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During February 1992, a series of relatively warm storms passed eastward across southern California, yielding intense precipitation that triggered widespread mass movement, flooding, property damage, and loss of life. These storms were triggered by an intense low pressure system (976 mb) off northern California which deepened as its eastward progress was initially blocked by a high pressure ridge (1040 mb) across western North America. Between February 10 and 13, large areas of Ventura and Los Angeles counties experienced cumulative precipitation of 200–400 mm with intensities reaching 40–50 mm hr-1. Mass movement, mainly as soil slips that transformed downslope into debris flows, occurred where cumulative precipitation exceeded 300 mm and when sustained intensities exceeded 25 mm hr-1. Stream response was rapid, particularly in urban areas where impermeable surfaces and storm drains fed concrete stream channels. The canalized upper Los Angeles River and Arroyo Simi exceeded all previous discharges for over 43 and 36 years of record, respectively. Other streams, from the large Santa Clara River to modest Malibu Creek, yielded recurrence intervals for the peak discharge of between 8 and 24 years, but the rapidity of flooding everywhere was remarkable. Whereas main trunk streams, canalized or not, responded predictably, the storm series emphasized the problems of poorly controlled development of potentially unstable hillsides and floodable lowlands and indicated a need to reassess the assumptions upon which such development is permitted. [Key words: climatology, cyclonic storm, geomorphology, mass movement, flooding, California]. 相似文献
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根据我国北方的热量平衡观测资料,地立了计算感热—潜热比的经验模式,用于计算黄河流域旱涝年(1972、1975、1986、1988年)及一般年(1971、1974、1985、1987年)夏季陆面蒸发,并分析其变化特点以及与旱涝的关系。 相似文献
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Although dust storms rarely occur in southern California's deserts, blowing dust often reduces visibility, and large spatial and temporal variability in the frequency of blowing dust occurs throughout the region. On average only 1.3 dust storms occur in the study area each year. The annual average number of dust events (visibility <11 km) is 18.0, with the Coachella Valley being dustiest region, averaging 37.8 dust events each year. Mean annual frequencies of dust events for 1973–1994 are mapped, showing a core of activity centered over the Imperial/Coachella Valley region, with fewer dust events around the periphery of the study area. Most stations show a coherent temporal pattern of dust frequency during the period 1973–1994, with the mid-1970s experiencing the most dust. Blowing dust generally was absent from all stations during 1979–1983, 1987–1989, and 1992–1994. The mid-1980s were moderately dusty and 1990–1991 saw a return to very dusty conditions, possibly resulting from below-normal precipitation and increased anthropogenic disturbances. Dust events in the Mojave Desert characteristically occur during the winter to spring months (February-May), associated with dry frontal activity, and are largely absent during the dry summer months. The Colorado Desert experiences a similar seasonal distribution of dust events, but has more summer events, usually associated with convective thunderstorms. Frequencies of blowing dust have weak, but statistically significant, correlations with mean annual and antecedent precipitation, suggesting that complex processes control dust emission. [Key words: blowing dust, dust storms, Mojave Desert, Colorado Desert, wind erosion.] 相似文献
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张清华 《云南地理环境研究》2007,(Z1)
