Introduction

Climatic parameters affect different parts of human life, one of these parts is tourism (Sobhani and Safarian 2019; Mieczkowski 1985). In recent years the rise in temperature has been clearly visible and it can be said that climate change in the tourism sector has both negative and positive effects (Sobhani et al. 2019b; Dominique et al. 2016; Manolis et al. 2016). Among environmental factors, climate parameters such as temperature and precipitation in tourism are important (Andrea et al. 2019; Olya and Alipour 2015; Sobhani et al. 2019a). Tourism is highly dependent on the climate of an area. Humans usually choose areas for tourism that are more climatically comfortable (Daniel et al. 2019, 2016; Ghislain et al. 2016). Climate and tourism affect each other as one of the main components of a system in different ways, and they interact with each other in a new discussion as tourism climatology (Matzarakis 2014; WTO 1998). Increasing temperature in recent years in the study area has been approved by most researchers. The climate is very important from the point of view of tourism planning, and tourists are usually looking for a favourable climate or climate of comfort (in which the person has no discomfort and the lack of thermal and climatic comfort (Scott et al. 2007; Safarianzengir et al. 2019; Amelung and Viner 2006; Sobhani et al. 2018).

Several studies have been carried out on the application of the TCI index in tourism planning, some of them are mentioned: Fang and Yin (2015) conducted the tourism climate assessment with the TCI in China for 4 years, and the results showed that Tibet Province has favourable tourism conditions one month a year and Yunnan province 10 months a year. Endler et al. (2010) studied horizontal slope changes of air and impact on the climate of the tourism of lush forests. Katerushak and Matzarakis (2016) studied the Thermal Bioclimatic Index and TCI in the Black Sea Coast of Odesa region. Kulendran and Dwyer (2012) examined the study of seasonal change in tourism with the climate index and the results showed that it was suitable for tourism at an optimum temperature. Nicholls and Amelung (2015) examined the application of climate change in the rural areas of the Nordic. Tzu and Liu (2016) studied the impact of climate change on Taiwan’s National Park tourism. Zhang and Kulendran (2016) studied the impact of climate change on tourism seasonal changes in Hong Kong. Ahmadi (2012) evaluated the comfort of the tourism climate of Sanandaj city and the results showed that the best time of tourism in Sanandaj is from late May to late October. Gandomkar (2010) studied the comfort of the tourist climate in Semirom and concluded that the city is suited to tourists in September and May, respectively. Astani and Sobhaniardakani (2012), in the evaluation of the TCI for the International Lagoon of Shadegan, concluded that June and August are the best climatic conditions for tourism. Esmaili et al. (2012) evaluated the comfort climate of some of Iran’s main tourism cities using the physiological equivalent temperature index and concluded that among the studied cities, Kish Island, Mashhad, Isfahan, and Rasht are the best destinations for Nowruz travels. The second priority of the Nowruz trips belongs to the city of Rasht. The cities of Mashhad and Isfahan have the limitations of cold stress during the Nowruz holiday. Asadollahi et al. (2012) in a study on the climate comfort of Cheghakhor Lagoon using the TCI method concluded that May and June are the best climates for tourists, and the months of December, January and February have inappropriate climates for tourists. Mohammadi et al. (2013) in a study titled “Determine the comfort index of the tourism climate in East Azarbaijan province using the TCI” concluded that the months of June, July, August, and September provide the best conditions for the tourists in the province. Yazdanpanah et al. (2013) studied the climatic conditions for the development of tourism using the TCI index for nine synoptic stations in East Azarbaijan province for a period of 20 years (1990–2010) and the results were entered into the GIS. Then, the zoning of the tourism climate conditions of the province was carried out using the GIS in different months, and it was concluded that the May, June, June, August, and September months have the best conditions for the climatic comfort of tourists. The months of December, January, February, and March are the worst conditions. Hassanpour (2012) in the evaluation of the climatic conditions of Bandar Anzali in terms of tourism based on the TCI showed that July and May months are most suitable for the presence of tourists in the city due to the favourable heat situation and lower rainfall. Jafari et al. (2014) determined the climate of tourism comfort of the Sarab Gian Nahavand with the TCI. The results showed that in the months of September and June, the climate comfort of the region has ideal conditions for the presence of tourists. Salmanimoghadam and Jafari (2015) evaluated the tourism comfort climate of Zanjan province using the TCI. The results showed that the months of May, June, August, September, and October are excellent and ideal for the presence of tourists in the province, and November, December, January, February, March, and April are not suitable for tourists. Astani and Sobhaniardakani (2011) evaluated the climate tourism index of tourism in Hamedan and the results showed that June and September are ideal for tourism.

