Of all the hazards that hurricanes bring, storm surge is the greatest threat to life and property along the coast. It can sweep homes off their foundations, flood riverside communities miles inland, and break up dunes and levees that normally protect coastal areas against storms.
As a hurricane reaches the coast, it pushes a huge volume of ocean water ashore. This is what we call storm surge.
This surge appears as a gradual rise in the water level as the storm approaches. Depending on the size and track of the hurricane, storm surge flooding can last for several hours. It then recedes after the storm passes.
Water level heights during a hurricane can reach 20 feet or more above normal sea level. With powerful waves on top of it, a hurricane’s storm surge can cause catastrophic damage.
What determines how high storm surge gets?
Storm surge begins over the open ocean. The strong winds of a hurricane push the ocean waters around and cause water to pile up under the storm. The low air pressure of the storm also plays a small role in lifting the water level. The height and extent of this pile of water depend on the strength and size of the hurricane.
As this pile of water moves toward the coast, other factors can change its height and extent.
If a coastal area has a sea floor that gently slopes away from the coastline, it’s more likely to see a higher storm surge than an area with a steeper drop-off. Gentle slopes along the Louisiana and Texas coasts have contributed to some devastating storm surges. Hurricane Katrina’s surge in 2005 broke levees and flooded New Orleans. Hurricane Ike’s 15- to 17-foot storm surge and waves swept hundreds of homes off Texas’ Bolivar Peninsula in 2008. Both were large, powerful storms that hit in vulnerable locations.
The shape of the coastline can also shape the surge. When storm surge enters a bay or river, the geography of the land can act as a funnel, sending the water even higher.
Other factors that shape storm surge
Ocean tides – caused by the gravity of the moon and sun – can also strengthen or weaken the impact of storm surge. So, it’s important to know the timing of the local tides compared to the hurricane landfall.
At high tide, the water is already at an elevated height. If landfall happens at high tide, the storm surge will cause even higher water levels and bring more water further inland. The Carolinas saw those effects when Hurricane Isaias hit at close to high tide on Aug. 3, 2020. Isaias brought a storm surge of about 4 feet at Myrtle Beach, South Carolina, but the water level was more than 10 feet above normal.
How storm surge and high tide add up to coastal flooding.(The COMET Program/UCAR and National Weather Service)
Sea level rise is another growing concern that influences storm surge.
As water warms, it expands, and that has slowly raised sea level over the past century as global temperatures have risen. Freshwater from melting of ice sheets and glaciers also adds to sea level rise. Together, they elevate the background ocean height. When a hurricane arrives, the higher ocean means storm surge can bring water further inland, to a more dangerous and widespread effect.
九 | 注意:员工在55岁生日当天被视为已达到55岁,并被归类为“55岁及以下”年龄段;在55岁生日后的第一天,他将被视为55岁以上。由于缴交率是按月适用的,因此在55岁生日后的那个月(即2024年2月),他将被归类为“55岁至60岁”年龄段。图/来源于CPF三、技能发展水SDL1、什么是SDL?新加坡技能发展税SDL(雇主承担,金额是薪水的0.25%,上限是11.25新币/月)。新加坡的SDL,全称为Skill Development Levy(技能发展税),是新加坡政府对所有实体(包括政府部门或法定团体)实行的强制性征税。这一税收制度旨在支持劳动力提升计划,并为雇主提供培训补助,以便雇员能够参加新加坡持续教育和培训系统内的培训课程。2、SDL的缴纳方式缴纳对象:雇主必须为所有在新加坡工作的雇员缴纳SDL,这包括拥有新加坡身份的全职、兼职、临时和短期雇员,以及外籍劳工(所有就业准证的持有者,如EP、SP、WP等)。缴纳标准:根据1979年《技能发展税法》第三章节,SDL的应缴纳金额自2008年10月1日起,税率为每月总薪酬的0.25%,最低为2新元,最高为11.25新元。