Abstract. The history of drought occurrence in Poland in the last millennium is poorly known. To improve this knowledge we have conducted a comprehensive analysis using both proxy data (documentary and dendrochronological) and instrumental measurements of precipitation. The paper presents the main features of droughts in Poland in recent centuries, including their frequency of occurrence, coverage, duration, and intensity. The reconstructions of droughts based on all the mentioned sources of data covered the period 996–2015. Examples of megadroughts were also chosen using documentary evidence, and some of them were described. Various documentary sources have been used to identify droughts in the area of Poland in the period 1451–1800 and to estimate their intensity, spatial coverage, and duration. Twenty-two local chronologies of trees (pine, oak, and fir) from Poland were taken into account for detecting negative pointer years (exceptionally narrow rings). The delimitation of droughts based on instrumental data (eight long-term precipitation series) was conducted using two independent approaches (Standard Precipitation Index, SPI, calculated for 1-, 3-, and 24-month timescales, and a new method proposed by authors). For delimitation of droughts (dry months), the criteria used were those proposed by McKee et al. (1993) and modified for the climate conditions of Poland by Łabędzki (2007). More than 100 droughts were found in documentary sources in the period 1451–1800, including 17 megadroughts. A greater than average number of droughts were observed in the second halves of the 17th century and the 18th century in particular. Dendrochronological data confirmed this general tendency in the mentioned period. Analysis of SPI (including its lowest values, i.e. droughts) showed that the long-term frequency of droughts in Poland has been stable in the last two or three centuries. Extreme and severe droughts were most frequent in the coastal part of Poland and in Silesia. Most droughts had a duration of 2 months (about 60 %–70 %) or 3–4 months (10 %–20 %). Frequencies of droughts with a duration of 5-or-more months were lower than 10 %. The frequency of droughts of all categories in Poland in the instrumental period 1722–2015 was greatest in winter, while in the documentary evidence (1451–1800) droughts in this season are rarely mentioned. The occurrence of negative pointer years (a good proxy for droughts) was compared with droughts delimited based on documentary and instrumental data. A good correspondence was found between the timing of occurrence of droughts identified using all three kinds of data (sources).

The objective of this study was to produce bactericidal polymer films containing birch tar (BT). The produced polymer films contain PLA, plasticiser PEG (5% wt.) and birch tar (1, 5 and 10% wt.). Compared to plasticised PLA, films with BT were characterised by reduced elongation at break and reduced water vapour permeability, which was the lowest in the case of film with 10% wt. BT content. Changes in the morphology of the produced materials were observed by performing scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis; the addition of BT caused the surface of the film to be non-uniform and to contain recesses. FTIR analysis of plasticised PLA/BT films showed that the addition of birch tar did not change the crystallinity of the obtained materials. According to ISO 22196: 2011, the PLA film with 10% wt. BT content showed the highest antibacterial effect against the plant pathogens A. tumefaciens, X. campestris, P. brassicacearum, P. corrugata, P. syringae. It was found that the introduction of birch tar to plasticised PLA leads to a material with biocidal effect and favourable physicochemical and structural properties, which classifies this material for agricultural and horticultural applications.

Trees are sensitive to extreme weather and environmental conditions. This sensitivity is visible in tree-ring widths and cell structure. In our study, we hypothesized that the sudden frost noted at the beginning of May in both 2007 and 2011 affected cambial activity and, consequently, the number and size of vessels in the tree rings. It was decided to test this hypothesis after damage to leaves was observed. The applied response function model did not show any significant relationships between spring temperature and growth. However, this method uses average values for long periods and sometimes misses the short-term effects. This is why we decided to study each ring separately, comparing them with rings unaffected by the late frost. Our study showed that the short-term effect of sudden frost in late spring did not affect tree rings and selected cell parameters. The most likely reasons for this are (i) cambial activity producing the earlywood vessels before the occurrence of the observed leaf damage, (ii) the forest micro-climate protecting the trees from the harsh frost and (iii) the temperature decline being too short-lived an event to affect the oaks. On the other hand, the visible damage may be occasional and not affect cambium activity and tree vitality at all. We conclude that oak is well-adapted to this phenomenon.Electronic supplementary materialThe online version of this article (doi:10.1007/s00484-015-1107-6) contains supplementary material, which is available to authorized users.

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Abstract. The paper presents the main features of droughts in Poland in recent centuries, including their frequency of occurrence, coverage, duration and intensity. For this purpose both proxy data (documentary and dendrochronological) and instrumental measurements of precipitation were used. The reconstructions of droughts based on all the mentioned sources of data covered the period 996–2015. Examples of megadroughts were also chosen using documentary evidence, and some of them were described. Various documentary sources have been used to identify droughts in the area of Poland in period 1451–1800 and to estimate their intensity, spatial coverage and duration. Twenty-two local chronologies of trees (pine, oak, and fir) from Poland were taken into account for detecting negative pointer years (exceptionally narrow rings). The longest chronology covers the years 996–1986 and was constructed for eastern Pomerania. The delimitation of droughts based on instrumental data (eight long-term precipitation series) was conducted using two independent approaches. In the first approach we used the globally and nationally popular Standard Precipitation Index (SPI), which was calculated for 1-, 3-, and 24-month time scales. Thus, three categories of droughts were analysed: meteorological (SPI1), agricultural (SPI3) and hydrological (SPI24). For delimitation of droughts (dry months), the criteria used were those proposed by McKee (1993) and modified for the climate conditions of Poland by Łabędzki (2007). Droughts were divided into three categories based on the following SPI values: moderate droughts (−0.50 to −1.49), severe (−1.50 to −1.99), and extreme (≤−2.00). The second approach includes the new proposed method for distinguishing droughts and quantitatively estimating their intensity and duration. More than one hundred droughts were found in documentary sources from the mid-15th century to the end of the 18th century, including 17 megadroughts. A greater-than-average number of droughts was observed in the second halves of the 17th century, and of the 18th century in particular. Dendrochronological data confirmed this general tendency in the mentioned period. The clearly greatest number of negative pointer years occurred in the 18th century and then in the period 1451–1500. In the period 996–2015, a total of 758 negative pointer years were recorded. Analysis of SPI (including its lowest values, i.e. droughts) showed that the long-term frequency of droughts in Poland has been stable in the last two or three centuries. Extreme and severe droughts were most frequent in the coastal part of Poland and in Silesia. Most droughts had a duration of two months (about 60–70 %), or 3–4 months (10–20 %). Frequencies of droughts with a duration of 5 and more months were lower than 10 %. The longest droughts had a duration of 7–8 months. The frequency of droughts of all categories in Poland in the period 1722–2015 was greatest in winter. This fact should be taken into account when analysing droughts delimited using documentary evidence. In Poland in 1451–1800, in light of this sort of information, droughts in spring and summer clearly dominated, while only three winter droughts were mentioned. The occurrence of negative pointer years (a good proxy for droughts) was compared with droughts delimited based on documentary and instrumental data. A good correspondence was found between the timing of occurrence of droughts identified using all three kinds of data (sources).