Standardized Reservoir Supply Index (SRSI)
Index name: Standardized Reservoir Supply Index (SRSI).
Ease of use: Yellow.
Origins: Developed by Gusyev et al. in Japan as a systematic way to analyse reservoir data in drought conditions.
Characteristics: Similar to SPI in that monthly data are used to compute a probability distribution function of reservoir storage data, to provide information on water supply for a region or basin within a range of -3 (extremely dry) to +3 (extremely wet).
Input parameters: Monthly reservoir inflows and average reservoir storage volumes.
Applications: Takes into account the total inflow and storage associated with any particular reservoir system, and provides information for municipal water supply managers and local irrigation providers.
Strengths: Easy to compute, as it mimics SPI calculations using a standard gamma distribution of the probability distribution function.
Weaknesses: Does not take into account changes due to management of the reservoir and losses due to evaporation.
Resource: The International Centre for Water Hazard and Risk Management has applied the SRSI methodology to several Asian river basins, http://www.icharm.pwri.go.jp/.
Reference: Gusyev, M.A., A. Hasegawa, J. Magome, D. Kuribayashi, H. Sawano and S. Lee, 2015: Drought Assessment in the Pampanga River Basin, the Philippines. Part 1: A Role of Dam Infrastructure in Historical Droughts. Proceedings of the 21st International Congress on Modelling and Simulation (MODSIM 2015), Broadbeach, Queensland, Australia.