HEAT STRESS CONDITIONS IN THE GREEK TERRITORY WITHIN THE WARM PERIOD OF THE YEAR

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1 HEAT STRESS CONDITIONS IN THE GREEK TERRITORY WITHIN THE WARM PERIOD OF THE YEAR Kostas P. Moustris 1, *, Kosmas Kavadias 2, Panagiotis T. Nastos 3, Ioanna K. Larissi 4 and Athanasios G. Paliatsos 4 1 Laboratory of Fluid Mechanics, Department of Mechanical Engineering, Technological Education Institute of Piraeus, Athens, Greece 2 Lab of Soft Energy Applications & Environmental Protection, Technological Education Institute of Piraeus, Athens, Greece 3 Laboratory of Climatology and Atmospheric Environment, Faculty of Geology and Geoenvironment, University of Athens, Panepistimiopolis, Athens, Greece 4 Laboratory of Environmental Technology, Electronic Computer Systems Engineering Department, Technological Education Institute of Piraeus, Athens, Greece Presented at the 17 th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region (MESAEP), September28 - October 01, 2013, Istanbul, Turkey ABSTRACT Human thermal comfort sensation is defined as the conditions in which human expresses satisfaction with the thermal environment, absence of thermal discomfort, or conditions in which a great percentage of the population (more than 80%) do not express dissatisfaction. The assessment of these conditions can be accomplished by the application of a large number of theoretical and empirical indices estimated using meteorological parameters such as air temperature, wind speed, air humidity and solar radiation. The aim of this work is to investigate the human sensation of heat stress in 30 different sites across the Greek territory, during the warm period of the year, for the period For that purpose, one of the widely used thermal index, Heat Index (HI), which was adopted by the USA s National Weather Service, is calculated. HI is an index that is also called "apparent temperature". This index is a measure of how hot someone feels when relative humidity is added to the actual air temperature. For the estimation of HI values, hourly values of air temperature and relative humidity were used. The aforementioned meteorological data have been recorded by the network of meteorological stations of the Hellenic National Meteorological Service. Results indicate a great variability of heat stress conditions, at the same time in different regions across Greece, within the warm period of the year. Furthermore, it seems that the height above sea level, geographical coordinates and the distance from the sea plays an important role in the establishment of asychronous heat stress conditions. In general terms, during the warm period of the year neutral human thermal conditions along the Greek territory are prevailing. These conditions, allow people to have a comfort thermal sensation as well as outdoor activities (agricultural activities, livestock, tourism etc). * Corresponding author Finally, the findings of this work are useful in the study of bioclimatic architecture and energy needs within the Greek territory. KEYWORDS: Human thermal comfort-discomfort; bioclimatology; Greece 1. INTRODUCTION During the warm period of the year (May- September), the human body uses the process of perspiration as defensive mechanism in order to maintain its temperature in a bearable normal range [1-2]. The high values of relative humidity and air temperature, respectively, considerably decrease the effectiveness of this defensive mechanism. Thus, the human body cannot remove the sum of heat via perspiration to the environment, resulting in thermal discomfort-feeling. Thermal comfort, as it is well known, is defined as the condition of mind which expresses satisfaction with the thermal environment, absence of thermal discomfort, or conditions in which 80% or 90% of humans do not express dissatisfaction [3]. Increasing research attention in the last decades has been dedicated to thermal comfort in relation to the outdoor urban environment [3-5]. The feeling of thermal discomfort that is created by high values of relative humidity and temperature varies from person to person as it is influenced by age, sex, weight, used clothing, shading, existence of wind, activity etc. Human thermal comfort or discomfort conditions may be assessed through a large number of theoretical and empirical indices usually requiring a larger or smaller number of input microclimate parameters such as air temperature, wind speed and air humidity [3,6-8]. 3068

