Maryana Nikolova, Carmen-Sofia Dragotă, Ines Grigorescu, Stoyan Nedkov,Gheorghe Kucsicsa

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1 Climatic hazards Maryana Nikolova, Carmen-Sofia Dragotă, Ines Grigorescu, Stoyan Nedkov,Gheorghe Kucsicsa By its position in the south-eastern part of Europe, overlapping the Lower Danube Valley in the Carpathian-Balkan region, the Calafat-Vidin - Turnu Măgurele-Nikopole Danube sector falls into the temperate continental climate with excessive-continental influences, thus being exposed to different pluvial and thermal climatic hazards. Methodology and joint approach The used methodology for the hazard assessment and mapping involves several steps starting from hazards identification and classification, assessment of the hazard frequency and probability; identification of hazard classes and assignment the most relevant indicators/indexes for hazard mapping delineation and ultimately regionalization and mapping. The hazard identification and ranking was based on cross-referencing the scientific literature in terms of climate hazards assessment in Romania (Croitoru and Moldovan 2005; Dragotă et al., 2011a; Dragotă et al., 2011b), Bulgaria (Nikolova, 2001; Nikolova, 2002; Nikolova, 2005; Bulgarian Geographic Atlas, 2010; Karagyozov et al., 2012) and worldwide (Bryant, 1991). Due to the difficulties related to database homogenization both spatially and temporally for the Romanian and Bulgarian sides, the hazard assessment has been differentiated according to the particularities of the each analysed phenomenon and available data. Therefore, for the climate phenomena which can be assess based on frequency of cases on an daily or monthly basis (i.e. hoarfrost and hail) the authors carried on the statistical reckoning of the mean and maximum absolute frequency (on annual multiannual basis) based on value classes. Furthermore, based on the selected class values (especially the maximum frequency which plays a key role in the hazard assessment) the probability of occurrence was computed which, ultimately, enabled the drawing up the hazard classes based on the frequency classes and their probability of occurrence (Grigorescu et al., 2013). Additionally to the proposed methodology, some parameters related to average and extreme date of occurrence of first/last day with such a phenomenon and the mean and maximum duration with/without the indicated phenomenon are analyzet. The current research relies exclusively on the real database for the time frame from the Calafat, Băileşti, Bechet, Turnu Măgurele (for the Romanian side) as well as Lom, Vidin, Novo Selo, Gramada, Oriahovo, Svishtov and Pleven weather stations and Gramada, Dolno Tserovene, Dolni Dabnik and Bardarski Geran polygons for hail suppression (for the Bulgarian side) provided by: Romanian National Meteorological Administration; National Institute of Meteorology and Hydrology, Bulgaria; National Yearbooks of the National Meteorological Administration ( ); National Yearbooks of the National Institute of Meteorology and Hydrology ( ); The Climate of Romania (2008); Bulgarian Geographic Atlas (2010); Hail Suppression Agency (HAS) of the Bulgarian Ministry of Agriculture and Food etc. Frost hazard

2 Hazard description Frost is a decline in the minimum temperature below 0 C at positive temperatures during the day. Under favorable humidity of the air in the ground layer in these days is possible to observe hoarfrost. Depending on the reasons causing them frosts are radiation, advective and advective-radiation. Radiation frost occurs due to long-wave radiation of the surface. It is typical for quiet cloudless nights and occurs most before the sunrise when the radiative cooling of the Earth s surface is greatest. Advective frost occurs during intrusion of air masses with temperature below 0 C and can occur at any time of the day. Advective-radiation frosts are formed by advection of relatively cold air with positive temperature and additional radiation cooling below 0 C at night. Physical properties The hazard is caused by the low temperature and it depends most on the timed and intensity of the cooling, on the vegetation type and on the time when is it s critical periods of growing like when the orchard trees are in blossom early in the spring or the harvest is still on the field late in the autumn. The reduction in temperature below 0 C may result in freezing of the water in the cells of plants, and to their destruction. Frost is very dangerous if occurs during the active growing season of plants when the average temperature is above 10 C. That is why it is important to know the average and the end days with frost in a particular agricultural area. Methodology and joint approach Based on the processed data and the hazard classes delineation, the map for hoarfrost was elaborated for common area. The areas most affected by hoarfrost phenomena are located in the Turnu Măgurele Corabia Nikopole area as well as in the upper parts of Prebalkan Plateau ( 58 cases pointing to strong hazard). Medium hazard-prone areas (between 33 and 57 cases) cover the floodplain sector unfolded between Lom-Rast and Oryahovo-Dăbuleni regions, with larger extension on the Romanian side and mainly along the Danube tributary valleys on the Bulgarian side (i.e. Iskăr, Ogosta, Lom) (fig.1). Spatial distribution Based on the data processed and zoning according to the hazard classes a map of the frost hazard is created for the study area. The most threatened areas of frost and hoarfrost are in Turnu Magurele - Ships - Nikopol, and north to the hills of the region. Medium hazard class is characterized by areas of floodplains unfolded between Lom-Rast Oriahovo-Dăbuleni, with wider range in Romanian side. In Bulgarian territory, this hazard class is represented mainly in the valleys of the Danube tributaries - Iskar, Ogosta and Lom. The lowest hazard class characterized the area of Vidin, Calafat and Lom, due to the local landscape characteristics (fig. 1).

