CLIMATE CHARACTERISTICS ALONG THE BULGARIAN BLACK SEA COAST FROM 1970 TO 2009

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1 CLIMATE CHARACTERISTICS ALONG THE BULGARIAN BLACK SEA COAST FROM 1970 TO 2009 VENETA IVANOVA TODOROVA 1 ABSTRACT. Climate characteristics along the Bulgarian Black Sea coast from 1970 to For the regime of meteorological elements in Bulgaria influence have air masses coming from Atlantic Ocean, Mediterranean and Black Sea, and from mainland Europe. Weather and climate along the coast are different than in inland of country, and often periods with extreme events are observed. The aim of this work is to investigate and analyze monthly and annual variations and tendencies of the main meteorological elements (temperature and precipitation) along the Bulgarian coastline, with direct impact on the peoples lives. Data for mean, maximum and minimum air temperature and daily precipitation were used for 40 years period ( ) from seven coastal meteorological stations. Statistics methods are used to calculate trend and determine his significance. Some periods differ from one another: i) like relatively dry and cool, ii) as relatively cool and moist, iii) like warm and relatively dry. Keywords: temperature, precipitation, Bulgarian coastline, variations, tendency 1. INTRODUCTION Trends of temperature and precipitations in Europe and Balkan peninsula during the 20 th century are well established it is observed droughts alternating to floods with increasing intensity (e.g. Klein Tank et al., 2002; Giorgi and Lionello, 2008). Some of reasons are consequences of changes in the atmospheric circulation, others - from several decades of human activity, third - by cycling processes, etc. Report of IPCC (2007) show increasing of mean global temperature with 0.74 C during the period The project CLAVIER ( ) developed for Central and Eastern Europe climate model shows for the territory of Bulgaria that during the period , the average temperature in the country will increase by 1.78 degrees and rainfall will decrease by 32 mm / year. Bulgaria is agricultural country and if this change in climate happens this will not be good for the local varieties of fruits and vegetables as well as for tourism. Climate changes for the greater part of the country during the 20 th century, extreme events as well as synoptic situations when they were happened has already 1 National Institute of Meteorology and Hydrology branch Varna, BAS, Bulgaria, veneta74@abv.bg, veneta.ivanova@meteo.bg 269

investigated and described (Koleva,1993; Koleva and Iotova, 1994; Alexandrov et al., 2004; Alexandrov et al., 2006; Bocheva et al., 2008; Latinov, 2009; Ivanova and Alexandrov, 2012).

2 investigated and described (Koleva,1993; Koleva and Iotova, 1994; Alexandrov et al., 2004; Alexandrov et al., 2006; Bocheva et al., 2008; Latinov, 2009; Ivanova and Alexandrov, 2012). In this work the main goal is to investigate in the recent year variations and tendencies of temperature and precipitation using some statistical methods. 2. DATA AND METHODS 2.1 Study area Bulgaria is situated in the south part of the Balkan Peninsula and its eastern border is the Black sea (Fig.1). The weather is defined from atmospheric circulation. The climate is mostly continental with differences along the coast where the maximum rainfall is generally in the winter, and the minimum is usually in August (particularly marked in the southern coast). Variations from this picture are resulting from meridional location of the coast. For example, on the northern part difference between winter and summer rainfall is low and south of cape Emine winter precipitation became larger. The average January temperature is positive. Over the northern part of the coast is most pronounced influence of continental air masses coming from the north and northeast and over the southern part - Mediterranean predominant influence coming from the southwest. The annual average precipitation for the climatic periods varied from 420 to 700 mm, and annual average temperature from 11,6 to 12,9 C. According to the Köppen climate classification, Bulgarian Black Sea coast is the type Csa (moderately warm Mediterranean) and according to the index of dryness de Marton, it belongs to the dry area (Ir <20). Fig.1 Geographical location of Bulgaria 270

