Online Drought Indicators and Indices

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.

    October 5, 2016 Reply

    How to calculate for RAI is there a software or excel sheet which you can help me with

  2. Robert Stefanski
    October 6, 2016 Reply

    Unfortunately, I am not aware of any software to calculate this index. Have you looked at the two references (Kraus, 1977 and van Rooy, 1965)??

    October 14, 2016 Reply

    Thank you for your reply.

  4. Renata
    November 10, 2016 Reply

    Look like there is a R package to compute RAI index

  5. Munmun Rahman
    March 21, 2018 Reply

    Can I get the calculation formula of RAI?

  6. Anudeep
    June 22, 2018 Reply

    How to understand whether to use positive or negative anomaly formula? How to comprehend that?

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