Seasonal Rainfall Intensity and Frequency of Turkey

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Seasonal Rainfall Intensity and Frequency of
Turkey

• Dr. Ihsan ÇIÇEK
• Dr. Necla TÜRKOGLU
• Abdullah CEYLAN
• Nese KORKMAZ

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RAINFALL DISTRIBUTION OF TURKEY
Total amount and distribution of rainfall in the
coastal parts are influenced by troughs and
frontal type mid latitude cyclones that are
associated with the prevailing upper level
westerly flows
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Mainland of Turkey is located in Mediterranean
macroclimatic region of subtropical zone. She has
a mean elevation of 1100 meters and is surrounded
by sea on three sides. Due to its complex
topographic features, its proximity to water,
being in a transition zone for different large
scale weather circulations systems, spatially
variable climatic features appear to be
dominant over the country
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Frontal Mediterranean cyclones associated with
the southwesterly air flows create favorable
conditions for heavy rainfall and thunderstorms
in the southern and western coastal parts of the
country in late autumn and early winter.
Orographic lifting is also a main cause of
heavy rainfall production that intensity of the
rainfall is further enhanced when the
conditionally unstable and extreme moist air
pushed upslope into higher terrain along the
Mediterranean coast. During the winter
season, she is under the influence of
Siberian high pressure centre bringing cold
air which produces heavy snow on the
mountains while summer seasons it is under the
influence of Arabian Gulf high pressure
which results in high temperature over the
continent. On the other hand, during the
transition seasons atmospheric instability
prevails producing severe floods across the
country.
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Frontal Mediterranean cyclones associated with
the southwesterly air flows create favorable
conditions for heavy rainfall and thunderstorms
in the southern and western coastal parts of the
country in late autumn and early winter.
Orographic lifting is also a main cause of
heavy rainfall production that intensity of the
rainfall is further enhanced when the
conditionally unstable and extreme moist air
pushed upslope into higher terrain along the
Mediterranean coast. During the winter
season, she is under the influence of
Siberian high pressure centre bringing cold
air which produces heavy snow on the
mountains while summer seasons it is under the
influence of Arabian Gulf high pressure
which results in high temperature over the
continent. On the other hand, during the
transition seasons atmospheric instability
prevails producing severe floods across the
country.
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Method

• In this study, the daily rainfall data of
  1960-1995 periods from 77 meteorological stations
  in Turkey were used in order to show the seasonal
  distribution of daily rainfalls in various
  intensities. The stations settled in city centers
  were selected mainly because of their long term
  observation records. But, the records of most of
  these stations had some missing data in 1950s.
  So, beginning date for the data was chosen as
  1960. The data obtained from Turkish State
  Meteorological Service were divided into
  different intensity classes to derive the
  seasonal daily rainfall intensity and then
  recurrence period for each class were identified.
  Five rainfall intensity classes were to show
  rainfall intensity. They were 0,1 mm, 10,0 mm,
  25,0 mm, 50,0 mm and 100,0 mm. The number of
  seasonal rainy days and their recurrence periods
  for the stations were mapped. Also, the rainfall
  intensity distribution maps were drawn related to
  these five intensity groups.
• Also, in order to analyze the average rainfall
  quantity in the range of classes, their
  percentages were determined. The classes were
• 0,1mm 9,9 mm less intensive rainfall
• 10,0 mm 24,9 mm normal rainfall
• 25,0 mm 49,9 mm less intensive shower
• 50,0 mm 99,9 mm intensive shower
• 100,0 mm and above more intensive shower.
• Thus, the recurrence period of rainfalls in a
  certain class, which is not seen in analysis of
  the number of rainy days, was obtained.

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Rainfall Intensity and Frequency in Winter
Figure1 Frequency of daily precipitation
according to precipitation intensity in
winter 1a Number of precipitation day less-equal
0.1 mm in winter 1b Number of precipitation day
less-equal 10.0 mm in winter 1c Frequency of
daily precipitation less-equal 25.0 mm in
winter 1d Frequency of daily precipitation
less-equal 50.0 mm in winter 1e Frequency of
daily precipitation less-equal 100.0 mm in winter
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Rainfall Intensity and Frequency in Spring
Figure 2 Frequency of daily precipitation
according to precipitation intensity in
spring 2a Number of precipitation day less-equal
0.1 mm in spring 2b.Number of precipitation day
less-equal 10.0 mm in spring 2c Frequency of
daily precipitation less-equal 25.0 mm in
spring 2d Frequency of daily precipitation
less-equal 50.0 mm in spring 2e Frequency of
daily precipitation less-equal 100.0 mm in spring
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Rainfall Intensity and Frequency in Summer
Figure 3 Frequency of daily precipitation
according to precipitation intensity in
summer 3a Number of precipitation day less-equal
0.1 mm in summer 3b.Number of precipitation day
less-equal 10.0 mm in summer 3c Frequency of
daily precipitation less-equal 25.0 mm in
summer 3d Frequency of daily precipitation
less-equal 50.0 mm in summer 3e Frequency of
daily precipitation less-equal 100.0 mm in summer
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Rainfall Intensity and Frequency in Autumn
Figure 4 Frequency of daily precipitation
according to precipitation intensity in
autumn 4a Number of precipitation day less-equal
0.1 mm in autumn 4b.Number of precipitation day
less-equal 10.0 mm in autumn 4c Frequency of
daily precipitation less-equal 25.0 mm in
autumn 4d Frequency of daily precipitation
less-equal 50.0 mm in autumn 4e Frequency of
daily precipitation less-equal 100.0 mm in autumn
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Result

• The average rate of rainfall intensity classes
  can be ordered by seasonal occurrence as follows
• For 0,1 9,9 mm daily total rainfalls summer gt
  spring gt winter gt autumn
• For 10,0 24,9 mm daily total rainfalls autumn
  gt winter gt spring gt summer
• For 25,0 - 49,9 mm daily total rainfalls autumn
  gt winter gt summer gt spring
• For 50,0 99,9 mm daily total rainfalls autumn
  gt winter gt spring gt summer
• For 100,0 mm daily total rainfalls autumn gt
  winter summer gt spring
• The average of autumn season is greater than
  almost all other seasons except the first class.

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• It can be seen that the lower intensity rainfalls
  are common over the country. In most parts of the
  country, the percentage of number of rainy days
  for 0,1 9,9 mm rainfalls is greater than 80.
  If the ratio of 10,0 24,9 mm rainfall intensity
  class, defined as normal rainfall, to be added
  the percentage exceeds 95. It means that the
  occurrence probability of intensive rainfalls is
  very low over Turkey. Because of the low
  occurrence probability, 50,0 mm and above
  rainfall were not taken into account. However,
  building infrastructures mainly depend on these
  types of rainfalls. Turkey has mostly experienced
  flood hazards caused by inadequate infrastructure
  systems.

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