Reg Environ Change (2014) 14:1967–1981 DOI 10.1007/s10113-013-0530-7

ORIGINAL ARTICLE

Assessment of bioclimatic conditions on Island,

Anastasia Bleta • Panagiotis T. Nastos • Andreas Matzarakis

Received: 3 May 2012 / Accepted: 30 August 2013 / Published online: 13 September 2013 Ó Springer-Verlag Berlin Heidelberg 2013

Abstract The objective of this study was to assess and island’s current bioclimate, in order to make any necessary analyze the human bioclimatic conditions of Crete Island, adaptations and become more resilient to the foreseen by applying two human thermal indices: physiological climate change. equivalent temperature (PET), derived from the Munich Energy-balance Model for Individuals human energy bal- Keywords Bioclimatic conditions PET UTCI ance model, and Universal Thermal Climate Index (UTCI), Crete Island based on the Fiala multi-node model of human thermo- regulation. Human bioclimatic studies provide a frame- work for considering the effects of climatic conditions on Introduction human beings and highlighting the social/economic factors that mitigate or amplify the consequences of environmental The quality of life in an urban or rural environment is changes. In order to estimate the thermal effect of the influenced significantly by bioclimatic conditions, both environment on the human body, it has been considered short and long terms. Bioclimatic conditions are modified that the total effects of all thermal components, not only of due to environmental factors and the complex structure and individual parameters, should be taken into account. The development of urban agglomerations as well. There has climatic data (air temperature, relative humidity, cloudi- been extended human biometeorological research indicat- ness, wind speed) used in this study were acquired from the ing the impact of urban bioclimate on human morbidity archives of the Hellenic National Meteorological Service, (Schwartz et al. 2004; Nastos and Matzarakis 2006; Mi- regarding ten meteorological stations in Crete Island. These chelozzi et al. 2007), mortality (Curriero et al. 2002; An- data, covering the 30-year period 1975–2004, were used for alitis et al. 2008; Baccini et al. 2008; Hajat and Kosatky the calculation of PET and UTCI in order to assess thermo- 2010; Almeida et al. 2010; Nastos and Matzarakis 2012), physiological stress levels. The findings of this analysis, tourism potential and decision making (de Freitas 2003; such as bioclimatic diagrams, temporal and spatial distri- Didaskalou and Nastos 2003; Hamilton and Lau 2005; Lin butions of PET and UTCI as well as trends and variability, et al. 2006; Matzarakis and Nastos 2011), and urban will help stake holders to understand and interpret the planning (Carmona et al. 2003; Nikolopoulou and Steemers 2003; Nikolopoulou and Lykoudis 2006; Thorsson et al. 2004; 2007). Over the last years, many attempts have been A. Bleta P. T. Nastos (&) made to formulate a reliable and user-friendly index for the Laboratory of Climatology and Atmospheric Environment, assessment of the physiological thermal response of the Department of Geography and Climatology, Faculty of Geology and Geoenviroment, National and Kapodistrian University of human body to climatic conditions (d’Ambrosio Alfano Athens, Panepistimiopolis, 15784 Athens, Greece et al. 2011), but only physiological equivalent temperature e-mail: [email protected] (PET) and Universal Thermal Climate Index (UTCI) seem to meet these requirements. PET is recommended for the A. Matzarakis Meteorological Institute, Albert Ludwigs University of Freiburg, evaluation of the thermal component of different climates 79085 Freiburg, Germany by VDI Guideline 3787 (VDI 1998). PET is based on the 123 1968 A. Bleta et al.

