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1.
Spatial Patterns and Temporal Variability of Drought in Western Iran   总被引:12,自引:5,他引:7  
An analysis of drought in western Iran from 1966 to 2000 is presented using monthly precipitation data observed at 140 gauges uniformly distributed over the area. Drought conditions have been assessed by means of the Standardized Precipitation Index (SPI). To study the long-term drought variability the principal component analysis was applied to the SPI field computed on 12-month time scale. The analysis shows that applying an orthogonal rotation to the first two principal component patterns, two distinct sub-regions having different climatic variability may be identified. Results have been compared to those obtained for the large-scale using re-analysis data suggesting a satisfactory agreement. Furthermore, the extension of the large-scale analysis to a longer period (1948–2007) shows that the spatial patterns and the associated time variability of drought are subjected to noticeable changes. Finally, the relationship between hydrological droughts in the two sub-regions and El Niño Southern Oscillation events has been investigated finding that there is not clear evidence for a link between the two phenomena.  相似文献   

2.
Fifty Years of Precipitation: Some Spatially Remote Teleconnnections   总被引:2,自引:1,他引:1  
In the present paper the authors analyse the drought occurrence over the European region by using the NCEP/NCAR reanalysis precipitation rates covering the period from 1948 to 2000. The drought assessment is based on the Standardized Precipitation Index (SPI), which has been proposed as an indicator of drought condition. At variance with other fields derived from precipitation, the SPI is, by construction, a Gaussian field. Thus, the understanding of its covariance structure exhausts the study of the associated density distribution. A method allowing a factorisation of a multivariate Gaussian distribution is the one known as Principal Component Analysis (PCA) or Kauman-Loeve decomposition. Therefore, a PCA is used to study the main spatial patterns and the time variability of drought first over Europe and then over the Northern Hemisphere. The analysis reveals a downward trend for the index over most of central Europe and the Mediterraneanbasin, implying an overall decrease of precipitation in the above mentioned regions. Moreover, the scores associated with the PCA covariance decomposition, besides the aforementioned trend, show few long-term periodicities.Similar drought analyses have been performed by considering the Palmer Drought Severity Index (PDSI).A preliminary comparison between the SPI and PDSI obtained by using the previously discussed data set is presented. It is shown that the indices compare favourably in assessing drought variability. Finally, when the SPI analysis is extended to the Northern Hemisphere some interesting spatially remote teleconnnections linking the Tropical Pacific with the European area are shown.  相似文献   

3.
Drought indices, such as the Standardized Precipitation Index (SPI) are used to quantify drought severity. Due to the SPI probabilistic and standardized nature, a given value of SPI computed in distinct time periods or locations indicates the same relative drought severity but corresponds to different amounts of precipitation. Thus, the present study aims at contributing for a comprehensive analysis of the influence of long-term precipitation variability on drought assessment by the SPI. Long records of monthly precipitation, spanning from 1863 to 2007 in several locations across Portugal, were divided into 30 years sub-periods and the SPI with 12-month time scale (SPI-12) was computed for each sub-period and for the entire period of records. The probability distributions adjusted to precipitation in those different time periods were compared envisaging to detect the SPI sensitivity to the reference period and, therefore, to changes in precipitation. Precipitation thresholds relative to the upper limits of SPI-12 drought categories were obtained and the influence of the time period was investigated. Results have shown that when SPI values derived from the full data record for a recent time period are lower/higher than the SPI values derived from data of the considered time period a recent downward/upward shift of precipitation has occurred. Coherently, a common pattern of drought aggravation from the initial until the more recent period was not detected. However, in southern locations, lower precipitation thresholds of the SPI drought categories were generally found in the more recent period, particularly for more severe drought categories, whereas in the northern locations Porto and Montalegre, an increase was detected. The impacts of the reference period on the computed SPI drought severity and frequency are shown, bringing to discussion the need for updating ´normal´ conditions when long term precipitation records are available and precipitation changes are observed.  相似文献   

