To reconstruct the series of annual temperature in Central China from 1850 to 2008, we have applied the following data, including the phenodate data series of plants in spring derived from historical records, the data related to snowfall days in 4 sites of Hunan province derived from Yu-Xue-Fen-Cun in the archives of the Qing Dynasty, data from five tree-ring width chronologies. In the reconstruction, the instrumental observation data of annual temperature anomaly for the whole region was adopted as the calibrated series, and the stepwise regression was used for calibration with leave-one-out validation, together with variance matching. The results show that: (1) In Central China, temperature fluctuated at inter-annual and decadal scales since 1850, but increased rapidly after 1990, which exceeded the inter-annual and decadal variability before. Although the warm interval lasted 20 years from the mid-1920s to the mid-1940s, its warmth could not match with that of the 1990s-2000s. The coldest decades are the 1860s, 1890s and 1950s, while 1893 witnessed the lowest temperature. (2) There were decadal cycles of 10-20 years and 35 years in temperature variation in Central China, which contained a cycle of 12-14 years before the 1920s and cycles of 18-20 years and 35-years after the 1940s.
The Qinling-Daba (Qinba) Mountains, a key ecological zone of terrestrial ecosystem, has experienced a significant change of vegetation coverage in recent years, which is characterized by rapid climate change. Using MODIS-NDVI dataset, the current study investigated the patterns of spatiotemporal variation of vegetation coverage in the Qinba Mountains during the period 2000-2014. In addition, possible environmental factors affecting this variation were identified. Sen+Mann-Kendall model and partial correlation analysis were used to analyze the data, followed by the calculation of Hurst index in order to analyze future trends of vegetation coverage. The results of the study showed that (1) the Normalized Difference Vegetation Index (NDVI) of the study area revealed a significant increase during 2000-2014 (linear tendency 2.8%/10a). During this period, a stable increase was detected before 2010 (linear tendency 4.32%/10a), followed by a sharp decline after 2010 (linear tendency -6.59%/10a). (2) In terms of spatiotemporal variation, vegetation cover showed a "high in the middle and low in surroundings" pattern. High values of vegetation coverage were mainly found in the Qinba Mountains of Shaanxi Province, while low values of vegetation coverage were mainly observed in Longnan, Tianshui, and Gannan prefectures occupied by arable land. (3) The area covered with vegetation was larger than the degraded area, accounting for 81.32% and 18.68% of the total area, respectively. Piecewise analysis revealed that 71.61% of the total study area showed a decreasing trend in vegetation coverage during 2010-2014, of which, the extremely significant and significant decrease accounted for 6.38% and 3.45%, respectively. (4) The reverse characteristics of vegetation coverage change were stronger than the same characteristic in the Qinba Mountains. Some 46.89% of the entire study area is predicted to decrease in future, while 34.44% of the total area will follow a continuous increasing trend. (5) The change of vegetation coverage was mainly attributed to the deficit of precipitation. At the same time, vegetation coverage during La Nina years was larger than that during El Nino years. Statistical analysis showed that positive and negative anomaly pixels accounted for 28.37% and 71.63%, respectively during El Nino years and 80.48% and 19.52%, respectively during La Nina years. (6) Human activities can induce ambiguous effects on vegetation coverage: both positive effect (through the implementation of the ecological restoration project) and negative effect (through urbanization) were observed.
Based on previous studies, the climate drought index can be used to assess the evolution trend of ecological environment under various arid climatic conditions. It is necessary for us to further explore the relationship between vegetation coverage (index) and climate drought conditions. Therefore, in this study, based on MODIS-NDVI products and meteorological observation data, the Palmer Drought Severity Index (PDSI) and vegetation coverage in North China were first calculated. Then the interannual variation of PDSI and vegetation coverage over 2001-2013 was analyzed by using a Theil-Sen slope estimator. Finally in an ecoregion perspective the correlation between them was discussed. The experimental results demonstrated that PDSI index and vegetation coverage value varied over different ecoregions. During the period 2001-2013, vegetation coverage increased in southern and northern mountains in North China, while it showed a decreasing trend in Beijing-Tianjin-Tangshan City Circle area and suburban agricultural zone. During the 13 years, the climate of the northeastern part of North China became more humid, while in the southern part of North China, it tended to be dry. According to the correlation analysis results, 73.37% of North China had a positive correlation between the vegetation coverage and climate drought index. A negative correlation was observed mainly in urban and periurban areas of Beijing, Tianjin, Hebei Province and Henan Province. In most parts of North China, drought conditions in summer and autumn had more influence on vegetation coverage.
