ABSTRACT: Forest fires are the most crucial natural threat to forests and wooded areas. They dest... more ABSTRACT: Forest fires are the most crucial natural threat to forests and wooded areas. They destroy many more trees than all other natural catastrophes such as parasite attacks, insects, extreme weather events and others. Forest fires, especially in summer and dry autumn/spring periods, are frequent in the Mediterranean basin and represent growing environmental and ecological problems. The aim of this investigation is to determine a climatic pattern of fire-meteorology over the Mediterranean basin via the frequency analysis of the forest fires weather index (FFWI) of Haines. The FFWI values were obtained by using the hourly data derived from reanalysis fields available from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) for the period 1980–2010. High frequency values of FFWI, taken to be a sign of moderate-level risk of forest fires, were obtained on the forests, scrubs, succulents and wooded areas in several countries facing the sea including Greece, Italy, Turkey, Syria, Lebanon, Cyprus, Macedonia, Albania, Serbia, Slovenia, France, Portugal, Spain, Morocco and Tunisia, almost all of which are characterized by dry summer, subtropical Mediterranean climates. As expected, the highest-level risk values are found in the arid desert climate regions: the desert areas of the Sahara and Libya in North Africa and the semi-arid steppe climate regions of the Middle East, as well as the semi-arid environments near the Caspian Sea basin.
Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature se... more Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature series at 70 stations of Turkey and the circulation types at 500-hPa geopotential height level were investigated to explain atmospheric controls of temperature variations during the extreme (weak and strong) phases and normal (negative and positive) phases of the North Atlantic Oscillation (i.e., Ponta Delgada-Reykjavik and the Gibraltar-Reykjavik) indices. During the positive phases of the North Atlantic Oscillation indices (NAOIs), northeasterly circulation increased, and thus spatially coherent and significant cold signals dominate over the majority of Turkey. This pattern is closely linked to anomalously low 500-hPa heights over the region of the Icelandic Low, and anomalously high geopotential heights over the regions of the Azores High, the western Mediterranean basin and the Europe, in general including the Balkans and northwest Turkey. Contrarily, during the negative phases of the NAOIs, prevailing westerly winds that originate from the subtropical northeast Atlantic increase, and thus spatially coherent and significant warm signals over the Anatolian peninsula appear. This pattern is closely linked to the increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey.
Relationships between the variability of the North Atlantic oscillation (NAO) indices and the nor... more Relationships between the variability of the North Atlantic oscillation (NAO) indices and the normalized precipitation at 78 stations in Turkey, and the influences of the extreme NAO index (NAOI) episodes and the year-to-year and longer time-scale variations in the NAO on the precipitation conditions were investigated. The results of the study have led to the following main conclusions and evaluations for Turkey:
Climatic factors that may lead to desertification in Turkey were investigated by analysis of the ... more Climatic factors that may lead to desertification in Turkey were investigated by analysis of the spatial and temporal variations of the precipitation and aridity index series, for the period 1930-1993. Semi-arid and dry sub-humid environmental conditions are dominant over the continental interiors and South-eastern Anatolia. Persistent dry conditions have been evident for the past two decades over a considerable part of Turkey. There has been a general tendency from humid conditions of around the 1960's towards dry sub-humid climatic conditions in the aridity index values of many stations and of Turkey, in general. At some stations in the Aegean Region, there has been a significant change from humid conditions to dry sub-humid or semi-arid climatic conditions. With regard to climatic factors, South-eastern Anatolia and the continental interiors of Turkey appear to be aridlands that are prone to desertification. When other natural and anthropogenic factors, such as high topography, forest fires and unsustainable use of agricultural lands are also taken into account, the Mediterranean and Aegean regions could be more vulnerable to desertification processes in the future.