4.
Drought is one of the most widespread and devastating extreme climate events when water availability is significantly below normal levels for a long period. In recent years, the Haihe River Basin has been threatened by intensified droughts. Therefore, characterization of droughts in the basin is of great importance for sustainable water resources management. In this study, two multi-scalar drought indices, the standardized precipitation evapotranspiration index(SPEI) with potential evapotranspiration calculated by the Penmane Monteith equation and the standardized precipitation index(SPI), were used to evaluate the spatiotemporal variations of drought characteristics from 1961 to 2017 in the Haihe River Basin. In addition, the large-scale atmospheric circulation patterns were used to further explore the potential links between drought trends and climatic anomalies. An increasing tendency in drought duration was detected over the Haihe River Basin with frequent drought events occurring in the period from 1997 to 2003. The results derived from both SPEI and SPI demonstrated that summer droughts were significantly intensified. The analysis of large-scale atmospheric circulation patterns indicated that the intensified summer droughts could be attributed to the positive geopotential height anomalies in Asian mid-high latitudes and the insufficient water vapor fluxes transported from the south.  相似文献   

5.
卫星实时降雨产品的出现为开展大范围干旱监测提供了可能。然而,卫星遥感降雨通常存在误差大、数据序列短等问题,限制了卫星降雨自身在干旱监测诊断方面的应用。本文通过误差矫正,将TMPA-RT卫星降雨数据无缝"拼接"具有长期历史序列(1961—2016年)的地面观测产品(CN05.1),以弥补卫星遥感数据序列短的不足。借助上述"拼接"的实时降雨序列,通过估算不同时间尺度下的标准化降雨指数(SPI)来实现干旱的实时监测诊断。以干旱频发的辽宁省为研究区,对比评估了矫正前后TMPA-RT产品在干旱识别方面的表现。结果表明,在辽宁省近半数地区,TMPA-RT原始数据与CN05.1地面观测两者存在明显的降雨误差(10 mm/月);经过误差矫正,TMPA-RT数据能够重现同期地面观测的降雨量及年际变化。基于3个典型干旱月的评估结果表明,基于TMPA-RT矫正数据与CN05.1"拼接"得到的序列能够重现观测的干/湿空间分布,准确监测辽西地区的干旱状况;而原始的TMPA-RT数据难以提供准确可靠的干旱信息。将上述框架实际应用于2011—2016年干旱监测,评估发现该框架不仅能合理地重现辽宁省干旱情况,还能提供不同等级干旱的面积分布信息。  相似文献   

6.
The Standardized Precipitation Index (SPI) is a well-established drought index that is based on transforming the interannual distribution of precipitation to a standard normal distribution. Because of its robust statistical basis, SPI is readily applicable to different regions making comparisons between locations and time windows possible. Nevertheless, the usability of SPI results is undermined by shortcomings that are partly resultant from data and model uncertainties. One such shortcoming is the inability of the existing SPI model to include change in variability of interannual precipitation from non-stationary normal – mostly caused by climate change. In addition, epistemic uncertainty in the form of incompleteness in station-wide precipitation records results in heterogeneity and inconsistency in SPI results. The effects of such epistemic uncertainty on the accuracy of estimations of long-term changes in drought frequency are mostly unknown. Given such deficiency, SPI’s procedure and subsequent results remain deterministic and inadequately informative. Here, we introduce modifications to the traditional SPI using Dempster-Shafer theory (DST) to enable modeling and propagation of variability and epistemic uncertainty with the regular SPI procedure. By generalizing the SPI model from a deterministic setting to an “uncertainty-driven setting” provided by DST, this work makes possible: (a) efficiently propagating data uncertainty in interpolation of station-wide precipitation and SPI, and (b) modeling the effects of shift in precipitation normals (due to e.g., climate change) on drought frequency. In addition, the significance of this shift may then be evaluated with respect to the epistemic uncertainty by measuring how much of the surrounding epistemic uncertainty this shift encloses (i.e., “probability of enclosing”). The latter is especially important due to large unknowns already associated with climate change modeling. We implement the model on summer extreme drought for the Okanagan Basin, BC, Canada. For a single general circulation model and scenario (CGCM3 A2) a maximum 7 % increase in summer extreme drought (for 2080s, as per current definition) is estimated with a maximum probability of enclosing of 36 %.  相似文献   

