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21.
In this study,we have used four methods to investigate the start of the growing season(SGS) on the Tibetan Plateau(TP) from 1982 to 2012,using Normalized Difference Vegetation Index(NDVI) data obtained from Global Inventory Modeling and Mapping Studies(GIMSS,1982-2006) and SPOT VEGETATION(SPOT-VGT,1999-2012).SGS values estimated using the four methods show similar spatial patterns along latitudinal or altitudinal gradients,but with significant variations in the SGS dates.The largest discrepancies are mainly found in the regions with the highest or the lowest vegetation coverage.Between 1982 and 1998,the SGS values derived from the four methods all display an advancing trend,however,according to the more recent SPOT VGT data(1999-2012),there is no continuously advancing trend of SGS on the TP.Analysis of the correlation between the SGS values derived from GIMMS and SPOT between 1999 and 2006 demonstrates consistency in the tendency with regard both to the data sources and to the four analysis methods used.Compared with other methods,the greatest consistency between the in situ data and the SGS values retrieved is obtained with Method 3(Threshold of NDVI ratio).To avoid error,in a vast region with diverse vegetation types and physical environments,it is critical to know the seasonal change characteristics of the different vegetation types,particularly in areas with sparse grassland or evergreen forest. 相似文献
22.
再论青藏高原范围 总被引：5，自引：0，他引：5
伴随青藏高原研究的深入,高原内外多学科研究程度和认识的提高,及地理大数据、地球观测科学和技术的进步,对青藏高原范围提出了新的要求。本研究系统论述了确定青藏高原范围的原则、依据和方法,分析探讨了高原地貌宏观结构（高原面、高原内低盆地与高原边缘河谷低地等）和周围边界各自然地段构成的基本特征。采用ArcMap软件,通过遥感影像和DEM数据及新资料对高原地貌比较研究,实现了1：100万比例尺地图精度的青藏高原范围的界定。研究表明,青藏高原北起西昆仑山-祁连山山脉北麓,南抵喜马拉雅山等山脉南麓,南北最宽达1560 km;西自兴都库什山脉和帕米尔高原西缘,东抵横断山等山脉东缘,东西最长约3360 km;范围为25°59′30″N~40°1′0″N、67°40′37″E~104°40′57″E,总面积为308.34万km2,平均海拔约4320 m。在行政区域上,青藏高原分布于中国、印度、巴基斯坦、塔吉克斯坦、阿富汗、尼泊尔、不丹、缅甸、吉尔吉斯斯坦等9个国家。其中中国境内的青藏高原面积约258.09万km2（占高原总面积的83.7%）,平均海拔约4400 m,分布在西藏、青海、甘肃、四川、云南和新疆等6省区,西藏和青海两省区主体分布在高原范围内（约占高原总面积的60.6%）。 相似文献
23.
1981-2001年珠穆朗玛峰自然保护区植被变化 总被引：1，自引：0，他引：1
Based on the NOAA AVHRR-NDVI data from 1981 to 2001, the digitalized China Vegetation Map （1：1,000,000）, DEM, temperature and precipitation data, and field investigation, the spatial patterns and vertical characteristics of natural vegetation changes and their influencing factors in the Mt. Qomolangma Nature Reserve have been studied. The results show that： （1） There is remarkable spatial difference of natural vegetation changes in the Mt. Qomolangma Nature Reserve and stability is the most common status. There are 5.04% of the whole area being seriously degraded, 13.19% slightly degraded, 26.39% slightly improved, 0.97% significantly improved and 54.41% keeping stable. The seriously and slightly degraded areas, which mostly lie in the south of the reserve, are along the national boundaries. The areas of improved vegetation lie in the north of the reserve and the south side of the Yarlung Zangbo River. The stable areas lie between the improved and degraded areas. Degradation decreases with elevation. （2） Degeneration in the Mt. Qomolangma Nature Reserve mostly affects shrubs, needle-leaved forests and mixed forests. （3） The temperature change affects the natural vegetation changes spatially while the integration of temperature changes, slopes and aspects affects the natural vegetation change along the altitude gradients. （4） It is the overuse of resources that leads to the vegetation degeneration in some parts of the Mt. Qomolangma Nature Reserve. 相似文献
24.
