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  • 2013 Volume 68 Issue 7
    Published: 27 July 2013
      
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  • Radiative forcing over China due to albedo change caused by land cover change during 1990-2010
    ZHAI Jun, LIU Ronggao, LIU Jiyuan, ZHAO Guosong
    2013, 68(7): 875-885.
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    Land cover change affects surface radiation budget and energy balance by changing surface albedo, and further impact the regional and global climate. In this paper, the high spatial and temporal resolution remote sensing data were used to analyze the driving mechanism for surface albedo change caused by land cover change during 1990-2010. In addition, the annual scale radiative forcing caused by surface albedo changes in national 50 ecological regions were calculated to reveal the biophysical mechanisms of land cover change affecting climate change at regional scale. Results showed that during 1990-2010, the national land cover change were mainly caused by land reclamation, grassland desertification and urbanization, which were all induced by human land-use activities. Grassland and forest area decreased by 0.60% and 0.11%, respectively; while construction land and farmland area increased by 0.60% and 0.19%, respectively. The mean radiative forcing caused by land cover change during 1990-2010 was 0.062 W/m2 in China, indicating a warming climate effect. However, its spatial heterogeneity was very huge in different ecological regions. Conversion of farmland to construction land, as the main type of land cover change in the Beijing-Tianjin-Tangshan urban and agricultural suburban agro-ecological region, caused an albedo reduction of 0.00456, and the maximum positive radiative forcing was 0.863 W/m2 with warming climate effect. Conversion of grassland and forest to farmland, as the main type of land cover change for the Sanjiang plain temperate-humid agriculture and wetland ecological region, caused an albedo increase of 0.00152 and the maximum negative radiative forcing was 0.184 W/m2 with cooling climate effect.
  • Spatial-temporal variations of lake area in Hoh Xil region in the past 40 years
    YAO Xiaojun, LIU Shiyin, LI Long, SUN Meiping, LUO Jing, FENG Yaya
    2013, 68(7): 886-896.
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    As one of the areas with numerous lakes on the Tibetan Plateau, the Hoh Xil region plays an extremely important role in the fragile plateau eco-environment. Based on topographic maps in the 1970s and Landsat TM/ETM+ remote sensing images in the 1990s and the period from 2000 to 2011, the data of 83 lakes with the area above 10 km2 were obtained by digitization method and artificial visual interpretation technology, and the causes for lake variations were also analyzed. Some conclusions can be drawn as follows. (1) From the 1970s to 2011, the lakes in the Hoh Xil region firstly shrank and then expanded. In particular, the area of lakes generally decreased during the 1970s-1990s. Then the lakes expanded during the 1990s-2000 and their area was slightly higher compared with the 1970s. The area of lakes dramatically increased after 2000. (2) From 2000 to 2011, the lakes with different area scales in the Hoh Xil region showed an overall expansion trend. Meanwhile, some regional differences were also discovered. Most of the lakes expanded and were widely distributed in the northern, central and western parts of the region. Some lakes merged together or overflowed due to their rapid expansion. A small number of lakes with the trend of area decrease or strong fluctuation were scattered in the central and southern parts of the study area. And their variations were related to their own supply conditions or hydraulic connection with the downstream lakes or rivers. (3) The increase in precipitation was the dominant factor resulting in the expansion of lakes in the Hoh Xil region. The secondary factor was the increase in melt water from glaciers and frozen soil due to climate warming.
  • The spatial-temporal changes of vegetation coverage in the Three-River Headwater Region in recent 12 years
    LIU Xianfeng, REN Zhiyuan, LIN Zhihui, LIU Yanxu, ZHANG Donghai
    2013, 68(7): 897-908.
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    The Three-River Headwater Region is the source areas of the Yangtze River, the Yellow River, and the Lancang River. The region is not only of key importance to the ecological security of China. Due to climate change and human activities, ecological degradation occurred in this region. Therefore, "The nature reserve of Three-River Source Regions" was established, and "The project of ecological protection and construction for the Three-River Headwater Nature Reserve" was implemented by Chinese government. This study, based on MODIS-NDVI and climate data, aims to analyze the spatial-temporal changes of vegetation coverage and its driving factors in the Three-River Headwater Region between 2000 and 2011 from three dimensions. Linear regression, Hurst index and partial correlation analysis were employed. The results showed that: (1) In the past 12 years (2000-2011), the NDVI of the study area increased, with a linear tendency being 1.2%/10a, of which the Yangtze and the Yellow river source regions presented an increasing trend, while the Lancang River source region showed a decreasing trend. (2) Vegetation coverage presented an obvious spatial difference in the Three-River Headwater Region, and NDVI frequency was featured by a bimodal structure. (3) The vegetation coverage improved area was larger than the degraded area, being 64.06% and 35.94% respectively in the 12 years, and presented an increase pattern in the north and a decrease one in the south. (4) The reverse characteristic of vegetation coverage change is significant. In future, the degradation trends will be mainly found in the Yangtze River Basin and north of the Yellow River, while the improving trend areas are mainly distributed in the Lancang River Basin. (5) The response of vegetation coverage to precipitation and potential evapotranspiration has time lag, while the temperature does not have. (6) The increased vegetation coverage is mainly attributed to the warm-wet climate change and the implementation of the ecological protection project.
