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Climate Conditions in the Biosphere Reserve “Srebarna” Region Julia Ivancheva, Anna Tzenkova, Ekaterina Koleva, Luchian Krastev National Institute of Meteorology & Hydrology Sofia , BULGARIA General climate conditions
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Julia Ivancheva, Anna Tzenkova, Ekaterina Koleva, Luchian Krastev
National Institute of Meteorology & Hydrology
Winter:t<5 oC110 – 120 days26 November– 12 March;mean January toC ––1.5 oC to –2.5 oC ; minimum t from –20 to –25 oC;microclimate variability – 5 – 6 oC; precipitation total is 105 mm. The snow cover onset is 13 November up to the mid-December – 48 days.
Spring: 5 oC<t<15 oC 12 March up to 2 May; Spring frosts are mostly in the end of March and in the beginning of April; 1 – 2 days with t < 5 oC, in 4 – 5 days of the month the tmin is under 2 oC; Precipitation total of the astronomic spring is about 122 – 128 mm, but for the biological – only about 70 mm.
Summer: t > 15 oC,about 2 May up to 2 October; Mean July temperature is 23 oC with maximum up to 39 – 40 oC; 80 – 85 % of the days (June – August ) t max > 25 oC, 40 – 45 % - with t max > 30 oC. The precipitation total is 159 mm. All in summer and autumn there are 4 – 5 rainless periods with average lasting about 16 – 20 days
Autumn: 5 oC < t < 15 oC– form about 2 October up to 26 November; Precipitation total of climatic autumn is 113 mm and of the biological – 66 mm; t < 10 oC about 15 – 20 November; The first autumn frosts set in still in the end of October or in the beginning of November
The annual value of I is about 22, which determine the region as moderate dry by the classification of Kirov and Kjuchukova (1955).
The values of I less then 20 determine the climate in a given region as semi arid. Such values are observed from during the four months - July – October for the period 1961-1990 and during May-August for the second period.1991-2004
For assessment of the aridity of the examined region Ped’s index is used. The values of Ped’s index have an increasing tendency. In the end of the last century the years 1992, 1994, 2000 are extremely dry. The same refer for 2001. For these years Ped’s index is above 2.
Long term variability of air temperature
It can be seen that the increasing trend of temperature during the considered period is well expressed.
In precipitation a slightly decreasing tendency is observed, but it is not significant.The last years in the region were warmer than the normal for the period of so-called “current climate” (1961-1990). Annual precipitation was aboutthe normal.During the last decade 1992, 1993, 1994, 1999 and 2002 winters were especially dry. Winter air temperature in this period was about 1.5o higher than the current climatic. Summer precipitation during the period 1991-2004 was about 88% of the normal and air temperature was with 1.2o above the normal
Long term variability of precipitation
The detected climate change tendencies may not be negative, but they may influence the reserve biota.
For example the decrease of the water area and its depth has as a consequence changes in the thermal regime of these water area. This leads to increasing of the temperature in the warm half-year, which will have as consequence increasing of the evaporation and in the cold - it is a cause for a lower temperature, which in some more shallow area can lead to lake freezing.
This problem can be resolved by carrying out of measures for cleaning up the lake bad as well as the vegetation of the “koch” if this is not harmful for the birds colonies.
The reserve is situated in the sphere of influence of industrial zones of Silistra, Calarash and even Ruse so the monitoring should not include only the basic meteorological elements but also of atmospheric pollution