Online Drought Indicators and Indices

Aridity Anomaly Index (AAI)


Index name: Aridity Anomaly Index (AAI).

Ease of use: Green.

Origins: Developed in India by the India Meteorological Department.

Characteristics: A real-time drought index in which water balance is considered. The Aridity Index (AI) is computed for weekly or two-weekly periods. For each period, the actual aridity for the period is compared to the normal aridity for that period. Negative values indicate a surplus of moisture while positive values indicate moisture stress.

Input parameters: Actual evapotranspiration and calculated potential evapotranspiration, which require temperature, wind and solar radiation values.

Applications: Impacts of drought in agriculture, especially in the tropics where defined wet and dry seasons are part of the climate regime. Both winter and summer cropping seasons can be assessed using this method.

Strengths: Specific to agriculture, calculations are simple, and descriptions of drought (mild, moderate or severe) are based on departure from normal. Responds quickly with a weekly time step.

Weaknesses: Not applicable to long-term or multiseasonal events.

Resource: India Meteorological Department (IMD) methodology of drought monitoring.

References: World Meteorological Organization, 2012: Chapter 6, Agrometeorological Forecasting. In: Guide to Agricultural Meteorological Practices (GAMP), WMO-No. 134, World Meteorological Organization, Geneva, Switzerland.

Currently used by: India.

  1. mamaru
    June 9, 2019 Reply

    Your message…

    1. Katrin Ehlert
      June 10, 2019 Reply

      Dear Mamarumuluken799

      Thank you for your message. Could you please specify your question regarding the Aridity Anomaly Index?

      Kind regards,
      IDMP Team

  2. Konan Bah
    September 21, 2018 Reply

    Bonjour M. Je suis étudiant en géographie en Côte d’Ivoire. Je travaille sur l’impact de la variabilité climatique sur l’agriculture dans le département de toumodi. Je souhaiterais analyser la sécheresse climatique par biais de SPI. Quels logiciels je pourrais utiliser à cette fin. Je rappelle que je dispose des logiciels statistiques suivants: spss xlstat et Excel. Existe t’il un logiciel approprié pour le SPI, comment, comment l’acquérir ?
    Meilleures salutations.

    1. Robert Stefanski
      September 23, 2018 Reply

      Bonjour Konan Bah,

      S’il vous plaît regarder les liens suivants:
      Page IDMP SPI –
      SPI version francais –

      Ce sont des liens vers le logiciel SPI.


  3. chander singh negi
    January 14, 2018 Reply

    sir this project side map

    1. Robert Stefanski
      January 15, 2018 Reply

      Dear Chander singh negi,

      Please be more specific in your request. YOur question is not clear.

      Best regards,


  4. YiJyun Lin
    September 23, 2017 Reply

    I am working on a research project, in which I examine the socioeconomic impacts of drought. I am interested in Aridity Anomaly Index (AAI), but could not find the data base. Thus, I wonder if you could provide me with the information about the link website for this index. Thank you in advance for your help!

    1. Robert Stefanski
      October 3, 2017 Reply

      There is no global database on the AAI. You will have to calculate the index using your own weather data.

    2. Katie
      November 25, 2018 Reply

      Hi Yijyun, I am working on a similar research project this year and would be very interested in reading your findings?



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