The Variability of Seasonal and Annual Extreme Temperature Trends of the Latest Three Decades in Romania

Abstract

Abstract In the latest IPCC report (2014) it was estimated that since the mid-20th century, the number of cold days and nights has decreased and the number of warm days and nights has increased in large parts of Europe. Some recent analyses have found that mean summer maximum temperature change over Europe was +1.6 ± 0.4 °C during 1880 to 2005. It seems that human influence has contributed to the observed global scale changes in the frequency and intensity of daily temperature extreme. The objective of this work was to identify spatial variations of the seasonal and annual extreme temperature variability and trends over Romania in the period 1985-2014. Starting with a large climatological database (30 years of daily data for 29 locations from Romania), daily minimum, maximum and amplitude temperature data were condensed into normal probability functions for which the assumption of normal distribution was accepted by the Shapiro-Wilk statistical test. These functions were then used to calculate the appearance probability of annual and monthly temperatures values. Temperatures which appear with different probabilities all year long were computed with “NORMDIST” function from Microsoft Office Excel. Based on these values data thematic maps were generated with isolines drawn by geo-statistical interpolation (kriging method of Surfer®, Golden Software, 2012). Comparing the increasing trend per decade expressed by probabilities, we found that the minimum temperature had almost the same rate (21.6% in a decade) as the maximum ones (21.0% in a decade) and mean daily temperature amplitude remained unchanged from 1985 to 2014. We identified the presence of an increased variability of annual mean temperature trends between the different climatological stations. It was noted that the level of statistical significance of maximum and minimum temperature linear trends per decade was low during winter, spring and autumn. But this level of significance was very high for June, July and August months.