SPEIbase v.2.6 [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°格点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遵循数据库内容许可证（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，自由对数据集进行共享、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，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，可生成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（降水量与潜在蒸散量之差）相对于长期气候平衡的偏差，以标准化变量形式表示（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所表征的干湿状况可在不同空间与时间维度上进行跨区域、跨时段对比。
SPEIbase中的潜在蒸散量计算基于FAO-56彭曼-蒙特斯方法。该数据集的数据类型为浮点型，单位为z值（标准偏差）。无陆地像素被赋值为1.0×10^30。在极少数情况下，无法实现对对数逻辑斯蒂分布的良好拟合，此时数据库中将记录为NAN（非数值，not a number）。
该数据集的维度为：经度（lon）=720，纬度（lat）=360，时间（time）=1356。数据集分辨率为：经度0.5°，纬度0.5°，时间步长为1个月。
本数据集通过R语言结合SPEI软件包（http://cran.r-project.org/web/packages/SPEI）构建完成。

搜集汇总

背景与挑战

背景概述

SPEIbase v.2.6是一个全球0.5度网格化的标准化降水蒸散指数(SPEI)数据集，提供1-48个月多时间尺度的月度干旱监测数据，基于FAO-56 Penman-Monteith方法计算，覆盖720×360网格点和1356个月的时间序列。