On the Flood Forecasting at the Bulgarian Part Of

BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 Study On Variability Of Temperature And Precipitation Conditions In The South Eastern Bulgaria Ivanka Koleva-Lizama University of Forestry Sofia, Bulgaria Bernardo Lizama Rivas National Institute of Meteorology and Hydrology Sofia, Bulgaria Abstract The impacts of climate change on water resources are displayed in every sector of water system. The temperature and precipitation are the important factors which affect on water resources. On the basis of meteorological data for more than 45 years from several gauging stations is made an analysis on the peculiarities of the climatic conditions in the south eastern Bulgaria. In order to trace the variability of historical precipitation and temperature series the analysis of trend and deviations from climate mean of recommended by WMO “climate normal” period – 1961 -1990 was used. Precipitation over the south eastern Bulgaria has a significant variability over wide range of temporal and spatial scales. The annual precipitation data were examined for evidence of a secular trend by calculation of a linear best fit for the 1952 to 2000. The tendency of rainfall decrease was determined. The drought period in the studied region is noticeable. Key-words: climate change; precipitation; temperature; trend Introduction Meteorological variability provides the driving force for hydrological variability in the landscape. However, the landscape has a modifying influence on the distribution of water in time and space in such a way that water quantity, as measured at any single point in the surface water network on the landscape, is not necessarily a direct result of recent meteorological events. The routing of water through the landscape transforms linear meteorological inputs into non-linear hydrological outputs. The purpose of this research is to analyze the variability of warm and humid conditions in the south eastern Bulgaria. The studied region is situated in the south eastern part of Bulgaria bordered by Black Sea on the East, by watershed of Kamchia River and Dvoynitsa River on the North, by Turkish on the South, by watershed of Tundzha River on the West. Small and independent rivers with small catchments areas debouch to Black Sea. The more important rivers in this region from the Kamchia River to the Turkish border are Dvoynitsa, Hadzhiyska, Aheloy, Aytoska, Rusokastrenska, Sredetska, Fakiyska, Ropotamo, Diavolska, Veleka and Rezovska rivers. The topography is characterised by lowland which cover the eastern and middle part of the studied region – sea coast, low plains and low mountainous area. The higher parts are the north and south regions – Strandja Mountain (up to 600 – 700 m asl), and low parts is the west regions (up to 400 m asl) and lower parts are the middle and east regions (up to 0 – 100 m asl). The region in concern is a very rural area. The forest types are broadleaf and coniferous. According to the climatic classification of the country, the region in concern belongs to the Black sea climate sub-type of the Continental Mediterranean climate type. The climate is generated from west and north continental influence, Black Sea influence from east and mediterranean influence from south. The South Eastern region climate is mainly transitional mediterranean climate. Local climatic differences are due, above all, to the proximity of the Black sea, which warms up the coastal zone in winter and cools it especially in spring. The topography, particularly heights in the south part of the region in concern (Strandja Mountain), plays an important role in the distribution of the precipitation. The territory concerned is one of the sunniest parts of Bulgaria. The considerable values of the radiation balance, positive for all months, fix the high thermal level. The average temperatures for all months are positive. Climate 1 BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 Data used To investigate the variability of temperature and precipitation conditions in the south eastern Bulgaria have used long term data (1952-2001) from several meteorological gauging stations (Aytos, Burgas, Grudovo, Tsarevo and Malko Turnovo). Before use, the data were carefully reviewed and adjusted. In order to trace the variability of historical meteorological series the analysis of trend and deviations from climate mean of recommended by WMO “climate normal” period - 1961-1990 (IPPC, 1995) was used. The data were processed with the help of statistical methods. Results and discussion On the basis of observation data for a period of 50 years the peculiarities in the regime of the climatic elements are determined. The average temperatures for all months are positive. The average annual temperature varies between 13.1 oC in the lower part and at vecinity of seashore and 11.3 oC in the higher part of region. The mean temperature in January range from 1.4 oC (inner part) to 3.2 oC (coastal part). Low