  • Discussion of the difference of the timing and extent of glaciers in the late Quaternary controlled by the westerly and East Asia monsoon as well as the tectonic movement
    ZHANG Wei, DONG Yingwei, YU Zhilong, HE Mingyue
    2013, 68(7): 909-920.
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    The mechanism of the evolution of the Quaternary glaciers in the high Asia in the low and middle latitude has been deeply researched during the last several decades with the increase of the absolute dates. Researchers definitely focused on the timing and extent of the glaciers in the Tibetan Plateau and the Himalaya. This provides the beneficial conditions for the recognition of the difference of the glaciers controlled by the westerly and the South Asia monsoon. However, lack of the wide study makes it difficult to examine the correlation of the glaciers evolution with the westerly and the East Asia monsoon in the central Asia and eastern China. Research result shows that the timing and extent between them are different. That is, the onset of the glaciers in the west China is earlier than that in the eastern China with the glacial sequence, and the glacial extent decreased with the time. Compared with the western China, only last glacial remains have been persevered in and along the islands of eastern Asia. The difference of the glacial timing and extent indicates that the factors influencing the glaciers are not only the regional climate but also the tectonic movement.
  • Spatial variation of hypsometric integral in the Loess Plateau based on DEM
    ZHU Shijie, TANG Guo'an, LI Fayuan, XIONG Liyang
    2013, 68(7): 921-932.
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    Hypsometric integral is a terrain analysis factor with apparent physical and geomorphologic meanings which could reflect the landform erosion stage and evolution process. As a macroscopic parameter and method in terrain analysis, the applications of hypsometric integral could reveal the quantitative characteristic of landform evolution in catchment scale. In this paper, 5 m resolution DEMs and 3 arc-second resolution SRTM DEMs are used respectively to identify the impact factors of HI and its spatial variation in the Loess Plateau. Firstly, the geomorphologic meaning is discussed and summarized. The effect of DEM resolution and the analysis area in HI calculating is probed. With different DEM resolutions, the HI values derived could keep almost the same. When the area of catchment reaches 10 km2, the HI tends to be stable, which is regarded as a critical area for extracting HI in this study. Then, the geomorphic feature HI is proposed and the correlation of each kind of HI is calculated. There exist two feature groups in which the correlation coefficient is rather large. They are respectively catchment HI, positive terrain HI, shoulder line HI and peak HI, ridge line HI, and catchment boundary HI. Finally, the landform division based on HI is created through multiresolution segmentation in loess area. The coupling relationships exist in this division and water & soil loss map, sediment transport value map. The division in this paper refines the original map to a certain extent.
  • Comprehensive analysis of lake sediments in Yanchi Lake of Hexi Corridor since the late glacial
    LI Yu, WANG Nai'ang, LI Zhuolun, ZHOU Xuehua, ZHANG Chengqi
    2013, 68(7): 933-944.
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    Yanchi Lake is located in the northern Qilian Mountains and the central Hexi Corridor, which is a key research area for the long-term northern boundary changes of the Asian summer monsoon. Modern climate research shows that the Asian summer monsoon moisture transport is limited to the eastern part of Qilian Mountains. On the Holocene millennial-scale, whether the northwest boundary of the summer monsoon varies according to climate change is a key scientific issue. Paleoclimatic data, including AMS 14C dates of pollen concentrates, lithology, grain-size, mineral composition and geochemical proxies were acquired from lake sediments of Yanchi Lake. The chronological results show that the lower part of the lacustrine section is formed mainly in the late glacial and early Holocene period, while the proxies' data indicate that the lake expansion is associated with high contents of mineral salts. The middle part of this section is formed during the transition period of the early and middle Holocene. The AMS 14C ages of pollen concentrates from the middle part of the section are generally older than those from the lower part. Proxy data indicate that the lake began to retreat since the transition period of the early and middle Holocene. When the lake level is relatively low, the location of the lacustrine section is near the lake edge. Reworking effects of lake sediments are strong on the lake edge; therefore, the ages are relatively old. Since the mid-Holocene, Yanchi Lake retreated significantly and the deposition rate dropped obviously. The Yanchi Lake record is consistent with the late glacial lake records on the Qinghai-Tibet Plateau and in the typical monsoon domain, which shows the late glacial and early Holocene lake expansion and the strong Asian summer monsoon. The long-term monsoonal pattern is different from that of the lake evolution in Central Asia on the Holocene millennial-scale. This study suggests that the monsoon has impacts on the northwest margin of the summer monsoon, and also proves the fact that the northern boundary changes of the summer monsoon are related to millennial-scale climate change.
