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Climatology

Volume XVI |

Considerations upon extreme temperatures on Romanian territory

Abstract: In this article we analyse the evolution in time of extreme temperatures significant for Romania with a focus on absolute extreme temperatures recorded on the overall present territory. After thoroughly investigating the credible sources referenced at the end of the paper, we present in chronological order the records for absolute minimum temperatures, and absolute maximum temperatures which were measured at the meteorological stations on the present territory of Romania, according to the availability of the data, i.e. the last two decades of the 19th century up until 2017.  We classify and discuss the sources of climatological data in the form of minimum and maximum temperatures. The measurements of meteorological parameters on the current national territory were recorded since 1770 at Iași (cf. Dissescu 1931 and also http://www.meteoromania.ro/anm2/despre-noi/istoric/ – page in Romanian as of 30.03.2017). For a systematic approach with credible data, at least another century passed, until Ștefan Hepites (1851-1922) founded in 1884 in Bucharest the Central Meteorological Institute of Romania (I.M.C. in Romanian) (Dissescu, 1931 and cf. the ANM web page quoted earlier). The newly created Institute did not include the meteorological stations which were present at that time in Transylvania, but only the ones on the official Romanian territory of 1859-1918 made up of Moldavia and Wallachia. This paper argues in favour of the process of global warming (GW) and its effects upon the evolution of extreme temperature values in a certain time interval. The conclusions stemming from the investigation of the dataset in this paper should provide a helpful and necessary point of departure in subsequent research of climatologists in their quest of identifying the correct model of future climate. Our article should be regarded as part of a series of analyses of the variability of the climate in Romania, the recent influence of global warming on it and on certain climatological parameters in particular.

Volume XVI |

Analysis of the Mean of Daily Maximum Temperature within the Romanian Plain (1961-2015)

Abstract: The present study aims at rendering the characteristics of the means of the daily maximum temperature at monthly, seasonal and annual level within the Romanian Plain, as well as their trends. The time series cover a 55-year period (1961-2015) and data come from 8 meteorological stations. In order to assess the distribution of the data, there were calculated two coefficients (Skewness – S and Kurtosis – K) and also applied the Kolmogorov-Smirnov test for normal distribution. The positive S values and negative K values indicate that the distribution is not symmetrical but, taking into account that the values are quite close to 0, we may assume, it is not far from normal. The KS test also indicates a normal distribution. Homogeneity of the annual temperatures was tested by means of Pettitt test, Standard Normal Homogeneity Test (SNTH) and t test, which emphasized that the change point was registered before 2000. At three stations (D.T. Severin, Bechet, Buzău) all three applied tests indicated the same year 1988, respectively 1989 as break point, while at the other stations, it is the same year according to SNHT and T test, and a different one based on MWP. Based on Mann-Kendall test and Sen’s slope estimation, there were emphasized temperature trends and their statistical significance. The highest temperature increase and upward trend was registered for mean annual and mean summer values (0.001 level of significance within the entire region). However, except for autumn, which is generally characterized by statistically insignificant negative trends, all the other seasons display significant upward trends. At monthly level, only the summer months registered upwards trends within the entire plain (level of significance oscillating between 0.05 and 0.001), while in autumn months there were not registered any statistically significant trends.

Volume XV |

The Mediterranean Oscillation (MOI) and the Forest Fires in Romania in the Period 1986–2014

Abstract: The study examines the connection between the Mediterranean Oscillation (MOI) and the forest fires (the annual number of fires, the annual burned area and the average burned area per fire) in Romania in the period 1986–2014. Pearson’s correlation coefficient (R) was used for determination of the correlation connection. Two MOI datasets were used: MOI-1 (Algiers and Cairo) and MOI-2 (Israel and Gibraltar). Monthly, seasonal and annual values of MOI were used in the calculations. Results for the number of fires and MOI-1: the highest values of R (statistically significant at the level of p≤0.05) were obtained for April (–0.446) and June (0.423), and for summer (0.432). The annual burned area and MOI-1: the highest values of R (statistically significant at the level of p≤0.05) were obtained for April (–0.459), and for winter (0.406). The number of fires and MOI-2: the highest values of R (statistically significant at the level of p≤0.01) were obtained for June (0.556) and February (0.475), and for summer (0.507). The annual burned area and MOI-2: the highest values of R (statistically significant at the level of p≤0.05) were obtained for June (0.449) and February (0.439), and for summer (0.439). Results of the research could be used for the long-term forecast of forest fires in Romania. However, further investigations of the connection between forest fires and other climate indices are necessary.

Volume XIV |

The North Atlantic Oscillation Influence on the Climate and Flow Variability of the Lower Danube Valley, between the Towns of Olteniţa and Călărăşi, Romania

Abstract: As previous international research has identified, the large-scale NAO atmospheric circulation pattern dominates climate variability in the northern hemisphere. In this study we investigate the impact of the North Atlantic Oscillation (NAO) index on annual/winter precipitation and river flow regimes for a sector of the lower Danube Valley. An important goal was to test the relation between the NAO pattern and the occurrences of extreme events. We assume that precipitation variability and river flow are harder to assimilate into a modified anthropogenic environment as the situation of the Danube in the study area. During the communist regime, this valley sector was transformed from a wetland environment into a farming area.
Understanding NAO – rainfall and NAO – river flow relationships were based on monthly data in the time period between January 1977 and December 2010 for the NAO index, the river basin average precipitation over the Danube and the Danube river flow measured at Oltenita and at Calarasi Stations. Results showed that the large inter-annual variability in the precipitation regime and flows of the Danube is largely modulated by the NAO phenomenon. The four-time series in study are weak stationary, which means that the natural events vary moderately along a constant mean and the extreme events do not have the power to propagate, vanishing after few time steps.

Volume XIV |

Evaluation of rainfall extremes. Northeast and West coast regions of India as case study

Abstract: The response of climate change is the increase in the frequency and intensity of extreme weather events. An attempt has been made to study the trends in heavy rainfall amount and the highest rainfall value in 24 hours over Northeast region (NER) and West coast region (WCR) of India with the period ranging from 1901-2009. A standard statistical analysis concludes that the majority of the stations in NER and WCR indicates increasing trend in annual and monsoon rainfalls. Further, the increasing trends in heavy rainfall were investigated and the associated synoptic conditions were identified. The study reveals that the increase in heavy rainfall over the WCR can be attributed to the synoptic systems namely monsoon trough, cyclonic circulation, depressions and lows.