全野外数字测图技术的现状及发展趋势   总被引：3，自引：0，他引：3  

马俊海  吕长广 《测绘与空间地理信息》2006,29(5):15-17

对全野外数字测图技术的现状进行归纳和分析,指出了目前各种全野外数字测图方法中存在的不足,提出了全野外数字测图技术的发展趋势。  相似文献   

全球清洁能源发展现状与趋势分析   总被引：1，自引：0，他引：1  

崔荣国  郭娟  程立海  张迎新  刘伟 《地球学报》2021,42(2):179-186

一次能源尤其是化石能源的大规模开发利用,导致环境破坏越来越严重,对人类生活造成了极大的负面影响,因此,清洁能源的开发利用引起全球的广泛重视,美国、日本、欧盟、中国、印度等国家或地区从20世纪开始开展清洁能源的开发利用工作.本文在前人的研究基础上,首先明确了清洁能源的概念和能源种类.其次,从投资、装机容量和消费变化等方面...  相似文献   

我国皱纹盘鲍底播增养殖历史、现状及未来发展趋势     

吴富村  阙华勇  张国范 《海洋科学》2020,44(8):56-68

皱纹盘鲍（Haliotis discus hannai）为我国原产贝类之一,自然分布于我国辽东和山东半岛等黄渤海海区,自古被誉为海珍之冠。我国皱纹盘鲍的资源调查、增养殖相关研究始于1958年,20世纪70年代突破了人工繁育技术并自20世纪80年代初开始人工种苗的试验性底播及人工养殖。鲍野生资源随着过度采捕而急剧下降,我国开始通过底播增养殖工作以恢复皱纹盘鲍的生物资源,其中底播养殖取得了一定进展,但生物资源恢复与增殖未能取得理想效果。20世纪90年代皱纹盘鲍杂交技术获得突破并产业化应用,推动了我国鲍养殖产业南移,目前福建养殖鲍产量已占到全国总产量的82.7%,而北方海区底播增养殖产业受养殖周期、成本和市场价格的冲击,以及底播越冬期间高死亡率等问题制约,已严重萎缩。自2009年起,在国家贝类产业技术体系支持下,相关研发及产业单位合作建立皱纹盘鲍底播型海洋牧场技术研发的产学研平台,进而于2013年提出并实施了“北鲍北养”产业计划。通过开展技术联合攻关及示范,部分地区的底播皱纹盘鲍已进入商业性收获等显著进展。本文针对我国皱纹盘鲍底播增养殖产业中亟需解决问题、发展目标、可实现途径以及未来发展趋势开展讨论,以期为我国皱纹盘鲍底播增养殖、原种保护、资源增殖提供借鉴。  相似文献   

1949—2019年中国乡村振兴主题演化过程与研究展望   总被引：1，自引：1，他引：0  

文琦  郑殿元  施琳娜 《地理科学进展》2019,38(9):1272-1281

实施乡村振兴战略是坚持农业农村优先发展、实现农业农村现代化总体目标、建立健全城乡融合发展体制机制和政策体系的重要途径。论文系统回顾了乡村发展的历程,将1949年以来中国乡村发展分为：人民公社为主体的城乡二元结构阶段、小农经济为主体的家庭联产承包责任制阶段、城市反哺农村的城乡统筹发展阶段、城乡融合发展与乡村振兴阶段4个发展时段。从时间序列深入刻画了乡村振兴的主体分化、产业演变、环境整治、文化重构、乡村治理5个振兴主题及乡村规划的演化过程与研究趋势。最后,着眼于新时代乡村振兴战略需求与研究热点,从学科交叉融合的理论与实践研究、城乡一体化与城乡融合发展研究、乡村产业融合发展与提质增效研究、乡村“三生”空间融合发展研究、乡村跨区域协作与联动研究5个方面对乡村振兴未来研究趋势展开了讨论。  相似文献   

Changes in snowmelt runoff timing in the contiguous United States     

Sukru Uzun  Tugkan Tanir  Gustavo de A. Coelho  Andre de Souza de Lima  Felicio Cassalho  Celso M. Ferreira 《水文研究》2021,35(11):e14430

