Standardized Streamflow Index (SSFI)

Standardized Streamflow Index (SSFI)


Index name: Standardized Streamflow Index (SSFI).

Ease of use: Yellow.

Origins: Modarres introduced SSFI in 2007, and Telesca et al. investigated it further. In the original work, Modarres described how SSFI was similar to SPI in that SSFI for a given period was defined as the difference in streamflow from mean to standard deviation.

Characteristics: Developed using monthly streamflow values and the methods of normalization associated with SPI. Can be calculated for both observed and forecasted data, providing a perspective on high and low flow periods associated with drought and flood.

Input parameters: Streamflow data on a daily or monthly timescale.

Applications: Monitoring of hydrological conditions at multiple timescales.

Strengths: Easy to calculate using the SPI program. A single variable input that allows for missing data makes it easy to use.

Weaknesses: Only accounts for the streamflow in the context of monitoring drought, with no other influences being investigated.

Resources: It is described well in the literature, with mathematics and case studies available. The SPI program can be used to calculate the SSFI and is available on the National Drought Mitigation Center (NDMC) website.

Modarres, R., 2007: Streamflow drought time series forecasting. Stochastic Environmental Research and Risk Assessment, 21: 223–233. DOI: 10.1007/s00477-006-0058-1. (For more information on this paper, please contact the IDMP HelpDesk).

Telesca, L., M. Lovallo, I. Lopez-Moreno and S. Vicente-Serrano, 2012: Investigation of scaling properties in monthly streamflow and Standardized Streamflow Index time series in the Ebro Basin (Spain). Physica A: Statistical Mechanics and its Applications, 391(4): 1662–1678. DOI: 10.1016/j.physa.2011.10.023. (For more information on this paper, please contact the IDMP HelpDesk).

7 Responses

  1. Here are 2 recent free French references for the same index but with another nickname “Normalized Hydrological Index”.

    Calculation Formula : IHN =(Di – Dm)/σ

    Where ∶ {(Di ∶ The flow rate of month or year i. Dm ∶ The average flow rate of the series on the time scale considered. σ ∶ The standard deviation of the series on the time scale considered.)┤

    Valeur de l’IHN Séquence de sécheresse Valeur de l’IHN Séquence humide
    -0,99 < IHN < 0 Légèrement sèche 0 < IHN < 0,99 Légèrement humide
    -1,49 < IHN < -1 Modérément sèche 1 < IHN < 1,49 Modérément humide
    -1,99 < IHN < -1,5 Sévèrement sèche 1,5 < IHN < 1,99 Sévèrement humide
    IHN < -2 Extrêmement sèche 2 < IHN Extrêmement humide

    [ 1 ] (On request from Researchgate) Sharma T.C., Panu U.S., 2010. Analytical procedures for weekly hydrological droughts: a case of Canadian rivers. Hydrological Sciences Journal, 55 (1), 79-92.

    [ 2 ] (IHN in Page 175) Faye, 2017. Evaluation comparative des séquences du stress hydrique et de la sécheresse par indicateurs et par échelles de temps dans le bassin du Bafing en amont de Manantali.

    1. Dear Alae,

      Thank you very much for sharing this, it is indeed very useful. Your suggestion to add the formula’s to the indices is definitely worth a discussion. Would it be possible to join our Community of Practice and open a discussion with that topic ( If the community agrees, we can see how to implement that best.

      Kind regards,
      Valentin from the IDMP team

  2. It will be better if you improve the site with the calculation equations for each drought index. Because some drought indices have multiple nicknames (like : Streamflow Drought Index (SDI) = Standardized Streamflow Index (SSFI)), so they have multiple versions of formulas. As well as some references are paid!!! you cannot check the version you want before purchasing the item.

  3. Is it possible to calculate the standard streamflow index by climpact2? If it is impossible pleas tell me other related one?

    1. Dear Lenka,

      Thank you for your request. They look to be very similar but I will contact some hydrology experts on this issue.

      Best regards,


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