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1.
祁连山中部公元904年以来树木年轮记录的旱涝变化   总被引：19，自引：6，他引：13  
利用取自祁连山中部地区的树木年轮样本和该地区3个站点的降水资料,应用年轮气候学方法,重建了祁连山中部地区的降水量.自公元904年以来,该地区历经了31次相对干期和30次相对湿润期,其中,连续两个10a以上的干期有17次,湿润期12次,最长的干期是1540—1590年间,长达60a,最长的湿润期是1240—1270年、1860—1890年,各有40a.世纪尺度范围内,16世纪是最干的100a,有80a为少雨年;最湿润的是13世纪和19世纪,这期间有60a为多雨.自公元904年以来,降水量共发生了35次突变,16次是由旱向涝的突变,19次是由涝向旱的突变.平均约30a发生一次.11世纪是该地区降水的多变时期,15～16世纪是降水的相对稳定时段,20世纪又进入了降水的多变时期.  相似文献   

2.
The study compared the sequences of daily rainfall over coastal southern and semi-arid northern Nigeria. Daily rainfall occurrences for 41 years (1971–2011) over four meteorological stations in Lagos, Rivers, Borno, and Katsina were analyzed using frequency analysis and Markov chain model. Findings indicate that the coastal area had a predominance of 2–4-day wet spells while the semi-arid area showed a wet spell distribution that is geometric in nature with 1-day spell predominance. The dry spell behavior was nearly the opposite of the wet spell occurrence. The coastal region showed a dry spell of 1–4-day spell predominance while the semi-arid region showed a predominance of higher dry spells of 2–6 days. Accumulation of the amount of rainfall in each spell also showed that much rainfall from the coastal area was obtained from rains of spells of 3 days and above while the semi-arid had more of its rain from spells of 1–3 days. The mean annual rainfall was 1423.75 mm (Lagos), 2173.56 mm (Rivers), 517.50 mm (Katsina), and 578.34 mm (Borno). The wettest month was June (274.08 mm) in Lagos, September (378.18 mm) in Rivers, and August in Katsina and Borno (172.98 and 184.81 mm, respectively). The driest months were January for Lagos and Rivers (15.77 and 18.96 mm, respectively) and November–February for Katsina and Borno (0–0.06 mm). This showed that the coastal areas had nearly three times the volume of rain in the semi-arid area. The study further showed that onset of rain for the coastal area was March/April while the cessation of rainy season was October/November. On the other hand, the onset of rainy season in the semi-arid area was May/June and cessation of rainy season was September. Findings portend drier days for the semi-arid area due to dry spell persistence and hence, the consequent challenges of providing artificial water supply for agriculture and other purposes especially from October to May.  相似文献   

3.
1962-2007年广东干湿时空变化特征分析   总被引：2，自引：0，他引：2       下载免费PDF全文
利用广东省74个气象站点1962-2007年的月降水与气温数据,计算多时间尺度的标准化蒸散发指数,采用旋转经验正交函数(REOF)、Mann-Kendall趋势检验和小波分析等方法分析广东近50年来的干湿时空变化特征。研究结果表明:① 广东20世纪70年代以来干旱发生事件随时间持续增多,空间范围扩展;② 根据REOF时空分解的前6个空间模态,可以将广东划分成6个干湿特征区域,分别位于珠江三角洲、韩江流域及东江流域上游、西江流域及北江中下游流域、粤东沿海区域、北江上游区域和粤西沿海区域;③ 广东干湿发展具有明显的东西部差异性,其中西江流域和北江中下游流域、雷州半岛为主的粤西沿海流域存在着显著的干旱趋势;④ 6个分区干湿变化普遍具有2~8年的振荡周期,但最强振荡周期有所差别。  相似文献   

4.
The theoretical probabilities of wet and dry spells derived from the Markov Chain Model were found to fit very closely the observed probabilities of various sequence lengths at Juba, S Sudan. Monthly variation in the probability values does not seem to follow a secular trend. Anomogram relating observed sequence length frequency of wet and dry spells versus those computed by Markov model is presented.  相似文献   