2 One widely used human thermal comfort-discomfort index is the Heat Index (HI). The HI (or apparent temperature) is the result of extensive biometeorological studies. The parameters involved in the calculation of this index referred in the scientific literature [9]. The main objectives of this work are the calculation of the hourly HI values and the detailed study of the human sensation of heat stress in 30 different sites within the Greek territory. DATA AND METHODOLOGY Hourly values of air temperature ( o C) and relative humidity (%) from 30 different monitoring sites along the Greek territory during a five-year period ( ) are used in order to calculate the hourly HI values. The 30 examined meteorological stations within the Greek territory and their characteristics are being displayed in Table 1. Fig. 1 present the whisker-box plots of relative humidity (RH) and air temperature and heat index (ΗΙ) at the thirty examined monitoring sites during the warm period of the year from 1995 to In all figures, the central mark is the median, the edges of the box are the 25 th and 75 th percentiles and the whiskers extend to the min and max value. As it seems, at the thirty monitoring sites the median value of relative humidity (Fig. 1 upper panel) ranges between 50% and 80%. The 25 th and 75 th percentiles of relative humidity range between 30% and 90% respectively, and the minimum and maximum values were observed equal to 5% and 100% respectively. Concerning the air temperature (Fig. 1 intermediate upper panel), at the thirty monitoring sites the median value ranges between 19 o C and 26 o C. The 25 th and 75 th percentiles of air temperature range approximately between 15 o C and 28 o C respectively, and the minimum and maximum values were observed equal to 2 o C and 44 o C respectively. Finally, at the thirty examined monitoring sites during the warm period of the year from 1995 to 1999, the median value of heat index (Fig. 1 lower panel) ranges between 25 o C and 55 o C with an average value around 30 o C in most of the stations. Regarding the maximum values of heat index, only few stations (5 out of 30) present values higher than 50 o C. Those stations future high values of temperature combined with increased humidity during calm periods may experience intense human thermal discomfort sensation. TABLE 1 - List of stations within the Greek territory and related information. Station Altitude Longitude Latitude Number Name m - amsl 1 Aghialos ' Ε ' Ν Agrinio ' Ε ' Ν Alexandroupolis ' Ε ' Ν Andravida ' Ε ' Ν Argostoli ' Ε ' Ν Arta ' Ε ' Ν Helliniko (Athens) ' Ε ' Ν Heraklio ' Ε ' Ν Hios ' Ε ' Ν Ioannina ' Ε ' Ν Kalamata ' Ε ' Ν Kasteli ' E ' N Kastoria ' Ε ' Ν Kerkyra ' Ε ' Ν Lamia ' Ε ' Ν Larissa ' Ε ' Ν Limnos ' Ε ' Ν Methoni ' Ε ' Ν Mikra (Thessaloniki) ' Ε ' Ν Mytilini ' Ε ' Ν Naxos ' Ε ' Ν Rethimno ' Ε ' Ν Rodos ' Ε ' Ν Santorini ' Ε ' Ν Serres ' Ε ' Ν Sitia ' Ε ' Ν Skyros ' Ε ' Ν Souda ' Ε ' Ν Tanagra ' Ε ' Ν Tripoli ' Ε ' Ν

3 RH (%). HI ( o C) Air temperature ( o C) Station s number FIGURE 1 - The Box & Whiskers plots at the thirty examined monitoring sites across the Greek territory, during the warm period of the year, from 1995 to 1999, of relative humidity (upper panel), air temperature (intermediate panel), and heat index (lower panel). For the calculation of HI values, the following formula was applied [10-12]. HI = ( T) + ( RH) ( T RH) ( T2 ) ( RH2 ) + ( T2 RH) + ( T RH (1) 2 ) ( T2 RH2 ) where, T is the ambient dry bulb temperature ( F) and RH is the relative humidity (%) and HI is the heat index value ( o F). Formula (1) is obtained by multiple regression analysis therefore the HI value has an error of ±1.3 F. Even though temperature and relative humidity are the only two variables in the formula (1), all the aforementioned variables in the introduction, related to the human thermal comfort-discomfort sensation, are implied. At this 3070

point, it has to be mentioned that formula (1) is only valid for temperatures greater than or equal to 26.7 C and RH levels greater than or equal to 40% [13].

