历史资料与旱涝划分

为了分析旱涝的历史演变规律,做好旱涝趋势预报,需要将历史旱涝资料按照统一的客观标准划分为等级,整理成旱涝的时间序列资料。所谓客观标准,就是要以实际旱涝情况作为确定旱涝等级的基本出发点,尽量地减小人为的主观性,从而提高旱涝分析预报的可靠性。现根据初步分析谈一点个人看法。一、旱涝标准根据旱涝标准的实际调查,确定涝、偏涝、正常、偏旱、旱五个等级的标准原则如下: 1.涝:指范围较大的区域性的洪涝灾害。区域性指主要河流或3县以上范围。洪涝即是由于暴雨原因致使河流泛滥,造成较严重的水涝灾害。     

西南及东,南沿海地区旱涝系统的动力学结构研究

利用５００年旱涝时间序列资料计算西南、东部沿海和南部沿海地区旱涝系统动力学结构表明，旱涝系统是一种浑沌系统，其关联维数分别约４．７，４．１，３．８，平均可预报时间为９￣１０、１１￣１４、１２￣１３年，最大可预报时间尺度分别为２２￣２７、２８￣３０、２８￣２９年。     

安徽省近554年旱涝演化规律和跃变现象

基于安徽省近 554年的旱涝等级资料 ,利用偏度系数、峰度系数、频次、累积距平等计算公式和方法进行分析。结果表明 :安徽省旱涝等级序列具有偏态分布性即涝明显多于旱的非正态分布特征 ,呈现干燥期、湿润期的阶段变化特性 ,以旱为主和以涝为主的现象间隔出现 ;旱涝序列分析和滑动t 检验法、Yamamoto法的检验方法都证明 1 72 3年附近、1 774年附近和 1 91 3年附近出现序列的跃变现象 ,数种方法都表明序列有基本相同的干湿转折点     

两河流域中下游地区旱涝系统的维数分析

利用浑沌理论，计算长江流域和黄河流域中下游地区近５００年旱涝时间序列资料表明，旱涝系统是一种浑沌系统，其吸引子维数约为３．３￣４．５，确定性的可预报时间尺度约为１１￣１６年。     

西北地区降水混沌特性的初步分析

利用西北地区３０个站月降水量序列（１９５１～１９９６年）,估计了分数维及平均可预报时长。对近月进行标准化处理后的序列,其分数维在３．７～６．２之间,极端干旱地区的分数维明显偏小,西北地区东部与我国其它地区分数维相比,基本在一个水平。根据二阶Ｒｅｎｙｉ熵（Ｋ２）表征的该地区平均可预报时长在２～３个月。     

对流层上部热状况异常对湖北省旱涝影响及环流预报模型在IBM机上的自动识

通过对对流层上半部平均温度场上冷暖中主变化的分析发现：由冬到夏过渡季节内，冷中心沿径向的偏态，与长江流域及湖北省旱涝的关系甚为密切，由此建立了以极地冷涡和副热带暖中心及副热带高压为作用背景的湖北省汛期旱涝预报概念模型，其模型简单概括是“北强南弱”要防涝；“北强南弱”要防旱；冷中心不发生沿经向的偏态，全省气候正常。     

用CAR模型作年旱涝长期天气预报的研究

年旱涝时间序列是一动态系统。我们采用特殊的ＣＡＲＭＡ模型即带受控制项的自回归模型对动态系统进行建模。并试图用较少的状态变量来描述系统的宏观行为。观察结果认为：用３个受控变量就可以描述安康市的年旱涝演变规律，并建立了ＣＲＡ模型。用ＣＡＲ模型作年旱涝预报能达到较高的精度，特别是大旱、大涝年预报效果最佳。试用表明预报与实况的相对误差为８．７％－１２．６％。     

对流层上部热状况异常对湖北省旱涝影响及环流预报模型在IBM机上的自动识别

通过对对流层上半部平均温度场上冷暖中心变化的分析发现:由冬到夏过渡季节内,冷中心沿经向的偏态,与长江流域及湖北省旱涝的关系甚为密切。由此建立了以极地冷涡和副热带暖中心及副热带高压为作用背景的湖北省汛期旱涝预报概念模型。其模型简单概括是“北强南强”要防涝,“北强南弱”要防旱,冷中心不发生沿经向的偏态,全省气候正常。     