Munich Energy-balance Model for Individuals (MEMI), purpose of the present study is to quantify the bioclimatic which describes the thermal conditions of the human body conditions on Crete Island, during the 1975–2004 period, in a physiological relevant way (Fanger 1972;Ho¨ppe based on PET and UTCI human thermal indices. 1993). UTCI was developed following the concept of an equivalent temperature and has been applied in recent human biometeorological studies, such as daily forecasts Data and analysis and extreme weather warnings, bioclimatic mapping, urban and regional planning, environmental epidemiology, and The climatic data used in this study concern mean daily climate impacts research (Jendritzky et al. 2012). The values of air temperature, relative humidity, cloudiness, UTCI represents an equivalent temperature that equals to and wind speed, acquired from the archives of the Hellenic the ambient air temperature resulting in the same level of 7 National Meteorological Service (HNMS) concerning ten crucial physiological parameters, which an average person meteorological stations in Crete, during the period would experience in a reference environment (Jendritzky 1975–2004. The geographic characteristics of the HNMS et al. 2002, 2008; Fiala et al. 2012). stations are presented in Table 1. The stations are divided The bioclimatic analysis in this study concerns Crete into three groups: stations located on the northern coasts, Island, a climate-sensitive area, affected by frequent Sah- mountainous stations, and stations on the southern coasts of aran dust episodes especially during spring and summer Crete Island. periods, when the development of suitable synoptic mete- The data sets have been tested for homogeneity in pre- orological conditions often occurs (Kaskaoutis et al. 2008). vious studies (Matzarakis and Nastos 2011; Nastos et al. Furthermore, the topography of the island and the conse- 2002) and were used for the calculation of PET and UTCI quent Fo¨hn winds develop worse bioclimatic conditions in order to assess the level of the thermo-physiological (Nastos et al. 2011), which are exacerbated due to atmo- stress. spheric pollution in urban agglomerations and strongly For bioclimatic purposes, the wind velocity for all the impact public health. examined stations was adjusted according to the following Climate change is considered to be the main driving formula (Kuttler 2000): force and its effects are expected to be more intense in the a WS1:1 ¼ WSh ð1:1=hÞ a ¼ 0:12 z0 þ 0:18 forthcoming years. The stake, therefore, lies in mitigating -1 the environmental, social, and economic impacts on the where WSh is the wind speed (m s ) at the station’s height lucrative sectors of the region and tourism, agriculture, and (h, usually 10 m), a is an empirical exponent, depending on services related to civil protection. An overarching priority the surface roughness, and z0 is the roughness length. Wind in future research is the adaptation to climate and envi- velocity was estimated at 1.1 m, which is the center of ronmental changes and related issues such as sustainable gravity of the human body, and builds the reference level cities and coastal zones as well as resilient societies, as for human biometeorological studies. In this study, three identified in the 7th Framework Program. Coastal areas are different values of roughness length were applied highly threatened since they are hotspots for pollution, depending on the landscape around the examined station. increased water demands, and high urbanization pressures. Thus, z0 = 0.2 for agricultural land with many houses, Located on the land and sea boundary, they are particularly shrubs, and plants, or 8-m-tall sheltering hedgerows within vulnerable to climate and global changes. Thus, the a distance of about 250 m (stations: Palaiochora and

Table 1 Characteristics of the Code Station Latitude Longitude Altitude Period meteorological stations in Crete (degrees) (degrees) (m) Island 1 746 SOUDA 35.3 24.0 10 1975–2004 2 758 35.4 24.5 7 1975–2004 3 754 35.3 25.2 39 1975–2004 4 757 35.2 26.1 22 1975–2004 5 755 FOURNI 35.3 25.7 315 1975–2004 6 752 ANOGEIA 35.3 24.9 822 1975–2004 7 760 KASTELLI 35.2 25.3 333 1975–2004 8 751 PALAIOCHORA 35.2 23.7 4 1975–2004 9 759 TYBAKI 35.0 24.5 7 1975–2004 10 756 35.0 25.7 13 1975–2004

123 Bioclimatic conditions on Crete Island 1969

Kastelli); z0 = 0.4 for villages, small towns, agricultural physiological response to the meteorological input is based land with many or tall sheltering hedgerows, forests, and on a multi-node model of human thermoregulation (Fiala very rough and uneven terrain (stations: Souda, Anogeia, et al. 2001), associated with a clothing model. The UTCI Fourni, Tymbaki); z0 = 0.8 for larger cities with tall assessment scale is presented in Table 3. The assessment buildings (stations: Heraklion, Ierapetra, Sitia, Rethymno). scale is based on different combinations of rectal and skin The aforementioned values of roughness length for a spe- temperatures, sweat rate, shivering, etc., that might indicate cific terrain were derived from the European Wind Atlas ‘‘identical’’ strain causing non-unique values for single (Troen and Petersen, 1989). variables like rectal or mean skin temperature in different PET is equivalent to the air temperature at which—in a climatic conditions with the same value of UTCI (Błaz- typical indoor setting (without wind and solar radiation)— ejczyk et al. 2012). Static clothing insulation is adjusted to the heat balance of the human body (work metabolic rate the ambient temperature considering seasonal clothing 80 W of light activity that should be added to the basic adaptation habits of Europeans, which notably affects metabolic rate 86.5 W, Stolwijk and Hardy 1977; heat human perception of the outdoor climate (Havenith et al. resistance of clothing 0.9 clo, which is the reference 2012). In this point, it is worth mentioning that while in clothing insulation value used for the formulation of PET) principle the PET scale represents thermal sensations of is maintained with core and skin temperatures equal to thermal environment experienced by specific population, those of the under assessment conditions (Mayer and the UTCI scale represents heat/cold stress intensities Ho¨ppe 1987;Ho¨ppe 1999). The following assumptions are regardless the population type. The UTCI scale can be made for indoor reference climate: Mean radiant temper- applied to a very wide range of temperatures, from -70 to ature equals air temperature (Tmrt = Ta). Air velocity is ?50 °C. set to 0.1 m/s. Water vapor pressure is set to 12 hPa The input variables in modeling mean daily PET and (approximately equivalent to relative humidity of 50 % at UTCI are mean daily values of air temperature, relative Ta = 20.0 °C). The PET assessment scale (Table 2)is humidity, wind speed, and radiant temperature. The input derived by calculating Fanger’s (1972) PMV for varying variable of mean daily radiant temperature (the uniform air temperatures in the reference environment using the temperature of a surrounding surface that results in the settings for the PET reference person (height: 1.75 m, same radiation energy gain on a human body as the pre- weight: 75 kg, age: 35 years, and sex: male; work meta- vailing radiation fluxes) is modeled based on mean daily bolic rate 80 W of light activity that should be added to the cloud coverage. In the study, both PET and UTCI were basic metabolic rate and heat resistance of clothing 0.9 calculated using ‘‘RayMan’’ model, appropriate to calcu- clo,) (Matzarakis et al. 1999). According to Ho¨ppe (1999), late radiative heat transfer and human biometeorological the assumption of constant values for clothing and activity indices (Matzarakis et al. 1999, 2010). The ‘‘RayMan’’ in the calculation of PET were made in order to define an model, developed according to Guideline 3787 of the index independent of individual behavior. German Engineering Society (VDI 1998), calculates the UTCI is defined as the equivalent ambient temperature radiative heat transfer in both simple and complex envi- (°C) of a reference environment providing the same ronments. The main feature and advantage of ‘‘RayMan’’ physiological response of a reference person as the actual compared to other similar models is the calculation of environment (Weihs et al. 2012). The calculation of the short- and long-wave radiation fluxes, the possibility to

