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Short-term or high-frequency variations in sea level include those associated with tides, storm surges, and ocean waves (swell and wind waves) leading to wave setup and/or wave runup. These effects can be large (on the order of meters or more), but the impacts are generally short-lived. Socially relevant extreme sea-levels result from the combination and interaction of these phenomena with lower-frequency variations, among them ocean dynamics, ice-mass loss and vertical land motion. High-frequency sea-level variability can cause flooding, coastal erosion and sediment transport, and destruction of shoreline defenses. The wide-ranging economic and environmental consequences of such events are driving significant efforts to understand the interaction of different sea-level components, and how they are modulated by climate change and variability, whether individually or in combination. A new NASA data tool combines information on shorter-term effects with projections of longer-term processes. The significance of these effects is highly variable, depending on detailed site characteristics and the magnitude, duration, and frequency of sea-level extremes. They can arise from particularly strong storms, as well as the indirect and cumulative effects of high-tide flooding at lesser extremes.
A variety of observing systems enhance our knowledge of high-frequency sea level. Tide gauges provide the longest records of high-frequency sea-level variability, but they are not intended to monitor waves and wave runup. Wind waves and swell instead are monitored by the global network of (mostly coastal) wave buoys, and, since 1993, satellite radar altimeters have routinely measured significant wave height. Observations of wave runup are not widespread but generally conducted for studies of coastal inundation.