It is very important to determine how many sedimentary cycles are in the flood sediments underground in Kaifeng city. But traditional method dividing sedimentary cycle with granularity cannot be used in the sediments under the city because the original granularity sequence of the sediments were greatly affected by human activities, such as city reconstructions and treasures excavation. after flood events. Therefore, it is necessary to use other proxy indicators instead of granularity. Black carbon (BC) is a chemically heterogeneous class of carbon compounds formed during incomplete combustion of biomass or fossil fuels. It is widely distributed in environmental mediums, and can be well-preserved for quite a long time. In this paper, we use BC content in flood sediments as a new proxy indicator to divide sedimentary cycles of the sediments underground in Kaifeng. Two sedimentary cores of 25 m were drilled in May, 2012. One (ZKsz) is at the central urban area of Kaifeng, and the other (ZKjm) is at the western suburbs. The core section was split fresh in the field at a 10 cm interval and a total of 434 samples were acquired and stored in boxes. The different grain sizes less than 0.25 mm of the sediments were measured with Laser Particle Size Analyzer (LA-9200, HORIBA, Japan), and those larger than 0.25 mm were measured by sieving. BC contents in bulk sediments were measured using the method recommended by Lim in 1996 with minor modifications. Sedimentary cycles were divided based on the wavelet analysis with the help of MATLAB 7.0 software. The results show that most boundaries of the sedimentary cycles based on granularity is consistent with BC contents in the ZKjm drill core, which was less disturbed by human activities, suggesting that BC contents can be used as another proxy indicator dividing sedimentary cycles. The boundaries of the granularity sedimentary cycles of the ZKsz core are almost the same as BC sedimentary cycles from 8.8 m to 23.5 m. The upper core from 0.3 m to 8.8 m of the ZKsz core that formed after the Song Dynasty can be divided into two granularity sedimentary cycles, but seven BC sedimentary cycles.
Multiple glacial advances/retreats have occurred in Kanas region of the Altay Mountains. Glacial erosive and accumulative landforms are not only very important for the analysis of the regional geomorphological process but also meaningful for the research on global change. According to the field investigation on the Quaternary geomorphology in the lower part of the Kanas Lake outlet in the main valley, this paper measured the altitude of multiple level U-shaped valley in different regions and confirmed the highest limit of glacial boulders and their spatial distribution. Using the electron spin resonance (ESR) method, we dated the glacial tills of the different moraines preserved along the main valley. Results of the glacial sequences, extent and glacial geomorphological process showed that four glacial advances occurred the lower part of the Kanas valley. Compared with the previous research results, these glaciations can be assigned as the Zhonglianggan glaciation, corresponding to the marine isotope stage 12 (MIS12), MIS8/10 glaciation, Penultimate glaciation (MIS6), and the last glacial cycle (LGC). LGC glacial advance can be further divided into three stages which correspond to MIS 4, 3, and 2. Based on the distribution of the three level U-shaped valleys, we concluded that the extent of glaciers decreased with time. The thickness of the glacier during Zhonglianggan glaciation was 50-395 m from the Glacial Station to the end of the glacier, and the length and width are also the largest at that time. The three-dimension extent showed that the glaciers were distributed in the main valley and on both sides of the ridges. The thickness was 102-199 m and 88-269 m during the MIS8/10 and the Penultimate glaciation, and the glacier reached near Tuojingwan. Well persevered multiple level U-shaped valley bottom on the eastern slope of the main valley near the region of Yazehu Lake indicated that the Quaternary glaciers have the warm glacier features such as strong activities, flowability and continuity. Clear asymmetry that occurred in the Kanas main valley showed that the development of the glacial valley was affected by regional climate and topography.
