This dataset is an inventory of reservoir details for the UK. It provides information, including reservoir location, type (impounding or non-impounding), use (water resources, hydro-electric, ecological, flood storage, canal), capacity, planning date, construction date, catchment National River Flow Archive (NRFA) gauge references and membership of a reservoir group, based on current usage within the CEH Monthly Hydrological Summary (https://nrfa.ceh.ac.uk/monthly-hydrological-summary-uk). The dataset comprises 273 individual reservoirs, which amount to approximately 90% of total UK reservoir storage. Data quality has been recorded, using a data flag system and a notes section, with references relevant to each reservoir provided. Full details about this dataset can be found at https://doi.org/10.5285/f5a7d56c-cea0-4f00-b159-c3788a3b2b38

Standardised Precipitation Index (SPI) data for Integrated Hydrological Units (IHU) Hydrometric Areas (Kral et al., 2015; https://doi.org/10.5285/3a4e94fc-4c68-47eb-a217-adee2a6b02b3). SPI is a drought index based on the probability of precipitation for a given accumulation period as defined by McKee et al. [1]. SPI is calculated for different accumulation periods: 1, 3, 6, 9, 12, 18, 24 months. Each of these is in turn calculated for each of the twelve calendar months. Note that values in monthly (and for longer accumulation periods also annual) time series of the data therefore are likely to be autocorrelated. The standard period which was used to fit the gamma distribution is 1961-2010. The dataset covers the period from 1862 to 2015. NOTE: the difference between this dataset with the previously published dataset 'Standardised Precipitation Index time series for IHU hydrometric areas (1961-2012)' [SPI_IHU_HA] (Tanguy et al., 2015; https://doi.org/10.5285/5e1792a0-ae95-4e77-bccd-2fb456112cc1), apart from the temporal extent, is the underlying rainfall data from which SPI was calculated. In the previously published dataset, CEH-GEAR (Tanguy et al., 2014; https://doi.org/10.5285/5dc179dc-f692-49ba-9326-a6893a503f6e) was used, whereas in this new version, Met Office 5km rainfall grids were used (see supporting documentation for more details). Within Historic Droughts project (grant number: NE/L01016X/1), the Met Office has digitised historic rainfall and temperature data to produce high quality historic rainfall and temperature grids, which motivated the change in the underlying data to calculate SPI. The methodology to calculate SPI is the same in the two datasets. This release supersedes the previous version, https://doi.org/10.5285/d8655cc9-b275-4e77-9e6c-1b16eee5c7d5, as it addresses localised issues with the source data (Met Office monthly rainfall grids) for the period 1960 to 2000. [1] McKee, T. B., Doesken, N. J., Kleist, J. (1993). The Relationship of Drought Frequency and Duration to Time Scales. Eighth Conference on Applied Climatology, 17-22 January 1993, Anaheim, California. Full details about this dataset can be found at https://doi.org/10.5285/a754cae2-d6a4-456e-b367-e99891d7920f

This dataset is model output from the GR4J lumped catchment hydrology model. It provides 500 model realisations of daily river flow, in cubic metres per second (cumecs, m3/s), for 303 UK catchments for the period between 1891-2015. The modelled catchments are part of the National River Flow Archive (NRFA) (https://nrfa.ceh.ac.uk/) and provide good spatial coverage across the UK. These flow reconstructions were produced as part of the Research Councils UK (RCUK) funded Historic Droughts and IMPETUS projects, to provide consistent modelled daily flow data across the UK from 1891-2015, with estimates of uncertainty. This dataset is an outcome of the Historic Droughts Project (grant number: NE/L01016X/1). The data are provided in two formats to help the user account for uncertainty: (1) a 500-member ensemble of daily river flow time series for each catchment, with their corresponding model parameters and evaluation metric scores of model performance. (2) a single river flow time series (one corresponding to the top run of the 500), with the maximum and minimum daily limits of the 500 ensemble members. Full details about this dataset can be found at https://doi.org/10.5285/f710bed1-e564-47bf-b82c-4c2a2fe2810e

