Eddy covariance sites are ideally suited for the study of extreme events on ecosystems as they allow the exchange of trace gases and energy fluxes between ecosystems and the lower atmosphere to be directly measured on a continuous basis. However, standardized definitions of hydroclimatic extremes are needed to render studies of extreme events comparable across sites. This requires longer datasets than are available from on-site measurements in order to capture the full range of climatic variability. We present a dataset of drought indices based on precipitation (Standardized Precipitation Index, SPI), atmospheric water balance (Standardized Precipitation Evapotranspiration Index, SPEI), and soil moisture (Standardized Soil Moisture Index, SSMI) for 101 ecosystem sites from the Integrated Carbon Observation System (ICOS) with daily temporal resolution from 1950 to 2021. Additionally, we provide simulated soil moisture and evapotranspiration for each site from the Mesoscale Hydrological Model (mHM). These could be utilised for gap-filling or long-term research, among other applications. We validate our data set with measurements from ICOS and discuss potential research avenues.

Czech University of Life Sciences Prague Faculty of Environmental Sciences Kamýcká 129 Praha Suchdol 165 00 Czech Republic

Friedrich Schiller University Jena Institute of Geoscience Burgweg 11 07749 Jena Germany

German Centre for Integrative Biodiversity Research Halle Jena Leipzig Puschstrasse 4 04103 Leipzig Germany

Helmholtz Centre for Environmental Research Permoserstraße 15 04318 Leipzig Germany

University of Potsdam Institute of Environmental Science and Geography Am Neuen Palais 10 14469 Potsdam Germany

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Multi-model hydrological reference dataset over continental Europe and an African basin

Long-term daily hydrometeorological drought indices, soil moisture, and evapotranspiration for ICOS sites