3 Fig. 1. Hoar - Frost hazard in the Vidin - Calafat - Turnu Magurele - Nikopol Sector (Grigorescu et al., 2013). Practical advices and recommendations for mitigation measures Between the most popular emergency frost reduction measures are direct heating of the field, overhead sprinkler irrigation, wind machines and appropriate land use practices. Direct heating is popular way for mitigation of frost hazard but it is fuel consuming and rather expensive. To achieve warming of 5-6 C about 125 heaters per a hectare are needed. The overhead sprinkler irrigation decrease frost hazard due to the latent heat liberated when a spray of water is applied on the plant surface. Depending on frost severity a single wind machine provide protection for an area of about 2-4 ha. However the most reliable way to protect the agriculture fields from frost hazard is an appropriate land use. The major frost risk zones can be identified on the topographic maps. It is well know that the frost-free sites are normally situated on open, sloping ground of 2, near to large bodies of water (as Danube River in the case of this study). Reference Grigorescu Ines, Dragotă Carmen, Kucsicsa Gheo Bryant E. A. (1991), Natural Hazards, Cambridge University Press, 294 Croitoru Adina, Moldovan F. (2005), Vulnerability of Romanian territory to climatic hazards, Analele Universităţii de Vest din Timişoara, Seria Geografia, XV/2005, Dragotă Carmen, Dumitraşcu Monica, Grigorescu, and Kucsicsa Gh. (2011a), The climatic water deficit in south Oltenia using the Thornthwaite Method, Geographical Phorum, Year 10, No. 10, Dragotă Carmen, Dumitraşcu Monica, Kucsicsa Gh., Grigorescu Ines, Dumitraşcu C., (2011b), Assessing dryness and drought phenomena in the South Oltenia, Proceedings of the 12th International Conference on Environmental Science and Technology (CEST 2011), Rhodes ISBN , (Chemical

