Climatic Disasters and Defense Countermeasures of the Oasis

City on Tropic of Cancer

Duan Peng LingZhao JiaFengWeng ( Meteorological Observatory, , 526060)

Abstract:This paper analyzes the climatic characteristics and climatic disasters of the oasis city of zhaoqing on the tropic of Cancer .The result indicates that the frequent meteorological droughts, and the frequent Geological disasters caused by heavy rain,and the high temperature,which cause energy consumption and electricity consumption, and the smog, the severe thunderstorms and short-term strong winds which effect on urban transport. And the impact of dominant winds on industrial layout, and some defense countermeasures have been put forward:Ecological city planning should consider meteorological risk areas according to meteorological conditions; Climate demonstration must be conducted for major urban projects;Strengthen the relevant research of meteorological planning for eco-city construction and other countermeasures. These efforts will provide scientific data for the government departments to plan for the sustainable development of ecological cities. Key words: Oasis City; Climate characteristics; Climate disasters;Countermeasure

1.Introduction

Zhaoqing City, Guangdong Province is located in the central and western part of Guangdong Province. It is located in the south of Nanling, with high mountains in the Northwest and low in the Southeast. The mountains, hilly basins, river valleys, and plains criss-cross each other. The topography is complex and diverse. The entire territory of Zhaoqing is between 22 ° 47 ′ and 24 ° 24 ′ north latitude, and the Tropic of Cancer runs through it. Due to the subtropical monsoon and monsoon humid climate and the high and low terrain in the Northwest and Southeast, the climate is hot and rainy. Zhaoqing has a forest coverage rate of 69.8 %. It has 104 forest parks and 3 wetland parks. The city has a total of 15,82,400 acres of forest land. It also has the world's closest tropical virgin forest with a history of more than 400 years from the city-. Known as the "oasis on the Tropic of Cancer." What causes such a unique oasis city? What are the climate characteristics? What about climate disasters? How do you defend yourself?

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As a huge man-made ecosystem, the chain reaction of urban disasters has obviously changed the original material energy cycle in nature. Cities rely heavily on the lifeline systems, and the links between industries and departments are closely and complex. Moreover, most cities have developed and utilized resources with long-term excessive intensity, discharged large amounts of exhaust gas, wastewater, and waste residue, resulting in resource destruction and environmental degradation[ 1-2] And ... In this case, the city is not only faced with natural disasters such as floods, internal floods, typhoons, landslides, mudslides, and cold hazards[ 3-5] , It is also faced with a variety of "man-made" disasters that are closely related to urban development, such as land subsidence, ground cracks, seawater intrusion, and water resources crisis. Once a certain disaster occurs, it often produces a chain reaction, resulting in a series of secondary disasters. And derivative disasters. In recent years, many scholars have paid attention to the occurrence law of urban meteorological disasters and put forward prevention and control measures. Wuyaling [6] Analysed the meteorological disasters in since 2000 and conducted a risk assessment. Linjisheng[ 7] The effects of meteorological disasters in were evaluated and predicted by expert evaluation method. At present, the future development plan of the Zhaoqing City People's Government is to build a new ecological city in Zhaoqing near Dinghu Mountain, a natural ecological area on the Tropic of Cancer. Therefore, the climatic characteristics of the oasis city and the laws governing the occurrence of climate disasters are analyzed in detail, and the meteorological problems caused by the catastrophic impact of the development of ecological cities are analyzed. It also expounds the meteorological factors that need special attention in the industrial layout of ecological cities, puts forward corresponding countermeasures, and provides scientific data for the government departments to do a good job in the sustainable development planning of ecological cities. 2 Urban climate characteristics of oasis on the Tropic of

Cancer

Zhaoqing City, Guangdong Province is located in the central and western

2 part of Guangdong Province. It is affected by subtropical monsoon and monsoon humid climates and high and low terrain in the Northwest and Southeast. The climate is hot and rainy, with an average annual temperature of 22.3 °C and an average annual rainfall of 1649 mm. Zhaoqing City has a forest coverage rate of 69.8 % and is known as the "oasis on the Tropic of Cancer." What causes such a unique oasis city? What are the climate characteristics? What about climate disasters? How do you defend yourself?