青藏高原植被覆盖变化与降水关系 总被引：15，自引：6，他引：9
The temporal and spatial changes of NDVI on the Tibetan Plateau, as well as the relationship between NDVI and precipitation, were discussed in this paper, by using 8-km resolution multi-temporal NOAA AVHRR-NDVI data from 1982 to 1999. Monthly maximum NDVI and monthly rainfall were used to analyze the seasonal changes, and annual maximum NDVI, annual effective precipitation and growing season precipitation (from April to August) were used to discuss the interannual changes. The dynamic change of NDVI and the corre- lation coefficients between NDVI and rainfall were computed for each pixel. The results are as follows: (1) The NDVI reached the peak in growing season (from July to September) on the Tibetan Plateau. In the northern and western parts of the plateau, the growing season was very short (about two or three months); but in the southern, vegetation grew almost all the year round. The correlation of monthly maximum NDVI and monthly rainfall varied in different areas. It was weak in the western, northern and southern parts, but strong in the central and eastern parts. (2) The spatial distribution of NDVI interannual dynamic change was different too. The increase areas were mainly distributed in southern Tibet montane shrub-steppe zone, western part of western Sichuan-eastern Tibet montane coniferous forest zone, western part of northern slopes of Kunlun montane desert zone and southeastern part of southern slopes of Himalaya montane evergreen broad-leaved forest zone; the decrease areas were mainly distributed in the Qaidam montane desert zone, the western and northern parts of eastern Qinghai-Qilian montane steppe zone, southern Qinghai high cold meadow steppe zone and Ngari montane desert-steppe and desert zone. The spatial distribution of correlation coeffi- cient between annual effective rainfall and annual maximum NDVI was similar to the growing season rainfall and annual maximum NDVI, and there was good relationship between NDVI and rainfall in the meadow and grassland with medium vegetation cover, and the effect of rainfall on vegetation was small in the forest and desert area. 相似文献
25.
Climate change on the southern slope of Mt. Qomolangma （Everest） Region in Nepal since 1971 总被引：1，自引：0，他引：1
Based on monthly mean, maximum, and minimum air temperature and monthly mean precipitation data from 10 meteorological stations on the southern slope of the Mt. Qomolangma region in Nepal between 1971 and 2009, the spatial and temporal characteristics of climatic change in this region were analyzed using climatic linear trend, Sen＇s Slope Estimates and Mann-Kendall Test analysis methods. This paper focuses only on the southern slope and attempts to compare the results with those from the northern slope to clarify the characteristics and trends of climatic change in the Mt. Qomolangma region. The results showed that： （1） between 1971 and 2009, the annual mean temperature in the study area was 20.0℃, the rising rate of annual mean temperature was 0.25℃/10a, and the temperature increases were highly influenced by the maximum temperature in this region. On the other hand, the temperature increases on the northern slope of Mt. Qomolangma region were highly influenced by the minimum temperature. In 1974 and 1992, the temperature rose noticeably in February and September in the southern region when the increment passed 0.9℃. （2） Precipitation had an asymmetric distribution; between 1971 and 2009, the annual precipitation was 1729.01 mm. In this region, precipitation showed an increasing trend of 4.27 mm/a, but this was not statistically significant. In addition, the increase in rainfall was mainly concentrated in the period from April to October, including the entire monsoon period （from June to September） when precipitation accounts for about 78.9% of the annual total. （3） The influence of altitude on climate warming was not clear in the southern region, whereas the trend of climate warming was obvious on the northern slope of Mt. Qomolangma. The annual mean precipitation in the southern region was much higher than that of the northern slope of the Mt. Qomolangma region. This shows the barrier effect of the Himalayas as a whole and Mt. Qomolangma in particular. 相似文献
26.
Based on the GIMMS AVHRR NDVI data(8 km spatial resolution) for 1982–2000, the SPOT VEGETATION NDVI data(1 km spatial resolution) for 1998–2009, and observational plant biomass data, the CASA model was used to model changes in alpine grassland net primary production(NPP) on the Tibetan Plateau(TP). This study will help to evaluate the health conditions of the alpine grassland ecosystem, and is of great importance to the promotion of sustainable development of plateau pasture and to the understanding of the function of the national ecological security shelter on the TP. The spatio-temporal characteristics of NPP change were investigated using spatial statistical analysis, separately on the basis of physico-geographical factors(natural zone, altitude, latitude and longitude), river basin, and county-level administrative area. Data processing was carried out using an ENVI 4.8 platform, while an ArcGIS 9.3 and ANUSPLIN platform was used to conduct the spatial analysis and mapping. The primary results are as follows:(1) The NPP of alpine grassland on the TP gradually decreases from the southeast to the northwest, which corresponds to gradients in precipitation and temperature. From 1982 to 2009, the average annual total NPP in the TP alpine grassland was 177.2×1012gC yr-1(yr represents year), while the average annual NPP was 120.8 gC m-2yr-1.(2) The annual NPP in alpine grassland on the TP fluctuates from year to year but shows an overall positive trend ranging from 114.7 gC m-2yr-1in 1982 to 129.9 gC m-2yr-1in 2009, with an overall increase of 13.3%; 32.56% of the total alpine grassland on the TP showed a significant increase in NPP, while only 5.55% showed a significant decrease over this 28-year period.(3) Spatio-temporal characteristics are an important control on annual NPP in alpine grassland: a) NPP increased in most of the natural zones on the TP, only showing a slight decrease in the Ngari montane desert-steppe and desert zone. The positive trend in NPP in the high-cold shrub-meadow zone, high-cold meadow steppe zone and high-cold steppe zone is more significant than that of the high-cold desert zone; b) with increasing altitude, the percentage area with a positive trend in annual NPP follows a trend of"increasing-stable-decreasing", while the percentage area with a negative trend in annual NPP follows a trend of "decreasing-stable-increasing", with increasing altitude; c) the variation in annual NPP with latitude and longitude co-varies with the vegetation distribution; d) the variation in annual NPP within the major river basins has a generally positive trend, of which the growth in NPP in the Yellow River Basin is most significant. Results show that, based on changes in NPP trends, vegetation coverage and phonological phenomenon with time, NPP has been declining in certain places successively, while the overall health of the alpine grassland on the TP is improving. 相似文献
27.