Normalized rainfall of Turkey tended to decrease in many annual and winter series and to increase... more Normalized rainfall of Turkey tended to decrease in many annual and winter series and to increase in some spring and summer series during 1930-1993. Low-frequency fluctuation of regional winter rainfall series was generally dominated by cycles of 3-3.2, 6-7, 7-8.4, and 14-21 years. Spring rainfall series depicted high-frequency oscillations with cycles of 2-2.2 years, and longer cycles of 4.2 -4.7 years. Mean 700 and 500 hPa geopotential heights over Turkey generally experienced positive anomalies from late 1970s to early 1990s, and showed an upward trend in winter and summer. Significant negative correlations were found between geopotential height and rainfall anomalies in winter over most of Turkey. Cycles of 2-2.2 and 3.2 -3.8 years in spring rainfalls appeared to be associated with similar oscillations of spring geopotential heights. Cycles of 13 years in both winter geopotential series reflected in a similar cycle of 14 years in annual and winter rainfall. The number of depressions reaching Turkey tended to decrease for about 10 years. Increased frequencies and intensities of dry conditions in the last ca. 20 years may have been related to increased geopotential heights and decreased frequency of depressions over Turkey.
The Coordinated Regional Climate Downscaling Experiment is a framework devoted to coordinate inte... more The Coordinated Regional Climate Downscaling Experiment is a framework devoted to coordinate international efforts on regional climate simulations. Region 8 of the CORDEX domains basically covers the Central Asia with corners of the domain at () with a horizontal resolution of 50 km. In the study, the results of an experiment with the RegCM4.0 model that is ran for analysis of extreme precipitation is presented. The experiment consists of one simulation from 1970 to 2000 by using the ERA40 reanalysis data as boundary condition, and another simulation for the period 2070-2100 using the ECHAM5 A1B scenario data as forcing. Between these two experiments we have determined the probable changes in the frequency of the extreme events for the Region 8 of CORDEX.
This paper focuses on the evaluation of regional climate model simulation for Turkey for the 21st... more This paper focuses on the evaluation of regional climate model simulation for Turkey for the 21st century. A regional climate model, ICTP-RegCM3, with 20 km horizontal resolution, is used to downscale the reference and future climate scenario (IPCC-A2) simulations. Characteristics of droughts as well as the crop growth and yields of first-and second-crop corn are then calculated and simulated based on the data produced. The model projects an increase in air temperature of 5 to 7°C during the summer season over the west and an increase of 3.5°C for the winter season for the eastern part of the country. Precipitation is predicted to be 40% less in the southwest, although it may increase by 25% in the eastern part of the Black Sea region and northeastern Turkey. Trends in drought intensity and crop growth are related to climate changes. The results suggest more frequent, intense and long-lasting droughts in the country particularly along the western and southern coasts under future climate conditions. A shift of climate classes towards drier conditions is also projected for the western, southern and central regions during the 21st century. Evaluating the role of the climate change trends in crop production reveals significant decreases in yield and shortened growth seasons for first-and second-crop corn, a likely result of high temperatures and water stresses. In addition to rising temperatures and declining precipitation, increasing frequency, severity and duration of drought events may significantly affect food production and socio-economic conditions in Turkey. Our results may help policy makers and relevant sectors to implement appropriate and timely measures to cope with climate-changeinduced droughts and their effects in the future.
This study examines the climatology of annual frost days, and analyses the size and behaviour of ... more This study examines the climatology of annual frost days, and analyses the size and behaviour of the longterm variability and trends in annual numbers of frost day at the 72 stations over Turkey from 1950 to 2010. The main results are summarized as follows: (1) The annual number of frost days has evidently decreased at most of the stations with some observed regional differences, (2) The decreasing trends are largest over the Eastern Anatolia, the Marmara regions and along the Mediterranean coastline. The meteorological stations located in the continental northeast and the easternmost parts of the Anatolian Peninsula, including Ardahan, Iǧdır and Van, show a negative linear trend with a rate of four days per decade, (3) As in other regions of the Earth, changes in number of frost days are very likely associated with changes in minimum air temperatures and increasing growing season lengths in Turkey, (4) The decreasing trends in number of frost days also indicated considerable decadal-scale variability. This variability is very likely attributable to the large-scale atmospheric circulation and atmospheric oscillations such as the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO) and the North Sea-Caspian Pattern, (5) Consequently, the long-winter (DJFM) composites of number of frost days were examined for extreme phases of the AO index during the period 1950-2010 in order to assess the influence of atmospheric oscillations on year-to-year variability in number of frost days. According to the Cramer's t k test, winter number of frost days tended to increase significantly during the high (positive) index AO phase, while they tended to decrease significantly during the low (negative) index AO phase. These relationships are statistically significant at the 1% level at the majority of stations.
