DOI: 10.5285/d201a2af-568e-4195-bf02-961fb6954c72
title: Gridded Standardized Precipitation-Evapotranspiration Index (SPEI) using generalised logistic distribution with standard period 1961-2010 for Great Britain [SPEIgenlog61-10]

description: 1km and 5km gridded Standardised Precipitation-Evapotranspiration Index (SPEI) data for Great Britain, which is a drought index based on the probability of Climatic Water Balance (CWB) - which is equivalent to the amount of precipitation minus the amount of evapotranspiration - for a given accumulation period as defined by Vicente Serrano et al. (2010). SPEI is calculated for different accumulation periods: 1, 3, 6, 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 generalised logistic distribution is 1961-2010. The dataset covers the period from 1961 to 2012. 
description: SPEI is calculated as originally defined in [1]. SPEI is based on the cumulative probability of a given Climatic Water Balance (CWB) - which is equivalent to the amount of precipitation minus the amount of evapotranspiration - occurring at a location. The historic CWB data of the station is fitted to a statistical distribution. For this dataset, the statistical distribution used is the generalised logistic distribution, which is recommended by [1]. The Maximum Likelihood method was used to estimate the generalised logistic distribution parameters. To calculate SPEI, the R package SCI was used [4]. The input data used is the monthly rainfall grids from CEH-Gridded Estimates of Areal Rainfall [CEH-GEAR] ([4], [5]), and CHESS PET data ([6],[7]).

[1] Vicente-Serrano, S. M., Beguería, S., López-Moreno, J. I. (2010) A Multiscalar Drought Index Sensitive to Global Warming: The Standardized Precipitation Evapotranspiration Index. J. Climate, 23, 1696-1718.
[2] Stagge, J. H., Tallaksen, L. M., Gudmundsson, L., Van Loon, A. F. and Stahl, K. (2015), Candidate Distributions for Climatological Drought Indices (SPI and SPEI). Int. J. Climatol. https://doi.org/10.1002/joc.4267
[3] Gudmundsson, L. & Stagge, J. H. (2014). Package 'SCI': Standardized Climate Indices such as SPI, SRI or SPEI. Repository CRAN, http://cran.r-project.org/web/packages/SCI/SCI.pdf
[4] Tanguy, M., Dixon, H., Prosdocimi, I., Morris, D. G., Keller, V. D. J. (2014). Gridded estimates of daily and monthly areal rainfall for the United Kingdom (1890-2012) [CEH-GEAR]. NERC-Environmental Information Data Centre https://doi.org/10.5285/5dc179dc-f692-49ba-9326-a6893a503f6e
[5] Keller,V. D. J., Tanguy, M. , Prosdocimi, I. , Terry, J. A. , Hitt, O., Cole, S. J. , Fry, M., Morris, D. G., Dixon, H. (2015) CEH-GEAR: 1km resolution daily and monthly areal rainfall estimates for the UK for hydrological use. Earth Syst. Sci. Data Discuss., 8, 83-112 https://doi.org/10.5194/essdd-8-83-2015.
[6] Robinson, E. L., Blyth, E., Clark, D. B., Finch, J., Rudd, A. C. (in preparation), Trends in evaporative demand in Great Britain using high-resolution meteorological data
[7] Robinson, E.L.; Blyth, E.; Clark, D.B.; Finch, J.; Rudd, A.C. (2015). Climate hydrology and ecology research support system potential evapotranspiration dataset for Great Britain (1961-2012) [CHESS-PE]. NERC Environmental Information Data Centre. https://doi.org/10.5285/d329f4d6-95ba-4134-b77a-a377e0755653