Comparisons on seasonal and annual variations of δ~(18)O in precipitation

interpretationofpaleoclimaticrecordsinicecore(Dansgaardetal.,1969;Rozanskietal.,1997;Yao,1999;Thompsonetal.,2000).SincethefirstdeepicecorewasdrilledinGreenlandin1966(Dansgaardetal.,1969),hundredsoficecoreswereobtainedsuccessivelyfromicesheetsinAntarcticaandArctic,andmountainglaciersatmid-highlatitudes,fundedbynumerousresearchprogramsonglobalclimateandenvironmentalchange.Theseicecoresprovideuniqueandvaluablefirst-handinformationinrecoveringglobalpaleoenvironmentalrecordsandforecastingfuturecl…     

塔里木盆地南缘历史时期气候环境变化的过程与特征

根据塔里木盆地南缘具较高分辨率的湖沼相沉积物碳酸盐δ^13C和粒度等记录，恢复出2162-850BC期间为一相对稳定的温暖干旱时期，之后迅速转冷湿，湿润程度呈持续、阶段式增加，50 BC至500 AD期间呈现的显著冷湿特征于550 AD之后突变转暖干而结束。550 AD和1000 AD前后的具突变性质的气候事件在南疆地区近2．0ka的气候变化中具有重要意义，反映气候状况有过重大调整。850—1300AD期间(相当于中世纪温暖期)冷暖、干湿多变，但温暖特征并不明显。特别是1100—1200AD期间气候快速、频繁变化之后，奠定了本地区现代稳定干旱环境特征。区域对比表明，尼雅剖面记录的气候变化具有广泛的区域一致性。     

20世纪中国气候变化研究

Studies on the 20th century climate change in China have revealed that under the background of global warming over the past century,climate in China has also experienced significant change with mean annual temperature increased by about 0.5 °C.More reliable results for the latter part of the 20th century indicate that the largest warming occurred in Northwest China,North China and Northeast China,and the warming in winter is most significant.Although no obvious increase or decrease trends were detected for mean precipitation over China in the past half century,regional differences are very distinct.In the middle and lower reaches of the Yangtze River,precipitation increased,while that in the Yellow River Basin markedly decreased.Studies suggest that climate change in China seems to be related not only with the internal factors such as ENSO,PDO,and the others,but also with the anthropogenic effects such as greenhouse gas emissions,and land use.The future climate change studies in China seem to be important in narrowing understanding the nature of China's climate change and its main causes,since it is significant for projection and for impact assessment of climate change in the future.     

Automatic Road Change Detection and GIS Updating from High Spatial Remotely-Sensed Imagery

This paper presents a tramework for road network change detectlon In order to upctate the Canadian National Topographic DataBase (NTDB). The methodology has been developed on the basis of road extraction from IRS-pan images (with a 5.8 m spatial resolution) by using a wavelet approach. The feature matching and conflation techniques are used to road change detection and updating. Elementary experiments have showed that the proposed framework could be used for developing an operational road database updating system.     

The influence of land use change on karst water quality of Shuicheng Basin in Guizhou Province

The influence of land use and land cover on ecological environment is a focus of global change research. The paper chooses an industrial city-Shuicheng in Guizhou Province-as a study area because the karst water quality around the city is deteriorating with land use and land cover change. The natural susceptibility of karst water system is an important factor leading to karst water pollution. But land use and land cover change is also a main factor according to the chemical analysis of karst water quality and land use change. So it is a good way to protect karst water through rational planning and managing of land use and land cover.     

Modeling Spatially and Temporally Complex Land‐Cover Change: The Case of Western Honduras*

This article presents an econometric analysis of land‐cover change in western Honduras. Ground‐truthed satellite image analysis indicates that between 1987 and 1996 net reforestation occurred in the 1,015‐km² study region. While some reforestation can be attributed to a 1987 ban on logging, the area of reforestation greatly exceeds that of previously clear‐cut areas. Further, new area was also deforested between 1987 and 1996. Thus, the observed land‐cover changes represent a complex mosaic of changing land‐use patterns across time and space. The analysis contributes to the literature on land‐cover change modeling in that: (1) it compares two econometric approaches to capture complex and often bidirectional changes in land cover from 1987 to 1996 as a function of agricultural suitability and transportation costs, and (2) it addresses techniques to identify and correct for spatial autocorrelation in a categorical regression framework.     

Channel Bed Mobility Downstream from the Elwha Dams,Washington*

Dams are a major source of fragmentation and degradation of rivers. Although substantial research has been conducted on the environmental impacts of large structures in the United States, smaller dams have received less attention. This study evaluated the impact of two dams of moderate size, the Elwha Dams, on the downstream channel system using field data collection at river cross‐sections. The relationship of average boundary shear stress (τ_o) to critical shear stress (τ_cr) served as the basis for determining channel bed material mobility under the two‐year and ten‐year flood events. The channel had the greatest channel bed mobility at the natural cross‐section upstream from the dams, low bed mobility between the structures, and an increase in channel bed mobility in the low gradient river segment near the mouth of the river. Low bed mobility tended to be associated with a lack of channel system complexity, including reduction or loss of bars and low alluvial terraces and their associated young riparian communities. Although these run‐of‐the‐river dams do not modify streamflow greatly, the loss of sediment from the channel system has had a substantial impact on bed mobility and geomorphic and biotic complexity of the Elwha River.     

IGGOS as a potential partner in IGOS

This short note reviews our thinking on how IGGOS can best achieve a high status within the set of global monitoring programmes. If such a high status can be obtained, then the importance of geodetic networks and services will be recognized more widely, and their activities will consequently be better resourced in the long term. One particular aspect concerns how IGGOS can complement the roles of the various IGOS partners within global monitoring. The different ways in which IGGOS can contribute to IGOS are outlined.     

Small inflation sources producing seismic and infrasonic pulses during the 2000 eruptions of Miyake-jima, Japan

During the 2000 activity of Miyake-jima volcano, Japan, we detected long period seismic signals with initial pulse widths of 1-2 s, accompanied by infrasonic pulses with almost the same pulse widths. The seismic signals were observed from 13 July 2000, a day before the second summit eruption. The occurrences of the seismic signals were intermittent with a gradual increase in their magnitudes and numbers building toward a significant explosive eruption on 18 August. After the eruption, the seismic and infrasonic events ceased. The results of a waveform inversion show that the initial motions were excited by an isotropic inflation source beneath the south edge of the caldera at a depth of 1.4 km. On the other hand, the sources of the infrasonic pulses were located in the summit caldera area. The times at which the infrasonic pulses were emitted at the surface were delayed by about 3 s from the origin times of the seismic events. It is suggested that small isotropic inflations excited seismic waves in the crust and simultaneously caused acoustic waves that traveled in the conduit and produced infrasonic pulses at the crater bottom. Considering the observed time differences and gas temperatures emitted from the vent, the conduit should have been filled with vapor mixed with SO₂ gas and volcanic ash. The change of the time differences between the seismic and infrasonic signals suggests that the seismic source became shallower within half a day before the August 18 explosive eruption. We interpret the source process as a fragmentation process of magma in which gas bubbles burst and quickly released part of the pressure that had been sustained by the tensional strength of magma.