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1.
40a来中国旱灾对ENSO事件的区域差异响应研究 总被引：4，自引：0，他引：4
利用中国各地区1949—1990年间旱灾的受灾面积比和成灾面积比,分别与ENSO指数进行相关分析.结果发现:ENSO指数与各地的旱灾事件有着一定的反相关关系,表明ENSO的发生对我国大部分地区有着显著的影响,特别是对华北、东北、华南、内蒙古和新疆等地区的相关性具有很好的显著水平.通过对比各个分区对ENSO事件的响应程度,分析了其空间差异性.ENSO指数的变化与中国各地的旱灾有密切的联系,全球升温通过影响ENSO事件而影响中国的旱灾面积:全球升温影响下,ENSO指数升高,旱灾减少. 相似文献
2.
Drought in Bulgaria is analyzed from the multiple viewpoints of statistical occurrence, spatial patterns, and synoptic conditions.
A new index of drought, the SD (spatial-dryness) index, characterizes drought by both intensity and spatial extent. The occurrence of the SD index is analyzed using global
gridded data sets. Examination of transitional probabilities of multiple months and years with drought occurrence suggests
persistence is sufficiently frequent to be important for climate-related environmental planning. Finally, it is shown that
specific seasonal synoptic patterns are associated with wet and dry conditions in Bulgaria.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Drought in the Sahel 总被引：3，自引：0，他引：3
The Sahel region of West Africa is well known as a region of environmental degradation. The reported incidence of desertification
has been challenged but persistent and widespread drought is still widely accepted. Drought, defined solely as a function
of rainfall, is believed to have commenced in the early 1970s and continued through to the present. It is usually defined
as a meteorological phenomenon and standardised rainfall anomalies are employed to indicate the severity of negative departures
from the ‘norm’. There are several difficulties with this approach. The period of standardising rainfall has changed from
1931–1960 to 1961–1990 but the impacts on drought occurrence have not been fully determined. The spatial aggregation of rainfall
anomalies may mask important local variation and the purely statistical approach to defining drought takes little account
of human impact. The first two issues, averaging period and spatial aggregation, are investigated through an analysis of rainfalls
in Continental Sahel (Bukina Faso, Mali and Niger). A new classification of drought classes is suggested. Despite the clear
evidence of negative rainfall anomalies for rainfalls aggregated across the Sahel region, it is found that the averaging period
has a significant impact on our perceptions of the occurrence of what can be considered to be meteorological drought according
to the definition employed and that there is significant spatial variation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
E. O. Oladipo 《Natural Hazards》1993,8(3):235-261
Drought has been a recurring feature of the arid and semi-arid areas of Nigeria. This paper reviews the extent, severity, and consequences of drought and desertification in Nigeria with particular emphasis on the northern part of the country. The haphazard manner in which these environmental hazards have been tackled is examined and a systematic approach for the formulation of a national policy is proposed. It is recommended that a detailed formulation and implementation of the proposed policy plan is imperative to mitigate the often devastating impacts of drought and desertification in the very prone areas of Nigeria. Until such is done, some areas of Nigeria will always be vulnerable to the whims of an inevitable climatic hazard of drought and associated land degradation in the form of desertification. 相似文献
5.
利用综合气象干旱指数(CI指数)和K干旱指数, 对贵州安顺地区1971-2011年41 a来气象干旱的时空分布状况、演变特征及突变情况进行了比较分析. 结果表明: 对严重的干旱时段, 两种指数均能表现出来, 对历年干旱过程及灾害的评定结果基本一致;CI指数对干旱的评定更为精细, 但K指数延续性更好;分季节的干旱分析中, 两种指数对于夏季出现干旱概率较小的结论一致, 对各季节平均干旱长度的评判基本一致. 对时间演变的线性变化趋势以及M-K检验结果对比分析表明, 春季和秋季干旱强度增强、夏季干旱强度减弱、年度平均干旱长度及春、秋季干旱长度增加的这几个趋势, 两种方法两种指数结果一致, 结论被认为是可信度较高的. M-K曲线检测表明: 年度干旱长度在2008年后为增加的趋势, 20世纪90年代以来春季干旱强度增强, 20世纪末以来夏季干旱强度趋于减轻, 秋季干旱强度增强, 1970年代中期后春季干旱长度有增加的趋势, 秋季干旱长度在20世纪80年代中期到90年代后增加的趋势可能发生了突变. 年度干旱强度存在12~14 a的长周期和年度干旱长度4~6a的短周期较为可信. 相似文献
6.