4 point, it has to be mentioned that formula (1) is only valid for temperatures greater than or equal to 26.7 C and RH levels greater than or equal to 40% [13]. Table 2, presents the HI classes as well as the general effects of HI on people in higher risk groups [14]. The hourly HI values for each one of the 30 examined monitoring sites are calculated and the human thermal comfort-discomfort sensation is studied for the four climate zones of Greece, according to the Greek regulation on the energy assessment of buildings which is known as KENAK [15]. According to KENAK, there are four climate zones (Fig. 2) defined on the basis of the heating degree days [16-19]. After the calculation of HI values a statistical treatment is applied. For the visualization of the spatial distribution of HI values along the Greek territory, the Radial Basis Funtion (RBF) interpolation was applied. The choice of the RBF method was based on the fact that it is ideal for small data sets. Concretely, the type of the applied Basis Function (BF) is the multiquadric which is expressed by the formula: B(h) 2 2 h R (2) where B(h) is the basis kernel function, (h) is the anisotropically rescaled (relative distance from the point to the node) and R 2 is the smoothing factor specified by the user, which in our case is equal to [20-23]. TABLE 2 - Heat index classes of assessment for heat stress conditions and the possible general effects on people in higher risk groups [14]. HI ( o F) HI ( o C) Description General effects on people in higher risk groups HI<80 HI<26.7 Neutral 80 HI< HI<32.2 Caution 90 HI< HI<40.6 Extreme Caution 105 HI< HI<54.4 Danger HI 130 HI 54.4 Extreme Danger Fatigue possible with prolonged exposure and/or physical activity --- Sunstroke, heat cramps and heatstroke possible with prolonged exposure and/or physical activity Sunstroke, heat cramps or heat exhaustion likely, and heatstroke possible with prolonged exposure and/or physical activity Heat/sunstroke highly likely with continued exposure. Extreme unhealthy conditions. FIGURE 2 - The four climate zones of Greece according to the national regulation, KENAK. 3071

5 TABLE 3 - Percentage (%) variation of HI hourly values ( C) for each class during the warm period stations within the Greek territory. Station number HI< HI< HI< HI< RESULTS AND DISCUSSION The percentage variation of HI hourly values and classes was studied. Table 3 presents the percentage variation of HI hourly values and classes during the warm period of the examined five-year period in thirty different sites in Greece. According to Table 3, the percentage variation of hourly HI values during the day with neutral human thermal sensation ranges between 63.4% (Rethimno - climate zone A) and 99.1% (Tripoli - climate zone C). This means that more than the half hours of the day, in all of the 30 examined regions within the Greek territory; a neutral human thermal comfort sensation is presented. The percentage variation of HI during the day with possible fatigue during prolonged exposure and/or physical activity ranged between 0.8% (Tripoli - climate zone C) and 30.6% (Rethimno - climate zone A). From 0.1% (Tripoli and Ioannina - climate zone C; Kastoria - climate zone D) to 11.6% (Agrinio - climate zone B) ranges the percentage variation of hours during the day with possible human sunstroke, heat cramps and heatstroke possible with prolonged exposure and/or physical activity. The percentage variation of hours during the day with possible human sunstroke, heat cramps or heat exhaustion likely, and heatstroke possible with prolonged exposure and/or physical activity possibly (danger) reach up to 0.6% (Agrinio - climate zone B). Finally, hours during the day with extreme human unhealthy conditions in all of the 30 examined sites all over the Greek territory are not appearing. The only exception was Tanagra. On 04/07/1998 four consecutive hours with extreme danger (HI>54.4 o C) were appeared, between 11:00 and 14:00 LST. Fig. 3 shows the mean diurnal variation of HI values in the four climate zones all over the Greek territory, from 1995 through From this figure, climate zone D (the coldest zone during cold period of the year) presents the most neutral human thermal comfort sensation from all 3072

