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Bulgarian Academy of Sciences. NATIONAL ... shown in bold and linear trend ... at Samokov (926 m a.s.l.), 5-year moving average shown in bold and linear trend ... – PowerPoint PPT presentation

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Title: BulgarianAcademyofSciences


1

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
2
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.
3
Location of weather stations used in the study
4
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.

5
Long-term variations in winter precipitation at
Borovetz (1264 m a.s.l.), 5-year moving average
shown in bold and linear trend
6
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
7
Long-term variations in snow depth at Samokov
(926 m a.s.l.), 5-year moving average shown in
bold and linear trend
8
Average snow depth at Borovetz (1264 m
a.s.l.) for different periods (1931-1990,
1961-2000 and 1982-1994)
9
SD(ti-t)/s
Thermal classification at Mt. Cherny vrah (2286
m a.s.l) for the period 1931-2000
10
40 - Normal winters   29 - Cold winters   31
- Warm winters
Frequencies of the consecutive classes
11
Since 1970 - 40 of the winters are classified
as warm. The last decade of the 20th century -
4 normal and 4 warm winters
12
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.
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