SPEIbase v.2.9 [Dataset]

The Global 0.5?? gridded SPEI dataset is made available under the Open Database License. Any rights in individual contents of the database are licensed under the Database Contents License. Users of the dataset are free to share, create and adapt under the conditions of attribution and share-alike. The Global SPEI database, SPEIbase, offers long-time, robust information on the drought conditions at the global scale, with a 0.5 degrees spatial resolution and a monthly time resolution. It has a multi-scale character, providing SPEI time-scales between 1 and 48 months. The Standardized Precipitatin-Evapotranspiration Index (SPEI) expresses, as a standardized variate (mean zero and unit variance), the deviations of the current climatic balance (precipitation minus evapotranspiration potential) with respect to the long-term balance. The reference period for the calculation, in the SPEIbase, corresponds to the whole study period. Being a standardized variate means that the SPEI condition can be compared across space and time. Calculation of the evapotranspiration potential in SPEIbase is based on the FAO-56 Penman-Monteith method. Data type: float; units: z-values (standard deviations). No land pixels are assigned a value of 1.0x10^30. In some rare cases it was not possible to achieve a good fit to the log-logistic distribution, resulting in a NAN (not a number) value in the database. Dimensions of the dataset: lon = 720; lat = 360; time = 1356. Resolution of the dataset: lon = 0.5??; lat = 0.5??; time = 1 month. Created in R using the SPEI package (http://cran.r-project.org/web/packages/SPEI).全球0.5°网格化标准化降水蒸散指数（Standardized Precipitation-Evapotranspiration Index, SPEI）数据集采用开放数据库许可（Open Database License）进行发布。数据库内各独立内容的相关权利则采用数据库内容许可（Database Contents License）进行授权。数据集使用者可在署名及相同方式共享的许可条款下，自由对数据集进行分享、创作与改编。 全球SPEI数据库（SPEIbase）提供了长时序、可靠的全球尺度干旱状况信息，其空间分辨率为0.5°，时间分辨率为月度。该数据集具备多尺度特性，可提供1至48个月的SPEI时间尺度序列。 标准化降水蒸散指数（SPEI）将当前气候平衡（降水量减去潜在蒸散量）相较于长期气候平衡的偏差，以标准化变量（均值为0、方差为1）的形式进行表达。在SPEIbase中，计算所用的参考时段对应于整个研究周期。作为标准化变量，意味着SPEI数值可在不同空间与时间维度间进行对比。 SPEIbase中潜在蒸散量的计算基于联合国粮食及农业组织（Food and Agriculture Organization, FAO）的FAO-56彭曼-蒙特斯（Penman-Monteith）方法。数据类型：浮点型；单位：z值（即标准差）。无陆地区域像素被赋值为1.0×10^30。在极少数情况下，无法对数据进行良好的对数逻辑斯蒂分布拟合，此时数据库中会出现NAN（非数值，not a number）值。 数据集维度：经度（lon）=720；纬度（lat）=360；时间步长=1356。数据集分辨率：经度分辨率=0.5°；纬度分辨率=0.5°；时间分辨率=1个月。本数据集通过R语言及其中的SPEI扩展包（http://cran.r-project.org/web/packages/SPEI）构建完成。