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. 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. 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,


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