Seasonal Rainfall Intensity and Frequency of Turkey

1. Seasonal Rainfall Intensity and Frequency of Turkey Dr. İhsan ÇİÇEK Dr. Necla TÜRKOĞLU Abdullah CEYLAN Neşe KORKMAZ

2. 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

3. 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

4. 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.

5. 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.

6. 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 1950’s. 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.

7. 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

8. 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

9. 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

10. 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

11. 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 > spring > winter > autumn • For 10,0 – 24,9 mm daily total rainfalls autumn > winter > spring > summer • For 25,0 - 49,9 mm daily total rainfalls autumn > winter > summer > spring • For 50,0 – 99,9 mm daily total rainfalls autumn > winter > spring > summer • For 100,0 mm ≥ daily total rainfalls autumn > winter = summer > spring • The average of autumn season is greater than almost all other seasons except the first class.

13. 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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