用自然正交分解作四川盆地旱涝气候变化趋势分析

本文根据近500年四川盆地六地区旱涝资料,通过五年平均旱涝等级与近百年各年旱涝等级作自然正交分解,建立了两种不同时间步长的时间序列,用其分析旱涝变化的气候特征,结果表明:旱涝频次接近Г分布,近百年旱涝年增多,连旱连涝年突出。与全国各地旱涝的关系是:阶段性与全国相似,同期相关与江淮地区最好;长周期(如340、36、20年)位相早于我国东部地区。根据自然正交时间序列,采用多种统计方法进行分析,预测90年代开始,四川盆地将逐渐转向偏旱。     

自然灾害时间分布序列的分形特征探索

通过采用分形理论中的Ｓｍａｌｌｅｙ法对中国历史上的旱、涝、飓风和地震４种自然灾害时间分布序列的分数维进行了计算，初步证实了自然灾害的时间分布在一定范围内的无标茺性。无标度区的跨度及相应的分形维数可作为自然灾害自组织程度的量度。     

Spatio-temporal variability of dry and wet periods in eastern China

Summary An analysis, based on rain gauge observations, of the time-space variability of dry and wet periods during the last fifty years in eastern China is presented. The Standardized Precipitation Index (SPI) is used to assess the climatic conditions of the area, and principal component analysis (PCA) is applied to capture the pattern of co-variability of the index at different stations. Results suggest that the northern part of eastern China is experiencing dry conditions more frequently from the 1970s onwards indicated by a negative trend in the SPI time series. Long-term fluctuations characterize the SPI signal and contribute to the power spectrum variance at periods ranging from interdecadal to interannual time scales, that is respectively, 24 years and from 16 to 4–3.7 years. These periodic components provide a useful resource for long-term predictability of dry and wet periods in eastern China.     

Climatic change and quasi-oscillations in central-west Argentina summer precipitation: main features and coherent behaviour with southern African region

Summer rainfall variability (October to March) shows inter-annual to multi-decadal fluctuations over a vast area of subtropical Argentina between 28°S–38°S and 65°W–70°W. Statistically significant oscillations of quasi-period in the bands of 18–21, 6, 4 and 2 years can be found throughout the region and intra-regionally, though the latter are variable. The lower frequency variation produces alternating episodes of above and below normal rainfall each lasting roughly 9 years. This quasi-fluctuation appears to be shared with the summer rainfall region of South Africa and were in-phase related one another until mid-1970s. The teleconnection between both subtropical regions could be generated by an atmospheric-oceanic bridge through the global sea surface temperatures (SSTs), particularly those of the equatorial-tropical South Atlantic. From mid-1970s, the alternating wet and dry pattern has been interrupted in the Argentine region producing the longest, as yet unfinished, wet spell of the century. Thus, a significant change of the long-term variation was observed around 1977 toward lower frequencies. Since then the statistical model that explains more than 89% of the variance of the series until 1977, diverges from the observed values in the 1980s and 1990s. In addition the Yamamoto statistical index, employed to detect a climatic jump, reaches its major value in 1973 at the beginning of the current long wet spell. Therefore the change could be located between 1973 and 1977. Application of the t-student's test gives significant differences of mean values for pre-1977 and post-1977 sub-samples from both individual time series and the regional index series. The spectral analysis also shows changes in energy bands in concordance with the features of the change that occurred from mid-1970s. The change gives rise to a significant increment of more than 20% in average of normal rainfall over the region. Conversely, a drought between mid-1980s and the 1990s has been observed in the South African counterpart with severe characteristics, thereby continuing the quasi-18-year oscillation. Consequently, the low-frequency coherent behaviour between both the Argentine and South African regions is lost from the mid-1970s. The analysis of association of wet/dry spells and warm/cold, El Niño/La Niña episodes appears to be not significant at scales of year-to-year variability although at decadal to multi-decadal scales the association could be relevant. More than one process of multi-decadal variability of global SSTs could influence the Argentine summer rainfall region and the former bi-decadal teleconnection. Finally, potential hypothetical factors of change are discussed, such as the strengthening of direct and indirect mechanisms of moisture flux transport associated with global warming, low-level atmospheric circulation changes and/or to SSTs mean condition long-term variations over tropical and subtropical South Atlantic and South Pacific oceans.     

