Lund University Global Drought Dataset (LUGD), 1981–2025: Weekly 0.1° SPEI with Accumulation Timescales from 1 Week to 48 Months – Northern Hemisphere

The SPEI was calculated for 12 accumulation timescales ranging from 1 week to 48 months. The temporal index represents a pseudo-weekly time step, defined as four time steps per month starting on the 1st, 9th, 16th, and 23rd day of each month. Daily precipitation (P) was obtained from the Multi-Source Weighted-Ensemble Precipitation dataset (MSWEP V2), which combines rain-gauge observations, satellite retrievals, and atmospheric reanalysis products to produce globally gridded precipitation estimates at 0.1° spatial resolution from 1979 to 2025. Daily potential evapotranspiration (PET) was obtained from the Bristol global PET dataset, which provides global PET estimates at 0.1° spatial resolution for the period 1981–2025. Bristol PET is calculated using the FAO Penman–Monteith formulation based on meteorological variables from ERA5-Land. The climatic water balance was first calculated as D=P−PET, for accumulation timescales of 1 week, 2 weeks, and 1, 2, 3, 6, 9, 12, 18, 24, 36, and 48 months, capturing drought variability from short-term events to multi-year conditions. The accumulated water balance series was then fitted to a three-parameter log-logistic distribution and transformed to a standardized normal distribution N(0,1), i.e. SPEI, following the method of Vicente-Serrano et al. (2010).