DESERTIFICATION IN CHINA: STATUS, TRENDS, AND STRATEGIES     

Zhu Zhen  Cui Shuhong 《地理学报(英文版)》1995,(3)

boncati0uofDcsendcahoninchhaboenificationisoneofthem0stseriotisenvirorunedlissuesoneafth.TheInteInaonalConedontoC0mbatbeeftifiCationswtinforberl994addressed[4]thadeSenificationislandhardation,resultingfromvariousfaders,indudingdiInaticvariationsandhuInana…  相似文献   

近20年国内外旅游环境承载力研究动态     

翁钢民  李建璞  杨秀平  李聪慧 《地理与地理信息科学》2021,37(1):106-115

作为旅游开发规划和旅游发展政策制定的重要依据,旅游环境承载力一直是国内外学者关注的焦点。运用CiteSpace知识图谱分析方法,从文献计量及信息可视化视角对近20年国内外旅游环境承载力主要研究成果进行梳理,基于时空维度和内容层次维度探讨国内外旅游环境承载力研究现状及发展趋势。结果显示:国内外旅游环境承载力研究的高影响力机构、学者合作网络均较为分散,尚未形成紧密的科研团队;国内外旅游环境承载力研究时间序列演变态势有所不同,国外研究呈现间歇式爆发增长趋势,而国内研究呈现循序渐进趋势。通过对国内外旅游环境承载力研究进行系统回顾与展望,可为未来该领域研究提供有益借鉴。  相似文献   

近60 a内蒙古不同草原类型区极端气温和干旱事件特征分析   总被引：1，自引：0，他引：1       下载免费PDF全文

薛海丽  张钦  唐海萍 《干旱区地理》2018,41(4):701-711

基于相对湿润度指数和非参数百分法,结合线性趋势法、Mann-Kendall非参数检验法和累积距平检验法,分析了1955-2015年内蒙古4个草原类型区（多伦、锡林浩特、海拉尔和四子王旗）温度和降水,以及极端气候事件变化特征。结果表明：（1）4个区域年平均气温均显著升高,升高速率约为0.40~0.47℃·（10 a）^-1,气温变化存在非对称性升温特征,多伦、锡林浩特、海拉尔和四子王旗最低气温上升速率分别为最高气温上升速率的1.61倍、1.86倍、2.73倍和1.65倍,春冬季气温增加速率高于夏秋季。（2）多伦、海拉尔、四子王旗和锡林浩特年降水量分别为381.6 mm、350.5 mm、318.6 mm和283.6 mm;降水天数显著增加,而降水量无显著变化,但多伦和锡林浩特降水量呈现略微降低的趋势,其它两个区域呈现略微增加的趋势。（3）4个区域极端高温事件频率显著增加,突变点均出现在1990 s,极端低温事件频率显著减少,突变点均出现在1970s末。（4）4个区域均呈现暖干化的趋势,锡林浩特干旱事件发生最为突出,四子王旗以中度干旱为主,海拉尔和多伦以无旱为主,2000年后,4个区域干旱事件发生频率均明显增加。降水量变化不显著,而气温和潜在蒸散量显著升高可能是导致4个区域不断干旱化的主要原因。  相似文献   

全球荒漠化的现状、未来情景及防治对策   总被引：1，自引：1，他引：0  

张永民  赵士洞 《地球科学进展》2008,23(3):306-311

简要介绍了千年生态系统评估（MA）项目针对荒漠化问题编写的《生态系统与人类福祉：荒漠化综合报告》的核心内容。报告表明：① 除南极洲以外的其它各洲均存在荒漠化土地,荒漠化是旱区居民满足基本生存需求的主要障碍,它已被列为当今世界具有局地与全球效应的最为严重的环境问题;② 根据MA构建的4种情景的分析结果,预计荒漠化在未来50年（2000—2050年）内仍会不断加剧,但是在不同情景条件下其发展程度也不相同;③ 荒漠化已成为实现联合国千年发展目标的主要障碍,为了有效地防治荒漠化,必须在局地至全球的各级层次上对当前的生态系统管理方式、习惯行为和政策做出重大调整,同时最好是将工作重点放在预防上,因为试图修复荒漠化区域不仅成本昂贵,而且往往收效甚微;④ 为了更好地认识荒漠化的本质,当前亟待在全球尺度上建立准确一致的荒漠化本底数据库和评估指标体系,并对科学认知方面的一些不确定性进行深入研究。  相似文献   

