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).

Soil moisture content is one of the most important parameters of hydrological studies. Cosmic-ray neutron sensing is a promising proximal soil moisture sensing technique at intermediate scale and high temporal resolution. In this study, we validate satellite soil moisture products for the period of March 2015 and December 2018 by using several existing Cosmic Ray Neutron Probe (CRNP) stations of the COSMOS database and a CRNP station that was installed in the south part of Turkey in October 2016. Soil moisture values, which were inferred from the CRNP station in Turkey, are also validated using a time domain reflectometer (TDR) installed at the same location and soil water content values obtained from a land surface model (Noah LSM) at various depths (0.1 m, 0.3 m, 0.6 m and 1.0 m). The CRNP has a very good correlation with TDR where both measurements show consistent changes in soil moisture due to storm events. Satellite soil moisture products obtained from the Soil Moisture and Ocean Salinity (SMOS), the METOP-A/B Advanced Scatterometer (ASCAT), Soil Moisture Active Passive (SMAP), Advanced Microwave Scanning Radiometer 2 (AMSR2), Climate Change Initiative (CCI) and a global land surface model Global Land Data Assimilation System (GLDAS) are compared with the soil moisture values obtained from CRNP stations. Coefficient of determination ( r 2 ) and unbiased root mean square error (ubRMSE) are used as the statistical measures. Triple Collocation (TC) was also performed by considering soil moisture values obtained from different soil moisture products and the CRNPs. The validation results are mainly influenced by the location of the sensor and the soil moisture retrieval algorithm of satellite products. The SMAP surface product produces the highest correlations and lowest errors especially in semi-arid areas whereas the ASCAT product provides better results in vegetated areas. Both global and local land surface models’ outputs are highly compatible with the CRNP soil moisture values.

Drought is a vital phenomenon in semi-arid regions; particularly in closed basins where water resources are scarce to meet demands. Konya Basin of Turkey is a closed basin which is susceptible to droughts at the ultimate level. In order to estimate drought risks and establish necessary measures against drought events, a Drought Management Plans is prepared for this basin. This study is aimed to share experiences achieved during the preparation of this plan and discuss essential tools to establish a comprehensive drought management plan. Preparation of a drought management plan includes, determination of prospective drought risks, climate change analyses, assessment of water budget, vulnerability assessment and essential measures to be taken at pre-drought, during drought and post drought stages.

Kozmik ışınlar yeryüzüne çarptığında ortaya çıkan nötronlar hidrojen ile temas ettiklerinde enerjilerini kaybetmektedirler. Enerjisi azalmış nötronlar sayılarak bir bölgenin toprak nemi yüksek başarı ile tespit edilebilmektedir. Bu prensip ile çalışan kozmik ışın nötron sayacı (CRNP) ülkemizde ilk olarak Niğde-Çakıt havzasında denenmiş ve elde edilen sonuçlar bu çalışmada sunulmuştur. Yaklaşık 670 metre çapında bir alan için toprak nemi bilgisini sürekli olarak sağlayabilen CRNP, yüksek mekânsal ve zamansal çözünürlükte toprak nemi verisine ihtiyaç duyan hidrolojik çalışmalar için önemli bir alternatif oluşturmaktadır. 11 Kasım 2016 ile 01 Temmuz 2019 tarihleri arasında, CRNP ile saatlik olarak düzenli veri temini yapılmış olup, elde edilen verilerin aynı bölgede bulunan zaman alanı reflektometresi (TDR) cihazıyla da çok uyumlu sonuçlar verdiği tespit edilmiştir. Biriktirmeli kavramsal bir model olan NAM modeli ile hidrolojik değişkenlerin akıma olan etkileri belirlenebilmektedir. Bu çalışmada CRNP ile elde edilen toprak nemi verileri NAM kavramsal modelinin iyileştirilmesinde kullanılmış, modelin kalibrasyonunda toprak nemi verilerinin de dikkate alınmasıyla Çakıt Havzası debi verileri için Kling-Gupta Verimlilik skoru 0,56(Kalibrasyon) ve 0,42(Doğrulama)'dan 0,81(Kalibrasyon) ve 0,64(Doğrulama)'ya yükselmiştir. Hem Çakıt Havzası hem de Darboğaz Alt Havzası için istatistiksel ölçütlerin çoğunda benzer gelişmeler kaydedilmiştir.

<p>Conceptual models are the most frequently used hydrological models in practical hydrological studies. These models are developed by considering the rainfall-runoff relation specific to the area of interest through a set of parameter values, which are calibrated by using the observed discharges, groundwater levels, etc. Although, it is a common practice to calibrate conceptual models by using observed run-off data, considering the direct relation of the other elements of the hydrological cycle with each other, it is expected that using as many elements as possible will enhance the capacity of the models. Cosmic Ray Neutron Sensing (CRNS) is one of the most promising soil moisture observation methods and it has a very good potential to be used in hydrological studies due to its relatively larger horizontal footprint thus better representation of the study area. In this study, benefits of introducing CRNS based soil moisture values in the calibration of NAM model has been discussed for semi-arid basin located in Turkey. NAM model has been studied for the entire basin (421 km<sup>2</sup>) and one of its sub-basins (121 km<sup>2</sup>) by introducing the soil moisture data. Objective functions for model calibration has been defined for three cases: Discharge, soil moisture and the combination of discharge and soil moisture. The results have been discussed by using several statistical measures such as NSE, logNSE and KGE. According to the comparisons between models with different calibration properties, utilizing CRNP soil moisture reduces the difference between observation and simulation for both basins. Peak discharge values are better simulated and volume errors are significantly reduced when the combined objective function is used. For both basins, basin water storage values are well correlated with the observed and simulated soil moisture values even in the validation period. This is an indication of the closed coupling between volume storage in the root zone and measured soil moisture by CRNS in the study area.</p>