2.1 Subtropical monsoon and monsoon humid climate effects

In winter, the cold and dry air from the North has greatly weakened after a long journey. When it reaches the north side of the , it has become denatured. After encountering the Nanling Mountains, it is blocked. The weaker cold air may even be difficult to climb over the mountains of Vietnam., blocked in Lingbei, When the stronger cold air reaches Zhaoqing across the Nanling Mountains, the wind speed has greatly reduced and the temperature has dropped slowly. The average monthly temperature of the coldest month is as high as 13.7 °C. The total rainfall from December to February of the following year was relatively small, accounting for only about 10 % of the annual precipitation, with an average rainfall of 164.7 mm. From the spring to the early summer, with the gradual weakening of the northern and northern cold air of the subtropical high, and due to the blocking effect of the Nanling on the cold air, the frontal movement was slowed down. The Zhaoqing area often has warm humid air masses from the South and the northern cold air masses. The confrontation forms a static front. Clouds and rain have caused long rainy weather in Zhaoqing City and heavy rain weather in the previous flood season. And since March, the warm and humid air flow in the South has gradually increased. Due to the existence of the Nanling Mountains, the terrain from Zhaoqing to Nanling has been from low to high, and the ultra-low South warm and humid air flow has a topographical uplift effect on the windward slope. The convergence of air flow increases, making the wet layer thicker, Finally, it reached saturation to form cloud rainfall, and the frequency of precipitation increased from March to June. The total rainfall averaged 830.6 mm, accounting for about half of the year, of which the number of monthly

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precipitation days from May to June was the highest. In summer and early autumn, tropical cyclones in the Western Pacific and Sea frequently hit Guangdong. Zhaoqing was affected by the tropical cyclone peripheral circulation cloud system and other tropical precipitation systems, resulting in heavy rainfall in the post-flood period of Zhaoqing City. The total rainfall from July to September averaged 549.2 mm. 2.2 Impact of local terrain The hills, basins, valleys, and terraces in Zhaoqing are criss-cross, and the terrain is complex, forming a diversified climate. The terrain is high in the Northwest, low in the East and South, and tilted from Northwest to Southeast. Mainly in the low and middle hills, there are fewer plains, forming mountainous landforms such as mountains, basins, hills, and alluvial plains. Mountains and hills are mainly distributed in Huaiji in the North, Guangning in the Northeast, and Fengkai and Deqing in the West. And other counties. The valley plains are distributed in the southeastern cities(districts) such as , Gaoyao, Dinghu and Duanzhou. Zhaoqing Ecological City is planned to be built in Zhaoqing New . Zhaoqing New District is located in the west of central Guangdong Province, North of the Delta, lower reaches of the Xijiang River, east of Sanshui and Sihui City, South of Gaoyao City, and west of . It was originally the of Zhaoqing City. The North and South sides of Zhaoqing New District are the Luanko Mountains and the Beiling Mountains, the West is the Valley, and the middle is the river network, forming a large "U" shaped plain. There are many types of landforms in the country, including mountains, hills, plains, and water surfaces. The terrain is complex and belongs to the subtropical monsoon climate zone and monsoon humid climate with sensitive climate change. Under the influence of the summer monsoon, Zhaoqing area is relatively easy to form medium and small scale convection systems. Dinghushan and other terrains have a certain role in promoting the rising movement of the precipitation system during the rainy season, which is conducive to the maintenance of precipitation and the increase of rain intensity, bringing abundant rainfall in the flood season of Zhaoqing City.. In the combination of subtropical monsoon and terrain, the total annual

4 rainfall in Zhaoqing City is 1,649 mm. At the same time, the average annual relative humidity is 80 %. From May to June, the maximum is 85 %. From October to January, it is the smallest, and it is also close to 75 %. The humid climate and abundant rainfall have freed Zhaoqing from the influence of the dry zone of the regression line and the letter wind zone. At the same time, under the influence of the summer monsoon, the airflow humidity from the ocean is large, and the rainy season is cloudy and rain weakens the direct radiation of the sun and reduces evaporation. Therefore, Zhaoqing City is long in summer but not very hot, and the hottest month has an average temperature of 28.8 ° C. The maximum daily temperature ≥ 35 °C is only 14 days. The annual sunshine hours are 1748 hours and each month is 190-210 hours. The annual sunshine percentage is 39 %. From July to November, the monthly average is more than 50 %. There is no cold in winter, no heat in summer, higher specific humidity, sufficient sunshine, and a unique climate that forms an oasis city.

3 Climate disasters

According to the statistics of the existing archives of the Zhaoqing Meteorological Bureau, the main climate disasters in Zhaoqing New District are: rainstorm floods, typhoons, thunderstorms, high temperatures, cold, lightning, dense fog, haze, hail, and drought(eg, Xijiang Tehong in 2005).Water, severe drought in autumn and winter of 2004, severe dragon boat water caused by continuous heavy rain in summer 2006, Xiajiyanzhong drought in 2007, severe and persistent cold freezing rain in early 2008, heavy rain and floods caused by Typhoon No. 11 "Van Yabi" in September 2010, 2011 "4.17" strong thunderstorms and other major winds Meteorological disasters). During the flood season, the flood waters of the rivers in the upper reaches of the Xijiang River are frequently encountered, and it is easy to form major floods and extraordinary floods from the West to the East. Zhaoqing New Area is located in the lower reaches of the Xijiang River, and the impact of torrential rains in the Xijiang River and landslides and mudslides caused by continuous heavy precipitation. The most serious Geological disasters. 3.1 Drought