Table 2 Physiological equivalent temperature (PET) for different Table 3 UTCI Assessment Scale: UTCI categorized in terms of grades of thermal sensation and physiological stress on human beings thermal stress (Bro¨de et al. 2012b) (Matzarakis et al. 1999) UTCI (°C) Stress category PET (°C) Thermal sensation Physiological stress level [ ?46 Extreme heat stress \4 Very cold Extreme cold stress ?38 to ?46 Very strong heat stress 4–8 Cold Strong cold stress ?32 to ?38 Strong heat stress 8–13 Cool Moderate cold stress ?26 to ?32 Moderate heat stress 13–18 Slightly cool Slight cold stress ?9to?26 No thermal stress 18–23 Comfortable No thermal stress ?9 to 0 Slight cold stress 23–29 Slightly warm Slight heat stress 0to-13 Moderate cold stress 29–35 Warm Moderate heat stress -13 to -27 Strong cold stress 35–41 Hot Strong heat stress -27 to -40 Very strong cold stress [41 Very hot Extreme heat stress \-40 Extreme cold stress

123 1970 A. Bleta et al. evaluate the thermal environment throughout the year for are not shown for brevity, but are also discussed along with both cold and hot seasons, and the use of a common unit PET diagrams further below. (°C). As far as the stations on the northern coasts of the island The Mann–Kendall rank statistic method was applied (Souda, Rethymno, Heraklion, and Sitia) are concerned, the concerning the trends of the time series of annual number analysis of the bioclimatic diagrams showed that the thermal of days with mean daily PET/UTCI falling in the extreme comfort class (18 °C \ PET \ 23 °C) occurs throughout classes of PET/UTCI (Mitchell et al. 1966). the year in all stations. The frequency of the thermal comfort class ranges from 0.3 % (August, in Souda) to 38.4 % (October, in Heraklion). The thermal comfort class presents Results and discussion frequencies from 1.3 % (August, in Tybaki) to 38.4 % (March, in Palaiochora) throughout the year, concerning the The northern, mountainous and southern meteorological southern coastal cities, while this class disappears in July stations of HNMS were kept in different groups (Table 1). and August in Palaiochora. Our findings indicate that the The northern coasts of Crete are under the influence of the thermal comfort class counts for higher frequencies for the northerly winds, especially during summer time and early northern stations against the southern ones. autumn, when the ‘‘Etesians’’ prevail. These are periodical Taking into account the thermal index UTCI, the class winds of the north section established over the Aegean Sea, of thermal comfort (9 °C \ UTCI \ 26 °C) for northern when a high-pressure center in the central and south Eur- stations is missing in December and January in Souda, ope is combined with the Indian low-pressure system over while it reaches 90.9 % in November in Heraklion. Con- Asia Minor and the Eastern (Metaxas cerning the southern stations, UTCI appears to be between and Bartzokas 1994). A characteristic effect of the Etesians 0.1 % (August, in Palaiochora) and 95.7 % (December, in regime is summer droughts and uniform weather conditions Palaiochora). in Greece (Nastos et al. 2002). This prevailing weather type The frequency of the strong heat stress class for PET on (cool and dry winds over the Aegean Sea) in summer the northern coasts of the island does not appear in cold moderates the intensity of heat stress at the northern coasts months (December to February, in Souda and Rethymno; of Crete. The beneficial impacts of ‘‘Etesians’’ winds do November to March, in Sitia; December to March, in not appear at the southern coasts, due to the blocking Heraklion), while the maximum frequency (31.8 %) comes induced by the mountain ranges, leading to increased heat up in August, in Rethymno. Concerning the southern stress within the summer period. In addition, the southern coastal cities, the strong heat stress class does not appear in coasts are protected against the winter northerly winds and, January in Tybaki, from December to January in Ierapetra, thus, mild bioclimatic conditions prevail during the cold and from December to March in Palaiochora, while the period of the year. It is evident that the topography of the highest frequency is 52.1 % in September, in Palaiochora. island is responsible for extreme weather conditions. This On the other hand, the strong cold stress class is absent is the case of Heraklion city located in the basin northward