7.
The lack of reliable and updated precipitation datasets is the most important limitation that hinders establishing a drought monitoring and early warning system in Iran. To overcome this obstacle, we have evaluated the applicability of GPCC and NCEP/NCAR precipitation datasets for drought analysis in Iran. For this purpose, drought variability across the country has been analyzed through the standardized precipitation index (SPI) on 12-month time scale based on the common period 1951?C2005. For each dataset, by applying the principal component analysis (PCA) to the SPI field and Varimax rotation, the studied area has been regionalized into a few distinctive sub-regions characterized by independent climatic variability. Results have been checked against observations at 32 rain gauge stations having reliable data for the study period. Both GPCC and NCEP/NCAR datasets identify the same sub-regions of drought variability and they are in good agreement with observations. However, the NCEP rotated principal component scores associated with the sub-regions show different time variability with respect to the behaviours captured by GPCC, on one hand, and observations, on the other hand. It seems that, in central Iran such differences concern mainly the period before the seventies. Thus, the results suggest that GPCC dataset is a useful tool for drought monitoring in Iran and it can be used to complement the information provided by rain gauge observations. The NCEP/NCAR reanalysis dataset shows a better agreement with observations for the period 1970?C2005 than for 1951?C2005, and its discrepancies in the regional time variability of drought with respect to GPCC and observations should be taken into account when periods before the seventies are considered.  相似文献   

8.
标准化降水指数与有效干旱指数在新疆干旱监测中的应用   总被引:1,自引:0,他引:1  
基于干旱监测理论,根据新疆测站1961—2010年逐日降水资料,对比分析了基于不同时间尺度(1、3、6、9、12、24个月)标准化降水指标(SPI)与有效干旱指数(EDI)对干旱监测的有效性与实用性。结果表明:不论针对短期干旱还是长期干旱,EDI监测能力均明显优于SPI。短时间尺度的SPI受短时间降水影响较大,能反映短时间新疆地区的干旱变化特征;随时间尺度的增加,SPI对短时间降水的响应能力较差,但仍可反映长时间序列下明显的干旱变化趋势。与SPI相比,EDI能够很好地反映出短期干旱和当时降水量的影响;同时能够随时间迁移,给每日降水量分配以不同权重,考虑前期降水量对当前干湿状况的影响。相关研究结果可为湿润区及其他气候区洪旱灾害监测提供重要理论依据。  相似文献   

9.
为探究贵州省未来干旱变化趋势,基于 CMIP5 全球气候模式预估的降水月值数据,利用标准化降水指数(SPI)分析了 2016—2050 年 RCPs 情景下贵州省干旱趋势。结果表明: 2016—2050 年间RCP2. 6、RCP4. 5 和 RCP8. 5 情景下贵州省 SPI 指数均呈现增加趋势。除特旱外,RCP8. 5 情景下轻旱、中旱、重旱发生频次高于 RCP2. 6 和 RCP4. 5 情景。2016—2030 年各情景下各干旱等级发生频次较高。不同情景下各干旱等级的干旱频率空间异质性突出。各情景下贵州省干旱站次比和干旱强度均呈现下降趋势,发生全域性干旱年份较多,发生区域性干旱和局域性干旱年份较少。发生轻度干旱强度年份较多,发生中度干旱强度和重度干旱强度年份较少。RCPs 情景下贵州省降水增加导致干旱风险降低。研究结果可为干旱监测和农业生产提供参考依据。  相似文献   

10.
The differences in spatial patterns of drought over a range of time scales were analysed by the Standardized Precipitation Index (SPI). In a climatic area with a wide range of precipitation characteristics (the Iberian Peninsula), Pearson III distribution is flexible enough to calculate the drought index on different time scales. The Pearson III distribution was adapted to precipitation frequencies at time scales of 1, 3, 6, 12, 24 and 36 months. Spatial patterns of drought were analysed by Principal Component Analysis. The number of components found increased as the time scale did, which indicates great spatial complexity in drought analysis and uncertainty in drought classification, mainly at scales of 24 or 36 months, since the relationships between SPI series of observatories becomes more distant as the time scale increases. We concluded that there were no homogeneous regions with similar drought patterns that could be used for effective drought management or early warning.  相似文献   

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