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.
References:
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.
14 Responses
Can we calculate RAI in 12month time scale?
Dear Sewinj
RAI can be calculated using precipitation data on monthly, seasonal and annual timescales.
Best regards
IDMP TSU
Very interesting
how can we interprete standardized rainfall anumalies
RAI can easily be computed with excel, check this:
https://www.youtube.com/watch?v=llTRuSJc2T4
The RAI formula gives two results, which of the results should be considered
How to understand whether to use positive or negative anomaly formula? How to comprehend that?
Dear Anudeep,
Please be more specific in your request? I am assuming that you talking about the RAI?
IDMP team
Can I get the calculation formula of RAI?
Dear Munmun Rahman,
We only have the two references of the RAI:
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.
Yon can download the first one here:
https://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%281977%29105%3C1009%3ASDACEE%3E2.0.CO%3B2
van Rooy, M.P., 1965: A Rainfall Anomaly Index independent of time and space. Notos, 14: 43–48.
IDMP Team
Look like there is a R package to compute RAI index
https://cran.r-project.org/web/packages/precintcon/precintcon.pdf
Thank you for your 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)??
How to calculate for RAI is there a software or excel sheet which you can help me with