from May to June and October in Sitia, and from May to the Mount Psiloritis (2,456 m), which is perpendicular to October in Souda, Rethymno, and Heraklion, regarding the the southern air mass flow, causing the so-called Fo¨hn northern coastal stations. Similar patterns occur in the winds. Coming down from the lee of the mountain, these southern coastal cities, where this class does not appear winds are getting warm at a dry adiabatic rate and arrive at from May to October at any of the stations, whereas it lower elevations both warmer and drier than they were at reaches maximum frequency (15.3 %) in February, in corresponding levels on the windward side. Descending to Ierapetra. the lowlands on the leeward side of the range, the air The strong heat stress for UTCI index on the north arrives as a strong, gusty, desiccating wind. The wind often coasts of the Crete Island does not appear from September lasts for 3 days or more, gradually weakening after the first to May in Souda, from November to April in Heraklion and or second day. Sometimes, it stops very abruptly (Nastos Rethymno, and from November to March in Sitia, reaching et al. 2011). its maximum frequency (55.8 %) in August, in Rethymno. Figures 1, 2, and 3 depict the bioclimatic diagrams for Regarding the southern coastal stations, this class does not PET with respect to the stations under examination taking come up from December to April in Palaiochora, from into consideration the aforementioned division in three November to April in Tybaki, and from November to groups (northern, southern, and mountainous stations). The March in Ierapetra, while the maximum frequency human thermal bioclimatic conditions are expressed in (79.0 %) appears in August in Palaiochora. The strong cold percentages of the occurrence of PET classes (Table 2) for stress class is really scarce for northern stations. More each month. The respective bioclimatic diagrams for UTCI specifically, this class does not occur at all in Souda and

123 Bioclimatic conditions on Crete Island 1971

Fig. 1 Frequencies of various classes of PET index for northern coastal areas of Crete Island (period 1975–2004)

123 1972 A. Bleta et al.

Fig. 2 Frequencies of various classes of PET index for southern coastal areas of Crete Island (period 1975–2004)

does not appear from April to December in Heraklion, from The extreme heat class for PET at the northern stations March to September and November in Rethymno, and from is absent from November to March in Souda, Rethymno, March to November and January in Sitia. The maximum and Sitia, and from November to April in Heraklion, pre- frequency is 0.6 % in February, in Heraklion. For the senting the maximum frequency (13.7 %) in July in Ret- southern coastal stations, the strong cold stress does not hymno. Similar temporal patterns appear at the southern exist throughout the year for Palaiochora and Tybaki, stations; there is no extreme heat stress from November to neither does it appear from April to November in Ierapetra. April in Palaiochora, from November to February in Ty- However, it reaches the maximum frequency 0.83 % in baki, and from November to March in Ierapetra. The February, in Ierapetra. maximum frequency (36.5 %) occurs in July in

123 Bioclimatic conditions on Crete Island 1973

Fig. 3 Frequencies of various classes of PET index for mountain areas of Crete Island (period 1975–2004)

Palaiochora. Taking into account the frequencies of the November in Tybaki, and from April to June, and August extreme cold class for northern stations, the highest fre- to October in Ierapetra, presenting the maximum frequency quency (4.9 %) appears in February in Souda, while this (4.2 %) in February, in Ierapetra. class does not exist from April to October in Souda, from The very strong heat class for UTCI at the northern April to November in Heraklion, from April to September stations ranges from 0.2 % (August, in Sitia) to 4.3 % and November in Rethymno, and in April, May, July, (July, in Rethymno) against 0.1 % (November in Palai- September, and October in Sitia. Regarding the southern ochora and September in Ierapetra) to 14.9 % (July, in stations, the class of extreme cold stress does not appear Palaiochora). The very strong cold class is not apparent at from March to November in Palaiochora, from April to the northern and southern stations throughout the year. The

123 1974 A. Bleta et al.

