Core Viewpoint - The article discusses the severe impact of Typhoon "Haikashan" on coastal areas such as Zhuhai, Hong Kong, and Macau, leading to significant seawater inundation due to storm surges combined with astronomical tides [1][3][4]. Group 1: Causes of Seawater Inundation - Seawater inundation occurs when seawater enters land through surface or underground pathways, often exacerbated by geological structures, tides, and typhoons [1]. - The phenomenon is driven by two types of tides: astronomical tides caused by lunar and solar gravitational forces, and storm surges resulting from strong winds and low atmospheric pressure during typhoons [1][5]. - During the impact of Typhoon "Haikashan," the coastal areas were experiencing astronomical high tides, which contributed to the abnormal rise in water levels [3]. Group 2: Impact of Typhoon "Haikashan" - The maximum storm surge recorded in Guangdong's coastal areas reached 278 centimeters, with the most affected region being the Pearl River Estuary [3]. - In Zhuhai, the storm surge combined with astronomical high tide resulted in a peak water level of 328 centimeters, exceeding the red alert level by 43 centimeters [3]. - The coastal areas experienced significant wave heights, with effective wave heights recorded at 6.5 meters, leading to damage to coastal defenses and further exacerbating seawater inundation [3]. Group 3: Historical Context - Similar seawater inundation events occurred in Guangdong last November due to Typhoon "Wangyi," which, despite being weaker, still caused tidal levels to exceed warning thresholds when combined with astronomical tides [5]. - It is noted that typhoons are not the sole cause of seawater inundation; astronomical tides also play a critical role in these events [5]. Group 4: Prevention and Mitigation Strategies - Effective storm surge warnings are crucial for coastal areas to prepare and mitigate the impacts of seawater inundation [6]. - Recommendations include preemptive measures such as installing flood barriers, sealing underground drainage systems, and preparing emergency response plans [6]. - In areas already affected by seawater inundation, immediate evacuation and drainage efforts are essential to minimize damage [6].

Core Points - The article reports on the impact of a typhoon in Zhuhai, Guangdong, leading to seawater backflow and significant flooding in multiple streets [1] - Residents were warned in advance by the Zhuhai Meteorological Bureau to stay indoors and avoid driving [1] Group 1 - The typhoon caused rapid water accumulation, with vehicles submerged within ten minutes [1] - The Zhuhai Flood Control Office confirmed the occurrence of seawater backflow in coastal areas [1] - It was noted that the water would naturally recede after the tide goes out post-typhoon [1]

Core Points - The article discusses the impact of Typhoon "Haikashan" on coastal areas in Guangdong Province, particularly the risk of seawater backflow in low-lying regions [1][2] - The typhoon is expected to make landfall between Taishan and Zhanjiang in Guangdong on the afternoon to evening of September 24, with maximum wind speeds of 55 m/s (approximately 198 km/h) [1] - A red alert for storm surges has been issued for several cities in Guangdong, indicating a significant risk of flooding [2] Group 1 - Coastal low-lying areas in Shenzhen, Dongguan, Guangzhou, Zhongshan, and Zhuhai are at high risk of seawater backflow due to Typhoon "Haikashan" [1][2] - The storm surge is expected to reach 60 to 120 cm in certain areas, with the highest levels of 120 to 280 cm forecasted for the coastline from Huizhou to Yangjiang [2] - Emergency response measures are in place, including the evacuation of residents in vulnerable areas and the closure of coastal recreational facilities [2] Group 2 - Citizens are advised to monitor storm surge warnings and prepare for potential urban flooding, including avoiding contact with metal objects during storms [3] - Recommendations for navigating urban flooding include using sturdy objects to probe for deep water and avoiding low-lying areas [3] - Precautionary measures for homes in low-lying areas include creating barriers to prevent water ingress and using waterproof materials for storage [3]

Group 1 - Typhoon "Hagupit" is expected to be the strongest typhoon to make landfall in China this year, with significant impacts anticipated [1] - The typhoon has a diameter exceeding 1000 kilometers, indicating its large energy and abundant moisture, necessitating high attention to its subsequent effects [1] - The cold air moving southward is influencing the typhoon's path, which will primarily move westward along the coasts of Guangdong and Guangxi [1] Group 2 - The typhoon's wind radius is 150 kilometers, and vessels in the affected sea areas are advised to return to port and secure port facilities [1] - The combination of the astronomical tide during the lunar calendar's third day and the storm surge from "Hagupit" may lead to seawater backflow in the Pearl River Estuary [2] - Residents are urged to prepare emergency supplies, secure windows and doors, avoid going outside, and closely monitor relevant warnings and forecasts [2]