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Climatology

Volume |

Climate aridity in southern Bulgaria for the period 1961-2015

Abstract: The climate change on a global, regional and local scale is one of the largest problems indicated by the 21st century studies. Some of the major climate changes on the Balkan Peninsula, and in particular in Bulgaria, are related to rising temperatures and decreasing precipitation, which leads to drought and climate aridity. The present study focuses on the investigation of the climate aridity in the non-mountainous part of Southern Bulgaria in order to assess the aridity condition in temporal and spatial scale. The main investigated period is 1961-2015 and the reference periods are 1961-1990 and 1986-2015. The aridity is analysed on the basis of monthly data for air temperatures and precipitation from eight meteorological stations by calculation of De Martonne aridity index and Emberger Index. The survey shows that in all the analysed meteorological stations in Southern Bulgaria there are periods which display characteristics of the semiarid or arid climate. The aridity is well-expressed in the southwest part of Bulgaria (station Sandanski) and the western part of the Thracian lowland (station Plovdiv). Despite the aridity conditions established in the investigated region the tendencies in multiannual variability of De Martonne and Emberger indices show decreasing of aridity during the last 30 years (1986-2015) of the investigated period.

Volume XVIII |

Climate parameters relevant for avalanche triggering in the Făgăraș Mountains (Southern Carpathians)

Abstract: The climate conditions may contribute significantly to the generation of several hazards in mountain areas, such landslides, wildfires, flash floods and avalanches. This study examines the variation of the main meteorological parameters with impact on avalanche triggering conditions at Bâlea-Lac Meteorological Station. At the best of our knowledge, this is the first overview of the basic climate parameters which are potentially avalanche triggers in the Făgăraș Mountains (Southern Carpathians). The study is based on data from only one weather station (Bâlea-Lac) from the period 1979-2017, assuming it is consistently relevant from climatic point of view for avalanche occurrence in the area. The results demonstrate that the theoretical circumstances for avalanche triggering (e.g. snow pack, fresh snow or wind) can be captured. This paper briefly describes the nivologic monitoring system run by the National Meteorological Administration and emphasises its utility for avalanche forecasting and alerts.

Volume XVIII |

Tracing the development of weather radar technology in Romania and worldwide

Abstract: Almost 90 years from the radar invention, the radar technology has evolved enormously and today it presents itself as an instrument of great importance in various research areas (meteorology, aviation, astronomy, air-ecology etc.). The main objective of the article is to identify the periods of development at the global level and also in Romania, as well as to identify the technology of most operational weather radars today. The article is based on publications from international journals and scientific books, covering the period of 1930-2018. The overview presentation demonstrates the reasons today’s weather radar is a powerful tool for studies concerning the atmospheric precipitations prediction, wind speed and direction, rainfall risk assessment and implementation of weather forecasts. Knowing the technological development is needed for the construction of the new generation radar and for exceeding the actual limits with regard to the accuracy of the radar data and the limits of observation. The purpose of this article is to summarize the evolution of the weather radar, with emphasis on the first experiments carried out during the analogue and digital period.

Volume XVIII |

A review of recent studies on heat wave definitions, mechanisms, changes, and impact on mortality

Abstract: Heat waves (HWs) represent a major danger to society and natural environment. The increasing occurrence of high magnitude and impact HWs has raised concerns worldwide and has attracted an increasing interest on this issue among climatologists over the past decade. In this review the research from 2007-2018 period on HWs definitions, driving mechanisms, present changes, future changes, and impact on human mortality is summarized. By reviewing the recent literature, it was found that whilst the atmospheric dynamic is considered to be the primary driver in HW occurrence, the sea surface temperature (SST) and land surface conditions are also essential driving components. The vastness of HW-definitions raises difficulties in selecting the appropriate methodology to identify heat episodes and to compare results from studies which used different definitions. However, by analyzing a sample of 109 papers, a preference for percentile-based definitions was observed. Therefore, 71.6% of the analyzed articles used only percentile-based definitions to identify HWs. Despite the wide variety of definitions, the analysis of changes in HWs converged to similar results. Thus, the existing recent literature provided extensive evidence of significant increase in HWs characteristics across large regions of the planet. Available scientific literature indicated that HWs have been responsible for a considerable increase in mortality in many regions of the world. In the future HWs are predicted to increase in their main characteristics leading to a greater impact on human mortality. Nevertheless, the implementation of rigorous adaptation measures can mitigate the negative impact on mortality. In conclusion, it was noted that a substantial progress has been done in the HW research, but there are still important gaps in this issue which need to be addressed.

Volume XVIII |

Aridity risk in the west of the Oltenia Plain: natural factors and human impacts on land degradation

Abstract: The lands of southern Oltenia had different evolution stages in the last century being influenced by the climatic factor but especially by the anthropic factor. From the extensive areas of ponds and marshes in the pre-war period to drainage, embankments, irrigation systems and planting of the windbreakers and shelterbelts in the 50s – 60s (reflected in the agricultural peak of the 70s – 80s) and to the present day, we are witnessing the aridization of the lands and the extension of the predominantly sandy areas, impracticable to the current type of agriculture.
After 1990, agriculture in the southern part of the Oltenia Plain had an accelerated decline caused by the destruction of the irrigation systems, the deforestation of the windbreakers and shelterbelts, the situation of land ownership and the failure of the adaptation of the crops to the soil types. In 2012 the percentages of irrigated areas reached 0% capacity used out of 76,820 ha in the Blahnița Plain and 1% capacity used out of 299,621 ha in the Oltenia Plain. All these have led to land degradation and amplification of geomorphological processes, especially on sandy surfaces, where the lack of vegetal layer together with the wind process lead to destabilization and movement of sand dunes. This article aims to conduct a spatial-temporal analysis of several types of lands exposed to drying, whose surface has increased considerably to almost 50,000 hectares. Another 50,000 hectares are predisposed to this phenomenon in the Oltenia Plain, on the western part of Jiu. An environmental management strategy for a sustainable development could be made for the protection of the lands against the winds by planting windbreakers and shelterbelts of fast growing species (acacia, hybrid poplar, wild pine, walnut tree). The research methodology involved the processing of the annual average data on temperature, precipitation and wind direction from the weather stations in south-west Oltenia, the processing of the data from the Landsat, Corine maps, as well as the analysis of the data provided by the examination reports on the occupation of land offered by the Ministry of Regional Development and Public Administration. In the analysis of land degradation as a result of the aridization process, the situation of the current vegetation layer was taken into consideration using the NDVI (Normalized Difference Vegetation Index) and data taken from Corine Land Cover between 1990 and 2006 regarding the change of the land use in the Oltenia Plain.