123 Bioclimatic conditions on Crete Island 1975 b Fig. 4 Time series of annual number of days within extreme classes class ranges from 0.3 % (August, in Anogeia) to 93.2 % of mean daily PET, along with linear trends, (left graphs) and intra- (November, in Anogeia). It is worth noting that the small annual variation of the daily composite (averages) of mean daily PET, as the highest and lowest mean daily PETs for each Julian day frequencies of extreme classes of UTCI can be explained through the period 1975–2004 for the examined stations of HNMS in by the nature of this index as its values and scale represent Crete (right graphs) a very wide range of air temperatures. The climate of Crete does not present extremely low or high temperatures, extreme heat class for UTCI index (UTCI [ 46 °C) does which accounts for the absence of extreme UTCI classes. not exist at the northern stations, with the exception of The findings extracted by the analysis of bioclimatic Sitia, where the class slightly appears from June to August diagrams using ground-based observations are in good presenting the highest frequency (0.5 %) in July. Besides, agreement with the results presented by Matzarakis and this class is absent at the southern stations with the Nastos (2011), who used climate data from the 10-min exception of Palaiochora, where it presents a value of climatology (New et al. 1999, 2000) in order to create a 0.4 % in July. The extreme cold class of the assessment PET map of high spatial resolution (1 km 9 1 km) for scale (UTCI \ -40 °C) does not appear at any of the Crete Island, within the period 1961–1990. northern and southern stations. The intra-annual variations of the daily composite Regarding the mountain stations, the main characteristic (averages) of mean daily PET, as well as the highest and is that the extreme cold stress class for PET appears within lowest mean daily PETs for each Julian day through the 7 months (October to April) in Anogeia and Kastelli, and period 1975–2004 for the examined stations in Crete are 6 months (November to April) in Fourni, ranging from depicted in Fig. 4 (right graphs). Looking at the extreme 0.1 % (April, in Fourni and October in Kastelli) to 18.8 % values of the mean daily PET, the highest mean daily PET (January, in Fourni). The strong cold stress is apparent at the northern coastal stations ranges between 14.1 °C within 8 months (October to May) in Kastelli and Anogeia, (February 20, in Heraklion) and 55.8 °C (July 27, in Sou- and 7 months (October to April) in Fourni, ranging from da), against 17.1 °C (January 16, in Ierapetra) and 56.8 °C 0.1 % (October, in Kastelli) to 27.4 % (January, in Kas- (July 20, in Tybaki), for the southern coastal stations. The telli). On the other hand, the class of extreme heat stress estimated highest mean daily PET remains above 41.0 °C has been decreased to 5–6 months (May to September in (extreme heat stress) for a long period in southern stations Fourni and Anogeia; April to September in Kastelli), compared to northern ones. As mentioned above, this is ranging from 0.1 % (September, in Anogeia and May in very likely due to the blocking of the northerly cold winds Fourni) to 6.9 % (July, in Anogeia). The strong heat stress by the mountain ranges along the island. Taking into is estimated to appear from March to November (in Kas- account the lowest mean daily PET, it appears within telli and Anogeia) and from April to October in Fourni, -6.1 °C (December 10, in Sitia) and 28.7 °C (August 9, in having frequencies from 0.1 % (March, in Anogeia) to Souda) concerning the northern stations, against -3.0 °C 37.5 % (July, in Anogeia). Finally, the thermal comfort (February 9, in Ierapetra) to 33.0 °C (August 14, in Pal- conditions range from 0.3 % (January, in Fourni) to 38.9 % aiochora), for the southern stations. Regarding the moun- (May, in Kastelli). tain stations, the highest mean daily PET varies between The extreme cold stress class for UTCI does not appear 13.0 °C (January 20, in Fourni) and 52.0 °C (July 10, in at any of the mountain stations, while the class of the very Kastelli), while the lowest mean daily PET presents values strong cold stress comes up only in January (0.1 %) in within the range -10.0 °C (February 18, in Anogeia) and Fourni. The strong cold stress is estimated to appear within 29.0 °C (July 19 in Anogeia). 2 months (January to February in Kastelli and Anogeia) The intra-annual variations of the daily composite and 4 months (December to March in Fourni), ranging (averages) of mean daily UTCI, as well as the highest and from 0.1 % (February, in Anogeia) to 1.9 % (February, in lowest mean daily UTCIs for each Julian day through the Fourni). On the other hand, the extreme heat stress class is period 1975–2004 for the examined stations of HNMS in missing throughout the year with an exception in July Crete are depicted in Fig. 5 (right graphs). The highest (0.1 %) in Fourni, against very strong heat stress, which mean daily UTCI at the northern coastal stations ranges appears within 4 months (June to September in Kastelli between 18.0 °C (January 12, in Herkalion) and 42.0 °C and May to August in Anogeia) and 2 months (July and (July 27, in Souda). At the southern coastal stations, the August in Fourni), ranging from 0.1 % (May, in Anogeia) highest mean daily UTCI lies between 21.0 °C (January to 2.5 % (July, in Fourni). The strong heat stress is esti- 10, in Ierapetra) and 47.0 °C (July 7, in Palaiochora). On mated to be within 7 months (April to October, in Fourni the other hand, the lowest mean daily UTCI for northern and Anogeia) and 5 months (May to September in Kas- coastal stations varies from -21.0 °C (February 18, in telli), taking frequencies from 0.1 % (April in Anogeia) to Heraklion) to 29.4 °C (August 9, in Souda), against 41.7 % (July in Anogeia). Finally, the thermal comfort -23.0 °C (February 9, in Ierapetra) and 32.3 °C (August 123 1976 A. Bleta et al.

