Abstract

Turkey lies in a critical region that is projected to be one of the most vulnerable to the impacts of climate change in the Mediterranean region. In this study, climatic zones of Turkey were classified with respect to their climatic and meteorological characteristics. The Thornthwaite precipitation efficiency index was used to identify aridity and humidity characteristics. The index values were mapped to determine climate zones and associated climate classes and to evaluate change in time and space. Two distinct periods (1950–1980 and 1981–2010) were used to assess climatic conditions and evaluate historical changes. The Thornthwaite index indicated significant spatial variations of climate parameters across Turkey with varying degrees of vulnerability. The results indicate that during the 60-year time frame, no arid zones had been experienced in Turkey. On the other hand, an increase of semi-dry and dry humid zones and a decrease of semi-dry–less humid, semi-humid and humid zones had been experienced. In this context, it is important to note that semi-arid zones have increased substantially (approximately 14%) between the two 30-year periods.

INTRODUCTION

Climate is a natural resource vital to our well-being, health and prosperity. Climate change can cause climatic hazards such as droughts and floods in the world. The information gathered, managed and analysed by National Meteorological and Hydrologic Services (NMHS), in collaboration with other regional and international stakeholder organizations and programs, helps decision-makers and end users in their activities and projects for planning and adaptation to expected conditions. As stated in the World Meteorological Organization report (WMO 2016), in this way, decisions may be taken into consideration for planning which reduce risks and optimize socio-economic benefits.

According to the results of the Intergovernmental Panel on Climate Change (IPCC), late 20th century levels of temperature will increase about 2 °C or more in some parts of the world if climate change adaptation cannot be achieved as it is expected. Some parts of the world may gain benefit from this temperature increase. However, if this increase reaches 4 °C or more, some other parts would be faced with risk of agricultural productivity, which in turn would negatively impact global food security. Moreover, renewable water resources would reduce and competition for water among sectors would increase starting from most dry regions (IPCC 2014).

The focus area of this study is Turkey, located in the eastern part of the Mediterranean region, which is particularly vulnerable to climate change (Figure 1). The Mediterranean region has been identified as one of the main climate change hotspots responsive to climate change due to water scarcity, concentration of economic activities in coastal areas, and reliance on climate-sensitive agriculture (EEA 2017).

Figure 1

The coverage and location of the study area.

Figure 1

The coverage and location of the study area.

Turkey is characterized by highly variable climatic conditions, and experiences semi-dry Mediterranean, semi-humid, and humid conditions. For the country as a whole, there is no dry zone. Most of the central Anatolia and some parts of the east and southeast of Turkey have experienced semi-dry periods, whereas the northeast Black Sea coastal areas have a relatively wetter climate (Deniz et al. 2011).

The coastal areas of Turkey, bordered by the Aegean Sea and the Mediterranean Sea, are characterized by Mediterranean climate with hot, dry summers and mild to cool, wet winters. The Black Sea region has a temperate oceanic climate with warm, wet summers and cool to cold, wet winters. Climate conditions can be harsh in the more arid interior regions. Mountains close to the coastal zone prevent propagation of maritime impacts into inland areas, resulting in a continental climate with sharply contrasting seasons in the central Anatolian plateau of the interior of Turkey. Winters on this plateau are especially severe. In this context, the coastal areas are characterised by milder climates, the inland Anatolian plateau experiences extremes of hot summers and cold winters with limited rainfall (Sensoy et al. 2016).

Both the observed decreasing trends in the Mediterranean Basin and Turkey's precipitation in winter and the rising trend in frequency for the occurrence of low intensity precipitation events in Turkey are the most substantial points in terms of the precipitation changes and variability (Turkes et al. 2009). These have also been indicating increased drying and desertification in the western and southern regions of Turkey, characterized generally by the Mediterranean climate.

