Istanbul, as one of the four anchor megacities of Europe, has shown a rise of 0.94°C in average annual temperature over the long period of 1912–2016 under impacts of anthropogenic climate change. A notable increase in temperatures has started after the 1940s, which is in parallel with the beginning of industrialization era in Istanbul. This warming is associated with an extensive population growth and accompanied the decrease in vegetation cover. Increasing in minimum series of temperature is more evident than maximum values and the rising rate of temperature values has been more pronounced during recent decades. The first significant upward trend in precipitation series has periodically started in 1920s, while there has been a stable trend from 2001 till today. The daily average of rainfall amount increased with a mean value of 58 mm during the total study period. Rising rate of daily maximum precipitation has been more evident in the last 3 decades, which is shown by the increased frequency of heavy rainfall. In this regard, both of the temperature and precipitation series had higher mean values (13.9°C and 878 mm) for the final period (1965–2016) compared to the mean values (13.6°C and 799 mm) belonging to the first period (1912–1964).
Modernization and industrialization and their socioeconomic effects have caused an increase in rapid urbanization all over the world. The probability of climate variability and climate change especially in megacities is the cause of great concern among scientists, governments, and lawmakers. Uncontrolled changes in demographic values, landuse area, vehicle and industrial product types, and building features can play an important role in regional climate change and can produce further problems in settlement areas due to more occurrences of climatic disasters. Previous researchers represent that since the beginning of the 20th century, average global temperature has increased about 0.6°C [
One of the consequences of climate change is the increasing frequency of extreme events [
In this regard, the reports of IPCC demonstrate that each of the last three decades has been warmer than all the previous decades [
The megacity of Istanbul with the geographical coordinates of 28°57′53′′E and 41°01′07′′N is the biggest city in Turkey and is one of the most populous cities in the world. Istanbul is geographically located in the northwest of Turkey and the weather station of Kandilli is in the middle of the Asian side of this city (Figures
Geographical location of Istanbul (a) and Turkey (b); population growth (c) and NDVI changes (d).
In this study, we used climatic data of Kandilli station which is located in a park and its neighboring site is an area without urban density. This is an advantage for recording the weather data which has not been affected by urban activities and the results of the data analysis can show reliable climate variability representing the region. For the quality analysis of the data, several methods are considered. There is no information about the history of meteorological instruments which have been used to record the data at the Kandilli station. Some of earlier records of instruments which are presented by Erinç [
Different time series of meteorological data at the station scale of Kandilli including daily temperature and precipitation are considered for analysis of the climate change effects in Istanbul city over the time. First, reliability and accuracy of these data at the significance level of 95 (Table
Statistical outputs of all tests for data quality control.
Cases  NPar tests 
Test of normality 
Test of homogeneity of variance 


Parameter  Station  Period  Total  Valid  Missing  Std.  Runs test  KolmogorovSmirnov  ANOVA 
Levene’s test  




Sig.  Mean  Test values  Statistic  Sig. 

Sig.  Statistic  Sig.  

Kandilli  1965–2016  18980  99.9%  23  6.6  −137  0.0  10.5  10.5  0.065  0.0  36.7  0.0  21  0.0 
Sarıyer  18998  100%  1  6.7  −136  0.0  10.9  10.9  0.061  0.0  
Kandilli  1st  38353  99.9%  23  6.6  −170  0.0  10.4  10.7  0.67  0.0  68.6  0.0  1.83  0.17  
2nd  



Kandilli  1965–2016  18985  100%  4  7.1  −138  0.0  13.9  13.9  0.07  0.0  0.31  0.57  1.08  0.29 
Sarıyer  18998  100%  1  7.1  −135  0.0  13.9  13.8  0.069  0.0  
Kandilli  1st  38353  100%  4  7.1  −169  0.0  13.8  14.1  0.07  0.0  33.2  0.0  5.09  0.02  
2nd  



Kandilli  1965–2016  18990  99.9%  18  8.4  −130  0.0  18.6  18.6  0.07  0.0  249  0.0  204  0.0 
Sarıyer  18998  100%  1  7.8  −129  0.0  17.5  17.5  0.068  0.0  
Kandilli  1st  38335  100%  18  8.3  −161  0.0  18.3  18.8  0.06  0.0  89.4  0.0  27.2  0.0  
2nd  


