, the urban population and area of construction land in Xinyang followed the allometric scaling law. During the period between 2007 and 2013, the scaling relation was disrupted due to the "city-making movement" in the context of an overheated economy based on real estate development and rapid urbanization. The following conclusion can be drawn: the urban evolution of Chinese cities follows the allometric growth law, but the allometric scaling can be disturbed by government policies in a largely command and control economy. The significance of this work lies in that, first, it provides a typical case of longitudinal allometry of China's cities for urban studies; second, it gives a set of models that can be used to estimate and project population size and urban land area of cities like Xinyang; and third, it lays a foundation for future allometric studies based on logistic growth rather than exponential growth.

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    Research progress and prospect on the identification of urban fringe
    Jian PENG, Jing MA, Yuan YUAN
    2014, 33 (8):  1068-1077.  doi: 10.11820/dlkxjz.2014.08.007
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    Urban fringe is a special region between urban and rural areas, and it is the most active and sensitive place in the process of urbanization. It is an independent and unified geographic entity with great change and diversity. Quantitative identification of urban fringe, that is, determining its location and defining its spatial reach based on the natural, social, and economic characteristics, is the starting point for further research on its social structure, landscape pattern, and development gradient, and is of vital importance for the research of ecological effects of urbanization. It has drawn great attention of scholars from different fields. However, the theories and methods of urban fringe identification have been lacking of focus and need a systematic research and review. Based on comparative analyses of related concepts of urban fringe, this article clarifies the essence and connotation of urban fringe and its identification. It then proposes a conceptual framework on the basis of "indicative factors-spatial units-identifying models" for implementing urban fringe identification and reviews the progresses both at home and abroad in these three aspects. Indicative factors are the quantitative elements that are chosen based on available socioeconomic statistics data or spatial data to distinctively represent the characteristics of urban area, urban fringe, and rural area. The selection of spatial units is subject to the indicative factors and identifying models, including grid cells and administrative units. Identifying models are critical in the identification process. This study found that urban fringe identification is changing from depending on statistical data to spatial data, and from using administrative units to spatial grids. Finally, this article presents the key directions of future research: examining interactions between urban and rural areas, which is the foundation of other research on urban fringe; comprehensive identification based on multi-factors and taking advantage of multi-source datasets; integrating non-parametric models for quantitative identification, which is more suitable for the non-linear human-environmental system; up-scaling/down-scaling and exploring the appropriate scale of analysis; and dynamic monitoring of long time series data.

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    Spatial-temporal evolution of Guangzhou subway accessibility and its effects on the accessibility of public transportation services
    Xiaoyan HUANG, Shuang ZHANG, Xiaoshu CAO
    2014, 33 (8):  1078-1089.  doi: 10.11820/dlkxjz.2014.08.008
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    Investigating effects of subway on urban public transportation network and accessibility is important because it contributes to sound planning of subway systems, improving urban public transport service accessibility, and providing possibility for the transformation of individual travel modes. This research uses the theories and methods of accessibility study to explore the relationship between the development of urban rail system and bus services, taking Guangzhou as an example. The study focuses on the status of public transportation system in four years (2000, 2003, 2009 and 2012). Data used in this study cover the stations and networks of buses and subways that come from our digital processing with GIS. Using published maps and Internet data as sources, this study established a database of public transport in different years. It uses complex network theory to establish the model of public transportation network in Guangzhou and quantitatively analyses the influence of urban rail system on bus accessibility through a comparison of the urban transportation network that incorporates urban rail system and the bus network that did not include urban rail system. The evolution of the spatial pattern of public transportation accessibility in different time periods is also discussed. Subway accessibility analysis is based on subway station and network accessibility and the change in center of high accessibility is analyzed to represent network accessibility change over time. The purpose of this study is to provide theoretical support for an integrated development of urban public transportation system through the analysis of the comprehensive influence of subway construction on urban public transportation. The principal findings of this study are as follows: (1) The Guangzhou subway network successfully completed the transformation from the tree-shaped to the loop network. The high accessibility center of the Guangzhou subway network moved to the east and south and this is consistent with the direction of the city's spatial expansion. (2) The incorporation of the urban rail system did have impacts on the overall accessibility of the public transportation network. (3) The subway network influences the spatial pattern of Guangzhou public transport accessibility. Along the metro line public transport accessibility is better than other regions. (4) Through the comparison of accessibility over years, we found that urban subway network expands residents' travel range and shorten travel time at the same time. As urban rail network continues to expand, public transport accessibility will steadily improve along the subway lines. This study only discusses transportation infrastructure-the subway and bus networks. Travel demand of city residents is not considered in this study. Future research can examine the coordination of the subway network and urban public transportation network and explore demand and supply of subway and bus networks by taking into account the distribution of resident travel demands..

