European daily dataset of soil moisture from in situ meteorological observations

Abstract. This paper documents the development and validation of an in situ dataset for daily soil moisture based on observed meteorological variables from the European Climate Assessment & Dataset (ECA&D). These data are input to the SoilClim model which provides soil water contents values for the upper 10 cm, the root zone and the deeper layer of the soil. Soil characteristics are taken from the widely used SoilGrids system. The meteorological input data are daily precipitation totals, daily averaged temperature, and global radiation sums. The pan-European dataset for soil water content results in a set of 5758 stations for which daily soil water content values are produced, for the surface zone (upper 10 cm) and for the root zone (upper 40 cm), for the period for which all input data is available. Model results are validated against observations of actual evapotranspiration (ET_a) from the FluxNet experiment. Calculated soil water content are compared against a selection of the observations of the International Soil Moisture Network (ISMN). In the comparisons against observations, calculated values of ET_a and soil water content (SWC) from the state-of-the-art soil dynamics model SWAP (Soil-Water-Atmosphere-Plants), which is more advanced than SoilClim, are used as well. The comparisons show that SoilClim and SWAP show generally the same behaviour albeit that SoilClim saturates quicker than SWAP. On average, the similarity between the models and observation for ET_a is higher (correlations 0.77 and 0.78 for SWAP and SoilClim respectively) than for the observed soil water content, where average correlations for the surface and rootzone vary between 0.52 and 0.62.

Based on the rootzone soil water content, four climate indices are calculated. These are the Soil Moisture Index (SMI) which is a metric to compare soil water content values across the diverse climatic zones which are present in Europe. This index relates to water content levels that are above or below the 50 % level of the field capacity. In addition, an index is introduced that simply counts the number of days where the soil water content drops below the 50 % level of the field capacity. In addition, two indices assess more extreme soil water content values: the number days where the soil water content is either nearly at field capacity or close to the wilting point. The 1991–2020 spring and summer climatology is provided for this dataset in terms of these indices. The relatively recent 2018 drought is put in a historical perspective by a comparison against the 1976 drought and a trend analysis of summer desiccation since 1979 is provided.

The use of in situ observations, the daily resolution and the climate indices included in the described dataset make it suitable as validation of other soil moisture datasets and the assessment of changes in the occurrence of extremes in soil moisture over the European domain. The dataset of daily soil moisture from in situ meteorological observations is available at https://doi.org/10.21944/phk8-at71 (van der Schrier et al. 2026).