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Effects of North Atlantic Oscillation on Precipitation and Stream Flow at Büyük Menderes Basin

Effects of North Atlantic Oscillation on Precipitation and Stream Flow at Büyük Menderes Basin. Dr. Necla TÜRKOĞLU Dr. Gürcan GÜRGEN Dr. İhsan ÇİÇEK Abdullah CEYLAN. Positive NAO. Negative NAO. Physical Map of Büyük Menderes Basin. Data and Method.

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Effects of North Atlantic Oscillation on Precipitation and Stream Flow at Büyük Menderes Basin

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  1. Effects of North Atlantic Oscillation on Precipitation and Stream Flow at Büyük Menderes Basin Dr. Necla TÜRKOĞLU Dr. Gürcan GÜRGEN Dr. İhsan ÇİÇEK Abdullah CEYLAN

  2. Positive NAO Negative NAO

  3. Physical Map of Büyük Menderes Basin

  4. Data and Method • In this study, precipitation and stream flow data of Büyük Menderes Basin for the period 1968-1999 were used. The monthly total precipitation data were obtained from Aydın Meteorological Station (operated by Turkish State Meteorological Service) and the stream flow data were obtained from Kocarlı Bridge stream flow observation station (operated by General Directorate of National Hydraulic Works). The Kocarlı Bridge station was mainly preferred because of its location near the river source. It also represents the main characteristics of all basins. The period of 1968-1999 was studied since the stream flow data is available for this period

  5. Mann-Kendall serial correlation method was used to identify the trends in precipitation and stream flow (WMO 1966, Sneyers 1990). Using the ordered numbers for all value, we can find a number denoting the number of elements which can be found by calculating the number of sequences. Test statistics value can be shown as: • The distribution function of test statistics value is an asymptotic normal ally under the null hypothesis. Mean value of the distribution function and the variance can be calculated as follows:

  6. and If the test statistics value U(t) calculated as: • Then according to two sided type of the null hypothesis is rejected for the greater value|u(t)|. If the calculated u(t) value is meaningful in the significance level 0,05 or 0,01 then depending on theu(t) eitheru(t)>0 or u(t)<0, increasing or decreasing trend can be accepted as statistically significant. Using theu(t) and the test statistics u(t) obtained by subsequent analysis of Mann-Kendall trend test, trends in annual and seasonal flow/precipitation has shown graphically. If u(t) and u’(t) curves coincide, it means that there is no trend in the given sequence. However, if these curves diverge from each other then there is a significant trend. The divergence points of the curves denote the starting date of increasing or decreasing trend. This is called the sequential version of the Mann-Kendall test (Sneyers, 1990).

  7. In this study, stream flow and precipitation data were normalized in order to compare the annual and seasonal stream flow/precipitation data to the NAO indices. Normalized precipitation and stream flow data were calculated by the equation where; x = the total precipitation/flow value in the given year ( or season ) for a station, x¯ = the average precipitation/flow value in the given year ( or season ) for a station, σ = annual ( or seasonal ) standard deviation value of precipitation/flow data.

  8. The relation between the NAO and precipitation/flow data as well as the magnitude and direction of this relation were calculated by using Pearson correlation coefficient test. This correlation denotes the relation between the variables. Correlation coefficient is a value between ±1. If is close 1, then the parallelism between the variables accepted as perfect and in the same direction. If is close -1, then the parallelism between the variables accepted as perfect and in the opposite direction. If it is close 0, then there is a weak parallelism between the variables (Kabukçu, 1994). To identify the significance level of correlation coefficients between the NAO andprecipitation /stream flow data, the Student-t test was used. In this test, 0,05 and 0,01 was taken as significance level The correlation coefficient was calculated by

  9. Relation between the NAO and Stream Flows in seasonal and annual basis Winter (red line precipitation, blue line stream flow, green line NAO) * 0.05 significance level

  10. Relation between the NAO and Stream Flows in seasonal and annual basis Spring (red line precipitation, blue line stream flow, green line NAO) * 0.05 significance level

  11. Relation between the NAO and Stream Flows in seasonal and annual basis Summer (red line precipitation, blue line stream flow, green line NAO) * 0.05 significance level

  12. Relation between the NAO and Stream Flows in seasonal and annual basis Fall (red line precipitation, blue line stream flow, green line NAO) * 0.05 significance level

  13. Relation between the NAO and Stream Flows in seasonal and annual basis Annual (red line precipitation, blue line stream flow, green line NAO) * 0.05 significance level

  14. Thank you for your attention !

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