6 FIGURE 3 - Mean diurnal variation of the hourly HI values in the four climate zones all over the Greek territory during the warm period of the year, from 1995 through the four Greek climate zones. The other three Greek climate zones present a similar behavior. Especially, the climate zone A seems to be cooler during the hot hours of the day (10:00-16:00 LST) in comparison to climate zones B and C. Taking into account that most areas with climate zone A are coastal areas or islands (Fig. 2), the aforementioned behavior may be attributed to the influence of the sea. According to Table 2, during the warm period of the year (May-September) in Greek territory there is a neutral human thermal comfort sensation. Finally, taking into account all the warm period of the year, neutral human thermal comfort feeling prevails throughout the Greek territory. The maximum HI value during the day, on average, appears between 11:00 and 14:00 LST (Fig. 3). According to Table 2, at the greater part of the Greek area, the human fatigue due to prolonged exposure and/or physical activity under the sun prevails during the two-hour time period between 12:00 and 14:00 LST. An exception is the region of Agrinio (west central Greece-Climate zone B) where during this two-hour period extreme caution is required. Sunstroke, heat cramps and heatstroke are possible with prolonged exposure and/or physical activity under the sun may occur. Taking into consideration that the region around Agrinio presents low height above mean sea level (25m), has rivers and lakes as well as an intensive agricultural activity the aforementioned behavior may be attributed to the influence of these factors. In order to study the absolute extreme conditions due to heavy hot weather along the Greek territory, the absolute maximum hourly HI value, in each one of the 30 monitoring sites, during the examined 5-year period, is calculated. Fig. 4, depicts the spatial distribution of the absolute maximum hourly HI values during the warm period of the year. According to Fig. 4 and Table 2, during summer heat waves at north Greece and central Aegean Sea extreme caution (32.2 o C HI<40.6 o C) is required. Sunstroke, heat cramps and heatstroke possible with prolonged exposure and/or physical activity. At the rest Greek territory, there is a human thermal discomfort (danger) according to HI values (40.6 o C HI<54.4 o C). Sunstroke, heat cramps or heat exhaustion likely, and heatstroke possible with prolonged exposure and/or physical activity. Finally, around the monitoring site Tanagra (central Greece) an extreme human thermal discomfort was appeared during 04/07/1998 between 11:00 and 14:00 LST. The HI hourly values were ranged on these hours between 55.6 o C and 75.6 o C. On the other hand, even the extreme thermal conditions last for short time, not more than four consecutive hours all over the Greek territory. Fig. 5 presents the spatial distribution of percentage (%) variation of HI hourly values during the warm period within the Greek territory, when HI 32.2 o C (extreme caution). As shown, along the Aegean Sea the percentage of hours with extreme caution during the warm period of the year ranges up to 10%. 3073

7 Latitude (degrees) HEAT INDEX Longitude (degrees) FIGURE 4 - Spatial distribution of absolute maximum HI values, all over the Greek territory during the warm period of the year, from 1995 through Latitude (degrees) Percentage (%) Longitude (degrees) FIGURE 5 - Spatial distribution of percentage (%) variation of HI hourly values during the warm period within the Greek territory, when HI 32.2 o C. 3074