Future climate conditions of Turkey are projected to be worsened in the fourth Assessment Report of IPCC. The report mentions already worsened climate conditions in Europe. According to the findings, Europe's average temperature has already risen 1 °C, which is above the global average. Moreover, the southern part of Europe has dried 20% in the last century. Water balance has changed as a result of the binary effects of climate change and changes in land use patterns. Thereof, the stream flow would decrease in south-east Europe, including Turkey (IPCC 2007). The Mediterranean climate zone is one of the most vulnerable zones to the climate change. Based on the IPCC findings, Turkey's climate change impacts are mainly characterized by an increase in temperature and a decrease in precipitation. The land use patterns of Turkey have been changing due to overpopulation and economic circumstances. As a result, the decrease of water resources may cause considerable water shortage, and Turkey is expected to be a ‘water scarce’ country.

The results of a recent study (Selek & Tuncok 2014) show that average temperatures within the Seyhan basin, which is located in the southern part of Turkey, can increase as much as 5 °C within the 2010–2100 time frame. In this context, it is apparent that many parts of the basin will suffer from significant water shortages. This will be further exacerbated by rising demand of limited water resources in many sectors, particularly irrigation water demand of the agricultural sector. Precipitation over the basin is expected to drop by 35% in the lower-segments, 23.5% in the middle-segments and 17% in the upper-segments within the 2010–2100 time frame, which will worsen the conditions for local communities and wildlife.

It is important to implement a structured approach to evaluate variations in climatic conditions. In similar applications, a climate index driven approach (Deniz et al. 2011) was used to characterize variations in climate. Typically, climate indices which are diagnostic tools to define the state of a climate system and understanding of the various climate mechanisms are described through climate variables. In parallel with this methodology, Turkes et al. (2016) examined consecutive periods of 1950–1980 and 1981–2010 via statistical comparative analysis and showed an increase in air temperature and a decrease in precipitation through central Anatolia.

There are many climate classification methods dating back to the 1900s which use spatial variations of hydro-meteorological parameters to differentiate climatic zones. For example, Köppen (1923), De Martonne (1926), Thornthwaite (1948), Erinc (1965) and Trewartha (1968) are only a few of the methodologies to be applicable. However, some difficulties have been experienced to apply any specific method to the study area due to lack of representative data sets. The respective formulations require the use of data sets, which are at times difficult to access and represent at the river basin scale. In this context, the Thorthwaite precipitation efficiency index, which can be accurately represented with available data sets, was used in this study as an indicator for the differentiation of climatic zones in time across Turkey.

The main objectives of this study were classification of climatic zones in Turkey with respect to their climatic and meteorological characteristics and delineation of temporal and spatial changes in the index values for water resources planners, irrigation water managers, water authorities, decision makers, etc. For this purpose, the areal change of climatic zones was evaluated in time by using observed historical hydro-meteorological data. In this study, the Thornthwaite index was used to identify aridity and humidity characteristics of basins and to map temporal and spatial changes. Two distinct periods (1950–1980 and 1981–2010) were used to assess the climatic conditions and evaluate historical changes.

METHODS AND DATA SETS

In order to determine climate change with its past, present and future, there have been a number of methodologies used including statistical analysis of datasets, marine biology, tree ring chronologies, etc. (Brown et al. 2011; Gholami et al. 2015; Turkes et al. 2016).

The Thornthwaite climate classification index (Thornthwaite 1948) was used to represent aridity and humidity characteristics, through use of precipitation, evapotranspiration and temperature. Thornthwaite index values were used to define climate zones and associated climate classes. Moreover, water budget components so called surplus and deficit were calculated by a water balance model. In order to interpret results with hydrological and regional perspectives, river basin and country scales were used respectively.

To determine the change of climate zones in time across Turkey, two distinct periods (1950–1980 and 1981–2010) were selected. The 30-year climate normal could be interpreted as the true background state, offset by decadal and longer-term tendencies, and further biases are introduced by inter-annual variability as well as random and systematic errors and for stationary time series. Since 1956, the WMO has recommended that each member country re-compute their 30-year climate normal during 10-year periods (Arguez & Vose 2011). It is important to note that a time interval of 30 years was selected in-line with international standards. The main driver behind the use of a 30-year time frame is the ability to set climate ‘normal’ as reference points, and to compare current climatological trends to that of the past or what is considered as ‘normal’. WMO (2016) stated clearly that the 30-year period is long enough to filter out any inter annual variation or anomalies, but also short enough to be able to show longer climatic trends.

