Mirosław Miętus

Abstract The aim of the analysis presented here has been to describe long-term variability in air temperature in Poland over the 1951-2010 period. Certain spatial aspects have also been discussed. In order to provide a representative and homogeneous temperature series, station data were averaged for 7 geographical regions of Poland, and for the country as a whole. The distinction drawn between shoreland, lakelands, lowlands, highlands, Subcarpathia, the Sudetes and the Carpathians is as adopted after Kondracki (2002). It takes account of such important factors underpinning spatial variability in temperaturę as altitude, relief, land use, and, indirectly (as a result of latitudinal distribution) also distance from the Baltic Sea and the amount of received solar radiation. In total, monthly average temperature values from 45 synoptic stations were used to calculate an area-averaged temperature for Poland (Table 1). Further study then entailed analysis of annual, seasonal and monthly series with a view to determining trends (at an adopted statistical signifi cance of =0.05), decadal average temperature variability, the longterm course to be noted for air temperature anomalies and the range of variability. The most signifi cant feature of the long-term (1951-2010) variability in annual air temperature in Poland is the statistically signifi cant increase that displays in every analysed region, with an average rate of change exceeding 0.2°C per decade (Table 2). At the seasonal level, an upward trend is to be noted for spring (+0.36°C/10 years) and summer (almost 0.2°C/10 years). In line with this, the decade 2001-2010 was the hottest in the analyzed period (Table 3, 8-10), with the exception of winter (Table 7), for which a slight decrease in average air temperature relative to the 1991-2000 period could be observed. When set against the whole 1951-2000 period, the rate of annual warming remains approximately constant though the summer-season contribution to the warming trendis clearly increasing, while the winter contribution is reduced. On a monthly basis, statistically signifi cant warming over the period is to be observed for February (by over 0.5°C/10 years – the highest rate for any month), during spring (i.e. in March, April and May), and in July and August. Analysis addressing the spatial distribution to the trend revealed that the highest rate of temperature increase is affecting northern Poland (the shoreland and lakeland belts) and the Carpathians, while the lowest rate of increases is to be observed for the highlands and the Sudetes. The long-term course of air temperature anomalies is dominated by short-term variability, which manifests itself in relatively large changes from year to year and with the occurrence of short warm and cold periods. However, where annual series are concerned there has been a noticeable run of warmer years since 1988 (Fig. 1), with only a few exceptions (e.g. 1996 and 2010). A similar situation applies to spring (Fig. 3) and summer (Fig. 4). Furthermore, the spatial cohesion displayed by air-temperature variability indicates that observed changes in thermal conditions in Poland are mainly driven by large-scale factor(s). Fluctuations in annual air temperature averaged for Poland do not exceed ±2°C. On the seasonal scale, variability range varies from 3.9°C in summer to 10.2°C in winter, while at the level of individual months the range is between 4.7°C in June and 16.3°C in February. Relatively small variations in air temperature characterisethe Baltic coast (the shoreland belt). Another feature of long-term air temperaturę change in Poland is that the values for extreme negative anomalies in winter are clearly larger than the positive ones. In the annual cycle, July is most often the warmest month (in 60% of the years during the 1951-2010 period), while the minimal average air temperaturę has most often been recorded in January (in 45% of years).

Mirosław Miętus

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