Therefore, knowledge of climate conditions and its application can be very valuable and useful for tourism designers. The northwest regions of the country have high potential in the tourist climate, due to attractive nature and diverse climate. Nevertheless, it is possible to plan for attracting tourists using the climate comfort index and identifying the climatic conditions and the potential of the region’s bioclimatic.

Materials and methods

Study area

The study area is located in the northwest of Iran, including the provinces of Ardabil, East Azerbaijan, and West Azarbaijan in geographical coordinates between 35 \(^\circ \) 58′ and 39 \(^\circ \) 46′ N latitude and 44 \(^\circ \) 3′–48 \(^\circ \) 55′ E longitude. The required climatic information was provided from 22 synoptic stations during the 26-year statistical period (1993–2018). Figure 1 shows the location of the study area.

Fig. 1
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Location of the study area

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Research methodology

The research approach is descriptive-analytic, due to components examined and the nature of the subject. In this research, the TCI and the climatic data of 22 synoptic stations of the province have been used in to evaluate the conditions of the tourism climate and northwest climate attractions from the point of view of tourism. At first, seven climatic parameters were extracted monthly from synoptic stations in the northwest during the 26 years (1993–2018). Then, the relevant database was formed and processed using the TCI. After calculating the TCI for each month of the year, given the results obtained as a point, the inverse-distance weighing method (IDW) was used to zone the regional tourism climate conditions and convert the point data from the stations to the surface information, and finally the map TCI was obtained for the northwest.

Introducing TCI

Tourism Climate Comfort Index (TCI) was introduced in 1985 by Mieczkowski. In fact, it is a combination of climatic factors affecting the tourist’s comfort. The advantage of the TCI than other indicators is more because it uses all the important climate variables, such as temperature, humidity, precipitation, wind and sunny hours in tourism, which control the human body’s thermal conditions (Mieczkowski 1985; Farajzadeh and Ahmadabadi 2010). There are seven variables used in this index (Mieczkowski 1985; Saeedi et al. 2012): (1) average daily maximum temperature, (2) average daily temperature, (3) average daily minimum relative humidity, (4) average daily relative humidity, (5) total monthly precipitation, (6) total sunny hours, and (7) average wind speed. These seven variables make up five sub-indicators in TCI, which are:

Daily Comfort Index (CID)

Includes maximum daily temperature and average daily relative humidity. This index shows the thermal comfort conditions at the maximum of tourism activity (Fig. 2) and its share is 40% in TCI.

Fig. 2
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Determination of the values of thermal indicators. Mieczkowski (1985)

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Temperature and humidity variables are based on the graph (comfort factor) used to measure the thermal comfort which expresses individual physiological and psychological sensation. It is obtained from the intersection of temperature and relative humidity. In the comfort index, the most favourable and optimal area for thermal comfort is between 20 and 27 °C and relative humidity of 70–30%. This area has optimum conditions for thermal comfort (Mieczkowski 1985; Jafari et al. 2014).

24-hour Comfort Index (CIA)

Includes daily average temperature and daily average humidity. This index shows the thermal comfort all day and night, and its share is 10% in the TCI. We used from the corresponding figure to calculate the Daily Comfort Index (CID) and the 24-h Comfort Index (CIA), the share of both indicators is 50% in the TCI, (CID is 40% and CIA is 10%). The CID is derived from the maximum daily temperature and minimum relative humidity variables (Mieczkowski 1985; Asadollahi et al. 2012).

Precipitation (P): in general, rainfall has a negative effect on recreational activities and tourism. The share of the sub-index is 20% in the TCI. The value of the precipitation rank is obtained using Table 1. In this system, precipitation ranking decreases with increasing precipitation, which shows the negative effect of precipitation on the pleasure, recreation, and comfort of the tourists.

Table 1 Monthly precipitation index (P), Mieczkowski (1985)
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Sunny hours (S): sunlight is considered as a positive factor in climatic comfort. The sunlight parameter, like rainfall, has a weight of 20% in TCI. This variable is obtained by dividing the average monthly hours of sunshine by the number of days in each month and we used Table 2 to determine the ranking.

Table 2 Sunny hours’ index (S), Mieczkowski (1985)
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Average wind speed: the effect of this variable depends on the air temperature. It has a positive effect in the hot climate, due to evaporation and cooling, but it has a negative effect on human comfort in a cold climate, due to the wind cooling effect. Also, increasing the wind speed will increase uncomfortable, as a result, it is considered a negative factor and its rank in the TCI index is lowered. Four types of wind speed ranking systems are considered for the TCI formula. In the normal system, the lowest average monthly wind speed has the highest rank and indicates its desirability for climatic comfort. The normal system is used when the average temperature is between 15 and 24 \( {^\circ{\rm C} }\) (Table 3).