As stated in the objectives, this research was focused to identify the areal changes in climate zones, both at the basin- and country-scales. Basin scale was used because it is the most representative geographical definition to evaluate hydrological processes such as droughts, floods, hydro-climatology, etc. Country scale was then used to evaluate the results of the study at a macro level.

Climate classification assessments require not only long-term historical records but also representative spatial coverage across geographic regions. In this context, systematic measurements administered by the Turkish State Meteorological Service were evaluated to select the optimum number of meteorological stations. The systematic meteorological measurements started in the 1930s, but the number of stations were not adequate in determining meteorological characterization of the whole country. That is why a total of 107 stations, which had continuous coverage over the 60-year time frame between 1950 and 2010 was selected. The selected stations also have good geographical representation at the basin and country scales. The meteorological parameters recorded at the stations included precipitation and temperature which are the key inputs to the Thornthwaite precipitation efficiency index. Therefore, temperature and precipitation series of meteorological observation stations were used in the study. To this end, quality controlled data sets were obtained from Turkish State Meteorological Service data gaps were completed using historical statistics at respective stations. The list of stations used in the analyses is given in Table 1, including their geographical coordinates across Turkey.

Table 1

List of meteorological stations used in the study

Name Longitude Latitude Altitude (m) Name Longitude Latitude Altitude (m) 
Adana 35,3500 36,9833 27 Iğdır 44,0500 39,9167 858 
Adıyaman 38,2833 37,7500 672 İnebolu 33,7833 41,9833 64 
Afyon 30,5333 38,7500 1,034 İpsala 26,3667 40,9167 10 
Ağrı 43,0500 39,7333 1,632 İskenderun 36,1667 36,5833 
Akçakoca 31,1666 41,0833 10 Islahiye 36,6333 37,0167 518 
Akhisar 27,8167 38,9000 93 Isparta 30,5500 37,7500 997 
Aksaray 34,0500 38,3833 961 İzmir 27,0667 38,3833 29 
Akşehir 31,4167 38,3500 1,002 K. Maraş 36,9333 37,6000 572 
Alanya 32,0000 36,5500 Kangal 37,3833 39,2333 1,512 
Amasya 35,8500 40,6500 412 Karaman 33,2167 37,2000 1,024 
Anamur 32,8333 36,0833 Kars 43,1000 40,5667 1,775 
Ankara 32,8833 39,9500 891 Kastamonu 33,7833 41,3667 800 
Antakya 36,1667 36,2000 100 Kayseri 35,4833 38,7167 1,093 
Antalya 30,7000 36,8667 42 Kilis 37,1000 36,7000 638 