123 Bioclimatic conditions on Crete Island 1977 b Fig. 5 Time series of annual number of days within extreme classes very strong/strong cold stress and very strong heat stress is of mean daily UTCI, along with linear trends, (left graphs) and intra- missing for the majority of the examined stations with the annual variation of the daily composite (averages) of mean daily UTCI, as well as the highest and lowest mean daily UTCIs for each exceptions of Palaiochora and Tybaki (southern coastal Julian day through the period 1975–2004 for the examined stations of stations) presenting increasing and decreasing trends of HNMS in Crete (right graphs) strong heat stress, respectively (Table 5). The dominant class is that of strong heat stress indicating significantly 14, in Palaiochora), with respect to the southern coastal increasing trends in Souda and Ierapetra, and decreasing stations. Finally, the highest mean daily UTCI for the trends in Sitia and Tybaki. This is in agreement with the mountain station ranges between 16.7 °C (January 20, in trends appearing in the time series of PET strong heat stress. Fourni) and 49.2 °C (July 5, in Fourni), while the lowest Further, a comparison between the examined thermal mean daily UTCI presents values within the range indices, UTCI, and PET is made. High correlations were -30.0 °C (January 7, in Fourni) and 29.3 °C (August 10, in found for these two thermal indices (Table 6), namely the Anogeia). R-squared varies from 89.7 % in Fourni to 96.4 % in An analysis of the trends of the time series of annual Anogeia, with slopes from 0.715 in Palaiochora to 0.954 in number of days with mean daily PET within classes of Ierapetra. This is in agreement with the findings of Błaz- strong heat stress, extreme heat stress, strong cold stress, ejczyk et al. (2012), who concluded that the values for and extreme cold stress is presented, during the period indices deriving from human heat balance models, i.e., 1975–2004 (Fig. 4, left graphs). We only focus and com- PET, PT (perceived temperature), and SET* (standard ment on statistically significant trends of p \ 0.05 effective temperature), were most similar to those of UTCI, (Table 4). Regarding the northern coastal cities, only in the because these indices indicate equivalent temperature. case of Sitia, the days with strong cold stress show an In our case, the lowest mean daily PET values range increasing trend (0.460 days/year), while days with from ?0.2 °C (at Palaiochora) to -10.1 °C (at Anogeia), extreme and strong heat stress have a decreasing trend. against the lowest mean daily UTCI values ranging from Concerning the mountainous stations, Fourni station indi- -7.6 °C (at Palaiochora) to -30.0 °C (at Fourni). The cates an increasing trend in extreme heat stress, against scattering pattern of UTCI versus PET increases with Kastelli, where an increasing trend in extreme cold stress decreasing UTCI, and this can be explained due to the PET occurs. On the southern coasts, Tybaki presents an fixed clothing insulation under cold conditions against the increasing trend of extreme cold stress and decreasing wind-dependent clothing insulation of UTCI. As Blaz- trends of strong/extreme heat stress during the study per- ejczyk et al. (2012) commented UTCI is very sensitive to iod. Furthermore, an increasing trend of strong heat stress changes in air temperature, solar radiation, humidity, and appears in Ierapetra. especially wind speed, whereas PET is more closely related Additionally, the trends of the time series of annual to air temperature. number of days with mean daily UTCI within extreme Thorsson et al. (2007) showed good agreement of PET classes during the period 1975–2004 are depicted in Fig. 5 with the perception of interviewees by comparing the (left graphs). It is worth mentioning that the time series of results of structured interviews and of PET evaluation in an

Table 4 Trends of the time series of the annual number of days with mean daily PET within specific classes, representing the extreme/strong cold and heat stress Station PET \ 4 °C4°C \ PET \ 8 °C35°C \ PET \ 41 °C PET [ 41 °C b ± SE b ± SE b ± SE b ± SE

