Rainfall Anomaly Index (RAI)
Index name: Rainfall Anomaly Index (RAI).
Ease of use: Yellow.
Origins: Work began in the early 1960s by van Rooy.
Characteristics: Uses normalized precipitation values based upon the station history of a particular location. Comparison to the current period puts the output into a historical perspective.
Input parameters: Precipitation.
Applications: Addresses droughts that affect agriculture, water resources and other sectors, as RAI is flexible in that it can be analysed at various timescales.
Strengths: Easy to calculate, with a single input (precipitation) that can be analysed on monthly, seasonal and annual timescales.
Weaknesses: Requires a serially complete dataset with estimates of missing values. Variations within the year need to be small compared to temporal variations.
Kraus, E.B., 1977: Subtropical droughts and cross-equatorial energy transports. Monthly Weather Review, 105(8): 1009-1018. DOI: 10.1175/1520-0493(1977)105<1009:SDACEE>2.0.CO;2.
van Rooy, M.P., 1965: A Rainfall Anomaly Index independent of time and space. Notos, 14: 43–48.