Ardahan 42,7167 41,1167 1,829 Kırklareli 27,2167 41,7333 232 
Artvin 41,8167 41,1833 628 Kırşehir 34,1667 39,1500 1,007 
Aydın 27,8500 37,8500 56 Konya 32,5500 37,9833 1,031 
Balıkesir 27,8667 39,6500 147 Kuşadası 27,2500 37,8667 25 
Bandırma 27,9833 40,3167 51 Kütahya 29,9667 39,4167 969 
Bayburt 40,2333 40,2500 1,584 Malatya 38,2167 38,3500 948 
Bilecik 29,9833 40,1500 539 Malazgirt 42,5333 39,1500 1,565 
Bingöl 40,5000 38,8667 1,177 Manavgat 31,4333 36,7833 38 
Bodrum 27,4333 37,0500 26 Manisa 27,4333 38,6167 71 
Bolu 31,6000 40,7333 743 Mardin 40,7333 37,3000 1,050 
Burdur 30,3000 37,7167 967 Marmaris 28,2500 36,8500 16 
Bursa 29,0000 40,2167 101 Mersin 34,6333 36,8000 
Cihanbeyli 32,9500 38,6500 969 Merzifon 35,4500 40,8333 755 
Cizre 42,1833 37,3167 400 Milas 27,7833 37,3167 52 
Çanakkale 26,4000 40,1333 Muğla 28,3667 37,2167 646 
Çankırı 33,6167 40,6167 751 Muş 41,4833 38,6833 1,320 
Çemişgezek 38,9167 39,0667 953 Niğde 34,6833 37,9667 1,211 
Çorum 34,9667 40,5500 776 Ordu 37,9000 40,9833 
Denizli 29,0833 37,7833 425 Polatlı 32,1500 39,5833 886 
Dikili 26,8833 39,0667 Rize 40,5000 41,0333 
Dinar 30,1667 38,0667 864 Sakarya 30,4000 40,7667 30 
Diyarbakır 40,2000 37,9000 677 Samsun 36,2500 41,3500 
Düzce 31,1667 40,8333 146 Siirt 41,9500 37,9167 896 
Edirne 26,5500 41,6833 51 Silifke 33,9333 36,3833 15 
Edremit 27,0167 39,6000 21 Sinop 35,1667 42,0333 32 
Elazığ 39,2500 38,6500 990 Sivas 37,0167 39,7500 1,285 
Ereğli 34,0500 37,5333 1,044 Siverek 39,3167 37,7500 801 
Erzincan 39,5167 39,7000 1,218 Sivrihisar 31,5333 39,4500 1,070 
Erzurum 41,1667 39,9500 1,758 Şanlıurfa 38,7833 37,1500 547 
Eskişehir 30,5167 39,8167 801 Şile 29,6000 41,1667 83 
Fethiye 29,1167 36,6167 Tekirdağ 27,5000 40,9833 
Gaziantep 37,3500 37,0500 855 Tokat 36,5667 40,3000 608 
Gediz 29,4167 39,0500 825 Trabzon 39,7500 40,9833 30 
Giresun 38,3833 40,9167 37 Tunceli 39,5500 39,1167 981 
Göztepe 29,0833 40,9667 33 Uşak 29,4000 38,6833 919 
Gümüşhane 39,4667 40,4667 1,219 Van 43,3500 38,4667 1,671 
Güney 29,0667 38,1500 806 Yalova 29,2833 40,6667 
Hakkâri 43,7333 37,5667 1,728 Yozgat 34,8000 39,8167 1,298 
Hınıs 41,7000 39,3667 1,715 Zonguldak 31,8000 41,4500 137 
Hopa 41,4167 41,4000 33     
Name Longitude Latitude Altitude (m) Name Longitude Latitude Altitude (m) 
Adana 35,3500 36,9833 27 Iğdır 44,0500 39,9167 858 
Adıyaman 38,2833 37,7500 672 İnebolu 33,7833 41,9833 64 
Afyon 30,5333 38,7500 1,034 İpsala 26,3667 40,9167 10 
Ağrı 43,0500 39,7333 1,632 İskenderun 36,1667 36,5833 
Akçakoca 31,1666 41,0833 10 Islahiye 36,6333 37,0167 518 
Akhisar 27,8167 38,9000 93 Isparta 30,5500 37,7500 997 