Table 3 Wind speed index, km/h (W), Mieczkowski (1985)
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The above variables are weighed and ranked according to their relative importance in the comfort of tourism to calculate the tourism climate index and give the sub-indicators, and finally, the TCI is obtained based on the following equation:

$$ {\text{TCI }} = { 2}\left( {{\text{4CID}} + {\text{CIA}} + {2}P + {2}S + W} \right). $$
(1)

In this formula, the CID is a 24-h comfort index, P monthly precipitation, S sunny hours and W is the wind variable (Table 4). The ranking of each of the above variables should be placed in the formula to obtain the TCI value. The daily comfort index and the 24-h comfort index are obtained from the Michalowski index graph using maximum daily temperature and minimum relative humidity, daily average and average relative humidity. Further values represent ideal conditions. Also, dissatisfaction and unfavourable climatic conditions increase for tourists towards fewer values. The resulting number with the final table (Table 5) checks the quality of the tourism climate, and finally, the characteristic of the tourism climate of the region is obtained at that time (Mieczkowski 1985).

Table 4 Indicators effective on tourism, Mieczkowski (1985)
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Table 5 Final coefficient and quality of climate conditions for tourists, Mieczkowski (1985)
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Results and discussion

After calculating the five components based on Eq. (1), the numerical value of the TCI for each point was estimated and the numerical values of the tourism climate index and related climatic clusters were determined using Table 5. In the following, the maps were drawn using ArcGIS software for each month and based on the climate tourism index.

Maps of the northwest tourism climate in different months

The tourism climate in January (Fig. 3) showed that the northern regions (the southern range of the Aras River) around Lake Urmia and the Mianeh city are in a desirable condition with a numerical index of 30–52. Southwestern regions of West Azarbaijan Province, East Azarbaijan Province (Sahand Mountain), and Ardabil Province (around Sabalan Mountain) have unfavourable conditions and an index of less than 30, due to the presence of snow and cold in the region, which has lowered the tourism climate index in these areas. Farajzadeh and Ahmadabadi (2010) have introduced cold weather in the northwest region in January–February, causing the tourist undesirability. The tourism climate conditions in February (Fig. 3) showed that the southwestern parts of West Azerbaijan, centre and south of Ardebil province, the slope around Sabalan Mountain and north of Sahand Mountain have unsuitable climatic conditions with a numerical index of 32–40, and the south of the Aras River, around Lake Urmia and the Mianeh city shows an acceptable status with a numerical index of 40–45. The tourism climate situation in March (Fig. 3) shows that northern regions, except the Maku town, around Lake Urmia, the central, southern and northern parts of East Azerbaijan, are in an acceptable condition with a numerical index of 50–61. In the central and southern regions of the province of Ardabil and East Azarbaijan (the Sabalan and Sahand mountains), southwest and northwest of West Azarbaijan are in the marginal condition with rank 39–49, which includes most of the highland and mountainous parts (Rordeh et al. 2014) that have expressed the height factor in increasing and decreasing the TCI.

Fig. 3
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Climatic zonation of the northwestern of Iran, monthly, using the tourism climate index (TCI)

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The tourism climate in April (Fig. 3) shows that the northern regions of East Azerbaijan and the south of Ardabil and the south of West Azerbaijan province are in good condition with a numerical index of 60–69 and in other areas such as the Mianeh city, south of Lake Urmia, Moghan plain and the north of West Azarbaijan are in very good condition with index 70–80 (Hassanvand et al. 2011). April is the most suitable month with the ideal and excellent conditions, and January and February are the most unsuitable months for tourism in Lorestan province with the marginal conditions. The climate of comfort in May (Fig. 3) shows that the province of Ardabil and the northeast and northwest of the West Azarbaijan are in a very good condition with a numerical index of 71–80. The East and West Azerbaijan regions are in excellent condition with an index of 80–93. In Isfahan province (Gandomkar 2010), the May and April months have offered the best conditions for the presence of tourists based on the TCI.

Climatic comfort conditions in June (Fig. 3) show that Moghan plain (Parsabad, Bileh Savar and Germi), Mianeh and Bonab cities are in good condition with a numerical index of 64–75. The central parts of Ardabil province, north of West Azarbaijan have very good conditions with a numerical index of 70–79, northeast of East Azarbaijan and the south of Ardabil province are excellent with an index of 80–89, and the west and south of West Azerbaijan is ideal with a numerical index of 90–100. Sarisaraf et al. (2010) showed that June, July, August, and October are the most suitable months in the Arasbaran region with rank 90–100. Climate conditions (Fig. 3) in Parsabad Moghan, Jolfa and Bonab are good with a numerical index of 60–69. West Azarbaijan and the west of East Azarbaijan are in good conditions, Sardasht, Salmas, Marand, Kaleybar, and Mianeh have excellent conditions with a numerical index of 90–99, and the centre and south of Ardabil and Sarab have an ideal condition for the tourism climate with an index of 90–100.

