Theoretical derivation of precipitation coverage probability from a set of heterogeneous point probabilities

Various meteorological studies require probabilistic modeling such as the flood, drought, and wet and dry spell occurrences. The most commonly employed approaches are based on the binomial probability distribution function (pdf), which is valid for homogeneous temporal and spatial probabilities. However, in practice, heterogeneous probabilities are very common, and in this case, the classical binomial pdf cannot be employed. This paper presents a rigorous probabilistic methodology for heterogeneous probabilities by considerations from the random field concept. The general form of the binomial pdf is derived and it is shown that for homogeneous probabilities it yields the classical binomial pdf exactly. The necessary analytical formulations are derived with the assumption that the meteorological occurrences at a set of sites or time periods (day, month, and year) are independent from each other. The probability statements derived in this paper are helpful in predicting the regional and temporal probable potential future meteorological occurrences. The application of the proposed methodology is presented for annual precipitation occurrences at six meteorology stations around Istanbul, Turkey.     

径流量Z指数与Palmer指数对河西干旱的监测

利用河西内陆河水文代表站1959-2004年逐月径流量资料、内陆河流域灌溉区1949-2001年耕地面积及代表站1961-2005年的气象资料, 通过对径流量进行正态化处理来确定径流量Z指数, 并以径流量Z指数作为径流干旱指数, 对旱涝等级进行划分; 考虑径流量Z指数的旱涝等级与农业灌溉用水实际情况之间的关系, 给出了径流量Z指数的灌溉指标。将径流量转化为降水量, 改进Palmer旱度模式, 且在作改进后, 又将潜在蒸散量的计算法由利用桑斯威特公式改为利用彭曼公式。结果表明:将径流量考虑到Palmer干旱指数中并改变蒸散量的算法, 使得该指数对河西灌溉区干旱情况的监测均有所改善。对照河西地区的干旱事件, 径流量Z指数监测到的干旱情况, 比Palmer干旱指数改进前、后监测到的干旱情况效果更佳。径流量Z指数能更真实地反映河西灌溉区干旱状况。     

Analysis of drought condition and risk in Peninsular Malaysia using Standardised Precipitation Index

Contrary to the belief that Peninsular Malaysia experiences wet condition throughout the year, prolonged dry condition has lately become a recurrent phenomenon in this region. As a result, country's agricultural sector and water resources have been under severe constraints from this situation. To get a clearer picture of the dry condition in Peninsular Malaysia, the Standardised Precipitation Index, based on the data of monthly rainfall from 50 stations, is derived. Spatial analysis is used to illustrate the percentage of occurrences of dry and very dry events. To evaluate the potential risk due to the dry conditions, we modelled the joint distribution of severity and duration of dry condition by means of bivariate copula. Several copula models were tested, and the model, which best represents the relationship between severity and duration, is determined using Akaike information criterion. Based on the results, the return period for the drought severity, based on the longest duration of drought at each station, can be estimated. This enables the drought risk to be calculated, thus planning on the measures to minimise the impact of a prolonged drought to the societies, which can be done by the relevant authorities.     

Standardized Precipitation Index Reconstructed from Turkish Tree-Ring Widths

May–July Standardized Precipitation Index (SPI) for the land area of most of Turkey and some adjoining regions are reconstructed from tree rings for the period 1251–1998. The reconstruction was developed from principal components analysis (PCA) of four Juniperus excelsa chronologies from southwestern and south-central Turkey and is based on reliable and replicable statistical relationships between climate and tree ring growth. The SPI reconstruction shows climate variability on both interannual and interdecadal time scales. The longest period of consecutive drought years in the reconstruction (SPI threshold ≤−1) is 2 yr. These occur in 1607–1608, 1675–1676, and 1907–1908. There are five wet events (SPI threshold ≥+1) of two consecutive years each (1330–1331, 1428–1429, 1503–1504, 1629–1630, and 1913–1914). A 5-yr moving average of the reconstructed SPI shows that two sustained drought periods occurred from the mid to late 1300s and the early to mid 1900s. Both episodes are characterized by low variability.     