temperatures with significant minimal values caused by weak protection in respect to the north and north-west cold spell advections occur in winter. The mean values for July and August fluctuate from 23.0 oC (coastal part) to 20.7 oC (inner part). The average annual precipitation is above 600 mm for the coastal region and in the inner part above 900 mm. The winter precipitation (150 - 271 mm) is the highest seasonal precipitation in Bulgaria. During the winter precipitation is manly in the form of rain, but about one third of cases the precipitation is snow. The snow cover is of short duration (15 - 16 days per year). During the spring the mean seasonal amounts of precipitation are 120 - 180 mm. In summer is sunny, dry and very warm, the amounts of precipitation are 100 - 120 mm. The drought period is very noticeable in the end of summer. In order to evaluate the changes in precipitation and temperature over the south eastern Bulgaria, the warm and humid conditions were analyzed. On the basis of temperature and rainfall analysis it was determined that during the last decade there is the tendency to temperature increase with 0.4 – 0.7 oC over the “climate norm” (Fig. 1) and a good noticeable rainfall decrease (Fig. 2). 14 14 C) C) o 13 o 13 ( e ( e ur 12 ur 12 at at 11 er 11 y = 0.0039x + 4.7532 p mper 10 10 e y = 0.0119x - 12.183 T 9 Tem 9 1950 1960 1970 1980 1990 2000 1950 1960 1970 1980 1990 2000 Years Years Malko Turnovo Station Mean for 1961-1990 Linear Trend Burgas Station Mean for 1961-1990 Linear Trend Figure 1. Trend in annual temperature at Burgas and Malko Turnovo stations compared to climate norm (1961 – 1990) ) ) 1300 1300 m m m m y = -2.349x + 5312.3 1100 ( 1100 n ion ( t 900 tio 900 ita 700 pita 700 ip i c c e e 500 500 r y = -6.4607x + 13697 P Pr 300 300 1950 1960 1970 1980 1990 2000 1950 1960 1970 1980 1990 2000 Years Years Grudovo Station Mean for 1961-1990 Linear Trend Malko Turnovo Station Mean for 1961-1990 Linear Trend Figure 2. Trend in annual total precipitation at Grudovo and Malko Turnovo stations compared to climate norm (1961 – 1990) The temperature increase in the South eastern part of Bulgaria is more expressive in the mountain areas (Strandja Mountain) and weak in the Black Sea coastal zone. The precipitation decrease in the last years is more noticeable in the Strandja region compared to the rest of studied area. Climate 2 BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 It should be noted that high temperature and low precipitation conduct to drought in the region and appear unsuitable conditions for development of plants and water supply. To understand the different impacts that precipitation deficit has on ground water, reservoir storage, soil moisture, snow pack, and stream flow was used the Standardized Precipitation Index (SPI). In order to evaluate the intensity of drought was used the Ped index (Si) too. The SPI was designed to quantify the precipitation deficit for multiple time scales. These time scales reflect the impact of drought on the availability of the different water resources. Soil moisture conditions respond to precipitation anomalies on a relatively short scale, while groundwater, stream flow, and reservoir storage reflect the longer-term precipitation anomalies. The SPI was calculated for 12-month time scales. A drought event occurs any time the SPI is continuously negative and reaches an intensity where the SPI is -1.0 or less. The event ends when the SPI becomes positive. Fig. 3 shows the Standardized Precipitation Index (SPI) calculated for several meteorological stations located in the region. The general shape of the trend patterns is similar for all stations, but in the south part of the region there is remarkable tendency of negative SPI values. In accordance with the SPI values was determined a drought period from 1985 to 1994 in the studied region (Fig. 3). SPI - 12 month timescale y = -0.0272x + 0.6925 2.5 1.5 0.5 S P I -0.5 -1.5 SPI_Aytos Linear (SPI_Aytos) -2.5 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 19 20 SPI - 12 m onth tim escale y = -0.0165x + 0.4209 2.5 1.5 0.5 S P I -0.5 -1.5 SPI_Burgas Linear (SPI_Burgas) -2.5 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 2 4 6 8 0 195 195 195 195 196 196 196 196 196 197 197 197 197 197 198 198 198 198 198 199 199 199 199 199 200 SPI - 12 month timescale 2.5 y = -0.0137x + 0.3485 1.5 0.5 S P I -0.5 -1.5 SPI_Grudovo Linear (SPI_Grudovo) -2.5 952 954 956 958 960 962 964 966 968 970 972 974 976 978 980 982 984 986 988 990 992 994 996 998 000 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 Climate 3 BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004 SPI - 12 month timescale 2.5 y = -0.0344x + 0.8762 1.5 I 0.5 S P -0.5 -1.5 SPI_Malko Turnovo Linear (SPI_Malko Turnovo) -2.5 952 954 956 958 960 962 964 966 968 970 972 974 976 978 980 982 984 986 988 990 992 994 996 998 000 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 Figure 3.

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