Climatic conditions (Fig. 3) Parsabad, Moghan, Mianeh, Jolfa is good with numerical index 60–69 in August, around the Lake Urmia and Khoy are very good with a numerical index of 70–79. Maku town, Tabriz, and Salmas are excellent with a numerical index of 80–89 and centre and south of Ardabil province, the east of East Azarbaijan, Marand, Sardasht, Salmas and Sahand cities are ideal for tourism with a numerical index of 90–100. September climate conditions (Fig. 3) in Ardabil province and the east of East Azerbaijan was excellent with a numerical index of 78–90, and West Azerbaijan and the west of East Azarbaijan have ideal conditions for tourism with a numerical index of 90–100.

October climate conditions (Fig. 3) in Ardabil and Northeast of East Azarbaijan and Maku city are good with a numerical index of 60–69, Parsabad Moghan, Marand, Takab and Sardasht cities have a very good conditions with a 70–79 index, and the parts of West Azerbaijan and East Azarbaijan have excellent conditions with the index of 80–89 for the tourism climate. Gandomkar (2010) stated October, April, and May months are the most suitable months for the tourists, according to the TCI. November climate conditions (Fig. 3) of Ardabil province and southwest of Urmia and Maku are marginal with a numerical index of 44–54 and the climate conditions in the north of West Azerbaijan and north, northwest and south of East Azerbaijan are poor and good with the index from 55 to 65 for tourism.

Climate comfort conditions in December (Fig. 3) in the south of West Azerbaijan, south and centre and south of Ardabil province showed an inappropriate condition with the numerical index of 30–39. The northern and central parts of the East Azarbaijan Ahar and Parsabad have a marginal condition with the numerical index of 40–53. On the contrary, in Ilam province, November and December, and the southern regions of Iran are most suitable for tourists, according to the TCI.

Calendar of tourism climate in the northwest based on the TCI

The final coefficient of the tourism climate is presented monthly for each of the studied stations in the northwest of Iran (Table 6). This table is a tourism calendar that is presented based on the analysis of climatological data of the TCI for the northwest as follows: (1) in January only Parsabad Moghan station is acceptable with a numerical index of 50–59 for tourism. Other northwest regions are inappropriate for tourism, due to cold weather. (2) Parsabad, Kaleybar, Jolfa, Sahand, Maragheh, Marand, Mianeh and Salmas stations are acceptable for tourism in February, and other stations are unsuitable for tourism. (3) Meshkinshahr, Ahar, Maku, Piranshahr and Sardasht stations are inappropriate and other stations are acceptable and good for tourism in March. (4) Jolfa Station is in excellent condition and Parsabad, Bonab, Khoy, Mahabad are in very good conditions in April and other stations are in good and acceptable conditions. (5) The conditions are ideal to very good in June, July, August, September, and October months, for all the stations, and the Parsabad, Jolfa and Mianeh stations are in the good conditions for tourism in the summer months, due to the increase in the temperature. (6) Except for the station of Piranshahr, other stations are in good condition for the tourism climate in November. (7) Tourism climate in December is similar to April.

Table 6 Iran’s Northwest Tourism Calendar for 22 stations based on the TCI
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Conclusions

Northwest of Iran, with plenty of tourist attractions, can be the reason for the presence of domestic and foreign tourists. Beautiful and unique landscapes and diverse weather conditions in all seasons can be a step towards the development of this industry. Based on the climate comfort index of tourism (TCI) and the use of ArcGIS in the northwest, stations in which the tourism climate conditions are good and acceptable in the cold months (January, February, and March), the conditions are inappropriate in the warm months (June, July, August), due to the increase in temperature at those stations. Except for Parsabad Moghan station with rank 53 and acceptable for tourist climate, the rest of the stations are inappropriate for tourism in January. In other words, in the northwest, the most unfavourable month is January based on the TCI for the tourism climate. The most suitable month in September for the northwest tourism climate based on the TCI that its climate condition is very good to ideal with the numerical index of 78–100 in all stations. The cold months (December to March) on the South coast of Aras on the Iran border, especially in the Moghan plain, show the most favourable conditions for tourism according to the TCI. Mai station, which is located on the slopes of Sabalan, Sahand, Bozgush, Qarrah Dagh, Misho and western highlands of Urmia from mid-spring to mid-autumn (from May to November) have relatively good conditions for the presence of tourists.