1819年黄河中游极端降水:史实、特征及气候背景

据清官档案与方志记载,复原了1819年(清嘉庆二十四年)黄河中、下游大范围房屋倒塌、民田冲没、人口伤亡、黄河多处决溢等雨涝灾情图景及时空分异特征,这是在明清小冰期大气候背景下的极端气候事件和重大气象灾害.研究指出,该年黄河中游夏秋季雨期长(连阴雨)、且多大到暴雨,二级流域(汾河、渭河)6-9月份降水县区雨日高达40日以...     

Response and recovery of the Eel River, California, and its tributaries to floods in 1955, 1964, and 1997

Northwestern California is prone to regional, high magnitude winter rainstorms, which repeatedly produce catastrophic floods in the basins of the northern Coast Ranges. Major floods on the Eel River in 1955 and 1964 resulted in substantial geomorphic changes to the channel, adjacent terraces, and tributaries. This study evaluated the changes and the effects of a moderate flood in 1997 through field observations and examination of aerial photographs that spanned from 1954 to 1996. The purpose was to document the nature and magnitude of geomorphic responses to these three floods and assess the rates and controls on the recovery of the Eel River and its tributaries. Channel widening from extensive bank erosion was the dominant geomorphic change along the lower Eel River during major floods. As a result of the 1964 flood, the largest amount of widening was 195 m and represented an 80% change in channel width. Channel narrowing characterized the periods after the 1955 and 1964 floods. More than 30 years after the 1964 flood, however, the river had not returned to pre-flood width, which suggests that channel recovery required decades to complete. A long recovery time is unusual given that the Eel River is located in an area with a “superhumid” climate and has an exceptionally high sediment yield. This long recovery time may reflect highly seasonal precipitation and runoff, which are concentrated in 3–5 months each winter. In contrast to the main stem of the Eel River, the dominant effects of floods on the tributaries of the Eel River were rapid aggradation of channel bed and valley floor followed by immediate downcutting. Dendrogeomorphic data, aerial photographs, and field observations indicate that thick wedges of gravel, derived largely from hillslope failures in upper reaches of the tributaries, are deposited at and immediately upstream of the mouths of tributaries as the stage of the Eel River exceeded that of the tributaries during major floods. In the waning stages of the flood, the tributaries cut through the gravel at a rate equal to the lowering of the Eel and generated unpaired terraces and nickpoints. The complete process of deposition and incision can occur within a few days of peak discharge. Although reworking of some sediment on the valley floor may continue for years after large floods, channel morphology in the tributaries appears to be a product of infrequent, high magnitude events. The morphology of the tributary channel also appears to be greatly influenced by the frequency and magnitude of mass wasting in headwater areas of small basins.     

长江上游全新世特大洪水对西南 季风变化的响应

利用24次全新世特大洪水序列与川渝地区近两千年的洪灾史料,对长江上游特大洪水事件和气候变化的响应机制进行了分析。从长江上游特大洪水序列与阿拉伯海记录的西南季风气候变化对比分析来看,特大洪水事件与西南季风变化具有很好的响应关系,特大洪水事件多发生于西南季风较弱的阶段,这些阶段以西南季风气候快速变化为特征,是气候剧烈波动期或气候的转型期。与北大西洋、贵州董歌洞石笋所记录的气候变化比较,特大洪水有的与全新世气候突变一致,有的则不一致,可能特大洪水事件更多表现为地方事件。与文献记载的历史洪灾事件相比,长江上游低频高量级的特大洪水事件对西南季风的变化具有更好的响应关系,而高频低量级的洪灾事件具有更高的随机性,由于历史文献记载的洪水量级差异较大,如果将他们笼统地放在一起分析,可能会掩盖洪水事件对气候变化响应机制。     

1999年全球重大气候事件概述

１９９９年,全球气候仍持续较常年偏暖。赤道中、东太平洋的强拉尼娜事件维持并发展,对全球特别是热带地区的气候产生了较明显的影响。欧洲、北冬季连续遭受暴风雪袭击,出现严寒天气,夏季又经受了高温热浪的袭击。全球许多地区暴雨频繁,亚洲南部、欧洲中部、北美南部、南美北部以及非洲的一些地区都遇到了严重的洪涝灾害;而北美中部、西亚等地却干旱少雨,发生了凡十年来最严重的旱灾。北美、南亚、澳大利亚东北部先后遭到罕见     

