Online Drought Indicators and Indices

Drought Reconnaissance Index (DRI)


Index name: Drought Reconnaissance Index (DRI).

Ease of use: Yellow.

Origins: Work was initiated by Tsakiris and Vangelis at the National Technical University of Athens, Greece.

Characteristics: Consists of a drought index that contains a simplified water balance equation considering precipitation and potential evapotranspiration. It has three outputs: the initial value, the normalized value and the standardized value. The standardized DRI value is similar in nature to SPI and can be compared to it directly. DRI is more representative than SPI however, as it considers the full water balance instead of precipitation alone.

Input parameters: Monthly temperature and precipitation values.

Applications: Cases where impacts on agriculture or water resources are a primary concern.

Strengths: The use of potential evapotranspiration gives a better representation of the full water balance of the region than SPI provides, which will give a better indication of the drought severity. Can be calculated for many time steps, as with SPI. All the required mathematics are available in the literature.

Weaknesses: Potential evapotranspiration calculations can be subject to errors when using temperature alone to create the estimate. Monthly timescales may not react quickly enough for rapidly developing droughts.

Resource: DRI software is available at

Reference: Tsakiris, G. and H. Vangelis, 2005: Establishing a drought index incorporating evapotranspiration. European Water, 9/10: 3–11.

  1. Mohammad Hossein Mobin
    September 6, 2016 Reply

    Would you please inform me how can I have a hard copy or digital one of this book?

  2. adminIDMP
    September 7, 2016 Reply

    Dear Mohammad,

    Thank you for your question.
    I am assuming that you a requesting a hardcopy or digital copy of the Handbook on Drought Indicators and Indices.
    An electronic version of the Handbook can be downloaded at :

    I hope this answers your question.

    Best regards,
    Bob Stefanski

  3. ES
    December 9, 2016 Reply

    How I can calculate the RDI index (monthly) if the amount of precipitation for one or more month is zero?
    ln(ak) is unreachable when P is zero.

    1. Dimitris Tigkas
      December 13, 2016 Reply

      If there are zero sum precipitation values for the selected reference period, the log-normal distribution cannot be used for the calculation of the Reconnaissance Drought Index. In such case, the gamma distribution should be selected instead. For more information on this, you may also refer to the following papers:

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