The characteristics of climate warming in Zhaoqing are remarkable. Taking the high-profile meteorological observation station as an example, the average 5 annual temperature during the 63 years from 1954 to 2016 was 22.3 °C, and the trend of annual average temperature changes over the years was found to be 0.0168 °C using linear trend estimation. The correlation coefficient R = 0.6507 passed the significance test of α = 0.01, indicating that the annual average temperature in Zhaoqing City increased significantly at 0.0168 °C / year(Figure 2). Since 1997, the average annual temperature has been higher than the average of the calendar year for 11 consecutive years. The highest value appeared in 1998, reaching 23.3 °C, 1.05 °C higher than the average of the calendar year. The warming trend is particularly marked by an increase in the average temperature in winter, which increases by an average of 0.55 °C per 10 years, followed by spring, which increases by an average of 0.47 °C per 10 years, and then autumn, which increases by an average of 0.38 °C per 10 years. Warming has increased the frequency of droughts in autumn and winter, forest fire risk meteorological grades have continued to be high, and forest fires have increased accordingly. According to statistical data from 1962 to 2012, the probability of spring drought is about 6 times in 10 years, the average annual spring drought day is 20 days, and the maximum spring drought day is 75d; Autumn drought 5 times in 10 years, an average of 25 days of autumn drought; Since 1962, eight severe autumn droughts have occurred, of which four have occurred in the past 10 years and the longest number of autumn droughts has reached 154d. It can be seen that the frequency of drought is increasing. For example, in 2004, there was a severe autumn drought in the city for 50 years. From September 1 to November 22, 2004, the number of rain days was 83d. The severe autumn drought in 2007 was the lowest rainfall in the same period since the meteorological records in our city. On November 10, 2007, a serious mountain fire occurred in the Biling Mountain Forest Farm in Fulong Village, Lianhua Town, Dinghu District, Zhaoqing City. According to the statistics of the Zhaoqing Yearbook, forest fires have increased significantly in recent years, with an average annual forest area of 296.8 hectares, an increase of 25.7 per cent over the average forest area of 1997-2002. Among them, the number of forest fires in 2004 was as high as 63. It can be seen that severe autumn drought is an important reason for triggering mountain fires in our city.

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3.2 Heavy rainfall

In recent years, the extreme heavy precipitation in Zhaoqing City has increased, and the spatial and temporal distribution has been uneven. In the past five years, the number of heavy rain days ≥ 50 mm in the city has been 6 D, which is 1 D more than the average number of years. Among them, the number of heavy rain days in Zhaoqing New District in the past five years has been 7 D, which is 2 D more than the average number of years. In particular, in 2008, the average number of torrential rain days in Zhaoqing New District was as high as 10d, which was one times more than the annual average. The three-year sliding mean curve analysis was performed on the time series of torrential rain days per year from 1993 to 2016. The number of torrential rain days per year after 2005 was significantly higher than before 2005, although it decreased slightly in 2010-2011 and was generally in an upward trend. 3.3 High temperature

With the warming of the climate, the number of hot days in summer has increased significantly, thus increasing energy consumption and electricity consumption year by year. In the past 20 years, the average number of high-temperature days has been 36 D, which is about 15 D more than in the 1970s and 1980s. The average number of hot days in the past five years is 8D, which is 5D more than in the 1990s. The most severe high temperature weather was in 2003 and 2007, with 38 and 41 D of high temperature days per year, respectively. According to the statistical data of zhaoqing yearbook, in the past five years, the average energy consumption in our city has increased, and the average electricity consumption has increased. By deducting the energy consumption of industrial industries, the daily electricity consumption has also increased year by year, indicating that the impact of climate change on the increase in electricity consumption is obvious. 3.4 Haze

