Trend analysis of precipitation data in Turkey and relations to atmospheric circulation: (1955–2013)
From Firenze University Press Journal: Italian Journal of Agrometeorology
Muhammet Topuz, Hatay Mustafa Kemal University, Faculty of Arts and Sciences, Geography Department
Haralambos Feidas, Aristotle University of Thessaloniki, School of Geology, Department of Meteorology and Climatology,
Murat Karabulut, Kahramanmaras Sutcu Imam University, Faculty of Arts and Sciences, Geography Department
Precipitation is a highly variable climatological element both in space and time (Karabulut and Cosun, 2009). This variability results from changes in atmospheric circulation and complex topographic characteristics and affects many aspects of human life e.g. water resources, aridity and desertification conditions, agriculture (Sariş et al., 2010). The global mean precipitation is likely to increase due to increases in the atmospheric moisture-holding capacity associated with global warming (IPCC, 2007). However, future changes in precipitation will not be uniform. An increase in annual mean precipitation is likely by the end of the 21st century over the high latitudes, the equatorial Pacific and in many mid-latitude wet regions, while a decrease is expected in many mid-latitude and subtropical dry regions (IPCC, 2014). Observations indicate an area-averaged precipitation increase since 1951 over the mid-latitude land areas of the Northern Hemisphere (IPCC, 2014).
The Mediterranean basin is deemed vulnerable to climate changes, due to the diverse topography and its position at the interface between the temperate climate of southern Europe and the arid climate of North Africa (Giorgi and Lionello, 2008). The winter precipitation in the Mediterranean region has experienced an overall de-creasing trend during the last few decades (Philandras et al., 2011; Norrant and Douguédroit 2006; Piervitali et al., 1997; Palutikof et al., 1996). The eastern Mediterranean has tended towards drying conditions since the mid 20th century (Feidas et al., 2007; Tomozeiu et al., 2005; Alexandrov et al., 2004).Turkey exhibits spatial differences in precipitation be-tween the southern coasts and the northern and western regions (Tayanç et al., 2009; Partal and Kahya 2006) and between coastal and mountainous regions (Türkeş 1996; Xoplaki et al., 2000; Kadioglu 2000). Toros et al (1994) used seasonal and annual precipitation data of 68 stations in the west part of Anatolia in Turkey for the period 1930–1992 to show a decline in precipitation after 1982 that was attrib-uted only to a fluctuation in precipitation. Kadioglu (1993) analyzed monthly precipitation data of 18 Turkish stations for the period 1929–1990 and found an overall decrease in winter precipitation and an increase in spring precipitation. Türkeş (1996) have conducted a spatiotemporal analysis of annual precipitation variability using monthly precipitation series from 91 stations in Turkey, during the period 1930–1993. They found a slight decrease in area-averaged annual precipitation series averaged over Turkey. Kadioglu (2000) has found a decrease in winter precipitation for Anatolia and Black Sea region and an increase for Mediterranean coastal regions for the period 1931–1990.
Partal and Kahya (2006) applied a trend analysis to long precipitation time series (1929–1993) of 96 stations in Tur-key and found a significant decreasing trend in the annual rainfall for southern and western Turkey as well as a the Black Sea coast. In another study, Türkeş et al., (2007), detected downward trends in annual and winter rainfall totals and a general upward trend in the spring, summer and autumn rainfall for the period 1930–2002. There are many reports on the subject published by public authorities. Toros (2012) examined expected spatiotemporal changes in precipitation time series of 165 Turkish stations for the period 1961 to 2008 in order to assess the impact of climate change on precipitation over Turkey. He found a significant decreasing trend at the 35, 13 and 12% of the stations in the winter, annual and rainy period precipitation totals, respectively, with some oscillations during the examined period (decrease during 1968–1973 and 1998–2008 and increase, during 1973–1981 and 1989–1998). In contrast, a significant increase was detected at the 19, 3 and 4% of the stations in the autumn, rainy peri-od and annual precipitation, respectively. It was concluded that climate dynamics such as the effect of NAO on the tracks of the Mediterranean storms are among the main causes of the precipitation variability in Turkey. According to Efe et al. (2015), trend analysis of the annual total precipitation for the period 1950–2013 showed a general increasing tendency in precipitation on the coast-line, mainly in the regions of Marmara and Black Sea. In contrast, a decreasing trend was found in annual total precipitation inland that could be a sign of evolving drought conditions. Sensoy et. al. (2013), found decreasing trends during the period 1960–2010 for annual precipitation totals in the northern Turkey, whereas Mediterranean Sea, Aegean Sea and south-eastern Anatolia regions presented decreasing trends. On the other hand, the number of days with heavy precipitation shows an upward trend in most of the stations with the exception of the Southeastern Anatolia and Aegean Sea regions.
Atmospheric circulation is a significant contributor to the precipitation variability in Mediterranean. Many studies have detected an important link between Mediterranean precipitation and various large and regional-scale circulation patterns such a North Atlantic Oscilla-tion (NAO), Mediterranean Circulation (MC), North Sea — Caspian Pattern (NCP) and Mediterranean Oscillation (MO) (Greatbach 2000; Cullen et al., 2000; Visbeck et al., 2000; Trigo et al., 2002; Erlat 2002; Karabork et al., 2002; Xoplaki 2002; Krichak and Alpert 2005; Türkeş and Er-lat 2005; Turp 2006; Bachmann 2007; Feidas et al., 2007; Lopez-Moreno et al., 2011; Karakoç and Tagil 2014). The variability of winter precipitation in Turkey (especially in the northern Marmara, northwestern Mediterranean and Central Anatolia) was found to be strictly related to the variability of NAO indices (Türkeş and Erlat 2005, 2006).This study aims primarily at investigating recent trends in the mean seasonal and annual precipitation observations in Turkey for the longest length of historical homogenous precipitation data available for analysis (1955–2013), using two statistical tests.
Another objective is to examine any likely link between precipitation variability in Turkey and atmospheric circulation using five atmospheric circulation indices.
DOI: https://doi.org/10.13128/ijam-887
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