SOUDA n.s. n.s. n.s. n.s. RETHYMNO n.s. n.s. n.s. n.s. HERAKLION n.s. n.s. n.s. n.s. SITIA n.s. 0.460 ± 0.155* -0.634 ± 0.138* -0.328 ± 0.090* FOURNI n.s. n.s. n.s. 0.144 ± 0.062* ANOGEIA n.s. n.s. n.s. n.s. KASTELLI 0.371 ± 0.145* n.s. n.s. n.s. PALAIOCHORA n.s. n.s. n.s. n.s. TYBAKI 0.110 ± 0.044* n.s. -1.001 ± 0.273* -1.352 ± 0.325* IERAPETRA n.s. n.s. 0.950 ± 0.172* n.s. * Statistically significant values at p \ 0.05, while n.s. for not significant relationships

123 1978 A. Bleta et al.

Table 5 Trends of the time series of the annual number of days with mean daily UTCI within specific classes, representing the very strong/ strong cold and heat stress Station -40 °C \ UTCI \ -27 °C -27 °C \ UTCI \ -13 °C32°C \ UTCI \ 38 °C38°C \ UTCI \ 46°CC b ± SE b ± SE b ± SE b ± SE

SOUDA – – 0.820 ± 0.388* – RETHYMNO – – n.s. – HERAKLION – – n.s. – SITIA – – –0.963 ± 0.208* – FOURNI – – n.s. – ANOGEIA – – n.s. – KASTELLI – – n.s. – PALAIOCHORA – – n.s. 0.377 ± 0.145* TYBAKI – – -1.080 ± 0.321* -0.174 ± 0.754* IERAPETRA – – 1.010 ± 0.195* – * Statistically significant values at p \ 0.05, while n.s. for not significant relationships

Table 6 Statistical characteristics of the relationship between Uni- versal Thermal Climate Index (UTCI) and physiological equivalent Further to the above discussion, we must acknowledge a temperature (PET), for the examined sites in Crete Island, during the constraint related to the PET assessment scale. We used the period 1975–2004 PET scale for Western/Middle European countries taking Stations Slope R-squared (%) into consideration that Crete Island has a temperate cli- mate, not significantly different from the climate of Wes- SOUDA 0.813 94.2 tern/Middle European countries. Thus, the use of the PET RETHYMNO 0.894 91.4 assessment scale for Western/Middle European countries is HERAKLION 0.940 91.5 almost acceptable. A recent study by Cohen et al. (2012) SITIA 0.901 91.7 confirms our assumption, revealing that the acceptable FOURNI 0.922 89.7 comfort range of PET for the Mediterranean climate of Tel ANOGEIA 0.728 96.4 Aviv is 19–26 °C, against 18–23 °C for the acceptable KASTELLI 0.887 92.8 comfort range of PET for Western/Middle European PALAIOCHORA 0.715 95.2 countries. Besides, the assessment scale is frequently used TYBAKI 0.829 92.6 in international literature (Matzarakis et al. 1999) to esti- IERAPETRA 0.954 90.3 mate bioclimatic conditions in different places, such as Istanbul and Paris (Bouyer et al. 2007), Goteborg (Svens- son et al. 2003), Szeged (Gulyas et al. 2006), Matsudo (a urban park and a square in Matsudo, a satellite city near satellite city near Tokyo), Japan (Thorsson et al. 2007), Tokyo, Japan. Besides, PET has been used in urban built- Far-Eastern Federal District of the Russian Federation up area with complex shading patterns and generated (temperate monsoon climate zone, which is characterized accurate predictions of thermal environments (Thorsson by an extreme continental regime of annual temperatures) et al. 2007; Gulyas et al. 2006). Svensson et al. (2003) (Grigorieva and Matzarakis 2011). Another important issue presented the PET distribution map of Goteborg using the of using this assessment scale concerns international tour- geographic information system. Gulyas et al. (2006) eval- ists, who visit the Island of Crete, meaning that the thermal uated thermal comfort in Szeged, Hungary. Bouyer et al. comfort of international tourists coming from areas of high (2007) evaluated the thermal comfort in two stadia (Stade latitude (or moderate climate zones) differentiates from de France, Paris, and the Atatu¨rk Olympic stadium, Istan- that of local tourists on Crete Island. International tourists bul), using wind tunnel experiments and PET. They con- want to know the bioclimatic conditions of a region cluded that PET maps should not be regarded as according to their thermal sensation and not to the ‘‘absolute’’ results, and detailed analysis of the main heat respective one of the local people. This conclusion is in transfers, due to wind and radiative contributions, is nec- agreement with Lin (2009), who compared a modified PET essary. A high (or even unacceptable) level of wind scale for Taiwan with the PET scale for Western/Middle velocity combined with a high amount of solar loads leads European countries. He concluded that compared to the to PET values that could have been obtained with mild thermal acceptable range on Western/middle European conditions. scale (18–23 °C PET), the thermal acceptable range in 123 Bioclimatic conditions on Crete Island 1979