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    Review on distributed hydrological modelling software systems
    Jingchao JIANG, A-Xing ZHU, Chengzhi QIN, Junzhi LIU, Lajiao CHEN, Hui WU
    2014, 33 (8):  1090-1100.  doi: 10.11820/dlkxjz.2014.08.009
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    Distributed hydrological modelling software systems are crucial because they provide technical support to the application of distributed hydrological models. Currently, applications of distributed hydrological models have exhibited new characteristics including multi-process synthesis simulation, a wide range of users, and intensive computation. Because of these new characteristics, the existing software systems are facing great challenges with respect to flexibility, usability, and efficiency. This paper reviews existing software systems for distributed hydrological models. Firstly, we analyzed the distributed hydrological modelling applications workflow including model structure determination, parameter extraction, model running, and calibration. The characteristics of existing software systems are discussed: (1) model structure flexibility of the existing software systems is divided into three types: no support of process and algorithm selection, only support of algorithm selection, and support of both process and algorithm selection; (2) parameter extraction methods of the existing software systems are divided into menu/command line and wizard method; (3) computing forms of the existing software systems are divided into parallel computing and serial computing; (4) computing modes of the existing software systems are divided into stand-alone and network mode. Secondly, we summarized the limitations of existing software systems with respect to their flexibility, usability, and efficiency. The limitations include the following: (1) contradiction between model structure flexibility and user knowledge dependence-the more flexible the model structure is, the more knowledge users need to have; (2) the existing methods of parameter extraction are too fussy for non-expert users; (3) the serial and stand-alone softwares usually encounter computing bottleneck as the appliaction scenario is data and/or computing intensive. In the last part of this paper, the emerging trends of distributed hydrological modelling software systems are discussed. These include (1) Modular modelling. The modular development ensures software reuse, but it is not enough when scale or semantic is unmatched, so the ontology knowledge needs to be considered; (2) Intelligent modelling. Using expert knowledge to realize model structure determination and parameter extraction and combining expert knowledge and optimization algorithm to parameter calibration is needed in future work; (3) On-line modelling. The development of cloud computing and network techniques makes on-line modelling practical. In addition, mobile terminals with powerful computing and storage capacity could be potential application platforms. This means that special user interface and data format are needed; (4) Parallel computing. Taking full advantage of new parallel programming standards (CUDA, OpenCL) and exploring the finer granularity parallelizability is an emerging trend. In addition, virtual simulation is another important trend.