Precip.  Kandilli  1965–2016  7691  38.9%  12238  9.6  −13  0.0  6.12  6.12  0.26  0.0  1.04  0.31  1.35  0.24 
Sarıyer  7855  35%  11074  9.2  −10  0.0  6.27  6.3  0.0253  0.0  
Kandilli  1st  38353  37.1%  24121  9.6  −16.4  0.0  6.1  2.5  0.26  0.0  7  0.0  0.799  0.37  
2nd 
“
Then, an upward or downward trend is given by a positive or negative value of
Trend analysis of the temperatures and precipitation series using the method of the linear bestfit curve and ManKendall test are applied for subperiods throughout the whole period of 1912–2016. In this case, the first half of studied period (1912–1964) is compared to second half of studied period (1964–2016) for knowing the actual changes in climatic parameters. Also, since the globe on average was hotter in the early 1960s according to fifth assessment report of IPCC in 2013, a comparing analysis between two subperiods of 1912–1980 and 1981–2016 is performed by choosing the turning point in the year of 1980. In this case, the results of basic quality tests for all studied periods showed that the distribution of alltime series at the significance level of 95% does not follow the randomness principle by use of Run test and the normality principle by using KolmogorovSmirnov test for both of Kandilli station and its nearby station of Sariyer. Then, the results of Levene’s test of homogeneity and ANOVA test for assessing the absolute homogeneity showed that minimum temperature and precipitation time series of the Kandilli station are homogeneous by comparison between two subperiods’ data including 1st and 2nd parts of the entire period of 1912–2016. Also, in the case of assessing the relative homogeneity between two separate data groups including the Kandilli station and its nearby station of Sariyer showed that the average temperature and precipitation time series are homogeneous for the same studied period of 1965–2016. Moreover, results of the homogeneity test showed no homogeneity in the other series whether between meteorological series at the Kandilli station and its nearby station of Sariyer in the same period or between two subperiods of the Kandilli station’s series (Table
The analysis of average yearly, maximum, and minimum temperature has been carried out using the statistical method of least squares and the MK test at the significance level of 5% is shown with a dashed line (±2) in Figures
Trend analysis of average annual temperature (a) and average monthly temperature (b).
Trend analysis of the temperatures time series using linear bestfit curve and MK test for daily minimum temperature (a1, a2), daily average temperature (b1, b2), daily maximum temperature (c1, c2), number of days with daily maximum temperature > 30°C (d1, d2), number of days with daily minimum temperature < 0°C (e1, e2), and daily temperature range (f1, f2).
Time series of total annual precipitation (a) and total monthly precipitation (b).
Trend analysis of the precipitation time series using least squares linear regression and MK trend test for total annual precipitation (a1, a2), daily maximum precipitation (b1, b2), daily maximum precipitation greater than 25 mm (c1, c2), and standard deviation in the daily precipitation series (d1, d2).
Nevertheless, the data time series of Kandilli station shows that the increase in temperature parameter after the 1940s is in parallel with the beginning of industrialization era in Istanbul. Of course, regime changes in temperature time series on regional scales cannot be totally explained by the nature destruction and pollutant emissions in and around Istanbul, alone. These effects can also be considered as a reflection of the general situation happening in the world on a larger scale. Temperature time series of the Kandilli station shows an annual average about 13.7°C and absolute minimum and maximum in 1920 with a value of 12.4°C and in 1966 with a value of 15.3°C, respectively (Figure
A general tendency of a warming trend in the daily temperature series is found for the whole studied period of 1912–2016 by using the least squares regression analysis. Therefore, the trend analysis revealed that the daily average of temperature has increased by a rate of 0.9 for the period from 1912 to 2016 (Figures
Statistical analyses outputs of temperature and precipitation parameters (SD: standard deviation; Inc.: increase; dec.: decrease).
Parameters  Minimum temperature (°C)  Average temperature (°C)  Maximum temperature (°C)  Precipitation (mm)  

Statistics  Periods  
1912– 
1965– 
Inc. or dec.  1912– 
1981– 
Inc. or dec.  1912– 
1965– 
Inc. or dec.  1912– 
1981– 
Inc. or dec.  1912– 
1965– 
Inc. or dec.  1912– 
1981– 
Inc. or dec.  1912– 
1965– 
Inc. or dec.  1912– 
1981– 
Inc. or dec.  
Average 
10.2  10.7 

