Drought characteristics of European river basins derived from GRACE and GRACE Follow-On total water storage (2002–2026)

Hydrological drought, i.e. a persistent deficit of water stored on and below the land surface, is poorly represented by traditional climate indices based on individual meteorological data. Now, well-established geodetic techniques provide a reliable insight into total water storage (TWS) anomalies. We analyze drought characteristics of 24 major river basins of Europe and its south-eastern margins using TWS from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions, computed from the recent JPL mascon solution for April 2002 to February 2026. For each basin, we compute the GRACE-based Drought Severity Index (GRACE-DSI) based on detrended TWS series, and further classify monthly conditions into wet and dry categories, and identify drought episodes. We show that 23 of 24 basins lose water, with trends from –0.06 cm/yr (Vuoksi–Neva) to –1.52 cm/yr (Kura–Ozero Sevan); only the Western Dvina basin shows no long-term change (+0.02 cm/yr). The greatest declines, below –0.75 cm/yr, occur in southern and south-eastern basins, i.e. the Po, Danube, Dniester, Don, Dnieper, Sakarya, Tigris–Euphrates and Kura–Ozero Sevan. We find that dry months exceeds wet months in 13 basins. We note that drought episodes last 3–19 months, on average 5.3 months, and the largest spatial extent of drought, with 16 of 24 basins in drought, occurred in July 2006 and November 2022. We find that the share of drought months increased in 19 basins, from 19.0% to 25.1% on average between GRACE and GRACE-FO periods, and the mean episode duration increased from 4.6 to 6.9 months, with the largest increase in the western and central basins. A detailed analysis of the Po, Vistula and Kura–Ozero Sevan basins shows that GRACE-DSI captures documented events, i.e. the 2022 Po drought, the 2024 2026 deficit in the Vistula basin, and the progressive water loss in the South Caucasus.