5.
The duration and extreme fluctuations of prolonged wet or dry spells associated with intraseasonal variability during extreme monsoon have devastating impacts on agrarian-based economy over Indian subcontinent. This study examines the potential predictability limit of intraseasonal transitions between rainy to non-rainy phases (i.e., active to break phases) or vice versa over central Indian region during extreme monsoon using very high-resolution (0.25° × 0.25°) daily rainfall datasets. The present study reveals that the transitions from both active to break and break to active conditions are more predictable by ~8 days during the weak monsoon (WM) years compared to the strong monsoon (SM) years. Such asymmetric behavior in the limit of predictability could be linked to the distinct differences in the large-scale seasonal mean background instability during SM and WM years. The achievability of such predictability is further evaluated in a state-of-the-art climate model, the climate forecast system (CFSv2). It is demonstrated that the observed asymmetry in predictability limit could be reproducible in the CFSv2 model, irrespective of its spatial resolution. This study provides impetus for useful dynamical prediction of wet/dry spells at extended range during the extreme monsoon years.  相似文献   

6.
新疆夏季变湿的大气环流异常特征   总被引：14，自引：3，他引：11  
利用1961-2003年NCEP/NCAR再分析资料和中国气象局整编的新疆夏季(6~8月)月降水量资料,分析了新疆夏季1971-1986年干旱期和1987-2003年湿润期的大气环流变化异常特征.结果表明:在平均环流场上,中亚-巴尔喀什湖槽及上下游地区脊的增强是新疆地区夏季变湿的环流场特征之一,且中亚-巴尔喀什湖槽随高度增加强度明显增强,200 hPa达到最强;源于低纬阿拉伯海向北直至中亚对流层低层偏南的强气流是湿润期环流异常、降水增多的又一特征,也是水汽重要来源之一;中亚上空高空急流轴南压是新疆夏季湿润期与干旱期高空急流最重要的差异特征.  相似文献   

7.
The Dead Sea is a terminal lake of one of the largest hydrological systems in the Levant and may thus be viewed as a large rain gauge for the region. Variations of its level are indicative of the climate variations in the region. Here, we present the decadal- to centennial-resolution Holocene lake-level curve of the Dead Sea. Then we determine the regional hydroclimatology that affected level variations. To achieve this goal we compare modern natural lake-level variations and instrumental rainfall records and quantify the hydrology relative to lake-level rise, fall, or stability. To quantify that relationship under natural conditions, rainfall data pre-dating the artificial Dead Sea level drop since the 1960s are used. In this respect, Jerusalem station offers the longest uninterrupted pre-1960s rainfall record and Jerusalem rains serve as an adequate proxy for the Dead Sea headwaters rainfall. Principal component analysis indicates that temporal variations of annual precipitation in all stations in Israel north of the current 200 mm yr−1 average isohyet during 1940–1990 are largely synchronous and in phase (70% of the total variance explained by PC1). This station also represents well northern Jordan and the area all the way to Beirut, Lebanon, especially during extreme drought and wet spells. We (a) determine the modern, and propose the past regional hydrology and Eastern Mediterranean (EM) climatology that affected the severity and length of droughts/wet spells associated with multiyear episodes of Dead Sea level falls/rises and (b) determine that EM cyclone tracks were different in average number and latitude in wet and dry years in Jerusalem. The mean composite sea level pressure and 500-mb height anomalies indicate that the potential causes for wet and dry episodes span the entire EM and are rooted in the larger-scale northern hemisphere atmospheric circulation. We also identified remarkably close association (within radiocarbon resolution) between climatic changes in the Levant, reflected by level changes, and culture shifts in this region.  相似文献   

8.
Sun  Peng  Zhang  Qiang  Cheng  Chen  Singh  Vijay P.  Shi  Peijun 《Natural Hazards》2017,89(2):963-983
Natural Hazards - Using daily precipitation data from 25 meteorological stations for a period of 1961–2014, spatiotemporal features of wet spells and droughts and related impacts on...  相似文献   

9.