10.2  10.9 

13.6  14.0 

13.6  14.1 

18.0  18.7 

18.1  18.7 

811.3  865.6  54.4  826.7  859.1 

SD  6.6  6.6 

6.5  6.7 

7.1  7.2 

7.1  7.3 

8.2  8.4 

8.2  8.5 

9.3  9.1  −0.3  9.1  9.3 

Minimum  −5.4  −4.2 

−5.3  −3.9 

−2.7  −2.1 

−2.7  −1.9 

−0.8  −0.1 

−0.7  0.0 

0.0  0.0  0.0  0.0  0.0 

Maximum  22.3  22.9 

22.2  23.2 

27.6  27.8 

27.7  27.7 

35.6  36.2 

35.8  36.1 

58.9  62.0  3.1  57.9  65.1 

Percentile 5%  −0.4  0.2 

−0.3  0.3 

2.1  2.5 

2.2  2.4 

4.5  5.0 

4.6  4.8 

0.1  0.1  −0.1  0.1  0.1 

Percentile 25%  4.7  5.2 

4.8  5.2 

7.7  8.0 

7.7  7.8 

11.4  11.9 

11.5  11.6 

0.7  0.5  −0.3  0.6  
Percentile 50%  10.6  10.8 

10.5  10.6 

14.0  14.1 

14.0  13.8  − 
18.6  19.0 

18.7  18.5  − 
2.6  2.1  −0.5  2.3  2.4 

Percentile 75%  15.9  16.5 

15.8  16.4 

19.9  20.4 

19.9  20.1 

25.0  26.1 

25.2  25.5 

7.6  7.2  −0.4  7.3  7.4 

Percentile 95%  19.6  20.3 

19.5  20.2 

23.6  24.2 

23.6  23.9 

29.6  30.7 

29.7  30.0 

22.9  22.6  −0.3  22.7  22.3  − 
>30 Cg/>80 mm  0  0 

0  0 

0  0 

0  0 

16  26 

17  28 

0  0  0  0  0 

>25 Cg/>40 mm  0  0 

0  0 

7  12 

7  14 

90  107 

94  108 

2  2  0  2  2 

<0 Cg, —  23  16  − 
22  16  − 
7  6  − 
7  6  − 
2  1  − 
2  1  − 
—  —  —  —  —  — 
<−5 Cg, —  2  1  − 
2  1  − 
0  0 

