Author: Meral BüYüKYILDIZ, Ali BERKTAY
Publishing Date: 2004
Volume 19 Issue 2
In this study, some trend analyses were made to determine the variations of monthly rainfall data belonging to Sakarya Basin which is one of the big and important basin in Turkey. Data records of monthly rainfall from 1960 to 2000 of 25 stations in Sakarya Basin were analyzed using four different non-parametric methods namely Sen’s T, Spearman’s Rho, Mann-Kendall and Seasonal Mann- Kendall to demonstrate the existence of any possible trends. Trend analyses were also divided into two phases. In the first phase, the monthly rainfall data was evaluated annually. In the second phase, variation of rainfall series belonged to 25 stations was evaluated for each month. Homogeneity of trends in monthly rainfall was also tested by using a procedure developed by Van Belle and Hughes. The linear slopes (change per unit time) of trends were calculated by using a trend slope method suggested by Sen. The starting points of trends for each month were defined by using the Mann-Kendall Rank Correlation test. Consequently, downward trends at the 0.05 significance were found at half of the investigated stations. Trends were found at total 44 months with in the months in which some trend exist at the 0.05 significance level in total 300 month. 20% of them trends is upward whereas 80% downward. The upward trends were found in October period at 6 stations and August period at 3 stations. Trends of remaining 35 months were downward.
Key Words: “Trend; Mann-Kendall; Sen’s T; climate change “