Variability and trends of extreme dry and wet seasonal precipitation in Argentina. A retrospective analysis     

B. Scian  J. Pierini 《Atmósfera》2013,26(1):3-26

The variability in seasonal mean and extreme precipitation is analyzed for several regions of Argentina to the north of 39º S, using long-term monthly time series data which expand from 1860 to 2006. The selected locations can be considered as representative of different climatic regions. This work focuses on the analysis of monthly rainfall distribution, significant seasonal trends, changes in variance and extreme monthly values, in order to establish the magnitude of the seasonal climatic rainfall variability through time for central Argentina. A 40-yr moving window was employed in order to analyze seasonal variability of rainfall extremes. Extremes were computed for different probability levels of a theoretical distribution function over/below the 80th/20th percentile. The gamma distribution was selected among five other theoretical distributions, and the scale and shape parameters were computed using the maximum likelihood estimation (MLE) and the bootstrap method for 1000 resample data sets, as well. Trend analysis was performed for each window on winter and summer means and tested for significance. The use of a moving window allowed detecting the window of maximum absolute values for the trends. Research results show significant temporal shifts in seasonal rainfall distribution and return values (RV) that were computed for different frequencies (once every five, 10 and 20 years). Generally, summer precipitation extremes have become wetter for the whole region. Rainfall amounts for summer wet/dry extremes (W/D) corresponding to the 90th (for W) and 10th (for D) percentiles were subjected to significant increase, but depending on the geographical area this effect spreads slightly differently over records of years. A common-for-all-stations period of such summer increase trend in extreme values spans from the window 1921-1960 to the last window analyzed: 1967-2006. This behavior was not observed for north and west Argentina during winter, except for the region represented by Bahía Blanca, where the 10% D extreme has increased throughout the study period.  相似文献   

基于GEE的阿坝红原机场建设前后植被覆盖度时空变化分析     

赵芮  李耀辉  王玮 《沙漠与绿洲气象(新疆气象)》2024,18(2):139-146

借助Google Earth Engine平台，以阿坝红原机场周边15 km缓冲区为研究区，选取30 m分辨率的Landsat系列卫星数据，并采用像元二分模型对该区域2004-2020年5-9月的遥感影像进行反演,从整体和像元尺度对机场建设前后的植被覆盖度的空间格局、结构变化及趋势进行了深入分析。研究结果表明：(1)机场通航后，其西北及东北方向的草地植被生长状况较好，且植被覆盖度随海拔增加呈下降趋势；(2)在2004-2020年期间，低植被度覆盖度和中低植被度覆盖度的面积分别减少60.04%和43.07%，而中植被覆盖度、中高植被覆盖度和高植被覆盖度的面积分别增长15.13%、50.11%和61.22%；(3)研究区植被覆盖度显著改善面积远超显著退化面积，改善区主要集中于机场的西北、东北及正南方向，显著退化区主要位于机场的正北、西南及东南方向。该研究结果能够更好地了解研究区植被覆盖度的动态变化，为机场周边生态环境的后续监测、修复和治理提供了基础数据，为生态环境保护和可持续发展提供更为科学的依据。  相似文献   

Climate change and warm‐water species at the north‐western boundary of the Mediterranean Sea          下载免费PDF全文

Valeriano Parravicini  Luisa Mangialajo  Laure Mousseau  Andrea Peirano  Carla Morri  Monica Montefalcone  Patrice Francour  Michel Kulbicki  Carlo Nike Bianchi 《Marine Ecology》2015,36(4):897-909