洞庭湖流域各季节旱涝及其与大气环流和关键区海温的关系

利用逐月降水数据和NCEP/NCAR再分析数据,分析了洞庭湖流域春、夏、秋季57年来旱涝异常的年际变化以及典型旱涝异常年份的全球海温分布形势,并利用降尺度和趋势分析方法探究气象因子对ENSO和关键区海温的响应,以加强对流域旱涝前期影响因素的认识.结果表明:1)流域在春、秋季旱涝变化趋势不明显,在夏季较明显地变湿.2)前...     

OBSERVATIONS ON THE QUATERNARY GEOLOGY OF THE LADAKH RANGE, NORTHWEST INDIAN HIMALAYA

OBSERVATIONS ON THE QUATERNARY GEOLOGY OF THE LADAKH RANGE, NORTHWEST INDIAN HIMALAYA     

鄂温克旗干旱、洪涝灾害期评定及预测方法

根据鄂温克旗1959—2008年气象历史资料,统一归类,并采用统计预报方法,简要评定预测出鄂温克旗50年来主要气象灾害之一的干旱、洪涝灾害期,为鄂温克旗防范旱涝灾害做参考。     

20世纪长江流域3次全流域灾害性洪水事件的气象成因分析

20世纪长江流域曾出现上游洪水7次,中游洪水16次,下游洪水7次,其中有3次是全流域性洪水,分别发生在1998、1954和1931年。1998、1954和1931年梅雨期开始前(3~5月),长江流域降水比常年偏多。进入梅雨季以后,先后出现两场持续性暴雨:第1场出现在6月中旬至7月上旬,这场暴雨造成中下游河流的水位达到或超过警戒水位,出现局地洪涝;7月下旬长江中下游又出现1场持续性范围广的暴雨,雨水只能作为地面径流汇集到长江干流,造成很高水位的洪流。第2场持续性暴雨使长江上下游强降水时段在7月下旬重合,导致长江中下游干流洪水与来自上游的洪水在8月初至中旬遭遇,造成长江中下游灾难性的大洪水。1998、1954和1931年长江全流域性大洪水与东亚中高纬地区大气环流和东亚夏季风活动异常有联系。大气环流和东亚季风活动异常导致7月下旬西太平洋副热带高压的位置偏南,梅雨期持续到7月底,有利于长江中下游持续性暴雨发生的环流条件在7月下旬仍然存在。     

试析刘宋统治区的气候波动与水旱灾害

刘宋时期虽然整体上属于历史气候变迁中的寒冷期,不过期间存在气温的波动。刘宋初年气温较低,元嘉中后期升至波峰,泰始年间降至波谷,刘宋末年气温再度升高。这种波动通过当时的各种气候资料表现出来,同时也反映在当时的水旱灾害发生特点上。一般在寒冷期,水灾发生的时间要晚,反之,则早。刘宋时期梅雨期到来的早晚和降水量的多少,受制于这种气候波动,同时也影响到当时水旱灾害的发生状况,是这种气温波动的集中表现。     

2003年淮河流域致洪暴雨的环流背景及其与大气热源的关系

利用NCAR/NCEP的逐日再分析资料和降水资料,分析了2003年夏季淮河流域致洪暴雨的环流背景及其与大气热源的关系.结果表明,2002-2003年的El Nino事件是本次暴雨的前期背景;南海地区的视热源和视水汽汇异常可能是副高偏南维持的重要原因之一.与2003年夏季相比较,6月21日-7月22日淮河流域为正的异常视热源和视水汽汇,并且二者的高值中心与该时段雨量中心位置基本一致.孟加拉湾地区的异常加热源在其西北侧强迫出的高层反气旋性环流有利于南亚高压在青藏高原、江南、华南地区维持,从而使得淮河流域位于高压北侧高空西风急流入口区南侧的上升运动区,有利于淮河流域强降水发生和维持,形成该流域洪涝.