  • Sedimentary and morphological evolution of nearshore coast of Yangtze Estuary in the last 30 years
    JI Na, CHENG Heqin, YANG Zhongyong, HU Hao, CHEN Zujun
    2013, 68(7): 945-954.
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    By analyzing the status quo of tidal flats and nearshore areas, including the sedimentary and morphology with different historical charts and observations of the Yangtze Estuary, the paper discusses the evolutions of nearshore coast of the Yangtze Estuary and its influencing factors in the last 30 years. The results show that: (1) the sediments collected on the tidal flats in the northern part of the Yangtze Estuary changed from coarse to fine, while sediments of the southern part became coarse, especially those near the large construction sites, including the north bank of Eastern Hengsha Shoal, Yangtze River Bridge and East China Sea Bridge; (2) the width of tidal flats in certain parts of the Yangtze Estuary decreased by more than 90%; the morphological characteristics of nearshore profiles were characterized by erosion, including concave and steep slope; the depth of closure (D℃) of Nanhuizui nearshore area from 1978 to 2004 kept at -8 m, while it was scoured by about 1 m because of the bottom erosion in recent 10 years; (3) the erosion characteristic of nearshore area in the Yangtze Estuary resulted mainly from the reduction of basin sediment loads; intensive human activities, including reclamations, Qingcaosha reservoir and bridge constructions resulted in the reduction of tidal flats and the coarsening of sediments; sand ridge migration had a great impact on the nearshore coast of the channels in the Yangtze Estuary.
  • A morphological analysis of tidal creek network patterns on the central Jiangsu coast
    WU Deli, SHEN Yongming, FANG Renjian
    2013, 68(7): 955-965.
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    This paper details the two-dimensional geomorphology of the tidal creek systems and their migration characteristics using MSS, TM/ETM + data of 1981-2010 and field investigation. The results show that the tidal creeks in this area could be divided into four grades according to their lengths: 7587±1544 m, 1921±916 m and 327±200 m with numbers of 21, 97 and 688 (1:5:33), respectively. The tidal creeks within the study area were well developed in the middle tidal belt, and their drainage density and bifurcation ratio were much greater than those in the high and low tidal belts. The curvature of main tidal creek decreased from high tidal belt to the low one. The development of tidal creeks are influenced by the exotic introduction of Spartina alterniflora, and obviously restrained by the reclamation activities. The lateral migration or sway of the tidal creeks exhibited significant difference in rank and region. Compared with the tidal creek systems in the northern part of the area studied, those in the southern part with a larger tidal range have a larger lateral movement ranges and migration rates; as for a tidal creek system, the sway intensity of a first-order creek is greater than that of a second-order creek, followed by a third-order creek; for a single tidal creek, the case is the lower segment > the middle segment > the upper segment; and within an individual segment, the migration intensity of the curving segment is greater than that of the straight segment. The lateral migration is not obvious in the upper segment of the first-order creeks, the middle and upper segment of the second-order creeks, the third-order creeks and the creeks in the S. alterniflora salt-marsh.
  • Temporal and spatial changes of river systems in Hangzhou-Jiaxing-Huzhou Plain during 1960s-2000s
    XU Guanglai, XU Youpeng, WANG Liuyan
    2013, 68(7): 966-974.
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    Based on the topographic map data in 1960s, 1980s and 2000s, the temporal and spatial changes of river networks of Hangzhou-Jiaxing-Huzhou Plain region were analyzed from aspects of the river density (DR), rate of water area (WP), development coefficient of the river network (Kω), the ratio of area-length of main river (RAL) and box dimension (D0) etc. The results showed that: (1) DR and WP presented a decline trend during the 1960s-2000s with river length decreased by 11023.33 km (about 38.67%) and water area decreased by 151.58 km2 (about 18.83%), and the trend was still intensifying. (2) Kω also showed a decline trend with K2 decreasing from 1.41 to 1.35 (a decrease of 3.9%) during the 1960s-1980s and to 0.15 during the period of 1980s-2000s (decreased by 88.6% ). And the main rivers were gradually dominant in river network in the process of urbanization. (3) The spatial variation of the river network was obvious, the southern regions with an intensive river network was the most dramatic. (4) Each river system has its characteristics under different underlying surface conditions. Wp was smaller with 4.9%-9.4% in city regions. The DR and WP had decreased since the 1960s. Some river channel projects for dredging and urban flood control were implemented in the process of urbanization. In the regions of intensive river network (DR was 2.1-5.3 km/km2), there was a significantly decreasing trend of tributary rivers, and an increasing trend of main rivers. In the lake regions with bigger WP (about 17.8%-19.7%), there were no significant changes of river system pattern.
