Abstract

Abstract. Climate change increases the occurrence and severity of droughts due to increasing temperatures, altered circulation patterns, and reduced snow occurrence. While Europe has suffered from drought events in the last decade unlike ever seen since the beginning of weather recordings, harmonized long-term datasets across the continent are needed to monitor change and support predictions. Here we present soil moisture data from 66 cosmic-ray neutron sensors (CRNSs) in Europe (COSMOS-Europe for short) covering recent drought events. The CRNS sites are distributed across Europe and cover all major land use types and climate zones in Europe. The raw neutron count data from the CRNS stations were provided by 24 research institutions and processed using state-of-the-art methods. The harmonized processing included correction of the raw neutron counts and a harmonized methodology for the conversion into soil moisture based on available in situ information. In addition, the uncertainty estimate is provided with the dataset, information that is particularly useful for remote sensing and modeling applications. This paper presents the current spatiotemporal coverage of CRNS stations in Europe and describes the protocols for data processing from raw measurements to consistent soil moisture products. The data of the presented COSMOS-Europe network open up a manifold of potential applications for environmental research, such as remote sensing data validation, trend analysis, or model assimilation. The dataset could be of particular importance for the analysis of extreme climatic events at the continental scale. Due its timely relevance in the scope of climate change in the recent years, we demonstrate this potential application with a brief analysis on the spatiotemporal soil moisture variability. The dataset, entitled “Dataset of COSMOS-Europe: A European network of Cosmic-Ray Neutron Soil Moisture Sensors”, is shared via Forschungszentrum Jülich: https://doi.org/10.34731/x9s3-kr48 (Bogena and Ney, 2021).

Highlights

  • The years 2003, 2010, 2015, and 2018 are considered as the most notable years of the 21st century in Europe in terms of summer drought and witnessed numerous heatrelated deaths (Stott et al, 2004; Ionita et al, 2017; Laaha et al, 2017; Schuldt et al, 2020; Sutanto et al, 2020) and extensive forest fires (Fink et al, 2004; Grumm, 2011; Turco et al, 2017)

  • This paper introduces the network of existing cosmic-ray neutron sensors (CRNSs) stations in Europe (COSMOS-Europe for short) and how the data are processed in a harmonized way

  • The soil samples were weighted vertically according to Schrön et al (2017); i.e., for each sample at depth d and penetration depth D, we evaluate the weight in the representative sample volume (d1 to d2) to generate the profile average soil moisture: θprofile =

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Summary

Introduction

The years 2003, 2010, 2015, and 2018 are considered as the most notable years of the 21st century in Europe in terms of summer drought and witnessed numerous heatrelated deaths (Stott et al, 2004; Ionita et al, 2017; Laaha et al, 2017; Schuldt et al, 2020; Sutanto et al, 2020) and extensive forest fires (Fink et al, 2004; Grumm, 2011; Turco et al, 2017). Recent advances in measurement techniques, such as cosmic-ray neutron probes, allow continuous non-invasive soil moisture measurements that integrate over scales beyond the traditional point measurement (Zreda et al, 2012; Bogena et al, 2015; Andreasen et al, 2017b). Neutron scattering is again considered one of the most promising soil moisture measurement techniques, as cosmic neutron sensors (CRNSs) provide non-invasive soil moisture at the field scale with an effective radius of 130 to 240 m and a penetration depth of 15 to 55 cm depending on soil wetness (Köhli et al, 2015; Schrön et al, 2017). Based on the processed CRNS soil moisture time series, we performed a brief analysis on the spatiotemporal occurrence of drought events in Europe

Overview of the COSMOS-Europe sites
Methods
Data pre-processing
Correction of raw neutron counts
Atmospheric pressure correction
Incoming neutron correction
Biomass correction
In situ reference soil data
Conversion of neutron count rate to soil moisture
Soil moisture uncertainty
CRNS footprint radius and penetration depth
Normalized quantiles of soil moisture
Implementation of the data processing
Spatiotemporal occurrence of drought events in Europe
How representative and accessible is the soil moisture data?
Conclusions and outlook
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