0  0 

0  0 

0  0 

—  —  —  —  —  — 
Winter  3.3  3.6 

3.3  3.8 

5.9  6.2 

6.0  6.2 

9.0  9.5 

9.1  9.5 

103.3  109.6  6.3  105.6  106.6 

Spring  7.4  8.7 

7.5  8.2 

11.1  12.4 

11.3  11.9 

16.0  17.1 

16.2  17.0 

49.6  51.3  1.7  51.5  51.1  − 
Summer  17.4  18.7 

17.4  18.6 

21.6  22.4 

21.6  22.5 

26.9  27.3 

27.1  28.2 

33.4  33.1  −0.3  33.0  36.8 

Autumn  12.4  12.7 

12.3  12.7 

15.6  15.6 

15.6  15.5  − 
19.9  19.7  − 
20.0  20.1 

84.2  83.1  −1.0  85.4  91.9 

Annual  10.1  10.9 

10.1  10.8 

13.6  14.1 

13.6  14.0 

17.9  18.4 

18.1  18.7 

67.6  71.9  4.3  68.9  71.6 

The comparison results between the periods of 1912–1964 and 1965–2016 and the periods of 1912–1980 and 1981–2016 showed that (Table
Comparison of the daily maximum temperature series for two periods of 1912–1964 and 1965–2016 revealed an increment of 0.8°C which can be divided into an average value of 18°C for the period of 1912–1964 and an average value of 18.7°C for the period of 1965–2016. On the other hand, comparison of the daily maximum temperature series for the periods of 1912–1980 and 1981–2016 has revealed an increment of 0.6°C with an average value between 18.2°C and 18.8°C for both of these periods, respectively. In addition, the standard deviation values are increased between 0.2°C and 0.3°C during the whole studied period. The increment in the minimum values of daily maximum temperature series is more evident than the maximum values. The minimum values of daily maximum temperatures have exhibited an increment of 0.8°C for the period of 1965–2016 compared to the previous period of 1912–1964 and also an increment of 0.7°C for the period of 1981–2016 compared to the previous period of 1912–1980. Also, the maximum values of daily maximum temperature series exhibited a mean increment of 0.5°C for both studied periods. Seasonal analysis of maximum temperature series for both of studied section periods showed that the highest rising temperature has been happened by a value of 1.2°C in summer. On the other hand, the lowest increment has happened in the autumn season. The monthly analysis of daily maximum temperature series showed that the highest increment took place during the last months of the spring season and the first month of the summer season in all of the studied periods. When the percentiles of daily maximum temperatures are analyzed, the temperature increment based on the 5th percentile threshold is 0.5°C for the periods of 1912–1964 and 1965–2016, while the increment is 0.3°C for the periods of 1912–1980 and 1981–2016. This can be considered as an important sign of rising temperature over the time. In this case, the value of percentile thresholds is increased with extending the length of the time period with extending the length of the first section of studied period in favor of last years than the previous ones. In this regard, these values are 0.5°C and 0.4°C at the 25th percentile, 1°C and 1.1°C at the 75th percentile, and 1.1°C and 1.2°C at the 95th percentile for both sections of studied periods, respectively. This situation shows that the increment of higher values in the daily maximum temperatures is greater than lower values.
The comparison analysis of daily minimum temperatures between the periods of 1912–1964 and 1965–2016 and the periods of 1912–1980 and 1981–2016 showed that there is a general increment of 0.5°C during the first section periods which can be given as 10.2°C and 10.7°C for the individual periods of 1912–1964 and 1965–2016 and also a general increment of 0.8°C during the second section periods which can be provided as 10.2°C and 11°C for the individual periods of 1912–1980 and 1981–2016, respectively. In addition, the standard deviation values increased among these section periods from 0°C to 0.3°C. The increment in the minimum values of daily minimum temperature series is more evident than the maximum values. The minimum values of daily minimum temperature series showed an increment of 1.2°C from the period of 1912–1964 to 1965–2016 and also an increment of 1.6°C from the period of 1912–1980 to 1981–2016. The maximum values of daily minimum temperature series have shown an increment of 0.7°C for the section periods of 1912–1964 and 1965–2016 and an increment of 1.2°C for the section periods of 1912–1980 and 1981–2016. Overall, the minimum values have had an average increment of 1.4°C, while the maximum values have had an average increment of 1°C during the last century, which can show the higher rate of upward trends in the temperature time series. Monthly analysis of minimum temperature series showed that the highest increment for the section studied periods of 1912–1964 and 1965–2016 has occurred by a value of 1°C in June, while the highest increment for the section studied periods of 1912–1980 and 1981–2016 has occurred by a value of 1.6°C in August. Meanwhile, there is a temperature decrement in November in both of these periods. However, there is a clear decrement in the first half of these periods in October and December, whereas there is an increment in the second half of these periods. The seasonal analysis of the daily minimum temperature series showed that the highest increment has happened in the summer season with a mean value of 0.7°C for the section periods of 1912–1964 and 1965–2016 and with a mean value of 1.3°C for the section periods of 1912–1980 and 1981–2016, respectively. Then, the increasing rate during the summer season became more evident during the recent decades. Analysis of the percentile thresholds of daily minimum temperature series showed that the temperature increment at the 5th percentile is 0.6°C for all studied time periods of 1912–1964, 1965–2016, 1912–1980, and 1981–2016. Also, these increment values indicate an increase of 0.4°C and 0.6°C at the 25th percentile, 0.7°C and 1.1°C at the 75th percentile, and 0.7°C and 1.4°C at the 95th percentile thresholds for the whole studied subperiods of 1912–1964, 1965–2016, 1912–1980, and 1981–2016, respectively. These rising rates in minimum temperature series are more evident for the periods of 1912–1980 and 1981–2016 than the periods of 1912–1980 and 1981–2016. Therefore, it can be said that the rate of temperature rising has increased further as long as the studied time period is closer to the last years.
