Climate Characteristics Along the Bulgarian Black Sea Coast from 1970 to 2009
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CLIMATE CHARACTERISTICS ALONG THE BULGARIAN BLACK SEA COAST FROM 1970 TO 2009 VENETA IVANOVA TODOROVA1 ABSTRACT. Climate characteristics along the Bulgarian Black Sea coast from 1970 to 2009. 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 (1970-2009) from seven coastal meteorological stations. Statistics methods are used to calculate trend and determine his significance. Some periods differ from one another: i) 1971-1990 like relatively dry and cool, ii) 1991-1997 as relatively cool and moist, iii) 1997-2009 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 20th 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 1906-2005. The project CLAVIER (2006-2009) developed for Central and Eastern Europe climate model shows for the territory of Bulgaria that during the period 2021-2050, 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 20th 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, E-mail: [email protected], [email protected] 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). 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 1961-1990 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 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 1961-1990. 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 1970-2009 cape Kaliakra 1970-2009 Varna 1970-2009 cape Emine 1970-2009 Burgas 1970-2009 Ahtopol 1971-2009 Rezovo 1970-2009 3. 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 deg C 30 Monthly average air temperature in Varna for period 1970-2009 25 20 15 10 5 0 -5 1970 1972 1975 1978 1981 1983 1986 1989 1992 1994 1997 2000 2003 2005 2008 Fig. 2: Monthly average temperature in Varna, Bulgaria, for the period 1970-2009. 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 20th century in Bulgaria is characterized by lower temperatures related to the period 1961-1990 (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 1998-1999 all variations are short-periodic with different sign. After that anomalies are high positive, excluding 2003. 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 2000. The amplitude of fluctuations is small in July. In August and September at the beginning of the 21st 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 Ts-ann-avr(1970-2009) Tmin-ann-avr-1970-2009 13.5 10.5 10.0 13.0 9.5 12.5 9.0 8.5 12.0 8.0 11.5 7.5 Mean Mean 11.0 ±SE 7.0 ±SE Shabla Varna Burgas Rezovo ±1.96*SE Shabla Varna Burgas Rezovo ±1.96*SE Kaliakra Emine Ahtopol Kaliakra Emine Ahtopol (a) (b) Tmax-ann-avr-1970-2009 18.0 17.5 (c) Fig. 3: Annual average temperature 17.0 along the Bulgarian Black sea coast for 16.5 the period 1970-2009 at two meter elevation(a), minimum(b) and 16.0 maximum(c). Dimension on the axis “Y” 15.5 is in degree Celsius 15.0 Mean 14.5 Mean±SE Shabla Varna Burgas Rezovo Mean±1.96*SE Kaliakra Emine Ahtopol deg C Anomalies of annual average temperature 2.0 Shabla Kaliakra Varna Emine Burgas Ahtopol Rezovo 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1970 1971 1972 1973 1974 1975 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Fig. 4: Anomalies of annual average temperature along the Bulgarian Black sea coast relative to the period 1961-1990 273 Table 2: Linear trends of averaged temperatures in January and July as well as of annual average values for the period 1970-2009 in weather stations along the Bulgarian Black sea coast.