Global CPC Unified Daily Precipitation: Drought Indices
National Weather Service Climate Prediction Center (CPC)
The National Weather Service's Climate Prediction Center (CPC) produces a Global Unified Daily Precipitation product from 1971-present. This product is the combination of all sources available to CPC with the goal of providing high quality and consistent precipitation data and offer a comprehensive view of precipitation patterns worldwide. The daily precipitation products are provided as aggregated 1, 2, 3, 6, 9, and 12-month accumulation periods with a 3-5 day latency.
SPI
The Standardized Precipitation Index, or SPI, is a drought index that captures how observed precipitation deviates from the climatological average over a given time period. This global SPI is derived from the CPC Daily Unified Precipitation dataset, using the Climate Engine tool, and includes timescales of 1, 2, 3, 6, 9, and 12 months. The SPI calculation uses a climatology period of 1991-2020 and non-parametric distribution type.
SPEI
The Standardized Precipitation Evapotranspiration Index (SPEI) is derived from the CPC Daily Unified Precipitation dataset, using the Climate Engine tool, and includes timescales of 1, 2, 3, 6, 9, and 12 months. The SPEI calculation uses a climatology period of 1991-2020 and non-parametric distribution type.
EDDI
The Evaporative Demand Drought Index (EDDI) is an experimental tool that examines how anomalous the atmospheric evaporative demand (E0; also known as "the thirst of the atmosphere") is for a given location and across a time period of interest. EDDI maps use atmospheric evaporative demand anomalies across a timescale of interest relative to its climatology to indicate the spatial extent and severity of drought. EDDI can serve as an indicator of both rapidly evolving "flash" droughts (developing over a few weeks) and sustained droughts (developing over months but lasting up to years).
This global EDDI is derived from the CPC Daily Unified Precipitation dataset, using the Climate Engine tool, a 1991–2020 reference period, nonparametric distribution, and Penman-Monteith PET (potential evapotranspiration). The timescales included are 1, 2, 3, 6, 9, and 12 months.