Annual average precipitation in Istanbul is 838 mm with a range of minimum value of 449 mm in 1921 and a maximum value of 1289 mm in 1981 based on the observatory data of Kandilli station during the whole studied period from 1912 to 2016 (Figure
Analysis of the trend in the annual average precipitation time series by the methods of linear regression analysis and MK trend test has shown that periodically there are partial increments and significant differences during the total studied period from 1912 to 2016 (Figures
The comparison of the results of statistical analysis between the daily average rainfall amounts belonging to the periods of 1912–1964 and 1965–2016 with those of the periods of 1912–1980 and 1981–2016 revealed that there is an increment of 78 mm from the period of 1912–1964 to the period of 1965–2016 and an increment of 38 mm from the period of 1912–1980 to the period of 1981–2016. In addition, the analysis of standard deviation exhibited a decrement from the period of 1912–1964 to the period of 1965–2016 and an increment from the period of 1912–1980 to the period of 1981–2016 (Table
Generally, the results of trend analysis of Kandilli station during the last 105 years of 1912–2016 showed that there is a warming significant trend in the precipitation time series by using both methods of linear regression analysis and MK trend test. On the contrary, previous climate studies conducted over Turkey put forward that there has been a decreasing trend in annual precipitation time series during the recent decades, regionally. The results of a previously conducted study by using the daily precipitation and temperature data sets of Florya and Göztepe meteorological stations in Istanbul area between 1960 and 2013 showed that most notably the precipitation during the warm periods has decreased, but the frequency of the intense rain has increased and the majority of these episodes of intense rain coincided with the warm periods. Other determinations were the rise in the annual average temperature and the extension of the warm periods in a year. This differentiation of the temperature features can lead to the aggravation of the evaporation and it can be effective for a longer period during the year [
Statistical analysis in temperature time series of the Kandilli station from 1912 to 2016 established that there is a notable increase in temperature values after the 1940s which is in parallel with the beginning of industrialization era in Istanbul. There has been a rise about 0.94°C in the daily average temperature series since the beginning of the last century. A significant positive trend in the daily maximum temperature series is found about 1.56°C. Also, there is a positive trend about 0.87°C in the daily minimum temperature series. On the other hand, analysis of the number of days with the daily maximum temperature higher than 30°C showed that there is an increasing trend. Meanwhile, analysis of the number of days with daily minimum temperatures lower than 0°C showed a decreasing trend. The increment in the minimum values of the daily minimum temperature series is more evident than the maximum values of this series. In this case, these rising rates in the minimum temperature series are more evident for the section periods of 1912–1980 and 1981–2016 than the section periods of 1912–1964 and 1965–2016. This again shows that there is an increment in the positive temperature trend from past to present decades. The increment in the precipitation time series is not as clear as the increment in the temperature time series due to periodic variability. The trend analysis in the total annual precipitation time series showed that the first significant upward trend has periodically been started from the 1920s, while there is a stable trend from 2001 till 2016. The daily average of rainfall amounts has increased with a value of 58 mm during the period of 1912–2016. Also, the analysis of heavy precipitation trend showed an increase of 6.1 mm. Overall, the total average precipitation of Istanbul increased, while this increasing trend is more pronounced during the early decades than the last 3 decades. On the other hand, the increasing rate of daily maximum precipitation is more pronounced in the last 3 decades than the previous decades. Then, it was shown that the frequency of heavy rainfall at Istanbul has increased during the recent decades. Thus, the precipitation changes in Istanbul have some differences compared to the general tendency in precipitation trend that was put forward by other studies as a decreasing trend over the whole of Turkey. This result can be expressed as a positive effect of population overgrowth of Istanbul megacity. Comparison of the results in the first half of the study period (1912–1964) with the second half of the study period (1965–2016) showed that both the average temperature and average precipitation have higher values of 13.9°C and 878 mm for the final phase compared to the values of 13.6°C and 799 mm belonging to the initial phase. Therefore, it can be stated that the megacity of Istanbul is directly affected by the climate change and its consequences. In this context, potential risks of climate change in Istanbul megacity under higher temperature conditions can be expressed as the rise in the sea level, increase in the rate of evapotranspiration, and increase in the frequency of heavy rainfall. Also, this city may not be able to handle this uncontrolled population growth and its associated irreversible changes, which is already pushing the natural limits by destroying the environment. Therefore, the local governors of any megacity like Istanbul should give more emphasis on the importance of sustainable urban dev
The authors declare that there are no conflicts of interest regarding the publication of this paper.
The authors are grateful to the Boğaziçi University, the observatory of Kandilli weather station, and the Earthquake Research Institute for providing the research data and technical support. The authors also gratefully acknowledge contributions of Assoc. Professor Dr. Yüksel Demirkaya, School of Social Sciences, Marmara University. This work has been supported by Scientific and Technological Research Council of Turkey (TUBITAK) under Grants 113R019 and 106Y258 and by Marmara University (BAPKO) with projects FENE1203140066, FENCYLP0904140102, FENL2504160180, and FENA1004130127.