基于NDVI-Ts特征空间的黑龙江省干旱监测

NDVI-Ts特征空间方法结合了卫星遥感地表反射率和热红外特性,能较好地反映一定时空尺度的地表干旱状况,该文基于Terra-MODIS归一化植被指数(NDVI)和地表温度(LST)产品,构建NDVI-Ts三角形特征空间,采用植被温度状态指数结合MODIS地表分类产品IGBP对黑龙江省2007年夏季干旱进行监测和分析。结果显示:此次夏季干旱的空间分布广,持续时间长,干旱程度重,西部松嫩平原和东部三江平原等地主要农作物产区普遍发生干旱,且旱情严重。结合同期地面气象观测的月降水量数据对监测结果进行验证和评估表明:植被温度状态指数是一项近实时的干旱监测指标,不仅与当地最近的降水事件有关,而且与前期一段时间内的总体降水事件相关,可以较真实地反映当地干旱发生、发展的动态过程。     

渭河流域干旱特征及干旱指数计算方法初探

利用游程分析、马尔可夫平稳概率、随机过程等方法分析了渭河流域的干旱特征。结果表明,近44年（1958-2001年）渭河流域降水连续多水（少水）期多持续2～3年,单独多（少）水年出现的概率比连续多水（少水）年的概率大,连少年的概率比连多年的概率大,平均连续少水年数大于平均连续多水年数;枯（丰）水与偏丰（偏枯）之间的转移突变较大,对用水可能带来不利影响;偏枯年出现的概率最大,偏丰年次之,丰水年最小;渭河流域连续少水2～3年不仅发生频率较高,而且干旱强度也较大。同时根据降水和同期气温、天然径流量资料建立了适用于渭河流域的S干旱指数。     

基于MCI指数的福建省干旱气候特征

采用目前国家干旱监测业务实行的MCI指数,利用Morlet小波、经验正交函数（EOF）等方法,分析了福建省1961—2019年全省66个气象站MCI指数表征的干湿状况和干旱变化特征。结果表明：福建省存在明显的干湿气候特征,具有显著的6—8 a和22 a的周期振荡,内陆山区干湿变化周期比沿海长,在季节尺度上各季均存在多时间尺度和地域差异化的特点;其空间变化具有3种典型模态,反映了季风降水多寡和地形差异。MCI表征的干旱过程时空分布与历史干旱事件相吻合,秋季和冬季是福建省干旱发生频率最高的季节,春季和夏季是干旱强度最强的季节;闽江口以南沿海地区干旱发生率明显高于内陆地区,全省出现同步干旱的机率较小（12%）。     

区域性极端低温事件的识别及其变化特征

区域性极端低温事件的客观识别方法主要包括4个部分:极端低温阈值的确定、极端低温事件空间区域的识别、空间区域的连续性过程提取和指标体系,结合个例分析验证了该方法在实际低温事件检测中的有效性。从空间分布和时间变化趋势等角度分析了近50年区域性极端低温事件的变化特征:区域性极端低温事件的发生频次较高的纬度带主要位于32°N和42°N附近,区域性极端低温事件的发生频次、强度和最大覆盖面积等存在总体减弱的趋势,在20世纪80年代后期存在显著的转折,90年代后期以来变化逐渐趋于平缓。此外,对各种单一指标与我国冷冻害造成的经济损失和受灾人口之间的相关分析,构建了体现区域性极端低温事件多方面影响的综合指标。     