长江南源当曲流域是我国高寒沼泽湿地的集中分布地区之一,是青藏高原腹地重要的水源涵养地。对该地区湿地资源及分布的正确把握直接关系到当地牧民的生产生活及下游地区的经济社会发展。由于湿地光谱特征复杂,易于其他地类混淆,传统的遥感信息提取方法很难保证湿地信息提取的精度。本文运用面向对象的图像信息自动分类方法,对当曲流域内的湿地信息进行提取。在对各类型湿地的光谱特征、纹理特征及空间特征进行分析的基础上,充分结合DEM及其衍生数据(坡度、坡向), 归一化植被指数 (NDVI), 归一化水体指数 (NDWI) 及缨帽变换(Kauth-Thomas transformation)得到的湿度图层等参数,设置各参数阈值,建立各湿地类型的信息提取知识规则,并结合野外实地调查对信息提取精度进行验证。经检验,湿地信息提取的总体精度达到89.00%。 相似文献
28.
黄河源地区草地退化空间特征 总被引：26，自引：1，他引：26
刘林山 张镱锂 摆万奇 YAN Jianzhong DING Mingjun SHEN Zhenxi LI Shuangcheng ZHENG Du 《地理学报(英文版)》2006,16(2):131-142
There are about 400 million hm2 of grassland in China, which account for 13% of the grassland in the world and 41% of the total land area of China. It is the biggest terrestrial ecosystem in China (Liu et al., 2003). Due to impacts of global change and ec… 相似文献
29.
拉萨河流域近50 年来径流变化趋势分析 总被引：10，自引：2，他引：10
以拉萨水文站以上流域为研究区, 基于拉萨水文站和唐加水文站的水文实测数据和当雄 县等3 个气象站的气候观测数据, 统计分析了1956~2003 年研究区径流的年内、年际变化, 利用 Mann- Kendall 趋势分析法和Pettitt 变点检验法分析了拉萨河流域径流的变化特征, 采用多元回 归方法分析了气候因素( 气温、降水) 对径流变化的影响。结果表明: ( 1) 研究时段内, 径流年际变 化波动较大, 在1970 年前后径流发生了较大的突变, 呈现出明显的增加趋势, 尤以近20 年来的 趋势最大; 月均径流的年际变化中, 有增加趋势的主要分布在冬半年( 11～4 月) 和夏半年的个别 月份( 5、7、9 月) ; ( 2) 流域内气候变化趋势与径流变化趋势基本一致, 但不同月/年均径流受不同 气候因素影响, 主要表现在年平均尺度上受降水影响较大, 在月平均尺度上, 夏半年径流增加趋 势受降水增加影响较大, 而冬半年径流变化则主要与气温有较显著相关性, 其主要原因可能是全 球变暖导致冰川融水增加。 相似文献
30.
In order to advance land use and land cover change(LUCC) research in Nepal, it is essential to reconstruct both the spatiotemporal distribution of agricultural land cover as well as scenarios that can explain these changes at the national and regional levels. Because of rapid population growth, the status of agricultural land in Nepal has changed markedly over the last 100 years. Historical data is used in this study, encompassing soils, populations, climatic variables, and topography. Data were revised to a series of 30 m grid cells utilized for agricultural land suitability and allocation models and were analyzed using a suite of advanced geographical tools. Our reconstructions for the spatiotemporal distribution of agricultural land in Nepal reveal an increasing trend between 1910 and 2010(from 151.2 × 10~2 km~2 to 438.8 × 10~2 km~2). This expanded rate of increase in agricultural land has varied between different eco, physiographic, and altitudinal regions of the country, significantly driven by population changes and policies over the period of this investigation. The historical dataset presented in this paper fills an existing gap in studies of agricultural land change and can be applied to other carbon cycle and climate modeling studies, as well as to impact assessments of agricultural land change in Nepal. 相似文献