Recent Precipitation Trends in Hungary in the Context of Larger Scale Climatic Changes 总被引：1，自引：0，他引：1
The time series of monthly precipitation totals from 14 Hungarian observing stations (1901–1998) were analysed to reveal the long term changes in precipitation characteristics occurred in the 20th century. A particular attention was given to the changes in the recent decades and their links with the larger scale climatic and circulation changes over Europe and the Atlantic.The statistical significancesof systematic changes are controlled by linear trend analysis and the Mann–Kendall test. The long term fluctuations are illustrated applying a 15-point Gaussian filter on the time series. The Standardised Precipitation Index is used to evaluate the changes in the drought event frequency. The relationships with larger scale changes are mostly discussed relying on contemporary papers, and the Grosswetterlagen Catalogue is used as well.The annual precipitation total decreased by 15–20% in Hungary during the 20th century. The decline is substantial in both halves of the century, but the precipitation sums in the transition seasons declined in the first 50 years, and the winter precipitation decreased in the latest decades. The precipitation total of the period November–February declined significantly in the last 50 years. In the same time the mean winter value of the North Atlantic Oscillation Index (NAOI) increased, the positions of the main pressure patterns over the Atlantic are shifted northeastward, and lot of other coherent changes detected in the winter climate of the European–Atlantic region. The mean summer precipitation total has hardly changed, but the frequency of summer drought events increased. There are some signs of a shift of the Hungarian summer climate towards a Mediterranean like climate. 相似文献
7.
Evaluating the Impact of Drought Using Remote Sensing in a Mediterranean,Semi-arid Region 总被引：2，自引：1，他引：2
Sergio M. Vicente-Serrano 《Natural Hazards》2007,40(1):173-208
This paper analyses monthly differences in drought impact on vegetation activity in a semi-arid region in the north-east of
the Iberian Peninsula between 1987 and 2000. The study determines spatial differences in the effects of drought on the natural
vegetation and agricultural crops by means of the joint use of vegetation indexes derived from AVHRR images, a drought index
(standardized precipitation index), and Geographic Information Systems. The results show that the effect of drought on vegetation
varies noticeably between areas, a pattern that is determined mainly by the location of land-cover types. The influence also
varies each month and, in general, is higher during the spring and summer. Aridity and vegetation characteristics similarly
account, in part, for spatial differences in the impact of drought on vegetation. In general, the most arid areas, where vegetation
cover and activity are low, are those in which the interannual variability of vegetation activity is more determined by the
drought occurrence. In assessing drought impact, this analysis takes into account the effects of drought on the vegetation
and also considers spatial and seasonal differences. The results should be useful for the management of natural vegetation
and crops and for the development of better drought mitigation strategies. 相似文献
8.
9.
为进一步分析日尺度有效干旱指数(Effective Drought Index,EDI)的适应性,基于雷州半岛1984~2013年逐日降水资料进行验证,对比EDI和月尺度标准化降水指数(Standardized Precipitation Index,SPI)的干旱识别效果,进而结合线性趋势、M-K趋势检验和空间插值方法 ,分析雷州半岛季节性气象干旱时空特征。结果表明:(1)日尺度EDI和6个月时间尺度SPI(SPI-6)适用于雷州半岛的干旱监测,但EDI对严重干旱和突发干旱的识别比SPI-6更准确;(2)1984~2013年,雷州半岛秋冬季干旱频率和干旱站次比均呈减少趋势,但春夏季干旱频率和干旱站次比略有增加趋势;(3)春旱频率从南向北递增,重旱高频地区位于西北部,而夏季重旱高频区位于西部沿海;秋旱南部重于北部,高频中心在雷中西部沿海和曾家周边;冬季重旱以西部沿海、雷州市和徐闻县交界处频率最高。 相似文献
10.