Taiwan, which has a hot and humid climate, is much higher compared to the respective PET class, for all the examined (21.3–28.5 °C PET), confirming the different thermal stations; especially, during the cold months, this UTCI requirements of people living in different regions. class dominates and in many cases exceeds 90 % against Concerning UTCI, one limitation might be the applica- PET thermal comfort class, reaching approximately 38 %. tion in studies concerning health risk assessment under Another finding is that the UTCI values of extreme/very extreme conditions (in extreme hot or extreme cold envi- strong/strong cold stress and very strong heat stress are ronments), where a one-scale deviation might already lead missing for the majority of the examined stations with the to a critical decision argument (Weihs et al. 2012). UTCI exceptions of Palaiochora and Tybaki (southern coastal has been applied in order to differentiate cities in terms of stations) showing increasing and decreasing trends of thermal stress. Idzikowska (2010) examining the biocli- strong heat stress, respectively. Taking into consideration matic conditions on the basis of the UTCI in four cities the scatter plots of UTCI versus PET, we found that scat- such as Rome, Budapest, Paris, and Warsaw showed that tering increases with decreasing UTCI, and this can be ‘‘no thermal stress’’ occurs throughout the year in all four explained due to the PET fixed clothing insulation under cities. Extreme values of heat appeared in Rome and cold conditions against the wind-dependent clothing insu- Budapest, while cold stress was observed in Warsaw, Paris, lation of UTCI. and Budapest. Furthermore, the application of UTCI in The analysis showed that during the summer period, the bioclimatic research was performed in Warsaw by Lindner intensity of heat stress decreases in urban areas on the (2011) and in Czech Republic by Nova´k(2011). Bakowska northern coasts of Crete, due to the cooling impacts of (2010) performed bioclimatic analysis concerning the daily ‘‘Etesians’’ winds, which do not appear on the southern course of UTCI in Koszalin, Warsaw, and Wroclaw for coasts. The ‘‘Etesians’’ winds are blocked by the mountain different air masses such as arctic, polar maritime, polar ranges along the island and thus the southern coastal continental, and tropical. The results showed that advec- regions experience longer periods with estimated PET tions of polar continental air masses in winter caused most extreme/strong heat stress. Nevertheless, the blow of severe bioclimatic conditions in Poland, while these masses southern winds (associated with Saharan dust episodes in were responsible for strong heat stress in summer. Kunert spring/summer time) exacerbates the bioclimatic condi- (2010), simulating UTCI in the landscape of the Warsaw tions at northern coastal urban areas (such as Heraklion), Lowland in different weather conditions, found that relief because of the development of the hot and dry Fohn winds features have the greatest influence on the modification of coming from the lees of the mountain ranges. On the other thermal conditions. Differences of UTCI between the hand, the bioclimatic conditions over the mountainous warmest and the coldest areas, in similar weather condi- regions indicate that the estimated PET extreme heat stress tions, rise above 30 °C. Besides, the impacts of bioclimatic class shows low frequencies from June to August against conditions with respect to UTCI in organic-cause mortality moderate frequencies of extreme cold stress appearing in Athens and Bangladesh have been analyzed by Nastos from October to April. and Matzarakis (2012) and Burkart and Endlicher (2010), In the region of Crete Island, the time series of the respectively. Besides, UTCI can serve as a suitable plan- annual number of days with mean daily extreme values of ning tool for urban thermal comfort in subtropical regions PET/UTCI do not present clear either increasing or (Bro¨de et al. 2012a, b). decreasing trends during the 30-year period 1975–2004. It is worthy to remark that the examined human thermal indices are based on the energy balance of the human body Conclusions and not on individual climatic parameters. Thus, the observed global warming, mainly referring to air temper- The assessment of the bioclimatic conditions on Crete ature trends, has had no important impacts on human Island was carried out based on the analysis of the human physiology in the region of Crete Island until now. This is thermal indices PET and UTCI. PET is a universal index very likely due to some kind of compensation among the and is irrespective of clothing and metabolic activity, while climatic parameters included in PET/UTCI modeling, such UTCI is very sensitive to changes in air temperature, solar as air temperature, relative humidity, wind speed, and radiation, humidity, and especially wind speed. Besides, cloudiness, and to the synergistic effects of all these the accuracy of PET and UTCI calculations depends on the parameters on thermal perception. accuracy and the uncertainties of the used meteorological Acknowledgments This research is supported by HERAKLEITOS parameters. project, which is co-funded by EU and National Resources. The The estimated UTCI thermal comfort class presents authors would like to acknowledge the Hellenic National Meteoro- higher frequencies and duration throughout the year logical Service for providing the long meteorological time series.

123 1980 A. Bleta et al.

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