The climate of Turkey, which is characterized mainly by the Mediterranean macroclimate, results f... more The climate of Turkey, which is characterized mainly by the Mediterranean macroclimate, results from seasonal alternation of the mid-latitude frontal lows, with the polar air masses, and the subtropical high pressures, with the subsiding maritime tropical and continental tropical air masses. The climate of Turkey is also characterized with both the seasonal and year-to-year variability and longer-term variations varying from decadal to centennial time-scales. On the other hand, climate change, whether its global or regional scale, is one of the most significant and far-reaching challenges that the human societies living on the Earth have faced in the 21 st century as it was in the 20 th century.
Mean, maximum and minimum surface air temperatures recorded at 70 climatological stations in Turk... more Mean, maximum and minimum surface air temperatures recorded at 70 climatological stations in Turkey during the period from 1929 to 1999 were analysed to reveal spatial and temporal patterns of long-term trends, change points, significant warming (cooling) periods and linear trend rates per decade. Annual, winter and spring mean temperatures have tended to increase, particularly over the southern regions of Turkey, whereas summer and particularly autumn mean temperatures have decreased over the northern and continental inner regions. Annual, winter, spring and summer maximum temperatures have indicated a positive trend at many stations, except those in the Central Anatolia and Black Sea regions and partly in the Eastern Anatolia region. Autumn maximum temperatures, however, have decreased slightly over much of Turkey, except for the Aegean region. The majority of the urbanized and rapidly urbanizing stations in Turkey have been experiencing an apparent night-time warming, especially during the warm and dry period of the year. Minimum temperatures have shown a statistically significant positive trend at 31 stations annually, 30 stations in spring and 33 stations in summer; most are significant at the 0.01 level. Winter and autumn minimum temperatures have indicated a general negative trend in some portions of the Marmara, Black Sea and Eastern Anatolia regions, whereas a general positive trend has been seen over much of Turkey along with the significant trends in the Mediterranean region of the country.
Persistence and periodicity in normalised precipitation anomaly series of 91 stations over Turkey... more Persistence and periodicity in normalised precipitation anomaly series of 91 stations over Turkey were analysed using serial correlation coefficients and power spectra. There were considerable geographical variations and inter-seasonal contrasts with respect to periodicity and persistence characteristics. Lag-one serial correlation (L-1SC ) coefficients for winter series were mostly positive and were significant at the 0.05 level for 31 stations. Annual variations at 17 stations also showed significant positive L-1SC coefficients. In contrast, year-to-year variations in spring series were characterised by negative L-1SC coefficients at most stations (significant at 18). Summer series were characterised by both positive and negative coefficients. Autumn series of most stations were random with regard to serial dependence. For winter series, long cycles of 8.4, 12-12.7, 14, 18 and 21 yr were dominant in the Marmara Transition and the Mediterranean regions, whereas short cycles of 2, 2.1, 3 and 3.2 yr were found for the Black Sea region. Major spectral peaks of most spring series occurred within spectral bands with cycles of around 2, 3, 4 and 5 yr; a 2 yr periodicity was obtained for many stations. Statistically significant negative relationships between precipitation anomalies and 500 hPa geopotential height anomalies in winter and autumn showed an apparent spatial coherence over most of Turkey. Prominent spectral peaks corresponding to about 2 and 3 yr cycles in spring precipitation anomaly series appeared to be associated with similar oscillations in spring geopotential height anomalies. A cycle of 14 yr was found for winter precipitation and geopotential height anomalies.
Spatial and temporal patterns of trends in the diurnal temperature ranges (DTRs) of the 70 statio... more Spatial and temporal patterns of trends in the diurnal temperature ranges (DTRs) of the 70 stations and the role of maximum and minimum temperatures on the year-to-year variability and the long-term trends of the DTRs in Turkey have been investigated for the period 1929-1999. The principal results of the study are as follows:
In this study, the hierarchical clustering technique, called Ward method, was applied for groupin... more In this study, the hierarchical clustering technique, called Ward method, was applied for grouping common features of air temperature series, precipitation total and relative humidity series of 244 stations in Turkey.
