IMPACTS OF CLIMATE VARIABILITY

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IMPACTS OF CLIMATE VARIABILITY ON THE RUNOFF
IN THE SOUTH EASTERN PART OF BULGARIA
Bernardo Lizama Rivas National Institute of
Meteorology and Hydrology, Sofia Ivanka
Koleva-Lizama University of Forestry, Sofia
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The aim of the paper is to study the runoff
variability in respect to climate change in the
south eastern Bulgarian watersheds. To
investigate possible impacts of climate
variability on the runoff were used long term
data (1952-2002) from several hydrological
(Razhitsa, Kameno, Prohod, Svetlina, Fakiya,
Zidarevo, Veselie, Zvezdets and Gramatikovo) and
meteorological (Aytos, Burgas, Grudovo, Tsarevo
and Malko Turnovo) gauging stations.
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The most important rivers in this region are
Dvoynitsa, Hadzhiyska, Aheloy, Aytoska,
Rusokastrenska, Sredetska, Fakiyska, Ropotamo,
Diavolska, Veleka and Rezovska rivers. The
streams which debouch to the Black sea have
rather diverse forestal communities.
The relief is characterised by lowland which
cover the eastern and middle part of the region
sea coast, low plains and low mountainous area.
Location of the Study Region
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The climate in the South Eastern region is
mainly transitional Mediterranean climate. The
topography in the south part of the region in
concern (Strandja Mountain), plays an important
role in the distribution of the
precipitation. The study on long time series of
hydrological data in the context of climate
variability is very difficult task because of by
disturbance mans activity. During the process
of time series selection was established that the
streamflow in the Veleka River at Zvezdets and
Gramatikovo is not disturbed, but in the
catchments of the North part of the studied
region exists relatively small disturbances, in
view of that, these catchments were not included
in this study.
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Table 1. The basic statistical parameters for the
catchments
Area (A)
The runoff regime in the studied catchments is
characterized by considerably variability. In
Table 1 are shown the statistical parameters of
annual runoff (mean, standard deviation,
skewness and the extremes values) for studied
period for the main gauging stations.
,
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In order to study the river runoff, variability
in respect to climate change, the warm and humid
conditions during the 50 last years were
analyzed. To examine the temperature and
precipitation variability, the time series of
their anomalies are obtained (Fig. 1, 2).
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• In the catchments the temperature increase is
  more expressive in the mountain areas (Strandja
  Mountain)

Fig. 1. Time series of temperature anomaly at
Grudovo and Malko Turnovo stations
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• The precipitation decrease is more noticeable in
  the Strandja region compared to the rest of
  studied area.

Fig. 2. Time series of precipitation anomaly at
Grudovo and Malko Turnovo stations
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• In order to quantify the precipitation deficit
  for different time scales the Standardized
  Precipitation Index (SPI) was used.
• In Fig. 3 is given the SPI for 3, 6 and 12 month
  time scales and its trends, from where is noted
  that the tendency to drought is evident in the
  studied region.

Fig. 3. Standardized Precipitation Index (SPI)
for 3, 6 and 12 month timescales and its trends
at Malko Turnovo station
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Fig. 4. Anomaly of annual runoff in the Veleka
River at Gramatikovo

• In Fig. 4 are shown the anomalies of annual
  runoff, the linear trend and the 5 years moving
  average for the Veleka River at Gramatikovo.
• It was found that up to 1975 prevail positive
  runoff anomalies. From 1976 to 1994 predominate
  negative runoff anomalies which characterize
  exceptionally a low waters period, the most low
  values are observed in 1993 (-6.4 m3/s). From
  1995 to 2002 the streamflow fluctuations are
  rather sudden with exceptional maximum in 1998
  (12.7 m3/s ).
• For the whole period 1952 2002 is observed a
  negative trend for the annual runoff.

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• CONCLUSION
• The analysis of long time series of river
  runoff, air temperature and precipitation allows
  us to draw some conclusions.
• The temperature increase is more expressive in
  the mountain areas (Strandja Mountain) and weak
  in the Black Sea coastal zone.
• The precipitation decrease is more noticeable in
  the Strandja region compared to the rest of
  studied area.
• The Standardized Precipitation Index (SPI) for 3,
  6 and 12 month timescales shows that the tendency
  to drought is evident in the South Eastern
  Bulgaria.
• For the whole period 1952 2002 is observed a
  negative trend for the annual runoff.
• There is the tendency to weak temperature
  increase and good noticeable rainfall and runoff
  decrease, which bring to drought in the region.