Aksaray 34,0500 38,3833 961 İzmir 27,0667 38,3833 29 
Akşehir 31,4167 38,3500 1,002 K. Maraş 36,9333 37,6000 572 
Alanya 32,0000 36,5500 Kangal 37,3833 39,2333 1,512 
Amasya 35,8500 40,6500 412 Karaman 33,2167 37,2000 1,024 
Anamur 32,8333 36,0833 Kars 43,1000 40,5667 1,775 
Ankara 32,8833 39,9500 891 Kastamonu 33,7833 41,3667 800 
Antakya 36,1667 36,2000 100 Kayseri 35,4833 38,7167 1,093 
Antalya 30,7000 36,8667 42 Kilis 37,1000 36,7000 638 
Ardahan 42,7167 41,1167 1,829 Kırklareli 27,2167 41,7333 232 
Artvin 41,8167 41,1833 628 Kırşehir 34,1667 39,1500 1,007 
Aydın 27,8500 37,8500 56 Konya 32,5500 37,9833 1,031 
Balıkesir 27,8667 39,6500 147 Kuşadası 27,2500 37,8667 25 
Bandırma 27,9833 40,3167 51 Kütahya 29,9667 39,4167 969 
Bayburt 40,2333 40,2500 1,584 Malatya 38,2167 38,3500 948 
Bilecik 29,9833 40,1500 539 Malazgirt 42,5333 39,1500 1,565 
Bingöl 40,5000 38,8667 1,177 Manavgat 31,4333 36,7833 38 
Bodrum 27,4333 37,0500 26 Manisa 27,4333 38,6167 71 
Bolu 31,6000 40,7333 743 Mardin 40,7333 37,3000 1,050 
Burdur 30,3000 37,7167 967 Marmaris 28,2500 36,8500 16 
Bursa 29,0000 40,2167 101 Mersin 34,6333 36,8000 
Cihanbeyli 32,9500 38,6500 969 Merzifon 35,4500 40,8333 755 
Cizre 42,1833 37,3167 400 Milas 27,7833 37,3167 52 
Çanakkale 26,4000 40,1333 Muğla 28,3667 37,2167 646 
Çankırı 33,6167 40,6167 751 Muş 41,4833 38,6833 1,320 
Çemişgezek 38,9167 39,0667 953 Niğde 34,6833 37,9667 1,211 
Çorum 34,9667 40,5500 776 Ordu 37,9000 40,9833 
Denizli 29,0833 37,7833 425 Polatlı 32,1500 39,5833 886 
Dikili 26,8833 39,0667 Rize 40,5000 41,0333 
Dinar 30,1667 38,0667 864 Sakarya 30,4000 40,7667 30 
Diyarbakır 40,2000 37,9000 677 Samsun 36,2500 41,3500 
Düzce 31,1667 40,8333 146 Siirt 41,9500 37,9167 896 
Edirne 26,5500 41,6833 51 Silifke 33,9333 36,3833 15 
Edremit 27,0167 39,6000 21 Sinop 35,1667 42,0333 32 
Elazığ 39,2500 38,6500 990 Sivas 37,0167 39,7500 1,285 
Ereğli 34,0500 37,5333 1,044 Siverek 39,3167 37,7500 801 
Erzincan 39,5167 39,7000 1,218 Sivrihisar 31,5333 39,4500 1,070 
Erzurum 41,1667 39,9500 1,758 Şanlıurfa 38,7833 37,1500 547 
Eskişehir 30,5167 39,8167 801 Şile 29,6000 41,1667 83 
Fethiye 29,1167 36,6167 Tekirdağ 27,5000 40,9833 
Gaziantep 37,3500 37,0500 855 Tokat 36,5667 40,3000 608 
Gediz 29,4167 39,0500 825 Trabzon 39,7500 40,9833 30 
Giresun 38,3833 40,9167 37 Tunceli 39,5500 39,1167 981 
Göztepe 29,0833 40,9667 33 Uşak 29,4000 38,6833 919 
Gümüşhane 39,4667 40,4667 1,219 Van 43,3500 38,4667 1,671 
Güney 29,0667 38,1500 806 Yalova 29,2833 40,6667 
Hakkâri 43,7333 37,5667 1,728 Yozgat 34,8000 39,8167 1,298 
Hınıs 41,7000 39,3667 1,715 Zonguldak 31,8000 41,4500 137 
Hopa 41,4167 41,4000 33     