2001～2007年初夏孟加拉湾共发生了6次风暴过程,结合风暴活动期间曲靖地区的降水概况,应用micaps常规气象资料和物理量场对这6次过程的环流背景及水汽、动力条件展开分析,结果表明:初夏孟湾风暴影响曲靖降水有3个较典型的环流类型,即与冷空气配合型、孟湾风暴云团北上引发强对流降水型以及孟湾风暴登陆减弱变性成南支东移影响型;孟湾风暴活动期间,90°E～120°E,15°N～30°N区域存在位置基本对应的东北-西南向强西南风速带、水汽通量大值带和强水汽通量辐合带,说明风暴的活动为云南降水提供了充足的水汽和动力条件。 相似文献
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1951-2008年中国西北干旱区降水时空变化及其趋势 总被引：1，自引：0，他引：1
在全球气候变化背景下,地处生态脆弱区的中国西北干旱区降水响应特征及其未来变化趋势的量化研究极为重要,依据中国西北干旱区95个站点1951-2008年月降水资料,运用自然正交分解法(EOF)、Morlet小波分析、轮次分析、游程理论、极差分析、季节性指数分析、Mann-Kendall检验及气候趋势系数分析等方法分析了西北干旱区降水时空变化特征及其未来趋势。结果表明:西北干旱区降水场前4个特征向量累计方差贡献率达81.61%,第一特征向量最高为48.53%,属"相间复杂"型,依据其荷载空间分布特征将研究区划分为北疆子区、南疆子区、河西子区、青海子区及内蒙古子区;西北干旱区及各子区降水存在9年及12年主周期;各地的极大丰水历时均小于极限枯水历时,单独丰水年的概率高于单独枯水年,连枯年的概率高于连丰年,干旱主要发生在新疆和河西地区;降水序列具有长期相关性,Hurst系数在0.629～0.845间波动;西北干旱区40.0%的地区降水具有明显的季节性分布;61%地区重现性指数大于0.7,降水年内分配的年际差异较小;86.3%地区降水量呈增加趋势,其中20.0%通过信度0.01的显著性检验,48.4%通过了0.05显著性检验,增幅16.6～0.1 mm/10a;11.6%地区呈减少趋势,减幅为5.2～0.3 mm/10a。 相似文献
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Based on the daily precipitation data of 27 meteorological stations from 1960 to 2009 in the Huaihe River Basin, spatio-temporal trend and statistical distribution of extreme precipitation events in this area are analyzed. Annual maximum series (AM) and peak over threshold series (POT) are selected to simulate the probability distribution of extreme precipitation. The results show that positive trend of annual maximum precipitation is detected at most of used stations, only a small number of stations are found to depict a negative trend during the past five decades, and none of the positive or negative trend is significant. The maximum precipitation event almost occurred in the flooding period during the 1960s and 1970s. By the L-moments method, the parameters of three extreme distributions, i.e., Generalized extreme value distribution (GEV), Generalized Pareto distribution (GP) and Gamma distribution are estimated. From the results of goodness of fit test and Kolmogorov-Smirnov (K-S) test, AM series can be better fitted by GEV model and POT series can be better fitted by GP model. By the comparison of the precipitation amounts under different return levels, it can be found that the values obtained from POT series are a little larger than the values from AM series, and they can better simulate the observed values in the Huaihe River Basin. 相似文献
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Seasonal controls on sediment delivery in a small coastal plain watershed, North Carolina, USA 总被引：1，自引：0，他引：1
Field measurements of drainage ditch sedimentation and suspended sediment transport were used to construct a simple sediment budget and relate seasonal variations in vegetation and the hydrological characteristics of storms to sediment dynamics in a small agricultural watershed in North Carolina. Results indicate that seasonal variations in crop coverage and vegetation in drainage ditches influence sediment delivery. Following the harvesting of crops and mowing of drainage ditches in late autumn, conditions are favorable to soil erosion and sediment transport through early spring. Storms need not be very intense or produce large rainfall totals to transport significant sediment loads. The maturation of field crops and ditch vegetation in spring produces conditions less conducive to both soil erosion and sediment transport. Intense summer thunderstorms, however, are capable of mobilizing and transporting significant amounts of sediment. The computed sediment yield of 0.1 Mg/ha/yr probably represents a low estimate that, nevertheless, is an order of magnitude less than measured ditch storage and more than two orders of magnitude less than regional estimates of soil loss on Coastal Plain croplands. The results show that headwater ditches may be decoupled from slopes so that much of the eroded soil is stored within small watersheds rather than being transported out of the basin. 相似文献