8 The same percentage ranges between 10% and 20% at the rest Greek territory. Especially, at the north east Aegean Sea around the island of Mytilini and at the west coastal Greek territory the percentage ranges between 20% and 30%. Finally, at the west central Greek territory around the cities of Arta and Agrinio, the percentage of hours with HI 32.2 o C (extreme caution) during the warm period of the year ranges between 30% and 40% which is the highest percentage across the Greek territory. 4. CONCLUSIONS The hourly values of the well known bioclimatic index HI, at thirty different Greek monitoring sites, were calculated using hourly values of air temperature and air relative humidity for the five-year period , in order to study the human thermal comfort-discomfort sensation during the warm period of the year (May- September) all over the Greek territory. From this analysis the following conclusions can be drawn: A great variability of heat stress conditions is presented at the same time in different regions all over Greece, within the warm period of the year (May- September). In general terms and on average, during the warm period of the year neutral human thermal conditions prevail all over the Greek territory. These conditions, allow people to have a thermal comfort sensation and outdoor activities (agricultural activities, livestock, tourism etc). Even during the hottest months (July and August), the mean HI values range up to 32.2 o C, which indicates that human fatigue is possible with prolonged exposure and/or physical activity under the sun. During extreme heat waves, great dangerous and extreme unhealthy conditions appear between the hours 11:00 and 14:00 LST. Finally, it seems that the combination of sea and north winds ( etesians ) creates a comfortable climate in all parts of the Greek territory that are influenced from such a combination. Taking into account the results of the present study it is obvious that further investigation is required, involving meteorological data from more monitoring sites and for long-term time-series for the depiction of a better and more sufficient picture of bioclimatic conditions during the warm season of the year, all over the Greek territory. The authors have declared no conflict of interest. REFERENCES [1] Moustris, K.P., Ziomas, I.C. and Paliatsos, A.G. (2009) 24 hours in advance forecasting of thermal comfort-discomfort levels during the hot period of the year at representative locations of Athens city, Greece. Fresenius Environmental Bulletin, 18, [2] Moustris, K.P., Proias, G.T., Larissi, I.K., Nastos, P.Τ. and Paliatsos, A.G. (2012) Bioclimatic and air quality conditions in the greater Athens area, Greece, during the warm period of the year: trends, variability and persistence. Fresenius Environmental Bulletin, 21, [3] Givoni, B. (1998) Climatic considerations in building and urban design. Van Nostrond Reinholds: New York. [4] Tseliou, A., Tsiros, I.X., Lykoudis, S. and Nikolopoulou, M. (2010) An evaluation of three biometeorological indices for human thermal comfort in urban outdoor areas under real climatic conditions. Building and Environment, 45, [5] Cohen, P., Potchter, O., Matzarakis, A. (2013) Human thermal perception of Coastal Mediterranean outdoor urban environments. Applied Geography, 37, [6] Becker, S., Potchter, O. and Yaakov, Y. (2003) Calculated and observed human thermal sensation in an extremely hot and dry climate. Energy and Buildings, 35, [7] Conti, S., Meli, P., Menelli, G., Solimini, R., Toccaceli, V., Vichi, M., Beltrano, C. and Perini, L. (2005) Epidemiologic study of mortality during the summer 2003 heat wave in Italy. Environmental Research, 98, [8] Matzarakis, A., Nastos, P.T. (2012) Humanbiometeorological assessment of heat waves in Athens. Theoretical and Applied Climatology, 105, [9] Steadman, R.G. (1979) The assessment of sultriness. Part I: A temperature-humidity index based on human physiology and clothing science. Journal of Applied Meteorology, 18, [10] Steadman, R.G. (1984) A universal scale of apparent temperature. Journal of Climate and Applied Meteorology, 23, [11] Rothfusz, L.P. (1990) The heat index equation (or, more than you ever wanted to know about heat index), Tech. Attachment, SR/SSD 90-23, NWS S. Reg. Headquarters, Forth Worth, Tex. [12] Diffenbaugh, N.S., Pal, J.S., Giorgi, F. and Gao, X. (2007) Heat stress intensification in the Mediterranean climate change hotspot. Geophysical Research Letters, 34, L11706, doi: /2007gl [13] Heat Index Campbell Scientific Inc. (2002) Available at: [14] USA's National Weather Service (2013) Office of Climate, Water, and Weather Services. Available at: [15] Dascalaki, E.G., Droutsa, K.G., Balaras, C.A., Kontoyiannidis, S. (2011) Building typologies as a tool for assessing the energy performance of residential buildings A case study for the Hellenic building stock. Energy and Buildings, 43, [16] Matzarakis, A. and Balafoutis, C. (2004) Heating degreedays over Greece as an index of energy consumption. International Journal of Climatology, 24, [17] Christenson, M., Manz, H., Gyalistras, D. (2006) Climate warming impact on degree-days and building energy demand in Switzerland. Energy Conversion and Management, 47, [18] Gelegenis, J.J. (2009) A simplified quadratic expression for the approximate estimation of heating degree-days to any base temperature. Applied Energy, 86,

9 [19] Papakostas, K., Mavromatis, T., Kyriakis, N. (2010) Impact of the ambient temperature rise on the energy consumption for heating and cooling in residential buildings of Greece. Renewable Energy, 35, [20] Franke, R. (1982) Scattered data interpolation: test of some methods. Mathematics of Computation, 38, [21] Hardy, R.L. (1990) Theory and applications of the multiquadric-biharmonic method. Computers & Mathematics with Applications, 19, [22] Powell, M.J.D. (1992) The theory of radial basis function approximation in In: Advances in Numerical Analysis (W. Light, Ed.), Vol. 2, pp , Clarendon, Oxford. [23] Carlson, R.E., Foleym, T.A. (1991) The parameter R 2 in multiquadric interpolation. Computers & Mathematics with Applications, 21, Received: September 25, 2014 Accepted: September 26, 2014 CORRESPONDING AUTHOR Kostas P. Moustris Laboratory of Mechanical Engineering Department of Mechanical Engineering Technological Education Institute of Piraeus 250 Thivon and P. Ralli Str Athens GREECE kmoustris@yahoo.gr FEB/ Vol 23/ No 12/ 2014 pages

ASSESSMENT OF THERMAL SENSATION OF RESIDENTS IN THE SOUTHERN GREAT PLAIN, HUNGARY

ASSESSMENT OF THERMAL SENSATION OF RESIDENTS IN THE SOUTHERN GREAT PLAIN, HUNGARY KOVÁCS A. 1, KÁNTOR NOÉMI 2, ÉGERHÁZI LILLA ANDREA 1 ABSTRACT. Assessment of thermal sensation of residents in the Southern