Climate related studies are required complete time series data to be used. On the other hand, con... more Climate related studies are required complete time series data to be used. On the other hand, considerable number of observations is missing in meteorological time series due to several reasons. This conflicting problem, however, can be overcame by imputing missing values using observations of correlated nearby climate stations. The main aim of this study, therefore, is to compare the performances of six different methods for imputing monthly total precipitation series obtained from stations located in two different climate regions of Türkiye. These include Single Arithmetic Average (SAA), Normal Ratio (NR), NR Weighted with Correlations (NRWC), Multi Layer Perceptron type Neural Network (MLPNN) and Expectation-Maximization Algorithm based on Monte Carlo Markov Chain (EMMCMC). In addition, we propose a modification in the EMMCMC method which uses the results of different imputation methods as reference series. Results show that both EMMCMC methods perform better than the other imputation methods considered in the study.
Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature se... more Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature series at 70 stations of Turkey and the circulation types at 500-hPa geopotential height level were investigated to explain atmospheric controls of temperature variations during the extreme (weak and strong) phases and normal (negative and positive) phases of the North Atlantic Oscillation (i.e., Ponta Delgada-Reykjavik and the Gibraltar-Reykjavik) indices. During the positive phases of the North Atlantic Oscillation indices (NAOIs), northeasterly circulation increased, and thus spatially coherent and significant cold signals dominate over the majority of Turkey. This pattern is closely linked to anomalously low 500-hPa heights over the region of the Icelandic Low, and anomalously high geopotential heights over the regions of the Azores High, the western Mediterranean basin and the Europe, in general including the Balkans and northwest Turkey. Contrarily, during the negative phases of the NAOIs, prevailing westerly winds that originate from the subtropical northeast Atlantic increase, and thus spatially coherent and significant warm signals over the Anatolian peninsula appear. This pattern is closely linked to the increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey.
The anomalous circulations at 500-hPa geopotential level during the extreme North Atlantic Oscill... more The anomalous circulations at 500-hPa geopotential level during the extreme North Atlantic Oscillation Index (NAOI) phases were investigated in order to explain atmospheric causes of the changes in precipitation of the 78 stations of Turkey during the extreme NAOI phases. We arranged and analysed the 500-hPa height data of the 231 grid points for a large region delimited by the 40 • W and 60 • E longitudes and by the 20 • N and 70 • N latitudes. The main conclusions of the study are as follows: 1) Annual, winter, spring, autumn and partly summer composite precipitation means are mostly characterised by wetter than long-term average conditions during the negative NAOI phase, whereas the positive NAOI responses mostly exhibit drier than long-term average conditions annually and in all seasons except summer. 2) Spatially coherent and statistically significant changes in the precipitation amounts during the extreme NAOI phases are more apparent in the west and mid Turkey. 3) The 500-hPa circulation corresponding to the negative NAOI phase brings above long-term average precipitation to Turkey in winter, spring and autumn and annually, associated with the NAO pattern in which the 500-hPa geopotential level is anomalously high in the area of the Icelandic Low and anomalously low across the regions of the Azores High and the Europe in general. 4) Contrary, the NAO pattern over the North Atlantic and the Europe is responsible for the drier than long-term average precipitation conditions in Turkey during the positive NAOI phase, when the 500-hPa geopotential level is anomalously low over the area of the Icelandic Low and the anomalously high across the subtropical and mid-latitude north-east Atlantic and the Europe regions.
ABSTRACT: Forest fires are the most crucial natural threat to forests and wooded areas. They dest... more ABSTRACT: Forest fires are the most crucial natural threat to forests and wooded areas. They destroy many more trees than all other natural catastrophes such as parasite attacks, insects, extreme weather events and others. Forest fires, especially in summer and dry autumn/spring periods, are frequent in the Mediterranean basin and represent growing environmental and ecological problems. The aim of this investigation is to determine a climatic pattern of fire-meteorology over the Mediterranean basin via the frequency analysis of the forest fires weather index (FFWI) of Haines. The FFWI values were obtained by using the hourly data derived from reanalysis fields available from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) for the period 1980–2010. High frequency values of FFWI, taken to be a sign of moderate-level risk of forest fires, were obtained on the forests, scrubs, succulents and wooded areas in several countries facing the sea including Greece, Italy, Turkey, Syria, Lebanon, Cyprus, Macedonia, Albania, Serbia, Slovenia, France, Portugal, Spain, Morocco and Tunisia, almost all of which are characterized by dry summer, subtropical Mediterranean climates. As expected, the highest-level risk values are found in the arid desert climate regions: the desert areas of the Sahara and Libya in North Africa and the semi-arid steppe climate regions of the Middle East, as well as the semi-arid environments near the Caspian Sea basin.
Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature se... more Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature series at 70 stations of Turkey and the circulation types at 500-hPa geopotential height level were investigated to explain atmospheric controls of temperature variations during the extreme (weak and strong) phases and normal (negative and positive) phases of the North Atlantic Oscillation (i.e., Ponta Delgada-Reykjavik and the Gibraltar-Reykjavik) indices. During the positive phases of the North Atlantic Oscillation indices (NAOIs), northeasterly circulation increased, and thus spatially coherent and significant cold signals dominate over the majority of Turkey. This pattern is closely linked to anomalously low 500-hPa heights over the region of the Icelandic Low, and anomalously high geopotential heights over the regions of the Azores High, the western Mediterranean basin and the Europe, in general including the Balkans and northwest Turkey. Contrarily, during the negative phases of the NAOIs, prevailing westerly winds that originate from the subtropical northeast Atlantic increase, and thus spatially coherent and significant warm signals over the Anatolian peninsula appear. This pattern is closely linked to the increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey.
Relationships between the variability of the North Atlantic oscillation (NAO) indices and the nor... more Relationships between the variability of the North Atlantic oscillation (NAO) indices and the normalized precipitation at 78 stations in Turkey, and the influences of the extreme NAO index (NAOI) episodes and the year-to-year and longer time-scale variations in the NAO on the precipitation conditions were investigated. The results of the study have led to the following main conclusions and evaluations for Turkey:
Climatic factors that may lead to desertification in Turkey were investigated by analysis of the ... more Climatic factors that may lead to desertification in Turkey were investigated by analysis of the spatial and temporal variations of the precipitation and aridity index series, for the period 1930-1993. Semi-arid and dry sub-humid environmental conditions are dominant over the continental interiors and South-eastern Anatolia. Persistent dry conditions have been evident for the past two decades over a considerable part of Turkey. There has been a general tendency from humid conditions of around the 1960's towards dry sub-humid climatic conditions in the aridity index values of many stations and of Turkey, in general. At some stations in the Aegean Region, there has been a significant change from humid conditions to dry sub-humid or semi-arid climatic conditions. With regard to climatic factors, South-eastern Anatolia and the continental interiors of Turkey appear to be aridlands that are prone to desertification. When other natural and anthropogenic factors, such as high topography, forest fires and unsustainable use of agricultural lands are also taken into account, the Mediterranean and Aegean regions could be more vulnerable to desertification processes in the future.
Normalized rainfall of Turkey tended to decrease in many annual and winter series and to increase... more Normalized rainfall of Turkey tended to decrease in many annual and winter series and to increase in some spring and summer series during 1930-1993. Low-frequency fluctuation of regional winter rainfall series was generally dominated by cycles of 3-3.2, 6-7, 7-8.4, and 14-21 years. Spring rainfall series depicted high-frequency oscillations with cycles of 2-2.2 years, and longer cycles of 4.2 -4.7 years. Mean 700 and 500 hPa geopotential heights over Turkey generally experienced positive anomalies from late 1970s to early 1990s, and showed an upward trend in winter and summer. Significant negative correlations were found between geopotential height and rainfall anomalies in winter over most of Turkey. Cycles of 2-2.2 and 3.2 -3.8 years in spring rainfalls appeared to be associated with similar oscillations of spring geopotential heights. Cycles of 13 years in both winter geopotential series reflected in a similar cycle of 14 years in annual and winter rainfall. The number of depressions reaching Turkey tended to decrease for about 10 years. Increased frequencies and intensities of dry conditions in the last ca. 20 years may have been related to increased geopotential heights and decreased frequency of depressions over Turkey.
The Coordinated Regional Climate Downscaling Experiment is a framework devoted to coordinate inte... more The Coordinated Regional Climate Downscaling Experiment is a framework devoted to coordinate international efforts on regional climate simulations. Region 8 of the CORDEX domains basically covers the Central Asia with corners of the domain at () with a horizontal resolution of 50 km. In the study, the results of an experiment with the RegCM4.0 model that is ran for analysis of extreme precipitation is presented. The experiment consists of one simulation from 1970 to 2000 by using the ERA40 reanalysis data as boundary condition, and another simulation for the period 2070-2100 using the ECHAM5 A1B scenario data as forcing. Between these two experiments we have determined the probable changes in the frequency of the extreme events for the Region 8 of CORDEX.