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雅鲁藏布江流域不同源降水数据质量对比研究 总被引：2，自引：0，他引：2
本文以雅鲁藏布江流域为研究区,利用13个气象站点的实测降水量数据在年和月尺度上验证了中国地面降水网格数据、CRU(Climatic Research Unit)降水数据和GLDAS(Global Land Data Assimilation System)降水数据的精度,并分析了不同源数据降水量年际变化特征和概率分布特性之间的差异。结果表明：4种不同来源的降水数据均存在一定程度的差异。年尺度和月尺度上中国地面降水网格数据与实测降水量数值最接近;而CRU降水数据和GLDAS降水数据与实测降水量相差较大,在使用时需谨慎。从空间差异性看,年尺度上CRU降水数据在每个站点与实测降水数据的相关性均高于GLDAS降水数据,说明前者的空间一致性较好,但相对误差却比GLDAS降水数据大。从年内变化趋势看,中国地面降水网格数据能较好地反映流域降水月尺度的变化特征,CRU降水数据则在流域大部分地区的汛期时段都存在明显的高估,而GLDAS数据无法反映月降水变化趋势,年内坦化现象十分显著。从年际变化特征看,中国地面降水网格数据能较好地反映实际降水量的年际变化特征,而GLDAS降水数据和CRU降水数据反映的降水量年际变化特征偏小,其中GLDAS数据的坦化现象更严重,会高估低降水值,低估高降水值。从降水概率分布情况来看,3种来源的降水数据均不能反映站点实测的极端降水事件。 相似文献
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M. V. Bolgov M. D. Trubetskova I. A. Filippova M. A. Kharlamov 《Geography and Natural Resources》2017,38(2):139-146
We investigated the precipitation characteristics for the summer period of 2013 on the basis of analyzing the daily precipitation amounts according to observational data from the Russian and Chinese meteostations on the territory of the Amur river basin. An analysis is made of the synchronism in the fluctuations of long-term series of precipitation amounts for two summer months (July and August) by using a modified algorithm for a classification of the fields of hydrometeorological characteristics, such as cluster analysis. The study revealed a poor correlation of precipitation amounts in different parts of the basin. We analyzed the interannual fluctuations in absolute maxima of the consecutive precipitation amounts for different periods of time (from 1 to 30 days). It is shown that precipitation over the summer period of 2013 that caused a disastrous flood in the lower reaches of the Amur were extreme primarily as regards the territory encompassed and the flood duration, which was due to a combination of synoptic processes of a different genesis. It was found that the precipitation amounts for periods shorter than 19 days in 2013 were not extreme in terms of intensity. A comparison was made with the year 1984 when there also occurred a flood on the Amur but not as violent. Parameters of the probability curves for 2013 and 1984 are presented for long-term series of maximum precipitation amounts for the summation period of 7 and 30 days. It is concluded that for calculating the maximum possible precipitation amounts which are necessary for assessing the maximum possible floods, it is appropriate to consider synoptic situations with long-lasting precipitation rather than separate short-lasting storm rains. 相似文献
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Lawrence C. Nkemdirim 《The Professional geographer》1988,40(1):65-76
Results of analyses of 86 years of precipitation records for Calgary, Canada, showed that there were three periods of above normal precipitation and three periods of precipitation significantly below normal. This pattern gave the precipitation climate a quasi-periodic appearance. The average number of precipitation-days was 134 per annum. The reduction in the frequency of precipitation-days in dry years was not as significant as the equivalent reduction in precipitation amounts. A significant upward trend in the frequency of precipitation-days, which correlated with a similar trend in cloud cover, was not repeated in precipitation amounts. The upward trend in both cloud cover and precipitation-day frequency is believed to be related to urban growth and the corresponding heat island. This enhancement is more pronounced in the fall and winter months than in the spring and summer. 相似文献