Changes in timing of snowmelt-fed streamflow have great importance for water supply, flood management, and ecological processes, as well as being a common indicator of climate change. In this study, snowmelt runoff timing change in the contiguous United States between 1957 and 2016 was investigated by analysing data from 97 streamflow gages. The annual snowmelt runoff timing shift was identified using ‘Center Time (CT)’ and ‘Spring Pulse Onset (SPO)’ methods, jointly with the monthly fractional streamflow (MFS) analysis, conducted between January and June. Since snowmelt-derived streamflow timing change is mainly induced by regional meteorological factors, such as air temperature and precipitation, their trends and relationship with CT were also examined. Shifts toward earlier snowmelt runoff timing were found by both methods, CT (8.3 days on average) and SPO (8.5 days on average). Although the results of the CT change are stronger than the SPO change, both outcomes are mostly correlated, particularly in the central and northwestern parts of the country. MFS trends support the outcomes of CT and SPO. In January, February, and especially March, a higher number of the stations indicated increasing trends in MFS. In April, May, and June, their number decreased and the number of gages with diminishing trends rose sharply. The timing difference is highly related to temperature change. Annual average temperature and temperature in the melting period increase considerably. The annual average temperature is significantly negatively correlated with CT in the vast majority of the regions. Although precipitation is not as effective as the temperature, its trends have impacts on snowmelt runoff timing change depending on the region and elevation. These results demonstrate the importance of the impacts of snowmelt runoff timing changes due to global warming on the regional and large-scale hydrology in the contiguous United States.  相似文献   

Variability in the discharge of South American rivers and in climate / Variabilité des débits de rivières d'Amérique du Sud et du climat     

《水文科学杂志》2013,58(3)

Abstract

Changes in trend and quasi-periodicities are sought in the time series of river discharges in all major South American basins. The relationship between trends and quasi-periodicities found and climate variations on interannual and longer time scales are discussed. Consideration of multiple rivers gives insight into the geographical extent of hydrological signals and climate impacts. It is found that the streamflow of all major rivers of South America has experienced an increased trend since the early 1970s. It is suggested that this simultaneity may reflect the impact of a large-scale climate change. All the time series of river streamflows that were analysed show El Niño-like periodicities. Only for La Plata Basin do these explain a larger part of the total variance than the other quasi-periodicities. There are two other quasi-oscillations in the time series analysed: one of them with a longer period—around 17 years—and the other of about 9 years. Previous work has related these oscillations to sea-surface temperature anomalies in the Atlantic Ocean.  相似文献   

Long‐term streamflow trends in the middle reaches of the Yellow River Basin: detecting drivers of change          下载免费PDF全文

Zhaoliang Gao  Lu Zhang  Xiaoping Zhang  Lei Cheng  Nick Potter  Tim Cowan  Wenju Cai 《水文研究》2016,30(9):1315-1329

The catchments in the Loess Plateau, in China's middle reaches of the Yellow River Basin, experienced unprecedented land use changes in the last 50 years as a result of large‐scale soil conservation measure to control soil erosion. The climate of the region also exhibited some levels of change with decreased precipitation and increased temperature. This study combined the time‐trend analysis method with a sensitivity‐based approach and found that annual streamflow in the Loess Plateau decreased significantly since the 1950s and surface runoff trends appear to dominate the streamflow trends in most of the catchments. Annual baseflow exhibited mostly downward trends, but significant upward trends were also observed in 3 out of 38 gauging stations. Mean annual streamflow during 1979?2010 decreased by up to 65% across the catchments compared with the period of 1957?1978, indicating significant changes in the hydrological regime of the Loess Plateau. It is estimated that 70% of the streamflow reduction can be attributed to land use change, while the remaining 30% is associated with climate variability. Land use change because of the soil conservation measures and reduction in precipitation are the key drivers for the observed streamflow trends. These findings are consistent with results of previous studies for the region and appear to be reasonable given the accelerated level of the soil conservation measures implemented since the late 1970s. Changes in sea surface temperature in the Pacific Ocean, as indicated by variations in El Niño–Southern Oscillation and phase shifts of the Pacific Decadal Oscillation, appear to have also affected the annual streamflow trends. The framework described in this study shows promising results for quantifying the effects of land use change and climate variability on mean annual streamflow of catchments within the Loess Plateau. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Trends and Spatial Patterns of Drought Incidence in the Omo‐Ghibe River Basin,Ethiopia          下载免费PDF全文