一种大范围干旱的识别方法及其应用

基于日本APHRO格点降水数据计算格点SPI序列,兼顾时空连续性,定义了一种大范围长历时干旱的识别方法。该方法以我国国土面积的10%作为大范围干旱事件影响范围的最小阈值,同时给定了干旱事件影响区域的空间连续和时间连续的判定标准,另辅以干旱烈度计算方法和干旱中心的识别方法,给出了此类干旱事件的面积、历时、烈度及干旱中心的指数定义和事件的识别过程。在此基础上,识别了我国1961—2015年以来的69次大范围干旱事件,得出这69次大范围干旱事件的平均面积指数为30.49%,平均干旱历时为8.15个月,平均干旱烈度为-4.192。利用此方法对1998—2002年发生在华北地区的持续性区域干旱事件进行再分析。结果表明,这一时期的干旱事件不仅局限于华北地区,同时也波及到东北、西北、西南和东南等地,涉及了4次大范围长历时的干旱过程。     

On the relationship of regional meteorological drought with SOI and NAO over southwest Iran

A fuzzy hierarchical clustering technique using the pairwise similarity matrix is employed to find the homogenous climate subregions over southwest Iran, based on the similarity of meteorological drought characteristics (i.e., duration, intensity, onset, and ending dates). The representative subregions are recognized for different rainy seasons; for each, the regional rainfall anomalies are computed. To find appropriate drought predictors, the lag relationships of regional rainfall with seasonal Southern Oscillation Index (SOI) and North Atlantic Oscillation (NAO) are examined using a conditional probability approach. The results suggest a significant negative correlation between autumn rainfall and June–August SOI. The NAO is also negatively correlated with autumn rainfall such that it is least likely for an extreme autumn drought to occur when June–August NAO is negative. A spring drought is preceded by an October–December NAO greater than 0.5. However, winter droughts do not appear to be lag-correlated with either SOI or NAO. In addition to the findings for droughts, these indices also emerged having considerable influence on wet seasons. A wet autumn tends to occur when either May–July SOI is less than ?0.5 or June–August NAO is less than about ?0.3. It is also apparent that the extreme wet springs are absent when October–December NAO is positive. This season is influenced most by NAO in both dry and wet spells. However, similar to droughts, the wet winter seasons are not found to be associated with either SOI or NAO.     

Rainfall characterisation by application of standardised precipitation index (SPI) in Peninsular Malaysia

The interpretations of trend behaviour for dry and wet events are analysed in order to verify the dryness and wetness episodes. The fitting distribution of rainfall is computed to classify the dry and wet events by applying the standardised precipitation index (SPI). The rainfall amount for each station is categorised into seven categories, namely extremely wet, severely wet, moderately wet, near normal, moderately dry, severely dry and extremely dry. The computation of the SPI is based on the monsoon periods, which include the northeast monsoon, southwest monsoon and inter-monsoon. The trends of the dry and wet periods were then detected using the Mann–Kendall trend test and the results indicate that the major parts of Peninsular Malaysia are characterised by increasing droughts rather than wet events. The annual trends of drought and wet events of the randomly selected stations from each region also yield similar results. Hence, the northwest and southwest regions are predicted to have a higher probability of drought occurrence during a dry event and not much rain during the wet event. The east and west regions, on the other hand, are going through a significant upward trend that implies lower rainfall during the drought episodes and heavy rainfall during the wet events.     

Power-law Relationship in Describing Temporal and Spatial Precipitation Pattern in Turkey

Summary Wet and dry spell properties of monthly rainfall series at five meteorology stations in Turkey are examined by plotting successive wet and dry month duration versus their number of occurrences on the double-logarithmic paper. Straight line relationships on such graphs show that power-laws govern the pattern of successive persistent wet and dry monthly spells. Functional power law relationships between the number of dry and wet spells for a given monthly period are derived from the available monthly precipitation data. The probability statements for wet and dry period spells are obtained from the power law expressions. Comparison of power-law behaviours at five distinct sites in Turkey provides useful interpretation about the temporal and spatial rainfall pattern. As in temperate areas such as Turkey the rainfall amounts change mostly due to one-month-long dry or wet spells. Received August 29, 1995 Revised November 9, 1995     