F.R. Zúiga J.F. Pacheco M. Guzmn-Speziale G.J. Aguirre-D&#x;&#x;az V.H. Esp&#x;&#x;ndola E. Nava 《Tectonophysics》2003,361(3-4):229-238
A sequence of small earthquakes occurred in Central Mexico, at the northern edge of the Trans-Mexican Volcanic Belt (TMVB) in the State of Queretaro, during the first 3 months of 1998. Medium to large events in the continental regime of central Mexico are not common, but the seismic history of the region demonstrates that faults there are capable of generating destructive events. The sequence was analyzed using data from a temporary network with the goals of identifying the causative fault and its relation to regional tectonics. Employing a waveform inversion scheme adapted from a method used for regional studies, we found that the source mechanisms conform to the style of faulting (i.e. extension in the E–W direction) representative of the Taxco–San Miguel Allende Fault system. This system has been proposed as the southernmost extension of the Basin and Range (BR) Province. The spatial distribution of hypocenters and source mechanisms indicate that the seismogenic segment was a fault with an azimuth of approximately 334° with almost pure dip slip. Since events which occurred just south from this region show features which are consistent with TMVB tectonics (i.e. extension in an N–S direction), the sequence may mark the boundary between the TMVB and BR stress domains. 相似文献
11.
Current states of stress in the northern Andes as indicated by focal mechanisms of earthquakes 总被引：1，自引：3，他引：1
Systematic inversion of double couple focal mechanisms of shallow earthquakes in the northern Andes reveals relatively homogeneous patterns of crustal stress in three main regions. The first region, presently under the influence of the Caribbean plate, includes the northern segment of the Eastern Cordillera of Colombia and the western flank of the Central Cordillera (north of 4°N). It is characterized by WNW–ESE compression of dominantly reverse type that deflects to NW–SE in the Merida Andes of Venezuela, where it becomes mainly strike–slip in type. A major bend of the Eastern thrust front of the Eastern Cordillera, near its junction with the Merida Andes, coincides with a local deflection of the stress regime (SW–NE compression), suggesting local accommodation of the thrust belt to a rigid indenter in this area. The second region includes the SW Pacific coast of Colombia and Ecuador, currently under the influence of the Nazca plate. In this area, approximately E–W compression is mainly reverse in type. It deflects to WSW–ENE in the northern Andes south of 4°N, where it is accommodated by right-lateral displacement of the Romeral fault complex and the Eastern front of the northern Andes. The third, and most complex, region is the area of the triple junction between the South American, Nazca and Caribbean plates. It reveals two major stress regimes, both mainly strike–slip in type. The first regime involves SW–NE compression related to the interaction between the Nazca and Caribbean plates and the Panama micro-plate, typically accommodated in an E–W left-lateral shear zone. The second regime involves NW–SE compression, mainly related to the interaction between the Caribbean plate and the North Andes block which induces left-lateral displacement on the Uramita and Romeral faults north of 4°N.Deep seismicity (about 150–170 km) concentrates in the Bucaramanga nest and Cauca Valley areas. The inversion reveals a rather homogeneous attitude of the minimum stress axis, which dips towards the E. This extension is consistent with the present plunge of the Nazca and Caribbean slabs, suggesting that a broken slab may be torn under gravitational stresses in the Bucaramanga nest. This model is compatible with current blocking of the subduction in the western northern Andes, inhibiting the eastward displacement of slabs, which are forced to break and sink in to the asthenosphere under their own weight. 相似文献
12.
自然界水循环中的水量平衡原理与干旱研究 总被引：1，自引：1，他引：0
概述了国际、国内干旱研究概况。指出区域多年平均降水量的多少,反映了区域中水资源对生态、经济发展承载力的大小。农业生产中把防止土壤蒸发措施叫抗旱;水利建设中拦河筑坝、引水灌溉、凿井汲水,叫兴修水利抗旱救灾。因此干旱的实质是径流消退、土壤蒸发自然衰减并达到区域内水资源对生态和经济发展的承载能力下降到某一限度或阀值的称谓,如人们感官中的小旱、大旱等。根据径流消退公式和土壤蒸发衰减曲线,参照大风、地震研究方法,输入降水、逐日蒸发观测值,即可成功实现统一干旱标准的实时旱情监测。 相似文献
13.