Drought monitoring is carried out using various drought indices, including SPI, to generate time series of dry and wet periods. Furthermore, the dispersion of dry and wet periods was embossed with different intensities (high, medium, and low) over the data record years. Although these results were very necessary for planning and predicting future droughts, it appeared that the application of any trend over dry and wet periods could provide more accurate and unbiased or safer predictions in terms of analysis process. Generally, most of the researchers believed that the results of a drought trend analysis have been influenced by short-term persistence or significant autocorrelation with different lags on drought event time series and the mentioned impact should be preferably removed. Accordingly, drought monitoring was accomplished using SPI and PNPI drought indices to extract time series of dry and wet periods in terms of 50-year (1965–2014) annual rainfall data of 40 synoptic stations over Iran. Having used the basic and modified Mann–Kendall nonparametric tests, it was attempted to analyze the trend of dry and wet periods extracted from mentioned indices. The results represent the relative advantage of using the modified Mann–Kendall test in drought trend analysis. Furthermore, it was shown that the trend of dry and wet periods was negative in the majority of selected stations and that this trend was significant at 95% confidence level in northwest of Iran. Also, the results indicated the similar performance of SPI and PNPI indices in trend analysis of dry and wet periods.

  相似文献   

10.
The distribution of snow in Israel   总被引：1，自引：0，他引：1  
A. Bitan  P. Ben-Rubi 《GeoJournal》1978,2(6):557-567
The area researched is characterized by changes in the weather according to fluctuations in the world pressure belts throughout the year. The temperature climate in this region is typified in winter by changes in the pressure system from cyclonic to anti-cyclonic conditions in spells of about 5 days.When Israel is under the influence of a low pressure system, and the 500 mb surfaces are approximately 250 m lower than average, the temperatures along the vertical cross-sections are 6° – 8° C lower than average on rainy days, then snow may be expected in various sections of the country.This paper investigated the 35 years period from 1938/9 to 1971/2, concentrating on two mountain stations — Jerusalem in the centre of the country and Mt. Kena'an in the north —because of the high snow incidence and its greater regularity than other stations.The conclusions are as follows: The maximum number of days of snow (between 2/3 and 3/4 of the annual total) is noted at all stations during January and February, although there are also years in which there was snow but not during those months. Regional devision of the snowy days indicates that the number increases with altitude, and decreases from north to south.Snowfall in regions which have lower incidence is less stable and given to greater fluctuations. There was no indication of periodity of the number of days of snow per season, nor did it appear that a very snowy year followed a dry one.Investigation of the lenght of the snowy and the number of days of snowfall does not indicate any connection between them, and there may well be a long season with few days of snow, or a short one with relatively many snowy days.Comparison between the shorter period of readings — from 1938/9 till 1971/2 — and the longer one — from 1860/1 till 1971/2 (111 years) — at the Jerusalem station shows the same trends, which reinforce the conclusions presented above.  相似文献   

11.
The effects of climate change on the groundwater systems in the Grote-Nete catchment, Belgium, covering an area of 525 km2, is modeled using wet (greenhouse), cold or NATCC (North Atlantic Thermohaline Circulation Change) and dry climate scenarios. Low, central and high estimates of temperature changes are adopted for wet scenarios. Seasonal and annual water balance components including groundwater recharge are simulated using the WetSpass model, while mean annual groundwater elevations and discharge are simulated with a steady-state MODFLOW groundwater model. WetSpass results for the wet scenarios show that wet winters and drier summers are expected relative to the present situation. MODFLOW results for wet high scenario show groundwater levels increase by as much as 79 cm, which could affect the distribution and species richness of meadows. Results obtained for cold scenarios depict drier winters and wetter summers relative to the present. The dry scenarios predict dry conditions for the whole year. There is no recharge during the summer, which is mainly attributed to high evapotranspiration rates by forests and low precipitation. Average annual groundwater levels drop by 0.5 m, with maximum of 3.1 m on the eastern part of the Campine Plateau. This could endanger aquatic ecosystem, shrubs, and crop production.  相似文献   

