Temperature-humidity index (THI) was proposed by a Russian scholar, which was initially known as effective temperature with the calculation formula: . Where, Td is centigrade temperature. Through the integration of temperature and humidity, temperature-humidity index reflects the heat exchange between human body and ambient environment. When the Fahrenheit temperature is converted to centigrade temperature, the calculation formula is as follows:

where, t is Celsius temperature (˚C) and f is relative humidity (%). On the basis of extensive experiments, it can be divided into 9 grades as per the size of temperature-humidity index value (shown in Table 2).

Wind effect index (k) was evolved from wind chill index. . Wind effect index takes heat dissipation of body surface and heat gain of human body after solar radiation into consideration. It reflects the heat exchange between body surface and ambient environment, i.e. heat exchange rate per unit area of body surface (positive value represents heat absorption and negative value represents heat dissipation). Its calculation formula is as follows:

where, t is Celsius temperature (˚C), V is wind speed (m/s), and S is sunshine duration (h/d). It can be divided into 9 grades as per the size of wind effect index value (shown in Table 2).

Index of cloth loading (ICL) was proposed by an Australian scholar named Freitas. He considered the fact that people changed uncomfortableness brought

by climate through wearing different clothes. This model is broadly used in practical studies. Its calculation formula is as follows:

where, t is Celsius temperature (˚C); H represents 75% of metabolic rate of human body, and its unit is W/m². This study took the metabolic rate under light activity content, so H = 87 W/m²; a represents the solar radiation absorption by human body, and here it took 0.06; R represents the solar radiation received by land per unit area in the vertical sunlight, and its unit is W/m²; a is solar elevation angle. The average condition was taken and the latitude was set as β. The solar elevation angle of different regions in summer is 90 − β + 23˚26', the solar elevation angle of different regions in winter is 90 − β − 23˚26' and the solar elevation angle of different regions in spring and autumn is 90 − β; V is wind speed (m/s). On the basis of extensive experiments, it can be divided into 9 grades as per the size of cloth loading index value (shown in Table 2).

Climate is a complex system, including solar radiation, atmospheric temperature, atmospheric humidity, wind speed and other climate factors. According to the studies made by Ma Lijun, et al., based on temperature-humidity index, wind effect index and index of cloth loading, and according to the actual conditions of the local area, the feelings of tourist towards temperature-humidity index, wind effect index and index of cloth loading could be determined and divided into 5 different comfort grades, namely most comfortable, comfortable, relatively uncomfortable, uncomfortable and extremely uncomfortable, using 9, 7, 5, 3 & 1 for quantitative calibration. The three tourism climate comfort grading standards, namely temperature-humidity index, wind effect index and index of cloth loading as well as body feeling, grade symbols and assigned value for rating are shown in Table 2. On this basis, marking by experts can be adopted to determine the weights of sub-indexes and establish a new comprehensive evaluation model for tourism climate comfort. Its calculation formula is as follows:

where, C is tourism comfort index; X_THI, X_K and X_ICL are grading assigned values of temperature-humidity index, wind effect index and index of cloth loading; 0.6, 0.3 & 0.1 are eight coefficients of sub-indexes. The tourism comfort index can be divided into four grades (see Table 3).

Heavy fog meteorologically refers to a kind of weather phenomenon that plenty of water droplet floating in the air, often in milk white results in horizontal visibility less than 1000 m. Located in the eastern coastal region, the resorts is the wooded hill in the city with a large relative humidity in the air, which is a place prone to heavy fog. According to the statistical data, the number of annual average foggy days was up to 30 days. It could be seen that fog appeared each month throughout the year, mostly in October-April. The influence of heavy fog on tourism is poor visibility and threat to the safety of trips and tourism trails. Meanwhile, heavy fog also has an impact on normal tourism activities. For instance, the heavy fog on 3 January, 1999 caused a traffic accident of rear-end collision of 6 cars on Shanghai-Hangzhou Expressway, one of the main roads near the scenic spot, and a person was injured. On 20-21 January, 2003, heavy fog lasted in Shanghai. The visibility in Songjiang District was only 50 meters, so all the expressways were closed till 11 o’clock at noon.

Thunderstorm refers to the electric discharge phenomena generated in cumulonimbus clouds or between clouds or between clouds and ground. According to the observational statistic data from 1955-2014, thunderstorm was likely to occur each month throughout the year, mostly from early summer till early autumn, namely from June to September. The number of annual average thunderstorm days was 24 days. The maximum number of thunderstorm days was 45 days (in 1956) while the minimum number was 1 day (1971 and 1978). Thun-