3 2.2 Data and methods Data for mean, maximum and minimum air temperature and daily precipitation from seven meteorological stations collected from the NIMH-BAS are used (Table 1). Series with more than 20% missing data are excluded from the analysis. Data quality control (QC) and homogenization procedure was made using a software package RHtestV3 (Wang et al., 2010) developed at the Meteorological service of Canada - all suspicious data and negative values for precipitation are replaced with -99.9, i.e. not available. The monthly average and annual average values for temperature are obtained as arithmetic average. All deviations are calculated compared with the normal period Trend is determined by assessing the slope of the linear approximation of the evolution of the ranks. A 5- year moving average was applied to eliminate the short-term fluctuations. Some climatic indices (calculated by STARDEX project) were presented except those for precipitation which already exist (Ivanova and Alexandrov, 2012). To check the trends for existence of statistically significance a non-parametric Mann-Kendall test and the Sen s method are applied. Table 1: Meteo stations (from north to south) and period with data Station Period of available data Shabla cape Kaliakra Varna cape Emine Burgas Ahtopol Rezovo RESULTS Relief of Bulgarian Black sea coast is highly varied and conditionally is divided on northern and southern part. Northern is from Shabla to cape Emine, and southern - from cape Emine to Rezovo. Regarding variations of monthly average temperatures nothing unusual stands - distribution follows diurnal course and like sinusoid (Fig. 2). The annual mean values of temperature in regarding period for all stations are presented in Fig. 3. It can be seen that the average values follow geographical location of the station higher temperature in south and lower in north. In the capes Kaliakra and Emine it is ordinary maximum temperature to be lower than other locations and minimum temperature to be higher. The reason is that they are very jutting into the sea. In summer and winter this nature in the course of temperature is best expressed. 271

4 30 deg C Monthly average air temperature in Varna for period Fig. 2: Monthly average temperature in Varna, Bulgaria, for the period Rezovo, the most southern station has different "behavior". Station location has changed during the observed period, but after homogenization procedure trend remained negative, although the slope changes slightly. When talking about observed climate change is reasonable to check deviations from the normal values of the elements. The beginning of the 20 th century in Bulgaria is characterized by lower temperatures related to the period (Alexandrov et al., 2004; Latinov, L., 2009) but compared values of the annual mean temperature in the recent years with this period we can see different period with following anomalies (Fig.4). Until all variations are short-periodic with different sign. After that anomalies are high positive, excluding This is due to the different type of predominant atmospheric circulation (Tomozeiu et al., 2002; Voskresenskaya and Maslova, 2011; Mokoric and Kalin, 2012). In Table 2 below calculated and presented data are in accordance with report of IPCC (2001) because the rate of temperature rise along the Bulgarian coast after 1970 is very high. Characteristics of precipitation anomalies are the following - decreasing trend in the end of past century. In January large relative dry period was found from 1986 to 2003 for all station. February became very dry (Fig. 5), especially along the north coast, and in March long dry or wet periods were not detected. Long dry periods are observed during the period April-June after year The amplitude of fluctuations is small in July. In August and September at the beginning of the 21 st century increasing of the large positive deviations are found. This is associated with increased frequency of extreme events (Bocheva et al., 2008). In October large positive and negative anomalies were found along the north coast. November after year 2000 remained mostly dry, and during December after year 2007 along the north coast predominate large positive diversion. 272

5 13.5 Ts-ann-av r( ) 10.5 Tmin-ann-avr Shabla Varna Burgas Rezovo Kaliakra Emine Ahtopol Mean ±SE ±1.96*SE Shabla Varna Burgas Rezovo Kaliakra Emine Ahtopol Mean ±SE ±1.96*SE (a) (b) Tmax-ann-avr (c) Fig. 3: Annual average temperature along the Bulgarian Black sea coast for the period at two meter elevation(a), minimum(b) and maximum(c). Dimension on the axis Y is in degree Celsius 14.5 Shabla Varna Burgas Rezovo Kaliakra Emine Ahtopol Mean Mean±SE Mean±1.96*SE deg C Anomalies of annual average temperature Shabla Kaliakra Varna Emine Burgas Ahtopol Rezovo Fig. 4: Anomalies of annual average temperature along the Bulgarian Black sea coast relative to the period

6 Table 2: Linear trends of averaged temperatures in January and July as well as of annual average values for the period in weather stations along the Bulgarian Black sea coast. Ts-temperature in two meters elevation, Tn-minimal, Tx-maximal Ts January Tn Tx Ts July Tn Tx Linear trend( ) Shabla ** Kaliakra ** Varna * Emine ** Burgas ** Ahtopol Rezovo SS - statistical significance of trend * SS with α=0.05, ** SS with α=0.01, + SS with α=0.1 About annual sums and theirs tendencies positive trends are found along the northern coast and negative - along the southern. From the synoptic point of view this is related to the reduced number of Mediterranean cyclones passing south of Bulgaria in the winter, and which determined autumn-winter maximum of precipitation. Precipitation trend in Shabla, Kaliakra and Varna is positive (statistically insignificant), in cape Emine negative (statistically significant with α=0.05) and in Burgas, Ahtopol and Rezovo - negative, statistically insignificant. Calculated with STARDEX project consecutive wet days and mean dry spell lengths of regarding period was found little positive annual trend. Warm nights have increased, and cold days have decreased mm Anomalies in February Shabla Kaliakra Varna Emine Burgas Ahtopol Rezovo Fig.5: Anomalies of precipitation sums in February along the Bulgarian Black sea coast 274