Evidence of climatic change in Nigeria based on annual series of rainfall of different daily amounts, 1919–1985

Annual series of light rainfall, moderate rainfall and heavy rainfall are computed for 4 zones arranged from south to north in Nigeria: Coastal, Guinea-Savanna, Midland and Sahelian zones. Daily rainfall data for the period 1919–85 are utilized. Each series is examined for evidence of change in structure in terms of pattern of decrease and increase in dry and wet years, the overall trend, and the occurrence of runs of dry and wet years. The northern Nigeria (Midland and Sahel) heavy rainfall series and the Sahel moderate rainfall series are found to depict evidence of climatic change as defined by Landsberg (1975) that climatic conditions must change to a new equilibrium position with the values of climatic elements changed significantly. On the other hand Landsberg's definition of climatic fluctuations as involving temporary deflection which can revert to earlier conditions is found to fit the 4 regional light rainfall series and the Midland area moderate rainfall series. The southern Nigeria moderate and heavy rainfall series are found to depict only evidence of high frequency oscillations about a stable long-term mean. The recent drought in Nigeria north of about 9° N is shown to be associated with a large decline in moderate and heavy rainfalls over this part of the country.     

Demarcating the worldwide monsoon

Summary The monsoon is a global climate phenomenon. This paper addresses the seasonal reversal of atmospheric circulation and the transition of dry/wet spells in the monsoon regions worldwide. The NCEP/NCAR 850 hPa wind reanalysis data for 1950–1999 and the upper-tropospheric water vapour (UTWV) band brightness temperature (BT) data observed by NOAA polar orbiting satellites for 1980–1995 are used. In the tropics, there are three large wet-UTWV centres. The summer monsoon in the subtropics can be defined as the expansion of these centres associated with the influence of cross-equatorial flows. Specifically, the dry/wet spell transition is determined by the BT values that are smaller than 244 K. The regions of the South and North African monsoons, the Asian-northwest Pacific and Australian-Southwest Pacific monsoons, and the North and South American monsoons are examined with a focus on the dry/wet spell transition and stream field features. Findings suggest that the summer monsoons over many subtropical regions can be defined by both cross-equatorial flows and dry/wet spell transitions. In the mid- and low-latitudes, there exist six major dry/wet spell transition regions with a dry or wet period lasting more than one month. The region of most significant change is located over the subtropical North Africa–Asia–northwest Pacific. The others appear over subtropical South Africa, Indonesia–Australia, southwest Pacific, the Mexico-Caribbean Sea, and subtropical South America. In addition, three regions exist where only one of the two indicators (cross-equatorial flow and dry/wet transition) is satisfied. The first is near the Equator where the directions of cross-equatorial flows alternate but a dry/wet spell transition is never experienced. The second is over North Africa where only the dry/wet spell transition can be found but not the cross-equatorial flows. The third is over the mid-latitude regions in North China, South Africa, and northern North America. These regions are influenced by cross-equatorial flows but the upper-tropospheric water vapour content is not as high as that in tropical regions. Received June 29, 2000 Revised May 15, 2001     

Stochastic Post-Processing of CFSR Daily Precipitation across Canada

Reanalyses, based on numerical weather prediction methods assimilating past observations, provide continuous precipitation datasets and represent interesting options for assessing the climatology of regions with sparse station networks (e.g., northern Canada). However, reanalysis series cannot be used directly because of possible biases and mismatch between their spatial and temporal resolutions with that needed for local applications. To address these issues, a Stochastic Model Output Statistics (SMOS) approach was selected to post-process precipitation series simulated by the Climate Forecast System Reanalysis (CFSR) across Canada. This approach uses CFSR precipitation as a covariate and is based on two regression models: the first one is a logistic regression that deals with precipitation occurrence, and the second is a vector generalized linear model for precipitation intensity. At-site post-processed daily precipitation series are randomly generated using the SMOS approach, and selected climate indicators from the Expert Team on Climate Change Detection and Indices, which is jointly sponsored by the Commission for Climatology of the World Meteorological Organization's (WMO) World Climate Data and Monitoring Programme, the Climate Variability and Predictability Programme of the World Climate Research Programme, and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology (CCI/CLIVAR/JCOMM) are estimated and compared with corresponding observed and CFSR values. The two models in the SMOS approach, in addition to adequately correcting systematic biases, produced better predictions than the climatology of the wet and dry and intensity sequences. Additionally, the SMOS generally yields consistent climate indices when compared with those from CFSR without post-processing, though there is still room for improvement for specific indices (e.g., annual maximum of cumulative wet days).     