A coastal dune, Dongshan (DS) dune in Changle of China's Fujian Province is selected as a research object based on the systematic field investigation. Combined with the environmental index analysis and geological radar images, the dune development history and paleoenvironment significance in the study area since the late Holocene are explored through optically stimulated luminescence (OSL) chronology. Results are shown as follows. (1) Five sedimentary periods and three sedimentary discontinuity in the DS dune can be defined, which reflects that the change of the East Asian monsoon, and the developmental process of DS dune are the result of regional response to the East Asian winter monsoon, and they are well correlated with volcanic activity, winter temperatures of East China and precipitation of summer monsoon at the same time. (2) Meanwhile, DS profile has preserved the sea-level change information of the Fuzhou Basin since nearly 6 ka BP. The widespread thalassocratic periods were recorded clearly in South China at 5.6-2.8 ka BP, 2.8-1.7 ka BP and 1.7-0.8 ka BP, respectively. (3) Artificiality and the mark of human activity are observed in the DS dune, and porcelain shards and conchs have been found in the cultural layer. The development processes of the DS dune accord well with the records of human activities and neolithic cultural sequences in northeast Fujian. The human activities are mainly affected by the natural environment at 5.6-2.8 ka BP and 2.8-1.7 ka BP, respectively. Tang and the Five Dynasties were the recovery stages of social economy in Fujian after 1.7 ka BP.
With the population increase and food consumption upgrade in China, the issue of food self-sufficiency attracts much attention from both Chinese government and international society. Under the circumstances of inadequate cropland resources supply and plenty of cropland occupied by urban construction, improving the utilization efficiency of arable land resources and increasing the cropland productivity have become the fundamental strategies of agricultural development in China. Since 1988, cropland improvement projects (medium-yield and low-yield field improvement and high-standard cropland construction) have been launched and implemented on a large scale, therefore a spatially explicit map for the distribution of high-, medium- and low-yield cropland was essential for cropland improvement planning. In this study, a new method for recognizing high-, medium- and low-yield field is developed based on cropland productivity, which is calculated by using a light use efficiency model and MODIS data with a 500-m resolution. This method can not only reflect the regional heterogeneity of cropland condition, but also express the spatial differences on a grid scale. At the same time, it effectively overcomes the shortage of statistical data based method in a county unit. The results show that the proportion of high-yield, medium-yield and low-yield cropland in China is 20.66%, 39.56% and 39.78%, respectively. About 3/4 of low-yield cropland is located in the hilly and mountainous regions, while 53% of the high-yield cropland is located in plain area. The five provinces with the largest area of high-yield cropland are Henan, Shandong, Jiangsu, Hebei and Anhui, which are all located in the Huang-Huai-Hai region. The sum of the high-yield cropland area in these five provinces accounts for 41.75% of the national total high-yield cropland area. In Heilongjiang province, Sichuan province and Inner Mongolia autonomous region, where the cropland area ranks the top three of China, the proportion of high-yield cropland area in each province only accounts for not more than 15%.