4 Abstracts, Global Nest network, SRCosmos databases). Nikolova, M., (2001), Natural Hazards in Bulgaria, Problems of Geography, 1-2, BAS, Sofia. Nikolova, M. (2002), Unfavourable agro-climatic phenomena in Bulgaria. In: Geography of Bulgaria. Physical Geography. Social- Economic Geography, monograph, ForKom, Sofia pp (in Bulgarian). Nikolova, M. (2005), Analysis of the hail risk for Bulgarian agriculture, Proceedings from scientific conference on Risk management and protection of the population, November 10, Sofia, pp (in Bulgarian). Bulgarian Geographic Atlas, (2010), edit. Iliya Kopralev, Institute of Geography, Bulgarian Academy of Siences, Printed by Alliance Print, Sofia. Karagyozov K., Razmov T., Todorova Mirena, Varadinova Julia, Dzhaleva-Chonkova Anna, (2012), Impact of Natural Disasters on Transport Systems Case Studies from Bulgaria. Report from the International Panel of the WEATHER project funded by the European Commission s 7th framework programme, Sofia, April 2012, 75 p. Clima României, 2008, Editura Academiei Române, Bucuresti. Grigorescu Ines, Dragotă Carmen, Kucsicsa Gheo Bryant E. A. (1991), Natural Hazards, Cambridge University Press, 294 Croitoru Adina, Moldovan F. (2005), Vulnerability of Romanian territory to climatic hazards, AnaleleUniversităţii de Vest din Timişoara, Seria Geografia, XV/2005, Dragotă Carmen, Dumitraşcu Monica, Grigorescu, and Kucsicsa Gh. (2011a), The climatic water deficit in south Oltenia using the Thornthwaite Method, Geographical Phorum, Year 10, No. 10, Dragotă Carmen, Dumitraşcu Monica, Kucsicsa Gh., Grigorescu Ines, Dumitraşcu C., (2011b), Assessing dryness and drought phenomena in the South Oltenia, Proceedings of the 12th International Conference on Environmental Science and Technology (CEST 2011), Rhodes ISBN , (Chemical Abstracts, Global Nest network, SRCosmos databases). Nikolova, M., (2001), Natural Hazards in Bulgaria, Problems of Geography, 1-2, BAS, Sofia. Nikolova, M. (2002), Unfavourable agro-climatic phenomena in Bulgaria. In: Geography of Bulgaria. Physical Geography. Social- Economic Geography, monograph, ForKom, Sofia pp (in Bulgarian). Nikolova, M. (2005), Analysis of the hail risk for Bulgarian agriculture, Proceedings from scientific conference on Risk management and protection of the population, November 10, Sofia, pp (in Bulgarian). Bulgarian Geographic Atlas, (2010), edit. Iliya Kopralev, Institute of Geography, Bulgarian Academy of Siences, Printed by Alliance Print, Sofia. Karagyozov K., Razmov T., Todorova Mirena, Varadinova Julia, Dzhaleva-Chonkova Anna, (2012), Impact of Natural Disasters on Transport Systems Case Studies from Bulgaria. Report from the International Panel of the WEATHER project funded by the European Commission s 7th framework programme, Sofia, April 2012, 75 p. Clima României, 2008, Editura Academiei Române, Bucuresti.

5 Hail hazard The Bulgarian climate is of a continental type. Geographical position and relief variety are playing the major role for Bulgaria being one of the European countries with very frequent hail events. In North Bulgaria the event is associated to the air mass invading from north with stationed atmospheric fronts due to the orographic effect of the Stara Planina Mountain. Hail occurrence is averages from 20 to 60 days per a year and has the highest intensity from May to August but it may happen during the whole warm semester of the year. Physical properties Measuring scales refers to the intensity of the precipitations, duration of hail fall in minutes and size of the hail stones. Usually hail stones have size between 10 and 60 mm. In depends of the intensity and the hail stones size the destructive potential is different. It is possible a hailstorm to destroy up to 100% of the crops or to cause significant damages on the property. Hail storm last usually 5, 10 to 20 minutes and most often is observed between 15:00h and 19:00h of a day during the period 15 May 31 July (Simeonov at at., 1990, Simeonov, 1980). The hail hazard is associated very often with the intensive rainfalls and thunderstorms which we interpret as hail storms. They may have complex impact on the affected territory causing river rising, soils degradation and lost of crops. Methodology and joint approach Both data bases represent observed number of hail falls in Romania (Calafat, Bechet, Bailesti and Turnu Magurele ( ) and in Bulgaria (Novo selo, Vidin, Gramada, Oriahovo, Svishtov and Pleven ( ). Period of observations for Bulgarian stations is and for April and September in Pleven and Svishtov. The data for Bulgarian stations are obtained from the Year books for the period of National Institute of Meteorology and Hydrology. These data are used for assessment of hail probability and hail hazard class s assignment. Hail is rear event with Poisson statistical distribution. Because there is serious discrepancy between both periods of observation in Romanian and Bulgarian data bases, we estimated the align frequencies of the empirical data distribution using mathematical and statistical tables. They present the theoretical probability for 0, 1 or 2 hail falls in frames of each one month from April to September. According to the distribution of probability of event are defined five hazard classes, Table 1. The hazard class for each station is estimated first for each one month. The hazard class for the period from April to September is defined as an average value of the month s hazard classes in each one station, Figure 4. Table 1. Probability and respective hazard class Probability (%) < Hazard class 1 Very low 2 Low

