Standardized Snowmelt and Rain Index (SMRI)
Index name: Standardized Snowmelt and Rain Index (SMRI).
Ease of use: Red.
Origins: Developed to account for frozen precipitation and how it contributes to runoff into streams as snowmelt. The work was conducted by Staudinger et al. and tested over several Swiss basins.
Characteristics: With methods similar to SPI, SMRI takes into account both rain and snow deficits and the associated impact to streamflow, including precipitation stored as snow. SMRI is most widely used as a complement to SPI.
Input parameters: Streamflow data, daily precipitation and daily temperature data. Gridded data were used in the initial study of MRI.
Applications: Focuses on the impact of frozen precipitation and the contribution of this stored water to future streamflows, this index is associated with the monitoring of drought situations.
Strengths: Accounting for snow and future contributions to streamflow, the index is capturing all the inputs into a basin. With the ability to use temperature and precipitation to model snow, actual snow amounts are not needed.
Weaknesses: The use of gridded data and the fact that the data used go back only to 1971 is a drawback when investigating performance using point data and longer periods of record. Not using actual snow depths and associated snow water equivalency can lead to errors in runoff projections.
Resources: Background to the methods and calculations is provided in the literature.
Reference: Staudinger, M., K. Stahl and J. Seibert, 2014: A drought index accounting for snow. Water Resources Research, 50:7861–7872, doi:10.1002/2013WR015143.