This dataset contains the Standardised Streamflow Index (SSI) data for 303 catchments across the United Kingdom from 1891 to 2015. The SSI is a drought index based on the cumulative probability of a given monthly mean streamflow occurring for a given catchment. Here, the SSI is calculated for the following accumulation periods: 1, 3, 6, 9, 12, 18 and 24 months. Each accumulation period is calculated for calendar end-months. The standard period used to fit the Tweedie distribution is 1961-2010. The SSI was produced by the RCUK-funded Historic Droughts project in order to characterise and explore hydrological drought severity over the period 1891-2015. This dataset is an outcome of the Historic Droughts Project (grant number: NE/L01016X/1). Full details about this dataset can be found at https://doi.org/10.5285/58ef13a9-539f-46e5-88ad-c89274191ff9