Modelling Wet and Dry Spells with Mixture Distributions

Summary The object of the study is to develop a discrete precipitation model which is able to simulate local, daily series of precipitation occurrences. The model is fitted to the observed data of two stations, Szeged and Szombathely, in Hungary (1951–1995), with pronounced attention to the reproduction of long dry periods, as characteristic features of the climate in Central Europe. The point of the approach is to model the duration of consecutive dry and wet series, i.e., spells, instead of individual wet or dry days. After having comparisons of three different aspects performed, the selected precipitation threshold is 0.1 mm. This threshold keeps the duration of dry and wet periods more or less balanced, whereas the value of the threshold does not fundamentally influence either the conditional distribution of macrocirculation types or the local weather statistics related to the so defined wet or dry days. The duration of both wet and dry spells are found to be independent of the length of either the preceding (opposite) or the last, but one (identical) state. It is also demonstrated that mixed distributions fairly fit to the wet and dry spells, whereas the simple geometric does not, especially due to the erroneous lack of long dry sequences. Weighted sum of two geometric distributions, as well as that of one geometric and one Poisson distribution exhibits good fitting for the dry spells, whereas only the latter one can be advised to employ for the wet periods. Parameters of the distributions obviously depend on the season and the site, in question. Received June 30, 1999 Revised February 3, 2000     

干湿地表的湍流特征及其对深对流影响的大涡模拟

利用大涡模式模拟了对流边界层结构演变以及深对流触发过程.通过改变鲍恩比的敏感性试验研究不同大气初始状况下湿润和干旱下垫面湍流特征及其对深对流触发过程的影响.结果表明:干旱下垫面的混合层干而暖,厚度较大;湿润下垫面相反.由于地表感热通量对热力湍流形成的作用更大,干旱下垫面上湍流混合和夹卷作用更强,使得水汽和相当位温在边界...     

1961—2010年云南干湿气候变化

利用15个站点1961—2010年日照时数、降水量和平均温度等气候资料,计算云南5个区域各季节相对湿润度指数,分析云南干湿气候变化特征。结果表明,相对湿润度指数可定量、准确地表达云南各区域自然气候干湿程度,能客观反映云南干湿气候的波动变化和区域性差别。20世纪90年代中期以来,云南干季、雨季潜在蒸散量呈增大变化趋势,同期降水量有减小的趋势变化,从而在气候变暖背景下引发云南气候的干旱化趋势。干季各地相对湿润度指数年际波动变化大,年代际差异明显;雨季各地干湿状况年际波动相对较小,且呈现明显的周期性波动变化趋势。云南5个区域的干湿气候变化既有一致性也有差异性：滇中和滇西南比较一致,滇西北与滇东南差异明显,滇西北与滇东北雨季差异突出、干季较为相似。     

Fitting the distribution of dry and wet spells with alternative probability models

The development of the rainfall occurrence model is greatly important not only for data-generation purposes, but also in providing informative resources for future advancements in water-related sectors, such as water resource management and the hydrological and agricultural sectors. Various kinds of probability models had been introduced to a sequence of dry (wet) days by previous researchers in the field. Based on the probability models developed previously, the present study is aimed to propose three types of mixture distributions, namely, the mixture of two log series distributions (LSD), the mixture of the log series Poisson distribution (MLPD), and the mixture of the log series and geometric distributions (MLGD), as the alternative probability models to describe the distribution of dry (wet) spells in daily rainfall events. In order to test the performance of the proposed new models with the other nine existing probability models, 54 data sets which had been published by several authors were reanalyzed in this study. Also, the new data sets of daily observations from the six selected rainfall stations in Peninsular Malaysia for the period 1975–2004 were used. In determining the best fitting distribution to describe the observed distribution of dry (wet) spells, a Chi-square goodness-of-fit test was considered. The results revealed that the new method proposed that MLGD and MLPD showed a better fit as more than half of the data sets successfully fitted the distribution of dry and wet spells. However, the existing models, such as the truncated negative binomial and the modified LSD, were also among the successful probability models to represent the sequence of dry (wet) days in daily rainfall occurrence.     

干湿持续期随机模拟

该文应用数据建模技术, 实现干湿期随机建模。主要包括:利用历史气象资料, 从中采集干湿期数据; 应用实测数据, 创建干湿期经验分布函数; 应用Monte Carlo方法和经验分布参数, 随机生成干湿期序列, 通过和Markov链模型输出的对比分析, 讨论生成序列的统计误差, 测试结果显示, 与两状态Markov链方法相比, 所建模型性能更好。