3.1 SARS in Beijing in 2003
In the spring of 2003 in Beijing, the remaining cold of the severe winter in 2002 was still there. Beijing stopped heating supply on March 15, and people felt it was cold. It was from this day or so that Beijing ushered in a SARS outbreak.
From the winter of 2002 to the spring of 2003, the climate in China was characterized by large fluctuations in temperature and severe changes on many occasions. In the main epidemic area, western South China, the temperature in spring is lower than usual, while the temperature in most parts of China is higher than usual . Gao et al.  analyzed the humidity, rainfall, air humidity and wind speed in the winter of 2002 and the spring of 2003 (November 6, 2002 to June 5, 2003) in Beijing for a total of 201 days. The climatic characteristics of the period are summarized as follows: Compared with previous years, the average maximum temperature is lower and the average minimum temperature is higher, the temperature is generally lower, and the temperature fluctuates greatly; the rainfall and air humidity are higher, and the wind speed is lower. The obvious increase in temperature and rainfall occurred after March 6. The abnormal climate change in the Beijing area in the winter of 2002 and the spring of 2003 may be an important factor that caused the SARS epidemic in the Beijing area in 2003. Zhang Yanling et al.  also pointed out that the development of the SARS epidemic in Beijing is related to high temperatures, humid air, and variable weather. The average temperature in Beijing in mid-January reached -0.1 ℃, the highest since 1916 in the same period. The average temperature in February was 1.8 ℃ higher than the historical average. In the spring of 2003 in Beijing, there were three cases where the temperature difference was greater than 15°C in a short period of time . Beijing has always been dry in spring, with high humidity in spring 2003 . The precipitation in the winter of 2002-2003 was 17.8 mm, 85% more than normal (9.6 mm). The precipitation in Beijing in March 2003 was 32.8 mm, 295.2% more than normal (8.3 mm). A total of 11 snowfalls or rains occurred in March. Among them, a moderately rainy weather with precipitation of up to 16.7 mm occurred on March 19, which is rare in the same period in history. The precipitation in the middle of the observatory is 31.7 mm, which is the highest value in the same period since the observation record of precipitation in 1875. Due to the heavy rainfall, there were more foggy days in the spring of 2003. Beijing is usually windy in spring, and there are more windy days, but in the spring of 2003, the wind in Beijing was weak and there was not a single dusty weather .
"Frozen three feet is not a day's cold." The SARS incident in Beijing in 2003 was a qualitative change, while the quantitative change began in 2002. In 2002, the weather in Beijing set several hundred-year records, which is relatively rare in recent years . Weather terms such as warm winter, rainy season, sauna, cold winter, cloudy and snowy days have become popular words in common people's lives. The autumn of 2003 in the capital was extremely short, and the winter quickly approached. The average temperature in October is the lowest since 1925 in the same period. The average temperature in late October was the coldest record for the same period since 1940. On October 27, the daily average temperature at the Observatory in the city was 2.0 ℃, which was the lowest day in the same period since 1949; the lowest temperature on October 29 was minus 3.4 ℃, which was the second lowest temperature in late October since 1953. From December 2002 to February 2003, the winter in Beijing was severely cold. Since December 18, 2002, there have been six consecutive days of snowfall, setting the longest number of snowfall days since Beijing had a meteorological record. The snowfall in Beijing is the largest in the past 50 years. In history, there were only 4 consecutive days of snowfall in 1916 and 1968, respectively.
3.2 COVID-19 in Wuhan from 2019 to 2020
Most studies have found that temperature is the most significant factor affecting the COVID-19 epidemic [41-45]. In general, as the temperature increases, the survival rate of the virus will decrease . Research by Riddell et al.  showed that low temperature is beneficial to the survival of SARS-CoV-2 virus. The South China Seafood Market, Beijing Xinfadi Wholesale Market, and Dalian Kaiyang Seafood Company's epidemic are all related to the transportation of cold chain food. The low-temperature and humid environment greatly prolongs the life cycle and spreading distance of the virus.
During SARS period, the air quality in surrounding cities such as Shenzhen, Zhuhai, Zhongshan, Foshan, and Dongguan was better than that of Guangzhou, but SARS broke out in surrounding cities . In recent years, China has been vigorously focusing on environmental protection, and in fact, air quality has improved greatly. At least, the air quality in Wuhan in 2019 and 2020 is better than in previous years, so it will not be a special factor.
The consensuses obtained from the analysis of synoptic and climatic features during SARS spreading in China 17 years ago are as follows: The average temperature of winter in 2002 is higher than in former years. There is a remarkable temperature-dropping process before SARS high incidence comes. The superior relative humidity is propitious to SARS incidence. The abnormal change of climate is the inducement of SARS [13-17]. Throughout history, the occurrence of major plagues is related to climate anomalies. There were also obvious climatic anomalies before the occurrence of COVID-19.
Joint report identified 174 SARS-CoV-2 infections throughout December in 2019, of which only some of the 74 clinically confirmed cases may be confirmed cases . The details of these patients have not been released, and many cases are retrospectively investigated. In addition, patients with mild and asymptomatic infections are rarely recorded. Therefore, this article does not attempt to correlate climate with the date of onset of the case.
