Spatial and Temporal Variations in Precipitation and Aridity Index Series of Turkey
Annual and seasonal precipitation series and annual aridity index series of Turkey were investigated with respect to spatial and temporal variations for the period 1930–1993. Analysis of normalized precipitation anomalies was also performed for the 1994–2
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Abstract Annual and seasonal precipitation series and annual aridity index series of Turkey were investigated with respect to spatial and temporal variations for the period 1930-1993. Analysis of normalized precipitation anomalies was also performed for the 1994-2000 period. Semi-arid and dry sub-humid climatic conditions are dominant over the continental interiors and continental Mediterranean region of Turkey. Normalized annual and winter precipitation series have tended to decrease over a considerable part of Turkey since the early 1970s. For the normalized annual and winter precipitation anomaly series, wet conditions generally occurred during the 1940s, 1960s, late 1970s, early 1980s and mid-late 1990s, whereas dry conditions generally dominated over the early-mid 1930s, early-mid 1970s, mid-late 1980s, early 1990s, and 1999/2000 in most of Turkey. Spring precipitation series generally indicated an upward trend from the mid 1940s to the late 1960s at many stations and to 1980s at some stations. This period was generally followed by a downward trend at many stations. Significant decreasing trends showed up in the annual precipitation series of 15 stations and in the winter precipitation series of 14 stations, mostly over the Mediterranean rainfall region. Summer rainfall series have tended to increase significantly at 7 stations. There has also been a general tendency from humid conditions of around the 1960s towards dry sub-humid climatic conditions in the aridity index values of many stations of Turkey. At some stations over the Aegean part of the Mediterranean region, there has been a significant change from humid conditions to dry sub-humid or semi-arid climatic conditions.
Key Words: Turkey, Precipitation, Aridity Index, Seasonality, Variability, Trend and Persistent.
H.-J. Bolle (ed.), Mediterranean Climate © Springer-Verlag Berlin Heidelberg 2003
182
Murat Tiirke~
1 Introduction Increased frequencies and intensities of the drier conditions in about last twenty-five years may have been related to dominance of the anticyclonic circulation during the same time period, due to mainly increased atmospheric geopotential heights and decreased cyclone activity over the Turkey region (Tiirke~, 1998a). Furthermore, various climate models predict a decrease in precipitation for future changes over many parts of sUbtropics including eastern Mediterranean Basin and Turkey, particularly in the winter or generally during cool part of the year (ECSN, 1995; UKMO, 1995; lacobeit, 1996; UKMOIDETR, 1999). In addition to the long-lasting summer dryness of the Mediterranean type climate, considerable persistent dry conditions during about last three decades and secular decreasing trends in the annual and particularly in the winter precipitation totals make the natural and socio-economic system of Turkey more vulnerable to the projected changes in the mean climate. Projected changes in the climatic variability in addition to the mean climate and changes in land use, which should be considered in the future especially with
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