Spatial and temporal analysis of annual rainfall variations in Turkey

This paper presents the spatial and temporal characteristics of Turkey's annual rainfall data in the context of climatic variability. Basic data consists of the monthly rainfall totals from 91 stations with a record length ranging from 54 to 64 years, during the period 1930-1993. Basic elements of the rainfall climatology have been examined and then normalized rainfall anomaly series have been analysed for long-term trend and fluctuation and changes in runs of dry and wet years, for all of Turkey, rainfall regime regions, and individual stations. All regional mean rainfall anomalies have tended to vary in a statistically coherent manner over the rainfall regions. Area-averaged annual rainfall series have decreased slightly over all of Turkey and apparently over the Black Sea and Mediterranean rainfall regions. Results of the Mann-Kendall test, however, have indicated that none of the decreasing trends in the area-averaged rainfall series were significant. Annual series of 17 stations showed a significant trend in the mean and a majority of these trends are downward. Many of the stations have experienced marked low-frequency fluctuations in the annual rainfall. The concurrences of the dry conditions between the rainfall regions and the rest of Turkey have appeared generally during the early 1930s, the late 1950s, the early 1970s, around the 1980s and the early 1990s and of wet conditions generally during the period 1935-1945, around the 1960s and the late 1970s. The change points for the beginning of drier than normal conditions occurred in the early 1970s and early 1980s over most of the country. Annual rainfall variations over the rainfall regions except the Black Sea region were related closely to those of the rest of Turkey.