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    Change in runoff seasonal distribution and the decomposition of contribution rate of impacting factors in the Wei River
    Shengzhi HUANG, Qiang HUANG, Yimin WANG, Yutong CHEN
    2014, 33 (8):  1101-1108.  doi: 10.11820/dlkxjz.2014.08.010
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    Investigating the change characteristics of seasonal runoff distribution and analyzing the contribution of the impacting factors will help to further understand the hydrological responses of river runoff to global warming and the increasingly intensified human activities in the Wei River Basin. In this study, concentration ratio and unevenness coefficient indices were employed to analyze the spatiotemporal trend of seasonal runoff distribution of the Wei River based on the runoff, precipitation, and potential evaporation monthly time series data in 1960-2005. The Mann-Kendall method was used to analyze the trend of the concentration ratio and unevenness coefficient at the Linjiacun, Zhangjiashan, and Huaxian Stations; the heuristic segmentation method was used to detect the change points of the runoff distribution characteristic values; and the slope change ratio comparison method was employed to quantitatively compute the contribution of climate change and human activities to the change in runoff seasonal distribution characteristic values. The results indicate that: (1) characteristic values of the observed season runoff distribution (concentration ratio and unevenness coefficient) of the Wei River show an upward trend and at the Zhangjiashan Hydrological Station these values show a remarkably increasing tendency, which is significant at the 99% levels. The risk of drought and flood has increased in this basin as a result of this change; (2) the characteristic values of the observed runoff seasonal distribution at the Linjiacun and Zhangjiashan Stations have a change point in 1973, while those at the Huaxian Station has no change point. The possible reason for this difference is that the Huaxian Station receives runoff from nearly the whole river basin where the effect of human activities, for example, construction of reservoirs and water diversion works, is limited. Part of the water diverted at the upper and middle reaches returns to the lower reach of the Wei River; (3) the contribution of climate change and human activities to the change in runoff concentration ratio and unevenness coefficient at the Linjiacun Station is 27.15%, 72.85% and 12.1%, 87.9%, respectively and that at the Zhangjiashan Station is 39.11, 60.89% and 4.62%, 95.38%, respectively. The main driving factor of the change in runoff seasonal distribution of the Wei River is human activities, but climate change has also played an important role. Since the Wei River Basin is a typical arid and semi-arid region, the findings of this research can be an useful reference for other similar areas of the world.

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    Classification and runoff simulation of data-scarce basins based on self-organizing maps
    Xuan YI, Feng ZHOU, Xinyu WANG, Yonghui YANG, Huaicheng GUO
    2014, 33 (8):  1109-1116.  doi: 10.11820/dlkxjz.2014.08.011
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    Runoff prediction in ungauged basins (PUB) is one of the difficult research areas in hydrological studies. Parameter replacement using data from similar basins is one of the common methods in dealing with the PUB problem. When basins are similar in physical properties, their hydrological behaviors are assumed to be also similar and thus the hydrological model parameters can be transferred from the donor basin to the target basin. However, it is hard to determine whether a donor basin is indeed similar to a target basin and therefore it is not always clear whether the parameters can be transferred between the basins. Existing research often focus on river basin PUB problem, with inadequate attention on lake basins that contain a number of river streams. This study addresses the PUB question using Lake Dianchi Basin as an example. Lake Dianchi Basin has a complicated river network as well as serious PUB problems. Self-organizing maps (SOM) and hierarchical clustering analysis (HCA) were jointly used to identify analogy basins based on 16 physical attributes, including area, length, slope, drainage density, Ke, mean elevation, average precipitation, six land use types and three soil types. SOM method with K-means cluster was applied to classify similar sub-basins into distinct groups and Davis-Bouldin index was used to determine the optimal group numbers. After 1000 iterations the 43 sub-basins were classified into seven groups (I-VII). This SOM-based classification result is the same as the result of HCA except for two sub-basins. Among the seven groups, group I, IV, and VII contains most of the sub-basins and the other four groups contain no more than three sub-basins each. Different groups have different characteristics and the classification result provides a guidance for local management of the lake basin. For instance, group I is located in high elevation area where the density of streams and infiltration rate of the soil are both low therefore the area is flood-prone, thus the local government should pay more attention on flood control in such area. HBV model was used to simulate the runoff process and for sub-basins where the simulation went well, their parameters were used in the cross-basin test. The cross-basins test was applied to test whether or not hydrological model parameters could be transferred between two sub-basins in the same group. Six stations in three groups were selected as examples and sub-basins in each two sub-basin pair are from the same group. The result shows that the HBV model performs well in the runoff simulation of Lake Dianchi Basin (R2≥0.718, NSE≥=0.495). The cross-basin test result is also very promising (R2≥0.654 and NSE≥0.472) — it proves that ungauged sub-basins could borrow the model parameters of gauged basins in the same group. Thus, this research provides a solution for solving the PUB problem in the Lake Dianchi Basin. This research provides a basis for solving the problem of lack of data for runoff modeling for the basin. Meanwhile, SOM visualizes multi-dimensional properties of the basin, which is useful for practitioners in water resource management to comprehensively understand the spatial distribution of hydrological characteristics of Lake Dianchi Basin.

