An observed increase in air temperature can lead to significant changes in the phenology of plants and, consequently, changes in agricultural production. The aim of the study was to evaluate the spatial differentiation of thermal resources in Poland and their variability during a period of changing thermal conditions in Europe. Since the variability of thermal conditions is of paramount importance for perennial crops, the study focused on apple, plum, and cherry orchard regions in Poland. The analysis was conducted for the period of 1951–2010 using air temperature daily data. Thermal resources have been defined using the growing degree days (GDD) index calculated independently for the whole year and during in frost-free season for three air temperature thresholds: 0, 5, and 10 °C, which determine the non-winter period, growing season, and the period of full plant growth, respectively. In addition, due to the high significance for perennials in particular, the incidence and intensity of frost during flowering were calculated. In this study, a detailed analysis of the spatial differentiation of thermal resources was first performed, followed by an evaluation of long-term variability and associated change patterns. The obtained results confirmed an increase in thermal resources in Poland as a consequence of the lengthening of the growing season. However, the frequency and intensity of spring frost, especially during flowering or even during ripening of plants, remain a threat to harvests in both the eastern and western parts of the country.

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The main objective of the present study is the construction of air temperature maps for the territory of

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Abstract:The aim of the study is to estimate the trend in summer maximum air temperature extremes in Poland during the period 1951-2015 by demonstrating the changes in the magnitude of temperature anomalies, temperature "surplus", as well as the area influenced by extreme temperature occurrence. To express the latter two variables, daily maps of maximum air temperature were created to calculate the total area affected by temperature extremes. To combine the effect of spatial extent and temperature anomaly, an Extremity Index was introduced. The results confirmed an increase in summer maximum air temperature of about 0.4 • C per 10 years, evidenced also in the increase of summer extremeness. Positive anomalies have dominated since the 1990s, with the largest anomalies occurring during the summers of 1992, 1994, 2010 and finally 2015, the most exceptional summer during the analyzed period.

Late spring freeze events, a significant agroclimatic hazard, are investigated for Poland. Daily minimum air temperatures from 184 stations for the period 1951-2010 were used to analyze the frequency and conditional probability of late spring freezes. In addition, three classification schemes were employed to investigate the atmospheric circulation responsible for late spring freezes events. The findings suggest that knowledge of the airflow influencing late spring freezes can help to understand the complex historical trends and projected future changes in freeze risk for perennial crops

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Abstract⎯ Heavy rainfalls and consequent floods are the most important extreme events in Central Europe in terms of frequency and economic losses. The purpose of the study is to evaluate regional extreme precipitation events in the Polish Carpathian Mountains as well as to determine the circulation basis for these events. Extreme precipitation values were identified based on daily precipitation totals measured at almost 70 weather stations in the Polish Carpathians between 1951 and 2015. The analysis concentrates on daily mean areal precipitation totals in excess of 100 mm per day as well as 50 and 30 mm, which causes flooding in the Carpathians. All extreme precipitation data were analyzed from a synoptic perspective, with special attention paid to pressure patterns over Central Europe. The analysis confirms that the heaviest rainfalls are affected by the situations with the N-NE airflow. However, analyses with the application of the upper tropospheric data brought some new findings on the precipitation extreme topic. It turned out that most cases with significant rains occurred when the mid-tropospheric advection was from the southern sector (during the typical N and NE advections in the lower part).