Thornthwaite climate classification index values were used to analyse spatial and temporal changes of climate zones. A representative set of climate classes were used to identify distinct climate driven pressures in 25 river basins. The geographical setting of river basins across Turkey is depicted in Figure 2.

Figure 2

River basins in Turkey.

Figure 2

River basins in Turkey.

The climate classification method, as developed by Thornthwaite (1948), is based on mainly water balance (precipitation and evapotranspiration) with a monthly time scale. If precipitation is higher than evaporation, then there is a potential for net rainfall excess. In this setting, the climate is classified as humid. In contrast, where precipitation is less than evaporation, there is a lack of water, and the climate can be identified as arid. Therefore, climate types in the Thornthwaite's classification vary between these two extreme events. In order to classify climate zones, Thornthwaite developed indices using precipitation, temperature and potential evapotranspiration. The Thornthwaite precipitation efficiency index (Im) is calculated using the following formula:  
formula
(1)
in which s= annual water surplus; d= annual water deficit; and ETp= annual evapotranspiration.

The Thornthwaite index and associated climate types are documented in Table 2. Letter designation reflects that Thornthwaite's original description of climate classes varies between very humid (A) and dry (E).

Table 2

Thornthwaite indexes and climate types

Im Letter designation Climate classes 
>100 Very humid 
100–80 B4 Humid 
80–60 B3 Humid 
60–40 B2 Humid 
40–20 B1 Humid 
20–0 C2 Semi-humid 
0–(–20) C1 Semi-dry–less humid 
–20–(–40) Semi-dry 
–40–(–60) Dry 
Im Letter designation Climate classes 
>100 Very humid 
100–80 B4 Humid 
80–60 B3 Humid 
60–40 B2 Humid 
40–20 B1 Humid 
20–0 C2 Semi-humid 
0–(–20) C1 Semi-dry–less humid 
–20–(–40) Semi-dry 
–40–(–60) Dry 
Potential evapotranspiration (ETp) was calculated by using the Hamon (1963) equation given below and a Thornthwaite-type monthly water balance model (Dingman 2002) was used to estimate monthly ET values. Although the Penman–Monteith (1965) equation estimates better ETp as compared to the Hamon equation it requires a wider range of input data. Because Turkey had a limited range of input data, especially in the former period, the Hamon equation was selected for practical purposes.  
formula
(2)
in which ETp = potential evapotranspiration (mm/day); k= proportionality coefficient (unitless); N= daytime length (x/12 hours); es= saturation vapor pressure = 6.108e((17.27T/(T+237.3)) (mb); and T= average monthly temperature (°C).

The point meteorological data sets obtained from meteorological stations, as listed in Table 1, were used to calculate associated values for the Thornthwaite index in a geographical information system (GIS) setting by using ArcGIS software. An inverse distance interpolation is one of the simplest and most popular interpolation techniques. It combines the proximity concept with the gradual change of the trend surface. An inverse distance weighted (IDW) interpolation is defined as a spatially weighted average of the sample values within a search neighborhood (Shepard 1968; Franke 1982; Diodato & Ceccarelli 2005).

The IDW method was used to analyze spatial variation of the index across geographical boundaries. It is a robust computational approach, and has a straightforward process for interpretation. Its general idea is based on the assumption that the attribute value of an unsampled point is the weighted average of known values within its neighborhood, and the weights are inversely related to the distances between the predicted location and the sampled location(s) (Lu & Wong 2008). The surface calculated using IDW depends on the selection of a power value (p) and the neighborhood search strategy (ESRI 2016).  
formula
in which = value to be estimated; = known value; …, = distances from the n data points to the power of p of the point estimated.

The optimal power is determined by minimizing the root mean square prediction error (RMSPE). In order to represent the conditions realistically at the river basin scale, the (p) value was selected as 2, in-line with the recommendations by Cetin & Diker (2003). The (p) value of 2 reflects the outcome of an iterative process to properly represent spatial distribution of the Thornthwaite index across the river basin systems in Turkey.

RESULTS AND DISCUSSION

It was noted that the index-based approach had similar findings in spatial and temporal representation of climate parameters and associated aridity conditions in comparison to climate change studies. The index based approach was used to realistically estimate climate conditions at various geographical scales in an accurate and representative manner. The outcomes were also assessed in the context of readily available climate change models and their spatial and temporal changes in the study area. In this study, climatic zones of Turkey were defined with respect to the Thornthwaite index based on their climatic and meteorological characteristics. In this context, climate driven conditions were first evaluated using climate parameters recorded at meteorological stations. The average representative observed values of meteorological stations for temperature and total precipitation during the 30-year periods of 1950–1980 and 1981–2010 are mapped as shown in Figure 3.

Figure 3

Average annual precipitation and temperature characteristics in Turkey. (a) Average annual temperature (°C) (1950–1980). (b) Average annual total precipitation (mm) (1950–1980). (c) Average annual temperature (°C) (1981–2010). (d) Average annual total precipitation (mm) (1981–2010).

Figure 3

Average annual precipitation and temperature characteristics in Turkey. (a) Average annual temperature (°C) (1950–1980). (b) Average annual total precipitation (mm) (1950–1980). (c) Average annual temperature (°C) (1981–2010). (d) Average annual total precipitation (mm) (1981–2010).