  • The relationship of nature runoff changes in flood-season of middle Yellow River and Yongding River, 1766-2004
    PAN Wei, ZHENG Jingyun, XIAO Lingbo, YAN Fangfang
    2013, 68(7): 975-982.
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    Reconstruction of river runoff has been an important component of paleo-climatology and paleo-hydrology. The Yellow River and Yongding River are two major surface drainage systems in North China. In this paper, both of them were studied to reconstruct annual flood-season runoff from 1766 to 2004 at Sanmenxia station (Yellow River) and Lugouqiao station (Yongding River) using the water level records and Yu-Fen-Cun records in the Qing Dynasty documents and modern hydrological records. We reconstructed the annual flood-season runoff of Yellow River (Sanmenxia station) and Yongding River (Lugouqiao station), with the average of 109.0 m3/s (Yongding River) and 5121.1 m3/s (Yellow River), respectively. In this article, the extreme flood/dry years are reconstructed based on a new method. Based on the two runoff series, we find that the synchronization of the Yellow River and Yongding River existed in a specific period, and during 1840-1860s and 1890-1910s, the synchronization disappeared, and the inverse correlation was very obvious. The wavelet shows that there was a 30-year cycle in both of the rivers; however, after the 1920s the cycle disappeared in the Yongding River. On a 60-80a scale, the changing runoff of the Yellow River was earlier than that of the Yongding River. In MWP, the inverse correlation in the trend of the two rivers was more obvious. Warm period, PDO and sunspot number have affected the changes of river runoffs in North China.
  • Wide expansion of glacial lakes in Tianshan Mountains during 1990-2010
    WANG Xin, WU Kunpeng, JIANG Lianghong, LIU Shiyin, DING Yongjian, JIANG Zongli, GUO Wanqin
    2013, 68(7): 983-993.
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    The variations and impacts of glacial lakes on glacier melting runoff in the Tianshan Mountains from 1990 to 2010 were assessed on the basis of Landsat TM/ETM images. In the 20 years, glacial lakes in the Tianshan Mountains expanded at a rate of 0.689 km2 a-1 or 0.8% a-1. The glacial lakes in the eastern Tianshan Mountains contributed over half of area expansion at a rate of 0.352 km2 a-1, followed by northern Tianshan Mountains (0.165 km2 a-1), with rates of 0.089 km2 a-1 and 0.083 km2 a-1 in western and central Tianshan respectively. The lake area increased in most of 100-elevation bands except altitudes of <2900 m and >4100 m. The fastest growth bands were observed between 3500 m and 3900 m with an average rate of 1.6% a-1. Both regional warming and wide glacier wastage led to glacial lake expansion, while small and medium-sized (<0.6 km2) lakes were most sensitive to glacier retreat. To some degree, evident glacial lake expansion can slow down regional glacier melting water losses due to climate warming and ~0.006 Gt glacier melting water (or ~2‰ of total glacier melting water) was held in glacial lakes each year in the Tianshan Mountains from 1990 to 2010; however, it may simultaneously increase frequency and damages of the glacial lake outburst floods (GLOFs) or debris flows in this region.
  • Changes in 0 ℃ isotherm height of Southwest China during 1960-2010
    ZHAO Aifang, ZHANG Mingjun, SUN Meiping, WANG Baolong, WANG Shengjie, WANG Qiong
    2013, 68(7): 994-1006.
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    Based on the aerological meteorological data at 14 sounding stations in Southwest China from 1960 to 2010, as well as the corresponding 5 temperature and 2 precipitation factors measured at ground, Mann-Kendall test, linear trend estimate, correlation analysis and R/S analysis were applied. The changes in spatial and temporal distribution of 0 ℃ isotherm height and their relationships to temperature, precipitation and altitude were analyzed, and the future trends and constancy were predicted. The results indicated that the 0 ℃ isotherm height increased after a sudden decrease in the 1970s, and the patterns of different seasons varied. An increasing trend can be found in the annual, autumn and winter series, and only the trend in winter is statistically significant. A latitude gradient is generally shown from south to north with a decreasing pattern, and the distribution in summer is relatively even. The diversity of annual and seasonal series can also be detected at a spatial view. Significant spatial diversity for temperature and precipitation can be found, and the 0 ℃ isotherm height correlated well with temperature, instead of precipitation. The correlation between isotherm height in summer and altitude is more significant than in other seasonal and annual series. The changing trends in annual and seasonal series can be maintained in future, and evidenced constancies can be found at most of the stations.