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青藏高原自然植被总生物量的估算与净初级生产量的潜在分布* 总被引：32，自引：0，他引：32
以800多块样地资料及森林和草地资源调查数据为基础,按县级为单位估算了青海和西藏两省区的自然植被总生物量,分别为2.586×108t和1.282×109t.建立的QZNPP模型显示,随着温度的增加,生物生产量呈S型曲面递增,且其递增速率随降水量增加而加快;当年均温度0℃～10℃和年降水量400mm～1000mm时,生物生产量增长最快;当年均温度>11℃和年降水量>1 100mm时,生物生产量趋向于20t/hm2·a;在年均温度<0℃时,相对降水量的增加,生物生产量呈缓慢的递减趋势,说明这时温度是影响生物生产量的主导因子。两省区115个县的生物量现实分布图显示,生物量最高值出现在西藏墨脱,其次是西藏的察隅、波密、林芝和米林,青藏高原中部及西北部的广阔地区最低。青藏高原自然植被净初级生产量最小值为0,最大值为20t/hm2·a,全区平均为6.03t/hm2·a,低于世界陆地植被的平均水平 相似文献
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ItisataskofNationaScienceandTechnologyProjectNo.75-62-03-05and06forthe7thFive-YearPlanperiod.InvestigationsinGansuandShanxiwereundertakenbyInstituteofGeography,CAS,whiiethatinShaanxiwascarriedoutbyNortllwestInstitllteofWaterandSoilConservation,CAS.**OthermembersintheGroupofEndemicDiseaseandEnvironment,InstituteofGeograpl1y,CASare:YangLinsheng,ZhaoYuanwei,ZhaoNaiqin,LiDezhu,WangLizhenandTanJianan.I.IntrodIlcti01llthasbeenreported[21thattwoendemics,KeshanandKaschin-Beck,arecl… 相似文献
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A two component mixed log-normal distribution effectively models annual precipitation totals at two stations in Peru characterized by widely differing interannual patterns of precipitation. Physical evidence supports the division of station records into two subsamples. Years with ENSO events and years without ENSO events identify the components of a mixed probability model. The mixed model produces a superior fit to the two parameter log-normal distribution. Model application provides a reliable means of precipitation prediction and also quantitatively describes the highly variable temporal and spatial pattern of annual precipitation in western Peru. 相似文献
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Philip W. Suckling 《自然地理学》2013,34(2):124-139
Significant snowstorm events occurring during the winters from 1948/49 through 1989/90 are studied using a network of 100 weather stations across the southern states of Mississippi, Alabama, Georgia and South Carolina. To qualify for entry into the snowstorm inventory, at least 10 out of the 100 sites need a minimum of 25 mm (1 inch) of snowfall. A total of 69 events are identified and further categorized into four magnitudes based upon areal coverage or total snowfall amount. The storms are also classified into regional categories based upon the dominant part of the study area affected. The spatial characteristics of the snowstorms are discussed and illustrated with maps showing snowfall distributions for representative storms. Most events impact the northern portions of the study area although some very major storms fit into a Miscellaneous category with unique snowfall distributions in the southern or central parts of the Deep South. The temporal character of snowstorm frequency reveals that a very low number of events occurred during the 1950s with peak occurrence during the 1960s. Snowstorms generally remained more frequent during the 1970s and 1980s compared to the 1950s. 相似文献
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本文以农田需水量作为供水余缺的标准,分析长江、淮河、海河流域降水的年内年际变化与季节需水的关系,论证了南水北调的必要性和引江济海的合理性。 相似文献
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根据中国西北地区东部59个气象台站1965-2014年的逐日降水资料,将降水划分为小雨、中雨和大雨3个等级,分析和比较了该地区夏季不同等级降水降水量、降水日数和降水强度的时间演变特征,并对各等级降水对总降水贡献的时间变化进行了讨论。结果表明：（1）西北地区东部降水量和降水日集中在夏季。降水等级越高,降水量和降水日的集中程度越高,夏季大雨量（日）达到了全年大雨量（日）的72.15%（69.19%）;（2）西北地区东部各等级降水量、降水日主要在1996年存在一个由多转少的突变,均存在较明显的2~3 a的短周期;（3）西北地区东部夏季降水总量与中雨等级以上降水量具有相似的年际和年代际变化,相关系数高达0.8,主要受中雨和大雨量的影响,仅在东南部和甘肃中部趋于增加,在甘肃南部和内蒙古中部趋于减少。总降水日则与小雨日变化一致,主要呈减少趋势,总降水强度的增强则主要源自大雨强度的增大。 相似文献