This paper focuses on the evaluation of regional climate model simulation for Turkey for the 21st... more This paper focuses on the evaluation of regional climate model simulation for Turkey for the 21st century. A regional climate model, ICTP-RegCM3, with 20 km horizontal resolution, is used to downscale the reference and future climate scenario (IPCC-A2) simulations. Characteristics of droughts as well as the crop growth and yields of first-and second-crop corn are then calculated and simulated based on the data produced. The model projects an increase in air temperature of 5 to 7°C during the summer season over the west and an increase of 3.5°C for the winter season for the eastern part of the country. Precipitation is predicted to be 40% less in the southwest, although it may increase by 25% in the eastern part of the Black Sea region and northeastern Turkey. Trends in drought intensity and crop growth are related to climate changes. The results suggest more frequent, intense and long-lasting droughts in the country particularly along the western and southern coasts under future climate conditions. A shift of climate classes towards drier conditions is also projected for the western, southern and central regions during the 21st century. Evaluating the role of the climate change trends in crop production reveals significant decreases in yield and shortened growth seasons for first-and second-crop corn, a likely result of high temperatures and water stresses. In addition to rising temperatures and declining precipitation, increasing frequency, severity and duration of drought events may significantly affect food production and socio-economic conditions in Turkey. Our results may help policy makers and relevant sectors to implement appropriate and timely measures to cope with climate-changeinduced droughts and their effects in the future.
This study examines the climatology of annual frost days, and analyses the size and behaviour of ... more This study examines the climatology of annual frost days, and analyses the size and behaviour of the longterm variability and trends in annual numbers of frost day at the 72 stations over Turkey from 1950 to 2010. The main results are summarized as follows: (1) The annual number of frost days has evidently decreased at most of the stations with some observed regional differences, (2) The decreasing trends are largest over the Eastern Anatolia, the Marmara regions and along the Mediterranean coastline. The meteorological stations located in the continental northeast and the easternmost parts of the Anatolian Peninsula, including Ardahan, Iǧdır and Van, show a negative linear trend with a rate of four days per decade, (3) As in other regions of the Earth, changes in number of frost days are very likely associated with changes in minimum air temperatures and increasing growing season lengths in Turkey, (4) The decreasing trends in number of frost days also indicated considerable decadal-scale variability. This variability is very likely attributable to the large-scale atmospheric circulation and atmospheric oscillations such as the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO) and the North Sea-Caspian Pattern, (5) Consequently, the long-winter (DJFM) composites of number of frost days were examined for extreme phases of the AO index during the period 1950-2010 in order to assess the influence of atmospheric oscillations on year-to-year variability in number of frost days. According to the Cramer's t k test, winter number of frost days tended to increase significantly during the high (positive) index AO phase, while they tended to decrease significantly during the low (negative) index AO phase. These relationships are statistically significant at the 1% level at the majority of stations.
The climate of Turkey, which is characterized mainly by the Mediterranean macroclimate, results f... more The climate of Turkey, which is characterized mainly by the Mediterranean macroclimate, results from seasonal alternation of the mid-latitude frontal lows, with the polar air masses, and the subtropical high pressures, with the subsiding maritime tropical and continental tropical air masses. The climate of Turkey is also characterized with both the seasonal and year-to-year variability and longer-term variations varying from decadal to centennial time-scales. On the other hand, climate change, whether its global or regional scale, is one of the most significant and far-reaching challenges that the human societies living on the Earth have faced in the 21 st century as it was in the 20 th century.
Mean, maximum and minimum surface air temperatures recorded at 70 climatological stations in Turk... more Mean, maximum and minimum surface air temperatures recorded at 70 climatological stations in Turkey during the period from 1929 to 1999 were analysed to reveal spatial and temporal patterns of long-term trends, change points, significant warming (cooling) periods and linear trend rates per decade. Annual, winter and spring mean temperatures have tended to increase, particularly over the southern regions of Turkey, whereas summer and particularly autumn mean temperatures have decreased over the northern and continental inner regions. Annual, winter, spring and summer maximum temperatures have indicated a positive trend at many stations, except those in the Central Anatolia and Black Sea regions and partly in the Eastern Anatolia region. Autumn maximum temperatures, however, have decreased slightly over much of Turkey, except for the Aegean region. The majority of the urbanized and rapidly urbanizing stations in Turkey have been experiencing an apparent night-time warming, especially during the warm and dry period of the year. Minimum temperatures have shown a statistically significant positive trend at 31 stations annually, 30 stations in spring and 33 stations in summer; most are significant at the 0.01 level. Winter and autumn minimum temperatures have indicated a general negative trend in some portions of the Marmara, Black Sea and Eastern Anatolia regions, whereas a general positive trend has been seen over much of Turkey along with the significant trends in the Mediterranean region of the country.
