SPEIbase v.2.8 [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°格网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证（Open Database License）发布。数据库中单个内容的相关权利，采用数据库内容许可证（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条款下，自由进行共享、创作与改编。全球SPEI数据库（SPEIbase）提供了长时序、稳健的全球尺度干旱状况信息，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（降水减去潜在蒸散量）相对于长期平衡的偏差表示为标准化变量（均值为0、方差为1）。SPEIbase的计算参考周期对应于整个研究时段。作为标准化变量，SPEI的状态可在不同空间与时间维度上进行对比。SPEIbase中潜在蒸散量的计算基于FAO-56 Penman-Monteith方法。数据类型为浮点型；单位为z值（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，无法与对数逻辑斯蒂分布获得良好拟合，此时数据库中将生成NAN（非数值，Not a Number）值。本数据集的维度为：lon（经度）=720；lat（纬度）=360；time（时间）=1356。数据集分辨率为：lon=0.5°；lat=0.5°；time=1个月。本数据集基于R语言及SPEI包（http://cran.r-project.org/web/packages/SPEI）构建。