A Conceptual Framework for Enhancing the Utility of Rainfall Hazard Forecasts for Agriculture in Marginal Environments 总被引：1，自引：0，他引：1
Semi-arid and dry sub-humid areas (especially in the tropics) are characterized by high inter-annual and intra-seasonal rainfall variability. Agriculture, which employs the bulk of the rapidly increasing populations, is largely rain-fed, low-input based and highly resource dependent. Recent spates of drought have, therefore, exacerbated the now-too-familiar specter of famine and starvation in these areas with glaring examples being the recurring episodes in sub-Saharan Africa since the great Sahel drought of 1969–1973. A great need for accurate and timely hazard forecast products in aid of agriculture thus exists.Several schemes are currently employed by various agencies around the globe in this direction. There does remain, however, a gap between product provision and user expectations. This paper examines this gap suggesting a five-point framework within which it can be addressed as an action agenda for the climate science community. The paper posits that changes are possible to existing methodologies (related to three of these points), which, within the context of current science, can greatly enhance the utility of forecast products for agriculture in marginal areas. The remaining two points have, however, been identified as requiring additional applied research and necessary pointers for addressing these issues are provided. First is the need for appropriate impact-related indicators for intra-seasonal and interannual rainfall variability that are easy to compute, amenable to forecasting and follow closely the experiences of farmers in marginal areas. The second is a consideration of appropriate forecast information formatting and communication medium that guarantee effective feedback between forecast producers and users. Specific examples of the status quo and of work currently underway are cited from southern Africa – a region currently attracting international attention as a result of recent droughts and the threat of famine. 相似文献
14.
D. M. Orazulike 《Natural Hazards》1993,7(2):109-119
Field and chemical data show that soils in some parts of Bauchi State, Nigeria, are rich in illite (20–35%), montmorillonite (60–75%), and kaolinite (45–73%). These expansive clays cause the soils to shrink and swell alternatively in response to the seasonal supply of moisture; resulting in observed damaging cracks. Plasticity index (PI) determinations on these soils are high (7–13.4%) suggesting that they are potentially hazardous. The attendant hazards and huge losses to the State are blamed on the expansive nature of these soils. The hazardous conditions can be mitigated by adopting proper construction precautions as well as by using chemical additives such as lime and phosphates, to lower the PI and help to increase the strength of the soils. 相似文献
15.
使用2009年DOY (Day of Year) 145~288时段与2001~2010年夏季(DOY 161~240时段)的Terra/MODIS 16 d合成的植被指数产品数据MOD13 A2和8 d合成的地表温度(Land Surface Temperature,TLS)产品数据MOD11 A2,构建TLS~IEV(Enhanced Vegetation Index,IEV)特征空间,从而得到了条件温度植被干旱指数(Temperature Vegetation Drought Index,ITVD)反映的藏北土壤湿度空间分布。对藏北高原2009年植被生长季内土壤湿度的季节性变化及2001~2010年夏季土壤湿度的年际变化特征进行分析,研究结论表明:随着植被盖度的增大,干、湿边斜率逐渐变小,植被对环境温度的变化具有缓冲效应;藏北高原土壤湿度的季节性变化明显,主要受温度、降水、植被覆盖和冻土过程等季节性变化的影响;近10年研究区内土壤湿度有轻微的旱化趋势,但不同气候区内的年际变化表现不一致;气温表现不同程度的显著升温趋势,部分站点的降水有不显著减少趋势,其它站点降水表现为年际波动,而区域统计的ITVD值年际波动与站点气温的变化大体一致。 相似文献
16.
利用内蒙古及周边地区70个气象站1951~2014年降水数据,采用标准化降水指数等方法,对内蒙古近64年气候干旱时空变化进行分析。结果表明:研究区近64年来除西部年际、春、秋、冬季,中部春、秋季及东部春、冬季气候趋于湿润外,其他均趋于干旱。中、东部年际、植(作)物生长期SPI在2001年和1990年左右发生突变,东部突变后趋于干旱并在2006年左右又发生明显转折后趋于湿润。西部在1960s干旱严重,中、东部在1990s至2000s干旱严重。西部年际SPI由西北向东南、东部由南向北干旱趋势速率呈阶梯状下降,中部干旱趋势速率较西、东部快;植(作)物生长期SPI空间变化与年际一致,但西、中部干旱趋势明显的区域有所扩大。 相似文献
17.