12.
基于不同积雪日定义的积雪资料比较分析   总被引：11，自引：4，他引：7  
利用天气现象定义与积雪深度定义两种方法对全国884个台站的积雪日资料进行统计处理, 分别整理出每一台站各个积雪年的积雪日数、积雪深度、 初终雪间隔日数3个要素的两套数据, 并进行对比分析. 结果表明: 在全国东部大部分地区及新疆地区, 两种数据差别不大, 但在东北及青藏高原两套数据的差别较大. 在积雪日数的比较中, 两种数据在东北及青藏高原的差别基本都在10 d以上, 积雪深度的差别在0.4 cm以上, 初终雪间隔日数的差别以青藏高原最明显, 大部分地区的差别在15 d以上, 甚至有达到30 d以上的区域. 对青藏高原东北边坡代表站的积雪平均值进行M-K突变检验发现, 积雪深度定义的积雪日数与间隔日数减少趋势略大于天气现象定义统计的数值;而在积雪深度的比较中则相反. 两种定义的积雪间隔日数均在1987年出现突变.  相似文献   

13.
Wetland ecosystems are particularly vulnerable due to flow of nutrients from the surrounding watershed. The study was performed in the Shadegan wetland, a Ramsar-listed wetland located in the south-west of Iran at the head of the Persian Gulf. The wetland plays a significant hydrological and ecological role in the natural functioning of the northern Gulf. The proposed wetland has different water quality characteristics in wet and dry years of study during 1994–2006. To determine the variables, sampling was carried seasonally for each year at six stations. The results indicate that wetland in wet years had high concentrations of nitrate and silicate, leading to oligo–meso eutrophic conditions. Wetland in dry years had high phosphate concentrations, resulting in meso-eutrophic conditions. Forcing functions, such as climatic patterns, water residence time, reduce runoff and increasing density of wastewaters from the surrounding urban, agricultural and industrial area are probably the main variables that explain the observed patterns.  相似文献   

14.
Large-scale interannual variability of the northern summer southwest monsoon over India is studied by examining its variation in the dry area during the period 1871–1984. On the mean summer monsoon rainfall (June to September total) chart the 800 mm isohyet divides the country into two nearly equal halves, named as dry area (monsoon rainfall less than 800 mm) and wet area (monsoon rainfall greater than 800 mm). The dry area/wet area shows large variations from one year to another, and is considered as an index for assessing the large-scale performance of the Indian summer monsoon. Statistical and fluctuation characteristics of the summer monsoon dry area (SMDA) are reported. To identify possible causes of variation in the Indian summer monsoon, the correlation between the summer monsoon dry area and eleven regional/global circulation parameters is examined. The northern hemisphere surface air temperature, zonal/hemispheric/global surface air and upper air temperatures, Southern Oscillation, Quasi-biennial oscillation of the equatorial lower stratosphere, April 500-mb ridge along 75°E over India, the Indian surface air temperature and the Bombay sea level pressure showed significant correlation. A new predictor parameter that is preceding year mean monsoon rainfall of a few selected stations over India has been suggested in the present study. The stations have been selected by applying the objective technique ‘selecting a subset of few gauges whose mean monsoon rainfall of the preceding year has shown the highest correlation coefficient (CC) with the SMDA’. Bankura (Gangetic West Bengal), Cuddalore (Tamil Nadu) and Anupgarh (West Rajasthan) entered the selection showing a CC of 0.724. Using a dependent sample of 1951–1980 a predictive model (multiple CC = 0.745) has also been developed for the SMDA with preceding year mean monsoon rainfall of the three selected stations and the sea level pressure tendency at Darwin from Jan–Feb to Mar–May as independent parameters.  相似文献   