The changes between the two distinct 30-year periods (1950–1980) and (1981–2010) were also mapped, as shown in Figure 4. Average precipitation showed an increasing pattern along the northeastern part of Turkey, with a maximum change of 23.2%. In contrast, the southeastern part experienced a drop with a maximum change of 23.2%. Average temperatures showed a decreasing pattern, up to 1.0 °C along the northern part of Turkey and an increasing pattern, up to 1.1 °C, along the southeastern part of Turkey. The combined impact of temperature and precipitation will potentially have multiplier impacts on various human needs (mainly potable water) and various strategic sectors including but not limited to agriculture, industry and energy. The ecosystems and associated environmental services will also be severely impacted.

Figure 4

Changes in climate parameters between 1950–1980 and 1981–2010. (a) Change in total precipitation (%). (b) Change in average temperature (°C).

Figure 4

Changes in climate parameters between 1950–1980 and 1981–2010. (a) Change in total precipitation (%). (b) Change in average temperature (°C).

The outputs of a study based on A2 scenario, which is a high emission scenario that was used in the fourth Assessment Report of IPCC, presented by Sen (2013), indicate that temperatures in Turkey are projected to increase between 1.0 and 2.5 °C by the mid-21st century and between 2.5 and 5.0 °C by the end of the century with the 1961–1990 period as reference (Figure 5). The changes are not uniformly distributed. The eastern and southeastern parts of Turkey illustrate comparatively larger increases in temperatures. On the other hand, annual precipitation is expected to decrease in the southern parts of Turkey while it will tend to increase in the northern parts, especially in the northeastern parts. The reductions along the Mediterranean coastal line could be as large as 20% by the mid-century and 30% by the end of the century. Similar magnitudes could be stated for the increases along the northeastern coastal areas of Turkey.

Figure 5

Climate change projections for precipitation and temperature (Sen 2013).

Figure 5

Climate change projections for precipitation and temperature (Sen 2013).

The outputs of the present study conducted by observed hydro-meteorological parameters (precipitation and temperature) show a significant consistency with the results of the previous study carried out by Sen (2013).

The spatial distribution of the Thornthwaite index is presented in Figure 6. According to the results of the index approach, no area with ‘dry zone’ was detected in Turkey during the 60-year period evaluated in this study. On the other hand, inland regions of Turkey are characterized by semi-dry zones. In addition to the analysis within the respective 30-year periods, relative changes between these two 30-year time frames were also evaluated. This comparison was undertaken at both basin and country scales. The outcomes of country-scale analysis are described in Table 3. By comparing the two periods, it can be seen that there are significant changes, especially in semi-dry and very humid zones, in the order of 14.2 and 13.9%, respectively. On the other hand, semi-dry–less humid and semi-humid areas show a decreasing trend. These trends are consistent with the outcomes presented in Figures 4 and 5.

Table 3

Areas of climatic zones and their changes in Turkey for periods of 1950–1980 and 1981–2010

Climatic zones Zone areas (km2)
 
Percentage change 
1950–1980 1981–2010 
Semi-dry 170.848 195.192 14.2 
C1 Semi dry–less humid 410.592 397.851 –3.1 
C2 Semi-humid 139.871 130.910 –6.4 
B1 Humid 48.298 43.554 –9.8 
B2 Humid 5.408 6.442 19.1 
B3 Humid 1.953 2.130 9.1 
B4 Humid 1.701 1.725 1.4 
Very humid 2.807 3.196 13.9 
Climatic zones Zone areas (km2)
 
Percentage change 
1950–1980 1981–2010 
Semi-dry 170.848 195.192 14.2 
C1 Semi dry–less humid 410.592 397.851 –3.1 
C2 Semi-humid 139.871 130.910 –6.4 
B1 Humid 48.298 43.554 –9.8 
B2 Humid 5.408 6.442 19.1 
B3 Humid 1.953 2.130 9.1 
B4 Humid 1.701 1.725 1.4 
Very humid 2.807 3.196 13.9 
Figure 6

Spatial variation of Thornthwaite index at country scale. (a) Period of 1950–1980. (b) Period of 1981–2010.

