The landscape of northern Poland is characterised by a very large number of ponds. Traditionally it has been assumed that their hydrology is determined by precipitation and evaporation, and that they are isolated from the adjacent river network. Recent studies, however, have shown that ponds contribute to river runoff for at least part of the year. Their existence is therefore additionally based on fluvial and underground water sources. In order to establish the principles of water circulation in typical ponds, we selected 14 ponds with seasonally intermittent streams. We measured water levels in these ponds and flows in the river segments that connect them. We also determined subsurface exchange fluxes from the water balance equation. Our results demonstrated that the hydrological functions of the ponds varied throughout the year and depended on the level of water storage in the pond's catchment. When the level of retention in the pond's catchment is low, the pond becomes a water body without surface outflow and a drainage base for groundwater. As the level of retention in the catchment rises, ponds develop surface outflows and reconnect with the river network. At this point, their main function becomes retention of water originating from subsurface and surface inflows. Any surplus water may be fed to underground or surface waters.

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Water is a basic element of the natural environment and the most important component in human water management. Rainfall is the main source of water. Therefore, determining the amount of precipitation reaching the ground using sensors is crucial information. Precise precipitation data are necessary for better modeling quality, as the observation data from weather stations are used as basics for weather model assessment. The authors compared precipitation from the Hellmann rain gauge (climatic precipitation, 1.0 m above the ground surface) measured throughout the year and the GGI 3000 rain gauge (actual precipitation on the ground level) measured from April to October. Measurement sequences from the years 2011–2020 were considered. The data for analysis were obtained from a weather station located in northern Poland. The authors analyzed the relationships between data from the two sensors. A comparative study showed that the measurements of actual precipitation are higher and there are strong relationships between actual and climatic rainfall (r = 0.99). Using the introduced coefficient it is possible to determine the full–year actual precipitation with high probability, taking into account the precipitation with a correction from the winter half-year and the actual precipitation from the summer half-year, which is of great importance in the calculation of the water balance.