Persistence and periodicity in normalised precipitation anomaly series of 91 stations over Turkey... more Persistence and periodicity in normalised precipitation anomaly series of 91 stations over Turkey were analysed using serial correlation coefficients and power spectra. There were considerable geographical variations and inter-seasonal contrasts with respect to periodicity and persistence characteristics. Lag-one serial correlation (L-1SC ) coefficients for winter series were mostly positive and were significant at the 0.05 level for 31 stations. Annual variations at 17 stations also showed significant positive L-1SC coefficients. In contrast, year-to-year variations in spring series were characterised by negative L-1SC coefficients at most stations (significant at 18). Summer series were characterised by both positive and negative coefficients. Autumn series of most stations were random with regard to serial dependence. For winter series, long cycles of 8.4, 12-12.7, 14, 18 and 21 yr were dominant in the Marmara Transition and the Mediterranean regions, whereas short cycles of 2, 2.1, 3 and 3.2 yr were found for the Black Sea region. Major spectral peaks of most spring series occurred within spectral bands with cycles of around 2, 3, 4 and 5 yr; a 2 yr periodicity was obtained for many stations. Statistically significant negative relationships between precipitation anomalies and 500 hPa geopotential height anomalies in winter and autumn showed an apparent spatial coherence over most of Turkey. Prominent spectral peaks corresponding to about 2 and 3 yr cycles in spring precipitation anomaly series appeared to be associated with similar oscillations in spring geopotential height anomalies. A cycle of 14 yr was found for winter precipitation and geopotential height anomalies.
Spatial and temporal patterns of trends in the diurnal temperature ranges (DTRs) of the 70 statio... more Spatial and temporal patterns of trends in the diurnal temperature ranges (DTRs) of the 70 stations and the role of maximum and minimum temperatures on the year-to-year variability and the long-term trends of the DTRs in Turkey have been investigated for the period 1929-1999. The principal results of the study are as follows:
In this study, the hierarchical clustering technique, called Ward method, was applied for groupin... more In this study, the hierarchical clustering technique, called Ward method, was applied for grouping common features of air temperature series, precipitation total and relative humidity series of 244 stations in Turkey.
Climate related studies are required complete time series data to be used. On the other hand, con... more Climate related studies are required complete time series data to be used. On the other hand, considerable number of observations is missing in meteorological time series due to several reasons. This conflicting problem, however, can be overcame by imputing missing values using observations of correlated nearby climate stations. The main aim of this study, therefore, is to compare the performances of six different methods for imputing monthly total precipitation series obtained from stations located in two different climate regions of Türkiye. These include Single Arithmetic Average (SAA), Normal Ratio (NR), NR Weighted with Correlations (NRWC), Multi Layer Perceptron type Neural Network (MLPNN) and Expectation-Maximization Algorithm based on Monte Carlo Markov Chain (EMMCMC). In addition, we propose a modification in the EMMCMC method which uses the results of different imputation methods as reference series. Results show that both EMMCMC methods perform better than the other imputation methods considered in the study.
Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature se... more Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature series at 70 stations of Turkey and the circulation types at 500-hPa geopotential height level were investigated to explain atmospheric controls of temperature variations during the extreme (weak and strong) phases and normal (negative and positive) phases of the North Atlantic Oscillation (i.e., Ponta Delgada-Reykjavik and the Gibraltar-Reykjavik) indices. During the positive phases of the North Atlantic Oscillation indices (NAOIs), northeasterly circulation increased, and thus spatially coherent and significant cold signals dominate over the majority of Turkey. This pattern is closely linked to anomalously low 500-hPa heights over the region of the Icelandic Low, and anomalously high geopotential heights over the regions of the Azores High, the western Mediterranean basin and the Europe, in general including the Balkans and northwest Turkey. Contrarily, during the negative phases of the NAOIs, prevailing westerly winds that originate from the subtropical northeast Atlantic increase, and thus spatially coherent and significant warm signals over the Anatolian peninsula appear. This pattern is closely linked to the increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey.