The temperature in winter 2019 is higher than in previous years. The cold wave caused by strong cold air will significantly increase the mortality and morbidity of cardiovascular, cerebrovascular, and respiratory diseases. Fig. 2 and Fig. 3 show the daily maximum temperature trends in November and December from 2011 to 2019, respectively. Between 11.23 and 11.25 in 2019, a large temperature drop occurred in Wuhan, and the temperature remained low for 7 days after the temperature drop (Fig. 2).
Table S1 gives an overview of the weather in Wuhan in 2017, 2018, and 2019 (clear, overcast, cloudy, rain, snow, fog, and wind). Fig. 4 and Fig. 5 show the average temperature and statistics of rainy days of Wuhan in November, December, and January from 2011 to 2020, respectively. The winter of 2019.11 to 2020.1 is very special, and the main feature is the existence of multiple mutations. Details as follows.
(1) The weather in November and December of 2019 has changed abruptly. ① From Fig. 2, it can be seen that the temperature drop range from 11.24 to 11.25 in 2019 is as high as 15 ℃, which is the largest temperature drop during the same period in history. The temperature of 11.25 is only 3 ℃, and the temperature for 7 consecutive days from 11.25 to 12.1 is less than 10 ℃. The temperature on November 23, 2016 was the lowest temperature in the history of the month, but after this day, the temperature was higher than the same period in 2019, and there was no continuous rain. From Table S1, there was only one light rain from 2016.11.24 to 2016.11.30, and the rest were cloudy or sunny. The weather for the six days from 2019.11.18 to 11.23 was overcast, light rain, cloudy, overcast, sunny, cloudy, and first wind, light wind, light wind, light wind, light wind, light wind. The reason for the heavy cooling of 11.25 was the northeast wind 6 and light rain on 11.24, which was in sharp contrast to the 5 days of breeze and 1 day of level 1 wind in the previous 6 days. There was also a heavy temperature drop at 11.17 (Fig.2), and there was also a light rain that day. The reason for the heavy temperature drop was northwest wind level 6. Before 11.17, the number of sunny, cloudy, and overcast days from 11.1 to 11.16 was 6, 6, and 4, respectively, which is rare in good weather compared to before 2019. From 2011-01-01 to 2020-03-01, there were no gales above 6 in Wuhan, and 6 gales occurred only in 3 days. Two of them occurred in 2019.11, all of which caused a large temperature drop. Among them, the great cooling of 11.25 is the largest cooling in November ever. In November and December of 2011-2019, Wuhan experienced only one heavy rain on December 18, 2019, and the rest was light or moderate rain. ② From Table S1, there was no rain between 12.1 and 12.16 in 2019, and there were 11 days of breeze. On December 17th and December 18th, two large temperature changes occurred, which were 8 ℃ and 13 ℃, and the historical rankings are 4 and 1, respectively. The high temperature of 12.17 jumped from 11 ° C at 12.16 to 19 ° C, and then quickly dropped to 6 ° C at 12.18. The winds from 12.16 to 12.18 were level 2. The reason for the heavy temperature drop at 12.18 was the only heavy rain in December in history, while the rest was light or moderate rain.
The two heavy winds of November 6 and heavy rain in December 2019 is responsible for the pneumonia epidemic, especially the two strong winds of six. There was very little wind for 6 days before the strong wind and a big temperature drop of 11.24. If the wind in the environment is strong, the wind will dry the environment and blow away the accumulated virus, which will greatly reduce its toxicity. The seafood market has small outdoor wind and no wind indoor, which is conducive to virus reproduction. There are many virus clusters. When encountering heavy rain, it will flow to the nearby area with sewage overflowing. Strong winds, heavy rains, and severe drops in temperature make people less resistant to diseases and are susceptible to diseases.
(2) From Fig. 4, the historical rankings in the same period of the average daily low temperature, average daily high temperature, and average daily temperature in November 2019 were 3, 2, and 2, respectively. The historical rankings of these three parameters in December 2019 were 2, 1, and 1, respectively. The temperature in January 2020 showed no obvious pattern, but its rainy day was 13 days, the highest in the same period of history, and the second (2016.1) was only 8 days (Fig. 5). Bad weather has significantly increased the number of patients in Wuhan. From January 13th to 22nd, the major hospitals in Wuhan were already overcrowded, and it took ten hours to wait for a needle. The general trend of the climate change from November 2019 to January 2020 is from the warm winter of November and December to the cold winter of January (the temperature is not very low, but it is rainy).
Why did the COVID-19 occur in Wuhan? The origin is that the special circumstances of Wuhan's dense population, a large proportion of the floating population, and extremely developed transportation have encountered extreme climatic. According to the weather change, the development of the COVID-19 epidemic in Wuhan can be divided into three stages: (1) The strongest wind and light rain on November 17, 2019, and the strong cooling caused. The temperature began to drop sharply on November 24 and the rainy weather continued for 7 days. (2) Heavy rain and strong cooling on December 17 and 18, 2012. (3) Rain and rain in January 2020.
Based on the above analysis, Fig. 6 shows the historical evolution of the occurrence of new coronavirus pneumonia in Wuhan.