BulgarianAcademyofSciences - PowerPoint PPT Presentation

Title: BulgarianAcademyofSciences


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Bulgarian Academy of Sciences NATIONAL INSTITUTE
OF METEOROLOGY AND HYDROLOGY Winter climate
variability and classification in the Bulgarian
mountainous regions
NADEZHDA PETKOVA, EKATERINA KOLEVA, VESSELIN
ALEXANDROV E-mail Nadejda.Petkova_at_meteo.bg
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Introduction
? Winter conditions play a key role in a number
of environmental and socioeconomic systems in
each country, especially in the mountain regions.
Snow determines the timing of peak river
discharge during the melting of the snow pack in
the spring. ? Lately, there is an increasing
interest in documenting and understanding the
problems of snowiness and thermal conditions of
winters in Bulgaria in response to increased
frequency and severity of droughts affecting a
region. ? The objective of this study was to
investigate climate variability and trend in
winter conditions in mountainous regions of
Bulgaria. On the base of mean winter air
temperature, winters in the Bulgarian mountains
were analyzed and classified.
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Location of weather stations used in the study
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Data and Method

• ? The data series have been compiled for 16
  mountain weather stations located mainly above
  800 m a.s.l. and include mean winter air
  temperature, winter precipitation, maximum snow
  cover depth and duration. The majority of data
  series cover the period from 1931 to 2000.
• ? The winter climate conditions were presented
  on the base of means for the investigated
  period. A comparison was also carried out of
  mean winter conditions during the 30-year normal
  period 1961-1990 and the 1982-1994 warm/dry
  period - an analogue of climate warming.
• ? The Mann-Kendal non-parametric test and the
  Spearman correlation coefficients, assuming the
  95 probability level were applied.
• ? As classification criterion the half value of
  SD (1/2s) from mean winter temperature for each
  consecutive class was accepted as follows
• -0.5ns ti t0.5ns,
  where n 1, 2, ,5.
• The eleven-degree scale for winter severity was
  taken.

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Long-term variations in winter precipitation at
Borovetz (1264 m a.s.l.), 5-year moving average
shown in bold and linear trend
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Long-term variations in winter air temperature at
Mt.Mussala (2925 m a.s.l.) 5-year moving
average shown in bold and linear trend
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Long-term variations in snow depth at Samokov
(926 m a.s.l.), 5-year moving average shown in
bold and linear trend
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Average snow depth at Borovetz (1264 m
a.s.l.) for different periods (1931-1990,
1961-2000 and 1982-1994)
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SD(ti-t)/s
Thermal classification at Mt. Cherny vrah (2286
m a.s.l) for the period 1931-2000
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40 - Normal winters   29 - Cold winters   31
- Warm winters
Frequencies of the consecutive classes
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Since 1970 - 40 of the winters are classified
as warm. The last decade of the 20th century -
4 normal and 4 warm winters
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Conclusions

• ? Winter precipitation and snow cover parameters
  have a decreasing trend. In many of the weather
  stations winter precipitation shows a significant
  decrease. Winter temperature has an increasing
  tendency.
• ? It can be concluded that the decrease observed
  in the snow cover depth and duration is mainly
  due to a decrease in winter precipitation and an
  increase of winter air temperature.
• ? In the Bulgarian mountain regions as normal
  winters can be classified about 40 of all
  considered winters. Almost the half of the other
  winters (31 ) is classified as warm and 29 as
  cold ones. Since 1970 the cold winters have
  decreased by 8-9 in the selected regions.