The effects of global change are particularly serious in areas where range shifts of species are physically constrained such as the Ligurian Sea, which is one of the coldest sectors of the Mediterranean. In this basin, historical information on water temperature (from the sea surface down to 75 m depth) dates back to the 1950s. Early studies also recorded warm‐water species occurrence. Thanks to these data we provide the first detailed characterization of water temperature variation from 1958 up to 2010 in the layer 0–75 m depth. We coupled this analysis with the available information on rocky reef epibenthic communities (literature review from 1955 to 1964 and field data from 1980 to 2010). The analysis of water temperature revealed several patterns of variation: a cooling phase from 1958 to 1980, a phase of rapid warming from 1980 to 1990 and a phase of slower warming from 1990 to 2010. Inter‐annual variation in temperature increased over the entire period for the water layer down to 20 m. Warm‐water native and alien species richness increased during the warming phases. Literature estimates suggest a decrease in warm‐water native species richness during the cooling phase. The analysis of quantitative data collected in the early 1990s and late 2000s indicated a decrease in the cover of warm‐water native species on shallow rocky reefs and an increase in deeper waters. We argue that increased inter‐annual variation in water temperature may disadvantage native warm‐water species in shallow waters. Our results indicate that the effect of temperature rises in cold, constrained basins may be more complex than the simple prediction of species changing their geographical range according to their thermal limits.  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   

An 80‐year record of sediment quality in the lower Mississippi River     

Peter C. Van Metre  Arthur J. Horowitz 《水文研究》2013,27(17):2438-2448

In 1937, the US Army Corps of Engineers cut through the “neck” of a large meander on the lower Mississippi River (below the confluence with the Ohio River) forming the Caulk Neck cutoff and creating Lake Whittington, a 26‐km long oxbow lake, in northern Mississippi. Since 1938, seasonal flooding and a boat channel connecting the lake with the Mississippi River have led to sediment accumulation in the lake, resulting in an 80‐year record of sediment quality in the river. On the basis of an age‐dated sediment core from the lake, trends in trace metals and hydrophobic organic compounds (except polycyclic aromatic hydrocarbons) follow well‐known patterns with upward trends from the 1930s to the ca 1970s, followed by downward trends to the present. Two factors contribute to these patterns: reservoir construction and changes in emissions. The construction of seven large reservoirs on the Missouri River, in particular the closure of the Fort Randall (1953) and Gavins Point (1955) Dams, greatly reduced the load of relatively clean sediment to the Mississippi River, likely contributing to downstream increases in contaminant concentrations in the Mississippi River. Increasing anthropogenic emissions also contributed to upward trends until ca 1970 when major environmental policy actions began resulting in broad decreases in emissions and downward trends in the concentrations of most of the contaminants monitored. Polycyclic aromatic hydrocarbons and phosphorus are partial exceptions to this pattern, with increases to the 1960s and variable concentrations showing no clear trend since. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

Reference evapotranspiration trends and their sensitivity to climatic change on the Tibetan Plateau (1970–2009)     

Hong Xie  Xuan Zhu 《水文研究》2013,27(25):3685-3693

Evapotranspiration is an important component of the water and energy balance. It is dependent on climate. Precipitation, solar radiation, temperature, humidity, and wind all contribute to the rate of evapotranspiration. In this study, the temporal trends of reference evapotranspiration (ET_ref) and four main ET_ref drivers, namely, mean air temperature (T_a), wind speed (u₂), net radiation (R_n) and actual vapour pressure (e_a) from 1970 to 2009, were calculated based on 75 meteorological stations on the Tibetan Plateau. The results showed that the ET_ref on the Tibetan Plateau decreased on average by 0.6909 mm a^‐1a^‐1 from 1970 to 2009. T_a and e_a showed an increasing trend, whereas u₂ and R_n exhibited a decreasing trend. To explore the underlying causes of the ET_ref variation, an attribution analysis was performed to quantify the contribution of T_a, u₂, R_n and e_a, which showed that the changes in u₂, R_n and e_a produced the negative effect, whereas T_a produced the positive effect on ET_ref rates. The changes in u₂ were found to produce the largest decrease (?0.7 mm) in ET_ref, followed by e_a (?0.4 mm) and R_n (?0.1 mm). Although the significant increase in T_a had a large positive effect (0.51 mm) on ET_ref rates, changes in the other three variables each reduced ET_ref rates, resulting in an overall negative trend in ET_ref. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献