Tree-ring reconstructed rainfall variability in Zimbabwe

We present the first tree-ring reconstruction of rainfall in tropical Africa using a 200-year regional chronology based on samples of Pterocarpus angolensis from Zimbabwe. The regional chronology is significantly correlated with summer rainfall (November–February) from 1901 to 1948, and the derived reconstruction explains 46% of the instrumental rainfall variance during this period. The reconstruction is well correlated with indices of the El Niño-southern oscillation (ENSO), and national maize yields. An aridity trend in instrumental rainfall beginning in about 1960 is partially reproduced in the reconstruction, and similar trends are evident in the nineteenth century. A decadal-scale drought reconstructed from 1882 to 1896 matches the most severe sustained drought during the instrumental period (1989–1995), and is confirmed in part by documentary evidence. An even more severe drought is indicated from 1859 to 1868 in both the tree-ring and documentary data, but its true magnitude is uncertain. A 6-year wet period at the turn of the nineteenth century (1897–1902) exceeds any wet episode during the instrumental era. The reconstruction exhibits spectral power at ENSO, decadal and multi-decadal frequencies. Composite analysis of global sea surface temperature during unusually wet and dry years also suggests a linkage between reconstructed rainfall and ENSO.     

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。     

地表温度-归一化植被指数特征空间干旱监测方法的改进及应用研究

地表温度-归一化植被指数(Ts-NDVI)特征空间干旱监测方法易受到监测期地表湿度、植被覆盖状况和卫星观测质量的影响,导致特征空间干、湿边不稳定,在基于长时间、大范围卫星观测资料的基础上对Ts-NDVI特征空间方法进行改进,将其称为通用特征空间方法.首先基于某观测时段,单独构建每年基于该单一年份单一时段卫星观测数据的T...     

Phenological observations made by the I. R. Bohemian Patriotic�CEconomic Society, 1828�C1847

Drought forecasting is a critical component of drought risk management. Identification of effective predictors is a major component of forecasting models. Sea surface temperature (SST) and sea level pressure (SLP) are relevant predictors for short- to long-term drought forecasts. However, these datasets are captured globally within a cell-wise network. This paper describes an approach to locate the most effective cells of the SST and SLP datasets using data mining. They are then applied as input to an adaptive neurofuzzy inference system (ANFIS) model to forecast possible droughts 3, 6, and 9?months in advance. Tehran plain was selected as the study area, and drought events are designated using the effective drought index (EDI). In another treatment, past values of the EDI time series were introduced to the ANFIS and the results compared with the previous findings. It was shown that R ² values were higher for all cases applying the SST/SLP datasets. Additionally, the performance of SST/SLP datasets and the ANFIS model was assessed according to ??drought?? or ??wet?? classification, and it was concluded that more than 90% of the time the ANFIS model detected the drought status correctly or with only a one class error.     

基于IWAP的广西干湿演变尺度效应与过程识别

伴随着全球变化和区域旱涝加剧,明晰最佳表达时间尺度,开展精细化旱涝演变监测和过程识别、支撑业务化精准预警是当前有效应对旱涝灾害的迫切需求。针对广西旱涝并存且频繁交替现象,采用距平改进的加权平均降水指数(IWAP)分析了区域日、候、旬、月、季尺度1961—2017年气象干湿演变监测的尺度效应;并结合游程理论和极端事件强度-过程检测方法(EID)对典型干旱、湿润事件过程进行识别。结果表明:(1)时间尺度越小(如日、候),IWAP对广西大气干湿快速频繁交替波动和空间格局变化监测效果越好;(2)日与候尺度IWAP对广西干湿面积变化监测具有强正相关一致性,其他尺度间的相关性普遍较弱,季尺度结果存在较显著的累加抵消现象,数值明显小于其他尺度;(3)各时间尺度IWAP对广西总干旱、总湿润事件频次监测差异小于各尺度间同等级干湿事件的频次差异,日与候、旬与月尺度分别表达了广西干湿事件相近的演变模态和强度分布;(4)文中方法对广西干湿演变过程及起讫时间识别效果良好,且日尺度能更好地揭示骤发性干旱和突发极端降雨湿润现象。     