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    Hydrodynamic characteristics of stable growth-rill flow on loess slopes
    Longsheng WANG, Qiangguo CAI, Chongfa CAI, Liying SUN
    2014, 33 (8):  1117-1124.  doi: 10.11820/dlkxjz.2014.08.012
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    : Rill erosion is the main way of slope erosion on farmland of the Loess Plateau. Rill erosion on slopes accounts for 70% of the total amount of erosion and plays an important role in soil erosion process on loess hillslopes. It is the beginning of qualitative change in the process of soil erosion. Studies of rill erosion can help control soil erosion on slopes, facilitate the development of agricultural production, and serve as the foundation of study of the development process of soil erosion. Natural rainfall may occur intermittently and rills may go through a second rainfall within a short time period. But studies on the dynamic characteristics of rill flow under these circumstances have been few. This research was carried out in the rainfall simulation lab of the State Key Laboratory of Soil Erosion and Dryland Farming on Loess from March to May 2010. Artificial rainfall was applied on a loess slope at an interval of 24 hours under two rainfall conditions, with the first rain that formed relatively stable rill followed by a light rainfall. The results show that: (1) rill flow velocity was impacted by slope length indistinctively. Average velocity of rill flow on slopes of different lengths was not very different. On the other hand, rill flow velocity was greatly influenced by rill morphology. Compared to 20° slope, rill density of 25° slope was higher, while its flow velocity was lower; (2) shear stress is jointly affected by flow discharge and slope. The Reynolds number and Froude number were significantly associated with flow shear stress-the Reynolds number is positively correlated with flow shear stress, but the Froude number had negative correlation with flow shear stress; (3) As the distance from the top of the hill increases, the Darcy-Weisbach resistance coefficient tends to increase as well. With the same rainfall intensity at the second time, the resistance coefficient of steep slope is higher. This indicates a close relationship between resistance coefficient and runoff and slope. There is a significant positive correlation between resistance coefficient and the Reynolds number. Higher Reynolds number means greater average flow rate and intensity. As a result of increased intensity of water flow, rill morphology is more complex and the flow resistance increases. Although the increased Reynolds number also means that the flow depth is larger, the test results show that the drag coefficient under the condition of steep slope is mainly affected by the velocity of flow.

