STH-net : a model-driven soil monitoring network for process-based 1 hydrological modelling from the pedon to the hillslope scale 2

The Schäfertal hillslope site is part of the TERENO Harz/Central German Lowland Observatory and its soil water 12 dynamics is being monitored intensively as part of an integrated, long-term, multi-scale and multi-temporal research 13 framework linking hydrological, pedological, atmospheric and biodiversity-related research to investigate the influences of 14 climate and land use change on the terrestrial system. Here, a new soil monitoring network, indicated as STH-net, has been 15 recently implemented to provide high-resolution data about the most relevant hydrological variables and local soil properties. 16 The monitoring network is spatially optimized, based on previous knowledge from soil mapping and soil moisture monitoring, 17 in order to capture the spatial variability of soil properties and soil water dynamics along a catena across the site as well as in 18 depth. The STH-net comprises eight stations instrumented with time-domain reflectometry (TDR) probes, soil temperature 19 probes and piezometers. Furthermore, a weather station provides data about the meteorological variables. A detailed soil 20 characterization exists for locations where the TDR probes are installed. All data are measured at a 10-minutes interval since 21 January 1, 2019. The STH-net is intended to provide scientists with high-quality data needed for developing and testing 22 modelling approaches in the context of vadose-zone hydrology at spatial scales ranging from the pedon to the hillslope. The 23 data are available from the EUDAT portal (https://b2share.eudat.eu/records/e2a2135bb1634a97abcedf8a461c0909) (Martini 24 et al., 2020). 25

Since 2012, a smaller hillslope area named Schäfertal Hillslope site, located downstream of the Schäfertal gauging station, 91 was instrumented for detailed investigations of the hydrological processes in the unsaturated zone. From 2012 to 2017, the 92 wireless soil moisture monitoring network SoilNet has delivered information about the soil water dynamics at three depths 93 within the unsaturated zone with high spatial coverage. In 2018, the SoilNet has been disposed and a new soil monitoring 94 network, named STH-net, has been installed aiming to improve the resolution in the vertical direction at a fewer locations 95 selected based on the knowledge about the soil spatial variability and soil water dynamics gained from the previous monitoring 96 experience (see Martini et al., 2015;2017a;2017b). The STH-net is described in the following sections of this manuscript and 97 its data are now available through the data portal EUDAT. The Schäfertal Hillslope site includes north-and south-exposed 98 slopes divided by the creek (Schäferbach) in the valley bottom (Fig. 1). In contrast to the slopes upstream of the gauging 99 https://doi.org/10.5194/essd-2020-363 station, which are primarily covered by cropland, this grassland transect is used as pasture and is not affected by agricultural 100 practices except that the grass is mowed typically once per year. The spatial extent of the hillslope is approximately 250 by 80 101 m and presents various topographical and pedological features. The STH-net is designed to cover the spatial variability of the 102 soil properties as well as the soil layering with high resolution. 103   density polyethylene) tubes and an AGM (i.e., absorbent glass mat) battery capable of supplying the required power in case of 132 power cut-off. Every TDR probe is connected to its station master by a 22-m long low loss coaxial cable, tested to be the 133 optimal length providing good signal quality while enabling enough flexibility in terms of network design. The TDR probes 134 have three 0.2 m-long rods, were self-produced and calibrated through measurements in air and in water with different salt 135 concentrations for water content and electrical conductivity estimation. The probes were installed horizontally in soil pits 136 which were carefully refilled after the installation. The installation was carried out between June and August 2018 and all the 137 measurements collected until the end of December 2018 were discarded to allow the soil to re-compact naturally during the 138 first rainy season. 139 From the TDR traces, the dielectric permittivity ε of the medium is calculated as: 140 based on the calibration measurements of travel time and dielectric permittivity in air (tair, εair) and water (twater, εwater), where where is the porosity which was calculated from the soil bulk density and εsoil is set to 4.6. Fig. 4 shows the hourly time 144 series of soil water content. Characteristic differences in the soil water dynamics are evident for the distinct soil profiles and 145 depths to be attributed, e.g., to the differences in soil texture and soil layering or, locally to groundwater dynamics.

Soil temperature 151
The stations P2, P4 and P6 are instrumented with one Th3-s soil temperature profile probe (UMS GmbH, Munich, Germany) 152 each, located nearby the instrumented soil profiles (Fig. 2) and connected via SDI-12 to the same data loggers and power 153 supply. The probes consist of six temperature sensors cased inside a tube made of glass-fibre reinforced plastic and placed at 154 the fixed depths of 5, 10, 20, 30, 50 and 100 cm. Soil temperature is measured at the same times as the TDR traces. The 155 measured data are shown in Fig. 5. The influence of the geographical exposure of the slopes is particularly evident, e.g. overall 156 higher temperature and stronger dynamics for the south-exposed slopes compared to the other areas, as well as the strongest 157 dynamics near the surface compared to the deepest sensors.

Meteorological data 167
In the central part of the Schäfertal Hillslope site, a WXT 520 weather station (Vaisala Oyj, Laskutus, Finland) equipped with 168 a CMP3-L pyranometer (Kipp & Zonen, Delft, Netherlands) installed at the height of 2 m measures the wind vector, air 169 temperature and pressure, relative humidity, liquid precipitation, hail and solar radiation. The system is fully integrated with 170 the data logger of the central monitoring station and the meteorological variables are measured at the same times as the TDR 171 and soil temperature profile probes. Fig. 6 shows the hourly time series of rainfall intensity, air temperature and solar radiation.

Soil properties 177
During the installation of the STH-net, one bulk soil sample and one volumetric soil sample were collected at every soil pit at 178 the same depth as each of the TDR probes installed. From the bulk samples, the percentage of sand, silt and clay in the fine 179 earth fraction was determined in the laboratory using the pipette method. The volumetric soil samples were collected with a 180 stainless stain ring and used for the soil bulk density estimation.

Data sets 202
The STH-net data are archived as separate text files for the different data types: soil water content, soil temperature, and 203 meteorological variables. Furthermore, the geographic coordinates of the measurement locations and the soil information are 204 available for download. The time series data start from January 1 st , 2019 and continue with hourly time steps until the most 205 recent update. At the time of the manuscript submission, the latest entry refers to September 30 th , 2020. 206