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For citation: Ilnicki P., Farat R., Górecki K., Lewandowski P. 2015. Long-term air temperature and precipitation variability in the Warta River catchment area. Journal of Water and Land Development. No. 27 p. 3-13. AbstractThe variability of the mean annual air temperature and precipitation totals in three periods: 1848-2010, 1951-2010 and 1981-2010 was investigated in the large Warta River basin, being the area with lowest rainfall in Poland. For the purposes of research, nine meteorological stations with the longest measurement series were selected. Air temperature increase in this river basin was similar than in neighbouring countries. In the last 30 years this trend kept increasing. The precipitation in the whole studied period was slightly increasing in the northern part of the Warta River basin, but decreasing in the southern part. The mean annual precipitation totals in the catchment area did not change visible. In the period 1981-2010, the precipitation totals show a small increase in the winter and spring and a decrease in summer. A negative influence of this climate change was not visible in the Warta River discharge. The main objectives of this study were the collection long-term records of air temperature and precipitation in the Warta River basin, and the statistical analysis of climate variability.

In the Powidzki Landscape Park, there are 150 peatlands of a total area of 1,250.2 ha. On its edge, brown coal strip mines are in operation, causing deep land drainage that resulted in a drastic (up to 5 m) lowering of the water table in lakes and accelerated peatland disappearance. To determine the extent of the process, a comparison was made of the types of surface soil layers and their ash content in 20 peatlands determined in 1957–1965 and in 2017. They are located in the farmland lying the closest to the strip mine, Jóźwin IIB, and in woodland lying further away. The results were compared with those for a peatland in Skulsk, which was not affected by the negative impact of the strip mine. Fen peat, occurring there about 55 years ago has largely turned into grainy moorsh. In the 20–50 cm layer, an ash content has grown almost twofold, while in part of the peatlands organic soils have changed into mineral and organic-mineral ones. The greatest changes have occurred in the farmland. In all Park peatlands, grasslands have contracted threefold, while the area of forests and woodlands has grown fivefold. Today, about 10% of the peatland area is taken up by arable land of which there was none before.

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Soil water hysteresis in organic soilsIn 20 undisturbed samples of peat, muck, peaty soil and humic sand, the hysteresis of the moisture characteristic by soil suction from 0 to -9,8 kPa and from 0 to -29,4 kPa was measured. The greatest hysteresis was found in peat. Suction values from -1 to -3 kPa caused differences of 0,076 cm3/cm3 in water content during drying and wetting. In muck with low ash content and in humic sand the hysteresis was smaller. In peaty soil and muck with high ash content (> 40 %) it diminished to twice or three times lower values in comparison with those in peat. In organic soils the hysteresis decreases clearly by soil suction higher than -6 kPa. Repetition of drying and wetting gave a diminution (ca. 30 %) of the hysteresis loop in peat and displaces it towards the field of lower water content. The hysteresis of muck did not change considerably. The change of the porosity structure (pore 0 > 30 pm) during the repetition of drying and wetting indicate that some soil shrinkage has occured.