15.
On breaks of the Indian monsoon   总被引：1，自引：0，他引：1  
For over a century, the term break has been used for spells in which the rainfall over the Indian monsoon zone is interrupted. The phenomenon of ’break monsoon’ is of great interest because long intense breaks are often associated with poor monsoon seasons. Such breaks have distinct circulation characteristics (heat trough type circulation) and have a large impact on rainfed agriculture. Although interruption of the monsoon rainfall is considered to be the most important feature of the break monsoon, traditionally breaks have been identified on the basis of the surface pressure and wind patterns over the Indian region. We have defined breaks (and active spells) on the basis of rainfall over the monsoon zone. The rainfall criteria are chosen so as to ensure a large overlap with the traditional breaks documented by Ramamurthy (1969) and Deet al (1998). We have identified these rainbreaks for 1901-89. We have also identified active spells on the basis of rainfall over the Indian monsoon zone. We have shown that the all-India summer monsoon rainfall is significantly negatively correlated with the number of rainbreak days (correlation coefficient -0.56) and significantly positively correlated with the number of active days (correlation coefficient 0.47). Thus the interannual variation of the all-India summer monsoon rainfall is shown to be related to the number of days of rainbreaks and active spells identified here. There have been several studies of breaks (and also active spells in several cases) identified on the basis of different criteria over regions differing in spatial scales (e.g., Websteret al 1998; Krishnanet al it 2000; Goswami and Mohan 2000; and Annamalai and Slingo 2001). We find that there is considerable overlap between the rainbreaks we have identified and breaks based on the traditional definition. There is some overlap with the breaks identified by Krishnanet al (2000) but little overlap with breaks identified by Websteret al (1998). Further, there are three or four active-break cycles in a season according to Websteret al (1998) which implies a time scale of about 40 days for which Goswami and Mohan (2000), and Annamalai and Slingo (2001) have studied breaks and active minus break fluctuations. On the other hand, neither the traditional breaks (Ramamurthy 1969; and Deet al 1998) nor the rainbreaks occur every year. This suggests that the `breaks’ in these studies are weak spells of the intraseasonal variation of the monsoon, which occur every year. We have derived the OLR and circulation patterns associated with rainbreaks and active spells and compared them with the patterns associated with breaks/active minus break spells from these studies. Inspite of differences in the patterns over the Indian region, there is one feature which is seen in the OLR anomaly patterns of breaks identified on the basis of different criteria as well as the rainbreaks identified in this paper viz., a quadrapole over the Asia-west Pacific region arising from anomalies opposite (same) in sign to those over the Indian region occurring over the equatorial Indian Ocean and northern tropical (equatorial) parts of the west Pacific. Thus it appears that this quadrapole is a basic feature of weak spells of the intraseasonal variation over the Asia-west Pacific region. Since the rainbreaks are intense weak spells, this basic feature is also seen in the composite patterns of these breaks. We find that rainbreaks (active spells) are also associated with negative  相似文献   

16.
鄱阳湖是我国最大淡水湖泊,湖泊水文节律变化显著影响着湖区生产生活、生态环境,但界定标准尚未形成统一认识。综合考虑水位变化规律、湖盆形态特点、水资源利用等特征指标,探讨鄱阳湖丰、平、枯水期界定标准。结果表明：以星子站作为鄱阳湖代表性测站,当星子站水位大于17.00 m时为丰水期,13.01～16.00 m为平水期,小于12.00 m（含12.00 m）为枯水期,16.01～17.00 m为平—丰过渡期,12.01～13.00 m为枯—平过渡期。枯水期多发生在10月下旬至次年4月上旬,发生日数平均为142 d;丰水期多发生在7月上旬至8月中旬,发生日数平均为40 d;平水期多发生在4月中旬至6月下旬、8月下旬至10月中旬,发生日数平均为117 d。  相似文献   

17.
采用高分辨率的3"数字高程模型及青藏高原东部102个常规气象观测站5～9月份的降水量资料,根据降水随高度分布将站点分为三类,再采用多元逐步回归的方法,建立了青藏高原40年(1961-2000年)逐年雨季降水量与经度、纬度、海拔、坡度、坡向、开放度等6个地理、地形因子关系模型,并以此为基础,分析了三类区域在丰枯水年里的因子系数的变化规律.结果表明,此法建立的关于高原降水量与诸因子之间方程的相关性显著,相对误差20%,平均相对误差4.4%,估算模型的相关系数均通过0.05的显著性检验;海拔低于1 400 m的第一类区域,主要受地形高度和开放度等局地地形的影响,来改变旱涝年的降水分布特征,海拔高度大于3 600 m的第三类区域,主要受开放度和坡度的影响,其他区域主要受地形的海拔、经度和开放度等局地地形的影响;高原季风是影响第三类区域水汽分布的主要因素,在季风加强时,开放度和经度的影响也随着加强,而坡度和海拔的影响减弱,从而使得水汽的局地性分布特征增强,东西分布差异加大,相应地局地降水分布特征加强,东西差异加大.地理地形因子影响大气的水汽输送和大气的垂直运动,从而导致其对空间降水分配的差异.  相似文献   

