Standardized Precipitation-Evapotranspiration Index (SPEI) 1950 - Present

Droughts are natural disasters characterized by atypical dry conditions and high temperatures that persist over a period of time. Droughts disturb natural ecosystems and human activities such as food production. The Standardized Precipitation-Evapotranspiration Index (SPEI) is used for the analysis and monitoring of drought events. SPEI is calculated from difference between precipitation (P) and potential evapotranspiration (PET). SPEI is calculated at different periods (e.g. 1, 3, 6, 9, or 12 months) for drought characterization at different time scales. P - PET is aggregated at different time scales for a given period, allowing drought characterization for short, medium, and long-term trends. This layer shows the classified SPEI values from the SPEI Global Drought Monitor. Each SPEI (e.g. SPEI3) shows the monthly drought index for the specified time scale (e.g. 3-month SPEI). What can you do with this layer? This layer can be used to identify areas subject to dry conditions and assess its frequency over time. Source: SPEI Global Drought Monitor Revisions: Feb 25, 2022: Official release of Feature Service offering.干旱是一类以持续异常干燥状态与高温为典型特征的自然灾害。干旱会干扰自然生态系统与人类活动，诸如粮食生产等领域均会受到影响。标准化降水蒸散指数（Standardized Precipitation-Evapotranspiration Index，SPEI）是用于干旱事件分析与监测的核心指标。该指数通过计算降水量（P）与潜在蒸散量（PET）的差值构建。SPEI可在1、3、6、9或12个月等不同时间尺度下计算，以表征不同时长的干旱特征。针对特定时段，将P-PET在对应时间尺度下进行聚合，即可实现短期、中期与长期干旱趋势的特征刻画。本图层展示了来自SPEI全球干旱监测（SPEI Global Drought Monitor）的分类SPEI数值。每个SPEI指标（如SPEI3）代表指定时间尺度下的月度干旱指数（例如3个月尺度SPEI）。本图层可用于识别受干燥条件影响的区域，并评估其随时间变化的发生频率。数据来源：SPEI全球干旱监测（SPEI Global Drought Monitor）；修订记录：2022年2月25日：要素服务正式发布。