The primary goal of this study is to build a resilience evaluation system with stability landscape based on the theory of basin model which reflects the characteristics of resilience. The study proposes the socio-ecological system resilience indicators of tourist destination, including the fragility, and response capacity in social, economic and ecological subsystems. In particular, by adopting the set pair analysis, the paper empirically measures the socio-ecological system resilience, identifies the main factors influencing resilience, and illustrates the mechanism that influences the tourism socio-ecological system. In addition, the paper introduces curve distribution patterns of Qiandao Lake. The results are as follows: (1) During the period 1987-2012, the socio-ecological system fragility index in the Qiandao Lake slowly increased from 0.4576 to 0.5622, the index of adaptive capacity rose rapidly from 0.0282 to 0.9725, and the resilience index rose steadily from 0.1276 to 0.8669. The resilience should be the result of the interaction between fragility and response capability. (2) The total fragility is mostly affected by the ecological subsystem, whereas the total response capacity, by the economic subsystem. The social and economic subsystems, however, directly affect the total resilience. As a matter of fact, the total response capacity plays a decisive role in resilience, in which response capacity of social and economic subsystems are more significant, although the system itself also has certain resistance and resilience. (3) In each subsystem, the resilience factors are divided into two categories respectively with regard to the fragility and response capacity. The fragility consists of the base elements of the subsystems and the relevant variables brought about by tourism development. The response capacity mainly includes the input and storage factors in every subsystem. (4) In the socio-ecological system of tourist destination, the relationship between the impact factors and the resilience falls into roughly six curve types. On the one hand, there are two types of linear relationships between the resilience and ecological background conditions, social stability, industrial livelihood and ecological control measures. The one is in the trend of progressive increase and the other, of progressive decrease. On the other hand, U-shaped curves or inverted U-shaped curves, are mainly related to fragility indexes and response capacity indexes brought by tourism development. In terms of impact direction, rates and ways, the influence curve of resilience factors can be divided into four types, namely U-shaped increasing curve, U-shaped decreasing curve, inverted U-shaped curve which increases fast at first and then decreases slowly, and inverted U-shaped curve which increases slowly at first and then decreases fast. In conclusion, nonlinear effects still dominate. There are differences and uncertainty in the direction and rate of the factors. The results, in fact, further confirm the nonlinear thought of resilience and the applicability of the set pair analysis method.
This paper presents an analysis of the spatio-temporal distribution of cultural sites in the Ili River Valley in Northwest China based on the application of ArcGIS software. It further explores the relationships between the spatio -temporal evolution of the sites, human history, and the natural environment. The results indicate that the numbers and proportions of the sites, and the frequency of their occurrence, exhibited an inverted V-shaped change trend during six historical periods. These covered the initial, peak, and declining stages of six periods extending from the Xia-Western Zhou dynasties to the Qing-Modern period. The spatial distribution pattern shifted from "high in the east and low in the west" during the first three periods to "high in the west and low in the east" during the latter three periods, illustrating a change in the spatial center of gravity of human activities. The sites were mainly distributed on slopes of grades 1-5. The proportion of sites increased from 75% during the Spring and Autumn-Qin dynasties to 93.75% during the Qing-Modern period. The concentrated distribution of site elevations shifted from grades 4-8 during the Spring and Autumn-Qin dynasties, and the Western Han-Northern and Southern dynasties to grades 1-4 during the latter three periods. The number of sites showed a shifting trend from high mountains and hills to low plains, and from high slopes to low slopes. In particular, the evolutionary pattern of sites in the study area exhibited a special "moist" pattern of migration from middle and upstream areas to downstream areas, as opposed to the migration pattern of sites located in typical arid areas. The paper also includes a discussion of factors influencing the distribution and spatio -temporal evolution of cultural sites, notably, human factors such as politics, economy, and productivity, and natural factors such as geomorphology, altitude, slope, and climate. Although the distribution and spatio -temporal evolution of cultural sites exhibited an orientation toward natural laws pertaining to factors such as river valleys, terraces, plains, and water resources, they presented a significant orientation toward laws, relating to human-driven forces including productivity levels, political stability, economic development, business and trade, and transport, which were more evident during the latter historical periods.
This paper provided a comprehensive review of evapotranspiration data assimilation based on hydrological model. The difficulty and bottleneck for ET was elaborated to construct data assimilation relationship as a non-state variable, with a discussion and analysis about the feasibility of various hydrological models to assimilate ET. Based on this, a new evapotranspiration assimilation scheme was proposed. The scheme presented developed an improved data assimilation system that use distributed time-variant gain model (DTVGM) which contains evapotranspiration-soil humidity nonlinear time response relationship. Moreover, the evapotranspiration mechanism in DTVGM was improved to perfect the ET data assimilation system.