Figure 6

Spatial variation of Thornthwaite index at country scale. (a) Period of 1950–1980. (b) Period of 1981–2010.

The trends at the country scale, specifically for two distinct classes of semi-dry and very humid zones, highlight the importance of evaluating spatial changes in climate conditions at the basin-scale. The basin-scale analysis will then allow identification of specific trends more accurately. The outcomes of the basin-scale analysis are presented in Figure 7.

Figure 7

Spatial variation of the Thornthwaite Index at basin scale. (a) Semi dry (arid). (b) Semi dry (arid)-less humid. (c) Semi-humid. (d) B1 humid (arid). (e) B2 humid (arid). (f) B3 humid. (g) B4 humid. (h) Very humid.

Figure 7

Spatial variation of the Thornthwaite Index at basin scale. (a) Semi dry (arid). (b) Semi dry (arid)-less humid. (c) Semi-humid. (d) B1 humid (arid). (e) B2 humid (arid). (f) B3 humid. (g) B4 humid. (h) Very humid.

In the context of semi-dry zones, Basin No. 11 (Akarcay basin), which is a closed basin, has experienced the highest level of increase (in the order of 35–45%) in semi-dry conditions. This is specifically important to evaluate the risks on the sustainability of the lake ecosystems (Eber and Aksehir lakes). Basin No. 21 (Euphrates-Tigris basin), which is a transboundary system accounting for approximately 30% of the water resources potential in Turkey, has experienced a high level of increase (in the order of 15–25%) in semi-dry conditions. This has important implications for both water resources management and hydroelectric power production. The two river systems in the basin account for approximately 40% of the hydroelectric power production potential in Turkey.

In the context of very-humid zones, Basin No. 22 (Eastern Black Sea basin), has experienced an increase in the order of 5% in very humid and a decrease in the order 5% in semi-dry–less humid conditions. Basin No. 23 (Coruh basin), which is a transboundary system with a share of 21% Turkey's hydroelectric potential, has also experienced an increase in the order of 5% in very humid and a decrease in the order 5% in semi-dry–less humid, semi-humid and B1-humid conditions. It is important to note that these two river basins account for 30% of the hydroelectric power production potential in Turkey.

CONCLUSIONS

In this study, a chain of structured processes were implemented by using an index based approach. In this context, the Thornthwaite index was introduced as a practical and robust approach to evaluate spatial and temporal changes in climate parameters, mainly driven by precipitation, temperature and evapotranspiration.

  • A two-step approach was undertaken by using climate conditions at country and basin-scale conditions. This scale was used as an alternative to the global and continental scales at macro-level and municipality scale at micro-level. These scales allowed more representative reflection of the spatial and temporal variations without unrealistic distortions driven by the global and continental processes. The outcomes were then evaluated to local and regional vulnerabilities as reflected through use of the Thornthwaite index. The country-scale analysis was undertaken and changes in precipitation, temperature and evapotranspiration were evaluated for two distinct 30-year time frames (1950–1980 and 1981–2010). These historical periods were used to better reflect the meteorological conditions and associated trends. It was determined that the changes in climate as calculated through the Thornthwaite index were consistent with climatic and meteorological processes at the country scale.

  • In the basin-scale analysis, it was determined that semi-dry and very-humid climate zones had experienced the largest amount of increase. This in turn has direct and indirect impacts on the sustainable use of water resources.

The results of the study indicate that during the 60-year time frame, no arid zones had been experienced in Turkey. On the other hand, an increase of semi-dry and dry humid zones and a decrease of semi-dry–less humid, semi-humid and humid zones had been experienced. The Thornthwaite index indicates that significant spatial and temporal variations of climate conditions have taken place across Turkey. Unless greenhouse gas emissions reduction measures are undertaken at the global scale, it will be challenging for Turkey to maintain a balanced portfolio of actions through use of climate change adaptation and mitigation measures. In this context, there is a high potential that semi-arid areas in Turkey will further increase in size in the coming decades.

ACKNOWLEDGEMENTS

We are grateful to Dr Hakan Aksu and Yeliz Tüzgen for helping us to use GIS applications and exchange thoughts through development of processes implemented in this study.

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