This dataset is a model output created using the BGS AquiMod model. It provides monthly groundwater level relative to the Ordnance Datum (maOD) from 1891 to 2015, reconstructed for 54 observation boreholes across the UK. Based on the Generalised Likelihood Uncertainty Estimation (GLUE) methodology, 90th percentile and 10th percentile confidence bounds have been estimated and are given for each of reconstructed groundwater level time series. Full details about this dataset can be found at https://doi.org/10.5285/ccfded8f-c8dc-4a24-8338-5af94dbfcc16

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

Standardised Precipitation Index (SPI) data for Integrated Hydrological Units (IHU) groups (Kral et al., 2015; https://doi.org/10.5285/f1cd5e33-2633-4304-bbc2-b8d34711d902). SPI is a drought index based on the probability of precipitation for a given accumulation period as defined by McKee et al. [1]. SPI is calculated for different accumulation periods: 1, 3, 6, 9, 12, 18, 24 months. Each of these is in turn calculated for each of the twelve calendar months. Note that values in monthly (and for longer accumulation periods also annual) time series of the data therefore are likely to be autocorrelated. The standard period which was used to fit the gamma distribution is 1961-2010. The dataset covers the period from 1862 to 2015. NOTE: the difference between this dataset with the previously published dataset 'Standardised Precipitation Index time series for IHU Groups (1961-2012) [SPI_IHU_groups]' (Tanguy et al., 2015; https://doi.org/10.5285/dfd59438-2170-4472-b810-bab33a83d09f), apart from the temporal extent, is the underlying rainfall data from which SPI was calculated. In the previously published dataset, CEH-GEAR (Tanguy et al., 2014; https://doi.org/10.5285/5dc179dc-f692-49ba-9326-a6893a503f6e) was used, whereas in this new version, Met Office 5km rainfall grids were used (see supporting information for more details). Within Historic Droughts project (grant number: NE/L01016X/1), the Met Office has digitised historic rainfall and temperature data to produce high quality historic rainfall and temperature grids, which motivated the change in the underlying data to calculate SPI. The methodology to calculate SPI is the same in the two datasets. This release supersedes the previous version, https://doi.org/10.5285/047d914f-2a65-4e9c-b191-09abf57423db, as it addresses localised issues with the source data (Met Office monthly rainfall grids) for the period 1960 to 2000. [1] McKee, T. B., Doesken, N. J., Kleist, J. (1993). The Relationship of Drought Frequency and Duration to Time Scales. Eighth Conference on Applied Climatology, 17-22 January 1993, Anaheim, California. Full details about this dataset can be found at https://doi.org/10.5285/a01e09b6-4b40-497b-a139-9369858101b3

Monthly and daily 5km gridded Potential Evapotranspiration (PET) data for the UK. PET was derived using temperature-based equation from McGuinness-Bordne calibrated for the UK (calibration period: 1961-1990). The units are mm/day for daily PET and mm/month for monthly PET. The dataset covers the period from 1891-2015. For both subsets (daily and monthly), a set of performance metrics were calculated, which are provided together with the PET grids. The list of metrics provided is: Mean Absolute Percent Error (MAPE), Nash-Sutcliffe Efficiency (NSE), Kling-Gupta Efficiency (KGE), Correlation Coefficient, Variability Ratio (VR), Bias Ratio and monthly MAPE. Full details about this dataset can be found at https://doi.org/10.5285/17b9c4f7-1c30-4b6f-b2fe-f7780159939c

Monthly Standardised Groundwater level Index (SGI) for observation boreholes across the UK from 1891 to 2015, based on reconstructed groundwater level time series (Bloomfield et al., 2018; https://doi.org/10.5285/ccfded8f-c8dc-4a24-8338-5af94dbfcc16). Standardised groundwater levels have been estimated using a non-parametric normal scores transform of groundwater level data for each calendar month. Probability estimates of an SGI being less than 0, -1, -1.5 and -2 are also provided. Full details about this dataset can be found at https://doi.org/10.5285/d92c91ec-2f96-4ab2-8549-37d520dbd5fc