The smog in Zhaoqing area is the most frequent from January to April and from November to December. From May to October, fog is relatively rare. February and March are the most frequent months of smog in Zhaoqing, with a total frequency of 200 in 10 years, which is nearly 5 times that of the least June. The frequency of smog varies greatly from month to month, with obvious 7 seasonal characteristics. From more to less, it is spring, winter, autumn, and at least summer. From the monthly distribution of minimum visibility at all levels, the probability of low visibility in winter and spring is higher, while the visibility of summer fog is mostly higher. The cases with the lowest visibility below 50m mainly occurred in February to April and November. These months are months where cold air activity is more frequent but strong cold air activity is less.During the 10 years from 2001 to 2010, the frequency of fog in Zhaoqing was radually declining in the first and middle periods. In 2007, it reached a low point and gradually increased in the later period. 3.5 Severe thunderstorms and short-term strong winds In recent years, the frequency and intensity of thunderstorms have been increasing under the background of global warming. Based on the high-level observation station, there were 4,965 thunderstorms in the 60 years from 1954 to 2013, and the average annual number of thunderstorms was 82.8 D. According to the criteria for the division of thunderstorm activity areas in China(the average annual number of thunderstorms is less than 15d, 15-40d is a middle minefield, 41-90d is a multi-minefield, and greater than 90d is a strong minefield), Zhaoqing belongs to a multi-thunderstorm area. Thunderstorm days vary greatly from year to year. 1954-1975 was a multiple period, with an average annual rate of 98.3 D; Since 1976, it has been a less developed period with an average annual average of 73.8 D. The annual number of thunderstorms reached a maximum of 118 D(1959) and a minimum of 53 D(1990), with a difference of 65 D.The daily changes in the storm winds in Zhaoqing are also characterized by strong and weak day and night. They occur mainly in the afternoon. The peak occurs at 15:00 in advance and enters a low-onset period after 20:00 at night. The period from March to June lasted until 3 a.m., gradually increased from 4 o'clock, reached a small peak at 5 o'clock, then slightly reduced, and entered a high period around noon. The period of low hair during the night of July to October can continue until 9 a.m., then gradually increase, and enter a high period in the afternoon.

4 Other meteorological factors considered in planning new eco-city area in Zhaoqing

4.1 Impact of dominant winds on industrial distribution 8

Whether the industrial layout is reasonable is one of the important indicators for measuring the quality of a city's planning. If the pollution coefficient of a certain wind downward is larger, it means that the pollution of downstream air by upstream pollution enterprises is more serious. On the contrary, the lighter. When planning the layout of industrial areas and residential areas, factories and industrial areas that emit harmful substances to the atmosphere should be arranged in the direction of the least pollution factor, and residential areas should be located in the direction of the direction of the prevailing wind direction with the highest pollution factor. To ensure that residential areas are least affected by the polluted atmosphere. Contaminated industries are not suitable for planning on the upper side; If the wind speed is large in a certain area, it is conducive to the spread of pollution and is more suitable as an industrial development zone. According to the wind direction and wind speed data from 1956 to 2017 according to the Zhaoqing City Meteorological Bureau, the main residential areas of Zhaoqing New District should be located in the east-northeast direction of the city, and the enterprises that cause pollution to the atmosphere should be arranged in the Southwest direction of the new district.

Figure 1 Wind Rose Map of Zhaoqing New District for the Last 30 Years

4.2 The impact of urban development on the atmosphere needs to be fully taken into account in the planning and construction of eco-cities Documentation[18] It is believed that the phenomenon of urban hot islands is the result of a combination of factors such as the condition of the underlying

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surface, urban population density, geographical location, and climate. It is closely related to the size of the city and is the most typical manifestation of the impact of urbanization on climate. The expansion of the scale of the city will lead to the enhancement of the urban heat island effect, the rain island effect, and the fog island effect, while the water landscape and greening can effectively reduce the temperature, so measures such as increasing the area of green space should be taken. Therefore, it is necessary to strengthen the city's functional area planning and environmental suitability analysis. 5 Countermeasure

1) Planning urban functions according to meteorological conditions. According to the accumulation of meteorological observation data and the study of climate change, Zhaoqing eco-city development planning should comprehensively analyze the relationship between urban planning and local climate and environment characteristics, revise the relevant planning and design index system and norms, and improve the city's own purification ability. 2) Ecological city planning should consider meteorological risk areas. As mentioned above, in the context of global warming, the frequency of various meteorological disasters is increasing. In order to cope with the effects of urban development on local meteorological conditions, we may consider the "strategy for regulating local meteorological conditions". For example, the overall layout of cities, urban ecological isolation corridors, urban ecological wetlands, urban green space layout, and urban building layout design should all be effectively adjusted to avoid meteorological risk areas and minimize possible hazards. 3) The construction of major urban projects must pass the climate demonstration. In the planning of major urban projects, the feasibility of climate and the risk of meteorological disasters should be considered in a comprehensive manner, and the possible impact of large-scale projects on local climate and carbon emissions should be demonstrated. If this impact is very large and has a negative impact on human activities around it, the site should be re-planned. At the same time, through the demonstration, the project can fully take into account some meteorological disasters or extreme climate events that may occur in the local climate in the course of the project, and avoid possible hazards to the project.

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4) Research on meteorological planning for eco-city construction should be strengthened. From two aspects, climate feasibility demonstration and monitoring and evaluation of urban meteorological conditions, the monitoring, early warning and service system are further improved, and the effects of meteorological conditions on the construction of ecological cities are monitored and analyzed.

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