Storm Surges: These are atmospheric-driven rises in sea level caused by low-pressure systems (depressions) and high-speed winds that push water toward the shore.
Subsidence: The sinking of land due to natural processes or human activities, such as groundwater extraction and the weight of urban infrastructure, effectively increases relative sea level.
Vegetation Loss: The removal of natural buffers like mangroves and salt marshes removes friction that normally absorbs wave energy and traps sediment to maintain land height.
Eustatic Sea-Level Rise: Global warming causes thermal expansion of seawater and the melting of terrestrial ice (glaciers and ice sheets), raising the global baseline sea level.
Increased Storm Intensity: Warmer ocean temperatures (typically above ) provide more energy for tropical cyclones, leading to higher wind speeds and more significant surges.
Salinization: As sea levels rise, saltwater can infiltrate freshwater aquifers and agricultural land, rendering them unusable for consumption or farming.
| Driver | Primary Cause | Duration | Scale |
|---|---|---|---|
| Storm Surge | Low pressure & Wind | Hours to Days | Regional |
| Sea-Level Rise | Thermal expansion/Ice melt | Decades to Centuries | Global |
| Tsunami | Seismic activity | Minutes to Hours | Basin-wide |
Identify the Scale: When analyzing a flood event, distinguish between global factors (eustatic rise) and local factors (isostatic change or subsidence).
Vegetation Statistics: Remember that natural buffers like salt marshes can reduce wave height by up to ; use this to justify nature-based solutions in management questions.
Check the Units: Sea-level rise is often discussed in millimeters per year (), but total rise over a century is usually expressed in meters (). Always convert to a consistent unit before calculating impacts.
Risk vs. Hazard: A 'hazard' is the physical event (the surge), while 'risk' includes the vulnerability of the population (e.g., 300 million people living below elevation).