derstorm days mainly concentrated in June and August in which the average number was respectively 7 days 6 days. But the average number of thunderstorm days was less than one day from October to February. The first thunderstorm day in each year occurred on 24 March on average, and the earliest first thunderstorm day was 12 January (1966) while the latest was 18 July (1970). The final thunderstorm day in each year occurred on 21 September on average, and the earliest final thunderstorm day was 3 June (1971) while the latest was 19 December (1979). Thunderstorm had obvious daily variation. Thunderstorm mainly occurred at 15 - 17 o’clock and least in 6 - 10 o’clock in a day. The tourism projects and attractions in the resorts are mostly located in wooden hill and open grassland. Scenic spots and recreation facilities are principally exposed. Some facilities are even equipped with metal handrails. In addition, under the influence of terrain, thunderstorm or gale weather often occurred in the scenic region, posing a large threat to tourism facilities and lives and properties of tourists. For example, a house near the scenic region was struck by lightning on 23 June, 2001, resulting in 11 people injured and 3 severely injured. On 29 August, 2003, thunderstorm occurred in the scenic region where a 800-year-old gingko tree was broken by lightning, resulting in heavy losses.

Any wind at an instantaneous wind speed of 17.0 m/s or above is meteorologically known as gale. According to the observational statistic data gale was likely to occur all the year round. Gale together with other disastrous weather (e.g. thunderstorm, snowstorm, hail, rainstorm, etc.) invaded and results in more damage. The number of average gale days was 13 days, and the maximum number of gale days was 61 days (1963) and the least was zero (1989, 1993 and 2003). From the perspective of interannual variance, the mid 1960s could be deemed as a divide. There were more gale days before that time, but gales occurred less and less after that time. Particularly, there were few gale days in the 1990s, which might be related to the urbanization effect near the observation station. Gale has a negative impact on the vehicle driving and the safe operation of the special entertainment equipments and the scenic region as well as the safety of tourists and trees. For instance, on 2 July 2008, influenced by severe convection weather, strong wind of 10 level occurred in the scenic region, resulting in fallen trees and damaged houses in different degree. Therefore, the scenic region was closed for some time and the tourism income was sharply decreased.

The day with daily maximum temperature ≥35˚C is meteorologically known as a high temperature day. It could be seen from Figure 3 that the overall variation trend of the number of high temperature days in Songjiang District was concave-down. The year 1980 was a demarcation point, and the number of annual high temperature days in 1980-2014 showed an apparent increasing tendency. The number of annual average high temperature days was 8 days. The earliest high temperature day occurred on 20 May (1963) while the latest occurred on 21 September (2005). The maximum number of high temperature days was up to 42 days (2013), while there was no high temperature occurred respectively in 1968, 1972 and 1999. The high temperature days were mainly distributed in July and August, and there were maximum high temperature days in July, accounting for nearly 60% of the total number of high temperature days. High temperature

lowers the comfort index in outdoor activities, and the number of tourists was influenced. For example, in 2013, the number of days with a temperature ≥35.0˚C was up to 24 days while the number of days with a temperature ≥37.0˚C was 26 days. The extreme maximum temperature broke the historic record and reaches 41.2˚C. According to the data from tourism sector, the total number of tourists in July and August decreased by almost 30% compared with a year earlier, resulting in a greater impact on tourism income.

The heavy rainfall with 24-hour precipitation of 50 mm or above was meteorologically known as rainstorm. According to the statistical data, the number of annual average rainstorm days was 3 days, and the maximum number of rainstorm days was 10 days (1999) and there was no rainstorm in some years. Rainstorm usually occurred from mid-June to mid-July and from mid-August to early September. There was generally no rainstorm from late November to mid- March. Rainstorm principally floods or destroys roads, affects traffic and does harm to life and property safety of tourists. Secondly, rainstorm tends to trigger meteorological derived disasters such as flood, landslide or debris flow, harming life and property safety of tourists. For instance, influenced by Meiyu Front, rainstorm occurred in the scenic region on 18 June 2011. The daily precipitation reached 127.5 mm, resulting in partial landslide. Influenced by Typhoon Fitow, the storm precipitation in the scenic region exceeded 300 mm on 2 - 8 October 2013, resulting in the destroy of partial roads up the hill by rush of water and seriously impacting the normal operation of the scenic spot.

According to the statistical data, there were 89 typhoons affecting Songjiang District. The number of annual average typhoon was 1.5, and the maximum number of typhoon was 4 and the least was 0. There were 70 typhoons accompanied by strong wind of 8 levels and above, accounting for 86% of the total number; there were 40 typhoons accompanied by rainstorm, accounting for 49% of the total number; there were 35 typhoons affecting wind and rain, accounting for 43% of the total number. The typhoons affecting Songjiang basically occurred from May to October. The maximum number of typhoons occurred in July, August and September, accounting for 87% of the numbers of typhoons throughout the year, particularly in August, accounting for 38% of the numbers of typhoons throughout the year. Typhoon often brings wind and rain, which has a negative impact on the vehicle driving, the safe operation of the scenic spot and the safety of tourists. For example, influenced by Typhoon Haikui, the storm precipitation in the scenic region reached 100 mm on 7 - 9 August 2012. Strong wind of Level 9 - 10 blew, resulting in damaged houses in different degree and fallen trees.