## 3 Experiment and Data Description  
The city of Wroclaw has characteristic geological, hydrogeological and hydrological conditions [45; 46]. Inhabited by nearly 650 thousand people, the city is one of the largest in Poland [47]. Its history is over 1000 years long and is closely connected to the hydrography of the city. Located on the river Oda with its many branches, tributaries and channels, this forms a unique system with groundwater aquifers and renders the water issues in the city very important. Geologically, Wroclaw is situated at the Middle Oda Fault Zone in the SW peripheral part of Fore-Sudetic Monocline, close to its border with the Fore-Sudetic Block. Its deep foundation is represented by Permian sandstones, conglomerates, anhydrite and limestone. Overlaying Triassic sandstones, limestone and marls are covered mostly by Miocene, Pliocene and Quaternary sediments [48]. Taking into account the 0-50 m thick Quaternary cover of Wroclaw, two types of geological conditions can be distinguished [49]: a moraine upland, covering generally the SW and NE parts of the city and Oda valley deposits which cover the central part of the city and a 100-2000 m wide belt running in a NW-SE direction. While the moraine upland is dominated by clayey moraine and fluvioglacial sands and gravels, the Holocene Oda valley fills are composed of fluvial sands, gravel and silts of flood terraces and palaeo-river beds (Figure 4). Typically, the moraine upland clays have a thickness of 3-5 m, and within the city's reach they are discontinuous, allowing the underlying Pliocene loans to surface. Groundwater levels in this part of the city are usually below 2 m. With a thickness of 20-50 m, the Holocene valley fills surpass the moraines' thickness by far and the groundwater level of these permeable sediments is usually between 0 and 2 m deep. Long-term observations of meteorological data, as well as groundwater levels, are run by the Observatory of the Department of Climatology and Atmospheric Protection at the University of Wroclaw since 1946. The observatory field is situated in the semi-urban part of the city, on an island surrounded by the river Oda branches (Figure 2). In this 'garden-lab', various data characterizing weather conditions, air quality and groundwater are collected daily. The observatory provided us with data on groundwater level, precipitation, air pressure, air temperature, air humidity and insolation data that have been gathered between 2003 and 2018, covering 15 hydrological years (Figure 5). The groundwater level was measured in a 2.26 m deep piezometer located next to the other measuring devices in the observatory's garden-lab with a float-meter installed in the borehole (Figure 3). The frequency of measurements was daily, with a gap between the 1 June 2014 and 3 July 2014 caused by a technical problem. That resulted in \(n=5779\) samples with a vertical accuracy of 1 cm. In the area of the monitoring well, the stratigraphy is dominated by sand and silty sand deposited during Holocene floodings of the river Oda (Figure 4). This sand can sometimes be coarse and it usually has a good hydraulic conductivity (1.7-2.6 \(\times\) 10\({}^{-3}\) cm/s [50]). Because the water level in the well ranges only between 1.2 and 2.2 m below the surface within these highly permeable sands,  
Figure 3: Panoramic view of ‘garden-lab’ (**a**) and location of the piezometer (**b**,**c**). Figure 2: Location of the experiment’s area. (latitude: 51\({}^{\circ}\)6’19.3\({}^{\prime\prime}\) N longitude: 17\({}^{\circ}\)5\({}^{\prime}\)20.7\({}^{\prime\prime}\) E altitude: 116.3 m a.s.l.). differences in the infiltration path length within the vadose zone were not taken into account for this study. In parallel to the groundwater level, also the precipitation (R) was monitored using a Hellmann lowland rain gauge. The upper edge of the rain gauge is located 1 m above ground, and the area of the gauge-hole is 200 cm\({}^{2}\).