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    Status and prospect of the hydrological effects of human activities in the Karst area
    Junyi ZHANG, Lachun WANG, Weici SU, Chunfen ZENG
    2014, 33 (8):  1125-1135.  doi: 10.11820/dlkxjz.2014.08.013
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    Under the background of global climate change and due to the vulnerability and sensitivity of Karst ecosystems and rapid exchange of surface water and groundwater, Karst hydrodynamic systems respond promptly to human activities and environmental change. Human activity has already become the main driving force of environmental change in Karst areas. Environmental degradation caused by the use of Karst water resources and human activities directly or indirectly influences the Karst water system. For example, biodiversity of caves have declined due to groundwater pollution. Vegetation degeneration, soil erosion, stone desertification, and other environmental problems caused by human activities have had a serious impact on the hydrological processes in the Karst region. Thus water problem has become an important limiting factor to the development of the Karst region. Based on the research of Karst ecological system and hydro-environmental characteristics, this paper focuses on summarizing works on the following water-related issues in Karst areas: hydrological effects of land use change; impacts of vegetation change caused by human activities on precipitation and runoff; hydrological effects of Karst water conservancy projects and water resource use; groundwater pollution and transmission and transformation of the main pollutants. On this basis, the paper summarizes the coupling mechanism between human activities and Karst water environment in the face of global climate change, the impact of human activities on the hydrological cycle and geological carbon cycle, as well as Karst water resource use, vulnerability assessment, and cave biodiversity, including the impact of environmental change on water cycle in Karst areas owing to short-term development, the effects of water conservancy projects, especially large-scale projects (such as cascade development) on hydrology and ecology. In recent years, concerns of global environmental change, especially global climate change promote the rapid development of the global carbon cycle research. Further study of the global carbon cycle and carbon accumulation process is dependent on a better understanding of the social-ecological-hydrological-Karst system. This system restricts material recycling and energy conversion of the carbon, water, and calcium cycles in the Karst area. Current research of such system focuses on the impact of human activities on Karst system structure and function, which ignores the variation of human adaptation in response to global climate change. Because of the fragile natural environment in Karst regions, the impact of global climate change is more significant than other areas of the same latitude, which results in more significant adaptive changes in the socioeconomic systems. The study of adaptive changes in socioeconomic systems in Karst areas and ecological processes and their environmental and hydrological effects, therefore, will further the analysis of environmental impacts of human activities from the systematic and global perspective, which has important theoretical and practical significance for further understanding of the role of human activity in global environmental change. The research of complex hydrological models and uncertainty quantification, and the study of human response to environmental changes and water cycle feedback mechanisms are the focus of future research.

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    Assessment of heavy metal pollution of bed sediment in the Lancang River
    Jilai ZHANG, Kaidao FU, Bo WANG, Liqiang CHEN, Jingyi SONG, Bin SU
    2014, 33 (8):  1136-1144.  doi: 10.11820/dlkxjz.2014.08.014
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    Bed sediment is the main carrier of heavy metals in rivers. Its heavy metal content is an important indicator of heavy metal pollution in the water environment. This study investigates heavy metal contents of bed sediments along the mainstream of the Lancang River in Yunnan and Tibet and assesses their pollution risks. In recent years, the accumulation of heavy metals in the aquatic system of the Lancang River has become a problem. With increasing industrialization of the region, water quality of the Lancang River is in general declining and sediments in many river segments contain a high concentration of heavy metals that is higher than the background values. As an international river, Lancang river's water quality affects the relationship of the riparian countries. This article focuses on the following three aspects of heavy metal pollution in the river: the distribution of heavy metals in the sediments of the river basin; the enrichment factors of heavy metal pollutants at the sampling sites along the main river stream; and geoaccumulation of heavy metals in bed sediments. This study uses 22 sediment samples collected from different control sites in the river basin. These samples were analyzed using X-ray fluorescence (XRF) analysis at the laboratory of Yunnan University for the content of eight heavy metals (Cr. Mn, Ni, Zn, As, Pb, Cu, and Co). Background values of these heavy metals used in the assessment of river sediment pollution came from the database of background of elements in soils of China. Two assessment methods (sediment enrichment factor and geoaccumulation index) were employed to evaluate the severity of contamination of various heavy metals in the river. The results of these assessments show that (1) the average concentration of the heavy metals in most parts of the main river stream is at the safe level, but the concentration is high in the middle reach of the river between Jiuzhou and Gongguo Bridge, due to the high geological background and Zn-Pb mining in the Bijiang River basin; (2) the result of sediment enrichment factor analysis indicates that anthropogenic influences concentrate mainly in the middle and lower reaches of the river. Geoaccumulation index analysis also shows that Cu, Pb, Zn contents of the sediments are higher in the transitional area between the middle and lower reaches of the river; (3) dams block the transportation of sediments and make heavy metal pollution of sediments discontinuous along the river. Human activities such as urbanizaion also have a clear impact on the heavy metal pollution of the nearby river sediments. Urban development, mining, and dam building have played a significant role in heavy metal pollution of the Lancang River. A comprehensive investigation of heavy metal pollution should be performed in the middle reache area where the concentration of heavy metals is at a high level.

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