Spatial and temporal variations of river systems in the Yangtze River Delta (YRD) during the 1960s-2010s were investigated based on streams derived from the topographic map in the 1960s, 1980s and 2010s. A list of indices, drainage density (Dd), water surface ratio (WSR), the ratio of area to length of main river (R), evolution coefficient of branch river (K) and box dimension (D), were classified into three types (quantitative, structural, and complex indices) and used to quantify the variation of stream structure. Results showed that: (1) quantitative indices (Dd, WSR) presented a decreasing trend in the past 50 years, and Dd in Wuchengxiyu, Hangjiahu and Yindongnan decreased by about 20%. Structurally, the Qinhuai river basin was characterized by a significantly upward R, and K value in Hangjiahu went down dramatically by 46.8% during the 1960s-2010s. A decreasing tendency in D was found to dominate the YRD, and decreasing magnitude in Wuchengxiyu and Hangjiahu peaked for 7.8%, and 6.5%, respectively in the YRD. (2) Urbanization affected the spatial pattern of river system, and areas with a high level of urbanization exhibited least Dd (2.18 km/km2), WSR (6.52%), K (2.64) and D (1.42), compared with moderate and low levels of urbanization. (3) Urbanization also affected the evolution of stream system. In the past 50 years, areas with high level of urbanization showed a compelling decreasing tendency in quantitative (27.2% and 19.3%) and complex indices (4.9%) and trend of enlargement of main rivers (4.5% and 7.9% in periods of the 1960s-1980s and 1980s-2010s). (4) Expanding of urban land, construction of hydraulic engineering and irrigation and water conservancy activities were the main means.
Based on the materials of water depth of 1958-2013 in the Yangtze Estuary channel, this article established the database of water depth during different periods with the aid of the Arcmap analysis software. The results showed that: (1) The state of the north passage channel was basically stable, and the river channel in the south passage was experiencing a developing stage. The developing center of the south passage channel was observed in the lower reach, while the upper reach of the north passage channel had slightly shrunk. (2) Currently, the south and north passages were still shifting under the effect of the project. The area where the tidal increased was mainly found in the south passage and south channel. The developing pattern in the north passage was fixed and confined. (3) In the study period, with the reduced amount of sediments from the catchment and the construction of the deep sea waterway project in the north passage, the tidal volume, suspended sediment flux and the ratio of them changed obviously. (4) The sediments in the north and south channels are concentrated in the lower part of the north channel and also in the south and north passages.
Sand mining has been practiced in rivers, lakes, harbors and coastal areas in recent years in China mostly because of the increasing demand for building materials in construction industry. Sand mining in Poyang Lake has been intensified since 2001 because such practice was banned in the Yangtze River and profitable. Meanwhile, the decline of water level of the Poyang Lake has aroused much more attention from researchers. The decline has been ascribed to a decrease in precipitation in Poyang Lake watershed, attenuation of congestion effect because of the Three Gorges Project and sand mining in the Poyang Lake.
In this study, we analyzed the magnitude of sand mining in Poyang Lake using Digital Elevation Model (DEM) data from two periods and sand vessels distribution detected by remote sensing images. Another two Landsat images were used to evaluate the morphologic change compared with natural sedimentation, inundation extent and shoreline shape. And a hydrological dataset including water level, water discharge rate and sediment content for a long time series were used to analyze the hydrological effect and sediment effect from sand mining. Results showed that: (1) sand mining region was mainly distributed in northern Poyang Lake before 2007, but was extended into the central region and even to the channels of major tributary rivers into the Poyang Lake; (2) the area of sand mining was about 260.4 km2. The magnitude of sand mining in Poyang Lake was about 2,154.3 Mt or 1.29×109 m3 during 2000-2010 with the assumption of sand bulk density of 1.67 t m-3. It is almost 6.5 times of the natural sedimentation in volume during 1955-2010; (3) sand mining affected the hydrologic regimes including increased areas of water discharge sections and water turbidity. Sand mining could be one of the most important factors that caused the decline of water level of Poyang Lake in drought season. It also affected the sediment pattern of the lower reaches of the Yangtze River.