An Analysis of Spatial and Temporal Dimension of Drought Vulnerability in Turkey Using the Standardized Precipitation Index 总被引：3，自引：1，他引：2
Drought has become a recurrent phenomenon in Turkey in the last few decades. Significant drought conditions were observed during years of late 1980s and the trend continued in the late 1990s. The countrys agricultural sector and water resources have been under severe constraints from the recurrent droughts. In this study, spatial and temporal dimensions of meteorological droughts in Turkey have been investigated from vulnerability concept. The Standardized Precipitation Index (SPI) method was used to detail geographical variations in the drought vulnerability based on frequency and severity of drought events at multiple time steps. Critical (threshold) rainfall values were derived for each station at multiple-time steps in varying drought categories to determine least amount of rainfall required to avoid from drought initiation. The study found that drought vulnerability portrays a very diverse but consistent picture with varying time steps. At regional scale, south-eastern and eastern Anatolia are characterized with moderate droughts at shorter time steps, while the occurrence of severe droughts at shorter time steps is observed at non-coastal parts of the country. A similar picture was observed with very severe droughts. The critical (threshold) values exhibited rising numbers during the growing season at 3-month step in the South-eastern Anatolia, which might have significant consequences considering presence of large irrigation projects under-development in the region. In general, rainfall amounts required for non-drought conditions decrease from the coastal parts toward the interiors with increasing time steps. 相似文献
18.
The northern China–Mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late Mesozoic time. Late Middle to early Late Jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated North China–Mongolia block and the Siberian plate, but widespread late Late Jurassic–Early Cretaceous extension has not been satisfactorily explained by existing models. Some prominent features of the extensional tectonics of the northern China–Mongolia tract are: (1) Late Jurassic voluminous volcanism prior to Early Cretaceous large-magnitude rapid extension; (2) overlapping in time of contractional deformation in the Yinshan–Yanshan belt with development of extension-related basins in the interior of the northern China–Mongolia tract; and (3) widespread occurrence of alkali granitic plutonism, extensional basins and metamorphic core complexes in the Early Cretaceous. A new explanation is advanced in this study for this sequence of events. The collision of amalgamated North China–Mongolia with Siberia led to crustal overthickening of the northern China–Mongolia tract and formation of a high-standing plateau. Subsequent breakoff at depth of the north-dipping Mongol–Okhotsk oceanic slab is suggested as the main trigger for late Mesozoic lithospheric extension of that tract. Slab breakoff resulted in mantle lithospheric stretching of the adjacent northern China–Mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust. Collectively, these phenomena triggered gravitational collapse of the previously thickened crust, leading to late Late Jurassic–Early Cretaceous crustal extension, and importantly, coeval contraction along the southern margin of the plateau in the Yinshan–Yanshan belt. The proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena, such as the synchronous extension of northerly terranes during major contraction in the neighboring Yanshan–Yinshan belt. 相似文献
19.
E. Olukayode Oladipo 《Natural Hazards》1989,2(1):1-16
The maximum entropy spectral technique is used to search for periodicities in drought indices over the Great Plains of North America, covering a period of at least 70 years. The results show that in general, quasi-biennial, quasi-triennial and quasi-five-year cycles dominate the spectra of drought indices of many stations in the region. These significant periodicities in the 2–6 year waveband are, however, sporadic in their spatial distribution; they can be evident at one station while being absent at another a few hundred kilometres away. From the results of the spectral analysis, it is concluded that significant peaks obtained in the drought indices are only short-lived time variabilities in drought as recorded by individual stations and do not represent any persistent drought characteristics over a broad geographical region. In general, the drought series display only what appears to be a random variation, with the possible exception of a systematic quasi-biennial oscillation. 相似文献
20.
Stefan B. Velev 《GeoJournal》1996,40(4):363-370
This article attempts to analyse the current climatic variations based on air temperature and precipitation data from 18 stations for the 1916–1993 period. No substantial changes have been established in the annual air temperatures, averaged over the whole country's area, but there is evidence of late fall cooling and winter warming in the recent decade. A marked drought set in during 1982–1993, which in SW Bulgaria which reached a record level for the last 100 years both in terms of its duration and intensity. Climatolgical patterns contributing to these observations are discussed. 相似文献