INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 23: 1045–1055 (2003) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.910 REDEFINING THE CLIMATE ZONES OF TURKEY USING CLUSTER ANALYSIS YURDANUR UNAL, a, * TAYFUN KINDAP b and MEHMET KARACA b,c a ITU, Department of Meteorology, 80626 Maslak Istanbul, Turkey b ITU, Eurasia Institute of Earth Sciences, 80626 Maslak Istanbul, Turkey c ITU, Maden Fak. Department of Geology, 80626 Maslak Istanbul, Turkey Received 19 September 2001 Revised 16 February 2003 Accepted 3 March 2003 ABSTRACT Climate zones of Turkey are redefined by using the mathematical methodology of cluster analysis. Data from 113 climate stations for temperatures (mean, maximum and minimum) and total precipitation from 1951 to 1998 are used after standardizing with zero mean and unit variance, to confirm that all variables are weighted equally in the cluster analysis. Hierarchical cluster analysis is chosen to perform the regionalization. Five different techniques were applied initially to decide the most suitable method for the region. Stability of the clusters is also tested. It is decided that Ward’s method is the most likely to yield acceptable results in this particular case, as is often the case in climatological research. Seven different climate zones are found, as in conventional climate zones, but with considerable differences at the boundaries. Copyright  2003 Royal Meteorological Society. KEY WORDS: cluster analysis; climate zones; Turkey 1. INTRODUCTION Many climatological studies have used a variety of data to define climatic types and delineate zones of similar climate. Several methods have also been applied for the climatic zones. The most famous examples are the Koeppen and Thornthwaite classifications. A principal advantage of these approaches is that they directly and quantitatively specify the climate types. A disadvantage is that the classification rules are subjectively formulated, and thus open to question. In this study, an alternative approach including cluster analysis methodology has been used. Cluster analysis applied to meteorological variables is a suitable approach for redefining the climate divisions, and its use is becoming increasingly more common in atmospheric research (Kalkstein et al., 1987; Fovell and Fovell, 1993). Choosing appropriate data to cluster is an initial consideration in cluster analysis. In climate classification, the variability of long-term precipitation and temperature data are the most readily available variables (Fovell and Fovell, 1993). The seven climate zones over Turkey, shown in Figure 1, are those that have conventionally been accepted by Turkish climatologists since the beginning of the 20th century (Erin¸ c, 1984): 1. The Black Sea region. 2. The Marmara region. 3. The Aegean region. * Correspondence to: Yurdanur Unal, ITU, Department of Meteorology, 80626 Maslak Istanbul, Turkey; e-mail: sunal@itu.edu.tr Copyright  2003 Royal Meteorological Society