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).