7 4. CONCLUSIONS Air masses coming from the sea or from the inland on the coast change their characteristics and properties. Hence weather and climate are different. Investigating tendency for annual and monthly temperature and precipitation sums for period with different statistical methods shows little change in the climatic conditions of the region. The results are consistent with previously obtained by other researchers. During the year linear trend of averaged monthly temperature is highest in July. Most of the trends for precipitation are statistically insignificant. Period is relatively dry and cool; climate along the Bulgarian coast is relatively cool and moist; warm and relatively dry years with increasing trend of extreme events. REFERENCES 1. Alexandrov, V., Schneider, M., Koleva, E. and J.-M. Moisselin (2004). Climate variability and change in Bulgaria during the 20th century. Theor. Appl. Climatol. 79, DOI: /s Alexandrov, V., B. Dubuisson, J-M. Moisselin and E. Koleva (2006). A case study on utilization of precipitation indices in Bulgaria. Proceedings of the International conference on Water Observation and Information System for Decision Support (BALWOIS), Ohrid, Macedonia, May 2006, (CD) 18 pp. 3. Bocheva Lilia, Simeonov Petio, Gospodinov Ilian, Marinova Tania (2008) - Torrential Precipitation Events in Bulgaria: A Comparative Analysis for East Bulgaria, BALWOIS 4. Intergovermental Panel on Climate Change Working Group I Third Assessment Report (IPCC WG1 TAR), Climate Change 2001: The Scientific Basis Giorgi, F. and Lionello, P. (2008). Climate change projections for the Mediterranean region, Global and Planetary Change Volume 63, Issue 2-3, September 2008, Pages , DOI: /j.gloplacha Ivanova, V., Alexandrov, V. (2012). Precipitation Variations along the Bulgarian Black Sea Coast from 1950 to Final Proc. of BALWOIS 2012 Ohrid, Republic of Macedonia, pp Klein Tank, A.M.G., Wijngaard, J.B., Können, G.P., Bohm, R., Demaree, G., Gocheva, A.,Mileta, M., Pashiardis, S., Hejkrlik, L., Kern-Hansen, C., Heino, R., Bessemoulin, P.,Muller-Westermeier, G., Tzanakou, M., Szalai, S., Palsdottir, T., Fitzgerald, D., Rubin, S.,Capaldo, M., Maugeri, M., Leitass, A., Bukantis, A., Aberfeld, R., Van Engelen, A.F.V.,Forland, E., Mietus, M., Coelho, F., Mares, C., Razuvaev, V., Nieplova, E., Cegnar, T.,Antonio Lopez, J., Dahlstrom, B., Moberg, A., Kirchhofer, W., Ceylan, A., Pachaliuk, O.,Alexander, L.V., Petrovic, P., (2002). Daily dataset of 20th-century surface air temperature and precipitation series for the European climate assessment. Int J Climatol. 22, Koleva E. (1993) Trend and variability of precipitation in Bulgaria. In: Sevruk B, Lapin M (eds) Precipitation variability & climate change. Proceedings of the 275

8 symposium on precipitation and evaporation 2. Bratislava: Slovak Hydrometeorological Institute, pp Koleva E. and Iotova A. (1994) Comparison between global and regional temperature trends. In: Global Climate Change. Phoenix 10. Latinov. L. (2009) Caprices of the weather in Bulgaria in XX-th century (in Bulgarian) 11. Mokoric, M. and Kalin, L. (2012). The weather circulation analysis over Adriatic coast in warm period Final Proc. of BALWOIS May-2 June 2012, Ohrid, Republic of Macedonia 12. Tomozeiu, R., Busuioc, A. and Stefan, S. (2002). Changes in seasonal mean maximum air temperature in Romania and their connection with large-scale circulation. Int. J. Climatol. 22: (2002). DOI: /joc Voskresenskaya, E.N. and Maslova,V.N. (2011). Winter-spring cyclonic variability in the Mediterranean-Black Sea region associated with global processes in the oceanatmosphere system. Adv. Sci. Res., 6, , DOI: /asr Wang, X. L., H. Chen, Y. Wu, Y. Feng, and Q. Pu (2010). New techniques for detection and adjustment of shifts in daily precipitation data series. J. Appl. Meteor. Climatol. 276

On the Risk Assessment of Severe Convective Storms and Some Weather Hazards over Bulgaria ( ) - Meteorological Approach

On the Risk Assessment of Severe Convective Storms and Some Weather Hazards over Bulgaria (1991 2008) - Meteorological Approach Lilia Bocheva, Petio Simeonov, Ilian Gospodinov National Institute of Meteorology