The anomalous circulations at 500-hPa geopotential level during the extreme North Atlantic Oscill... more The anomalous circulations at 500-hPa geopotential level during the extreme North Atlantic Oscillation Index (NAOI) phases were investigated in order to explain atmospheric causes of the changes in precipitation of the 78 stations of Turkey during the extreme NAOI phases. We arranged and analysed the 500-hPa height data of the 231 grid points for a large region delimited by the 40 • W and 60 • E longitudes and by the 20 • N and 70 • N latitudes. The main conclusions of the study are as follows: 1) Annual, winter, spring, autumn and partly summer composite precipitation means are mostly characterised by wetter than long-term average conditions during the negative NAOI phase, whereas the positive NAOI responses mostly exhibit drier than long-term average conditions annually and in all seasons except summer. 2) Spatially coherent and statistically significant changes in the precipitation amounts during the extreme NAOI phases are more apparent in the west and mid Turkey. 3) The 500-hPa circulation corresponding to the negative NAOI phase brings above long-term average precipitation to Turkey in winter, spring and autumn and annually, associated with the NAO pattern in which the 500-hPa geopotential level is anomalously high in the area of the Icelandic Low and anomalously low across the regions of the Azores High and the Europe in general. 4) Contrary, the NAO pattern over the North Atlantic and the Europe is responsible for the drier than long-term average precipitation conditions in Turkey during the positive NAOI phase, when the 500-hPa geopotential level is anomalously low over the area of the Icelandic Low and the anomalously high across the subtropical and mid-latitude north-east Atlantic and the Europe regions.
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Papers by Murat Türkeş
than all other natural catastrophes such as parasite attacks, insects, extreme weather events and others. Forest fires, especially
in summer and dry autumn/spring periods, are frequent in the Mediterranean basin and represent growing environmental
and ecological problems. The aim of this investigation is to determine a climatic pattern of fire-meteorology over the
Mediterranean basin via the frequency analysis of the forest fires weather index (FFWI) of Haines. The FFWI values were
obtained by using the hourly data derived from reanalysis fields available from the National Centers for Environmental
Prediction/National Center for Atmospheric Research (NCEP/NCAR) for the period 1980–2010. High frequency values of
FFWI, taken to be a sign of moderate-level risk of forest fires, were obtained on the forests, scrubs, succulents and wooded
areas in several countries facing the sea including Greece, Italy, Turkey, Syria, Lebanon, Cyprus, Macedonia, Albania,
Serbia, Slovenia, France, Portugal, Spain, Morocco and Tunisia, almost all of which are characterized by dry summer,
subtropical Mediterranean climates. As expected, the highest-level risk values are found in the arid desert climate regions:
the desert areas of the Sahara and Libya in North Africa and the semi-arid steppe climate regions of the Middle East, as
well as the semi-arid environments near the Caspian Sea basin.
than all other natural catastrophes such as parasite attacks, insects, extreme weather events and others. Forest fires, especially
in summer and dry autumn/spring periods, are frequent in the Mediterranean basin and represent growing environmental
and ecological problems. The aim of this investigation is to determine a climatic pattern of fire-meteorology over the
Mediterranean basin via the frequency analysis of the forest fires weather index (FFWI) of Haines. The FFWI values were
obtained by using the hourly data derived from reanalysis fields available from the National Centers for Environmental
Prediction/National Center for Atmospheric Research (NCEP/NCAR) for the period 1980–2010. High frequency values of
FFWI, taken to be a sign of moderate-level risk of forest fires, were obtained on the forests, scrubs, succulents and wooded
areas in several countries facing the sea including Greece, Italy, Turkey, Syria, Lebanon, Cyprus, Macedonia, Albania,
Serbia, Slovenia, France, Portugal, Spain, Morocco and Tunisia, almost all of which are characterized by dry summer,
subtropical Mediterranean climates. As expected, the highest-level risk values are found in the arid desert climate regions:
the desert areas of the Sahara and Libya in North Africa and the semi-arid steppe climate regions of the Middle East, as
well as the semi-arid environments near the Caspian Sea basin.