在用降水逐日监测干旱的方法中引入蒸发

降水是旱涝最重要的影响因子。在加权平均降水量WAP方法中,当目前没有降水,且前期降水的影响衰减掉以后,WAP便接近于0了,然而此时土壤可能还是较湿润的;若在随后的日子里仍没有降水,WAP则继续保持接近于0的值,但土壤会变的越来越干。为了区分出在WAP同样都为接近于0的状态下土壤湿度(反映在蒸发上)的差异,本文将WAP指数作了进一步的发展,即在所建立的模型中,将蒸发量E显式地表达出来。也就是,涝(旱)状态的变化不仅受降水量P所强迫,而是受P-E所强迫。新方法的基本原理和模型是与WAP方法相仿的,这个显式地考虑了蒸发的新指数WAPE,其值有正有负,接近于正态分布,因而不需再作正态化处理。结果表明,WAPE指数对旱涝的逐日监测有很好的效果。     

应用FY-2地表蒸散产品监测西南特大干旱

基于能量平衡原理的卫星遥感地表蒸散产品具有清晰明确的物理含义,广泛地应用于遥感干旱监测领域。本研究以中国能量与水平衡监测系统（CEWBMS）和近11年的静止卫星遥感数据集为基础,利用FY-2/VISSR数据生成相对蒸散距平百分率（Percentage of Relative Evapotranspiration Anomaly,PRETA）产品,应用于全国范围的旱情连续监测。与极轨卫星同类产品相比,基于FY-2的PRETA产品在监测范围和频次上都具有明显的优势。由于距平百分率的引入,PRETA干旱指数等级划分不再与季节和地域气候类型等因素相关。针对2009年秋季至2010年春季西南大旱的监测结果进行了对比分析和统计,结果表明PRETA干旱指数真实客观地反映了旱情时空变化,面平均的PRETA和降水距平百分率时间序列变化趋势显示出良好的一致性,PRETA与10 cm土壤相对湿度有较高的相关性。本研究为实时、大范围、高分辨率、定量和动态卫星遥感监测干旱提供了切实可行的方法。     

气候变化对澜湄流域上下游水资源合作潜力的影响

澜沧江-湄公河（澜湄）流域南北跨越了25个纬度,流域上下游气候差异明显。同时遭遇干旱或湿润通常不利于上下游水资源合作,而水文气象条件正常或上下游间的干湿条件不一样时有利于缓解流域内的竞争性用水状况。为探究气候变化对澜湄流域上下游水资源合作潜力的影响,基于普林斯顿降水数据集与全球气候模型预估数据,利用标准化降水指数（SPI）和Copula函数计算了历史时期（1985—2016年）与未来时期（2021—2090年）澜湄流域上下游同时面临干旱、湿润以及干湿存在差异的发生概率。基于典型浓度路径RCP4.5和RCP8.5情景的预估结果显示与历史时期相比,未来时期澜湄流域在RCP4.5与RCP8.5情景下具有相似的变化趋势,即：遭遇同期湿润的概率在逐渐增大（最大达到199.5%),遭遇同期干旱的概率则在逐渐减少(最小达到-35.9%),而遭遇干湿差异时期的概率在所有时段均大幅减少（-53.1%~-42.5%)。未来澜湄流域上下游同期湿润概率的增加和遭遇干湿差异概率的减少预计将加大上下游面临水资源竞争的可能性,从而对澜湄流域各国家之间的水资源合作产生不利影响。这一研究可以为澜湄流域水资源合作策略的制定提供科学参考和依据。