18.
Two sampling campaigns were carried out in March and August 2005 representing dry and wet seasons, respectively, to investigate the distribution patterns of Hg species in the water column and sediment profiles at two sampling stations in Aha Reservoir located in Guiyang, Southwestern China. Aha Reservoir has been contaminated by Hg due to small scale coal mining activities. Mercury concentrations in both water and sediment were elevated. A clearly seasonal variation of dissolved Hg (DHg), particulate Hg (PHg) and total Hg (THg) concentrations in the water column was observed. The concentrations of these Hg species in the wet season were significantly higher than in the dry season. Runoff input and diffusion of Hg from sediments could be the reasons for elevated concentrations of these Hg species in the wet season. The contaminated sediment is acting as a secondary contamination source for both inorganic Hg (IHg) and methylmercury (MeHg) to the overlying water. The cycling of Mn in the sediment governs the diffusion process of IHg to the water column. In the dry season (winter and spring), Mn occurs as MnO2 because the uppermost part of sediment is in an oxic condition and Hg ions are absorbed by MnO2. In the wet season (summer and fall), the uppermost part of the sediment profile is in a reduced condition because of stratification of the water column and MnO2 is reduced to Mn2+, which results in transformation of Hg2+ into porewater as Mn2+ became soluble. This causes a higher diffusive flux of IHg from sediment to overlying water in the wet season. Both sampling stations showed a consistent trend that THg concentrations decreased in the uppermost part of sediment cores. This demonstrated that the measures taken to reduce ADM contamination to Aha Reservoir also reduced Hg input to the reservoir. Methyl Hg diffusive fluxes from sediment to overlying water were higher in the wet season than the dry season demonstrating that high temperatures favor Hg methylation processes in sediment.  相似文献   

19.
Severe weather can have serious repercussions in the transport sector as a whole by increasing the number of accidents, injuries and other damage, as well as leading to highly increased travel times. This study, a component of the EU FP7 Project EWENT, delineates a Europe-wide climatology of adverse and extreme weather events that can be expected to affect the transport network. We first define and classify the relevant severe weather events by investigating the effects of hazardous conditions on different transportation modes and the infrastructure. Consideration is given to individual phenomena such as snowfall, heavy precipitation, heat waves, cold spells, wind gusts; a combined phenomenon, the blizzard, is also considered. The frequency of severe weather events, together with the changes in their spatial extension and intensity, is analyzed based on the E-OBS dataset (1971–2000) and the ERA-Interim reanalysis dataset (1989–2010). Northern Europe and the Alpine region are the areas most impacted by winter extremes, such as snowfall, cold spells and winter storms, the frequency of heavy snowfall. The frequency of hot days is highest in Southern Europe. Severe winds and blizzards are the most common over the Atlantic and along its shores. Although heavy rainfall may affect the whole continent on an annual basis, extreme precipitation events are relative sparse, affecting particularly the Alps and the Atlantic coastline. A European regionalization covering similar impacts on the transport network is performed.  相似文献   

20.
将DBM(Data Based Mechanistic)模型应用到辽东森林小流域——大湖沟,分别以其2006年6月和2007年7月数据构建研究区丰水期和枯水期的DBM模型,拟合效率系数分别为0.952 8和0.837 8,模型拟合效果在验证期的不同时段表现出明显的差异性。对丰水期模型参数用固定时间间隔法(FIS)进行时变性分析,发现参数b的取值随时间产生变化。对枯水期的二阶DBM模型进行快、慢流分解,得出了连续时间当量的快、慢流的平均滞后时间分别为5.3h和243.3h。  相似文献   

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