Mekonnen A. Degefu  Woldeamlak Bewket 《Geografiska Annaler: Series A, Physical Geography》2015,97(2):395-414

The objective of this paper is to evaluate trends and spatial patterns of drought incidence across the Omo‐Ghibe River Basin using monthly rainfall data from eight stations for the period 1972–2007. It also aims to estimate the probability of drought episodes for a 100‐year period. Drought indices were generated using the Standard Precipitation Index (SPI) computed at 3‐, 6‐, 12‐ and 24‐month time‐steps for three intensity classes: moderate, severe and extreme drought events. The Mann–Kendall's trend test and Sen's slope estimator were employed to detect temporal changes. The results show complex spatial patterns on the frequency and magnitude of drought events across the study area for all timescales and intensity classes. However, the total number of drought events for the three intensity classes for all timescales were larger in the southern lowlands, where there exists a serious water scarcity for the rain‐fed pastoral system, than in the northeastern part (around Wolaita Sodo area). In contrast to this, the longest and most extreme (SPI < ?4.0) drought events for all timescales were observed at Wolaita Sodo station. In a 100‐year period one could expect 57–69 drought events with 3 months' duration, 19–34 events with 6 months' duration, 9–16 events with 12 months' duration and 5–9 events with 24 months' duration. The SPI values show negative rainfall anomalies in the 1980s while positive anomalies have occurred in the 1990s and 2000s, which implies tendency towards decreasing drought events. The Mann–Kendall's trend test for the 12‐ and 24‐month timescales and for seasonal events also confirms this general trend.  相似文献   

Pan evaporation and potential evapotranspiration trends in South Florida   总被引：1，自引：0，他引：1  

Wossenu Abtew  Jayantha Obeysekera  Nenad Iricanin 《水文研究》2011,25(6):958-969

Declining trends in pan and lake evaporation have been reported. It is important to study this trend in every region to evaluate the validity of the trend and water management implications. Data from nine pan evaporation sites in South Florida were evaluated to see if there is a trend and if the quality of the data is sufficient for such analysis. The conclusion is that pan evaporation measurements are prone to too many sources of errors to be used for trend analysis. This condition is demonstrated in South Florida and in other regions by differences in magnitude and direction between spatially related pan stations and unexplainable observations. Also, potential evapotranspiration (ET_p) was estimated with the Simple (Abtew equation) and the Penman–Monteith method. Both cases indicated no decline in evapotranspiration for the period of analysis. Based on the decline in humidity and the increasing trend in vapor pressure deficit for the short period of analysis, 1992–2009, it appears that South Florida is experiencing increase in evaporation and evapotranspiration at this time assuming no systematic error in the weather stations' observations. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Monitoring of organic contaminants in sediments from the Korean coast: Spatial distribution and temporal trends (2001-2007)     

Choi HG  Moon HB  Choi M  Yu J 《Marine pollution bulletin》2011,62(6):1352-1361

Spatial and temporal trends of organic contaminants in sediments along the Korean coast were estimated through a nationwide environmental monitoring program from 2001 to 2007. The concentrations of organic contaminants in sediments along the Korean coast were relatively low or moderate compared with foreign studies. The mean detection frequencies of organic contaminants during the seven years were highest for PAHs and PCDD/Fs, followed by PCBs, DDTs, TBT and HCHs in decreasing order. Based on published sediment quality guidelines, the ecological risks of persistent organic pollutants in sediments along the Korean coast were low, despite exceedances of the ERL at 2-6 sites for DDTs, and the TEL at 9-18 sites for PCDD/Fs. Nonparametric tests to assess temporal trends revealed significant decreasing trends for PCBs and PCDD/Fs at four and three sites, respectively (p < 0.05). These results reflect the effects of regulations on the use of those contaminants.  相似文献