An overview of hydrometeorological datasets from a small agricultural catchment (Nučice) in the Czech Republic

We introduce the freely available web‐based Water in an Agricultural Landscape—NUčice Database (WALNUD) dataset that includes both hydrological and meteorological records at the Nučice experimental catchment (0.53 km2), which is representative of an intensively farmed landscape in the Czech Republic. The Nučice experimental catchment was established in 2011 for the observation of rainfall–runoff processes, soil erosion processes, and water balance of a cultivated landscape. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental (mean annual temperature 7.9°C, annual precipitation 630 mm). The catchment is drained by an artificially straightened stream and consists of three fields covering over 95% of the area which are managed by two different farmers. The typical crops are winter wheat, rapeseed, and alfalfa. The installed equipment includes a standard meteorological station, several rain gauges distributed across the basin, and a flume with an H‐type facing that is used to monitor stream discharge, water turbidity, and basic water quality indicators. Additionally, the groundwater level and soil water content at various depths near the stream are recorded. Recently, large‐scale soil moisture monitoring efforts have been introduced with the installation of two cosmic‐ray neutron sensors for soil moisture monitoring. The datasets consist of observed variables (e.g. measured precipitation, air temperature, stream discharge, and soil moisture) and are available online for public use. The cross‐seasonal, open access datasets at this small‐scale agricultural catchment will benefit not only hydrologists but also local farmers.


| DATA SET NAME
Water in an Agricultural Landscape-Nučice Database (WULNUD).

| SITE DESCRIPTION
The Nučice experimental catchment was established in 2011 with the main aim to study the water balance of cultivated fields and between 500 and 550 mm, and mean annual air temperature of 7.9 C (Hanel et al., 2013). The catchment is drained by a 950 m long, narrow stream which begins as a subsurface drainage pipe in the uppermost field. The channel has a trapezoidal cross-section that is 0.6 m wide at the stream bed with an average depth of 1.5 m .
The area of the catchment is almost exclusively covered by arable land. Less than 5% of the area consists of the stream, paved roads, and shrublands. The fields are tilled to the edge of the stream banks; grass strips are not present. Therefore, the surface runoff and eroded soil may enter the stream without significant transformation in a riparian zone. The catchment is divided into three parcels which have existed since 2000 (Noreika et al., 2020). The standard crop rotation is dominated by winter wheat (Triticum aestivum L.), rapeseed (Brassica napus), summer oats (Avena sativa), and alfalfa (Medicago sativa).
The soils are developed on Palaeozoic conglomerate and are classified as Haplic Luvisols and Cambisols. The soil texture is considered sandy loam (9% clay, 58% silt, and 33% sand, on average; Zumr et al., 2019). Several geophysical surveys using electrical resistivity tomography (ERT) have been conducted to capture the degree of homogeneity/heterogeneity present in the plough pan and to determine the depth of the bedrock (Jeřábek et al., 2017). Based on geophysical monitoring and a geological borehole survey conducted at a close by location, the bedrock ranges in depth from 6 to 20 m. The soil is tilled to approximately 12 cm and below the tilled topsoil there is a compacted plough pan with low hydraulic conductivity that ranges between 10 −8 m/s and 2.3. 10 −7 m/s (Zumr et al., 2015).
The catchment often exhibits dry conditions during the summer and the baseflow recorded at the catchment outlet declines to 0-0.2 L/s, while in winter and early spring the baseflow is around 4 L/s. The average annual runoff coefficient is 1%. The runoff coefficient is low since the ground water level is usually below the water level in the stream, some water leaves the catchment as unmonitored groundwater flow (Noreika et al., 2020;Zumr et al., 2015). Runoff exhibits a threshold response to rainfall. Based on the measured rainfall-runoff data, we have identified a rather scattered rainfall-runoff relationship with a strong dependence of the runoff on the actual topsoil saturation. Different runoff pathways and runoff mechanisms have been observed. Once the soil moisture conditions are below a certain threshold value, the magnitude of the stormflow is not correlated to rainfall total (Zumr et al., 2015). Therefore, the shallow topsoil and its water holding capacity play a significant role in runoff generation. As the topsoil becomes saturated over a large part of the catchment, water is quickly routed via surface (especially through the compacted wheel tracks in the slope wise direction) and shallow subsurface runoff processes towards the drainage channel. Even though the channel F I G U R E 1 Overview of the Nučice catchment: (a) catchment location, (b) catchment overview, (c) view from the lower part of the catchment, and (d) view from the upper part of the catchment is straight and short, it has a high retention capacity and the flood wave peaks during runoff events are attenuated. The channel serves as a trap for eroded sediment during the summer months due to dense instream vegetation .

| WATER IN AN AGRICULTURAL LANDSCAPE-NUČICE DATABASE
The catchment is equipped with instrumentation for basic meteorological, hydrological, and hydropedological monitoring. Most of the variables are recorded at 5-min intervals. As the experimental catchment does not belong to the World Meteorological Organization (WMO) nor the Czech Meteorological Institute monitoring networks, the monitoring scheme does not strictly follow WMO standards. A detailed description of the equipment, including sensor accuracies and calibration frequencies, is listed in Appendix (Table A1).
Discharge is monitored at two locations in the stream. Firstly, in the culvert below the upper field; a pressure probe is installed for water depth monitoring and the discharge is calculated based on the circular culvert free-flow discharge relationships, which has been recalibrated during flood wave experiments in 2013, 2014, and 2020   F I G U R E 3 Soil moisture dynamics during winter at SWC_2: (a) boxplot of the soil moisture content at six depths, (b) time series of soil moisture dynamics one is located near the outlet (SWC_1; at three depths from 10 to 40 cm) since the end of 2013, the other is close to the powerline (SWC_2; at six depths from 10 to 60 cm) since the end of 2019 ( Figure 1). In general, the soil moisture dynamics (especially the topsoil) are behaviorally similar to the runoff variation ( Figure 2). The soil moisture in the uppermost layer has a higher degree of fluctuation when compared to the deeper layers (Figure 3). To summarize the data and provide a more comprehensive perspective of the observations for each year, we have included metadata and annual reports in the dataset. However, since more devices have been deployed at the catchment recently, the dataset will be updated every 6 months with the observed data also from the newly deployed devices.

| Application of the data
The hydrometeorological dataset in Nučice has been primarily used for the investigation of hydrological responses under the impacts of agricultural activities. Zumr et al. (2015) shows that based on the rainfall-runoff event analysis, the subsurface runoff dominated the storm runoff generation. The topsoil physical properties (bulk density, porosity) exhibited expected changes with topsoil consolidation during a growing season. However, the unsaturated hydraulic conductivity showed inconsistent trends in subsequent growing seasons (Zumr et al., 2019). The data have also been used to calibrate and validate a hydrological model in the Soil and Water Assessment Tool (SWAT) to conduct scenario analysis to determine the effects of crop changes on in-basin water balance (Gómez et al., 2020;Noreika et al., 2020).

DATA AVAILABILITY STATEMENT
The main aim of the WALNUD dataset is to provide long term data of runoff dynamics and water fluxes within the soil-plant-atmosphere system in an intensively cultivated landscape of the Czech Republic.