6 31-40 > 40 3 Medium 4 High 5 Very high Spatial distribution Based on these data the area was delineated according to the spatial distribution of the phenomenon with a different probability of occurrence for one and two events in a month (Figure 1 and 2) and represented by it s hazard classes, Figure 4. % t1 t2 t1 t2 t1 t2 t1 t2 Calafat Bailesti Bechet Turnu Magurele IV V VI VII VIII IX Fig. 1. Distribution of the theoretical probability for 1 (t1) and 2 (t2) hail falls per a month in Romanian stations % IV V VI VII VIII IX 0 t1 t2 t1 t2 t1 t2 Vidin Gramada Oriahovo Fig. 2. Distribution of the theoretical probability for 1 (t1) and 2 (t2) hail falls per a month in Bulgarian stations The probability of occurrence of one event in a month is higher (30%) in April in Vidin and Oriahovo, in May in Gramada and Oriahovo, in June in Bailesti, Vidin, Gramada and Oriahovo, in July in Turnu

7 Magurele and Gramada. In August the higher hail hazard (20%) is in Calafat and Bechet and in September the hail hazardwith probability of 30% can be observed in Oriahovo, Figure 1 and 2. Probability of occurrence of two events in a month is very low and actually there is no such probability in 2 of the Bulgarian stations (Vidin and Gramada) and in 2 of the Romanian stations (Bechet and Turnu Magurele). In all the rest cases it is concentrated in May and June with very low probability of up to 10%. The most often in the study area hail falls are observed in June with the highest probability of 30% Figure 1 and 2. The theoretical probability 2 hail events to happen in one month are very low in all stations. That is why the map of hail hazard represents it by hazard classes for the period April- September on the base of the probability to have at least 1 hail fall over that period (Figure 4). With the highest hail hazard class 3 (Medium) is the area of Oriahovo, followed by Gramada (2 - Low) and Vidin (1- Very low). In the Romanian side only the area of Bailes ti has hazard class 2 Low and all the rest stations are characterized by hazard class 1 Very low. The hazard class 4 - High and hazard class 5 Very high are not represented in the study area for the observed period of 6 months. The spatial distribution of the hail hazard shows that the Bulgarian side is relatively more threatened from hail hazard than the Romanian side Figure 3 and Hazard class Calafat Bailesti Bechet Turnu Magurele Vidin Gramada Oriahovo Svishtov Pleven Fig. 3. Hail hazard classes spatial distribution We may conclude that the Bulgarian area is exposed on higher hail hazard than Romanian, but for both sides, Romanian and Bulgarian, hail hazard varies from very low to medium in respect of the probability of occurrence. In addition to this important indicator for the level of hail hazard we must pay attention also on the intensity and severity of the hail falls and associated storms. In only 10% of the days with hail are observed from 61% to 75% of the cases with 100% crop losses in Bulgaria (Simeonov et al., 1990). That is why, in spite of the lower probability of the event, it requires appropriate mitigation management, heaving in mind the importance of agriculture for the economy in the study area.

8 Fig. 4. Distribution of hail hazard classes in Romania and Bulgaria for warm semester of the year (April- September) Practical advices and recommendations for mitigation measures Hail suppression technologies are used for mitigation of the hail hazard. There are 4 polygons for hail suppression in Northwest part of Bulgaria: in Gramada (Gramada and the area of Vidin), Dolno Tserovene (Yakimovo and Valchedram), Bardarski Geran (Biala Slatina and Borovan) and Dolni Dabnik (Pleven and Dolna Mitropolia). Theirs activity mitigate the hail hazard in the study area significantly but however it is a common threat there. Insurance is an alternative way for mitigation of the losses from hail hazard. Zoning and mapping of hail hazard is the best way to provide information for decision makers and stakeholders about the spatial dimensions of the hazard for more sustainable hazard management. References Nikolova, M Hail hazard. In: Identification and collection of implementation-oriented technological and organizational practices and measures for the reduction of natural disaster risk. Report on Contract No , JRC, Ispra. Simeonov, P., P. Boev, R. Petrov, D. Sirakov, V. Andreev, Problems with the Hail Suppression in Bulgaria, SU Kliment Ohridski, Sofia (in Bulgarian) Simeonov, P. Seasonal Distribution of the Dates with Hail in the West Bulgaria Region, Hydrology and Meteorology, book 4, BAS, Sofia (in Bulgarian) Hail Suppression Agency, MAF,