Satellites measure changes in average global sea level, but coastal communities experience local water levels. Land can sink or rise, ocean currents vary and storms can temporarily push water towards the shore. These factors can make local change faster or slower than the global average.
Planning therefore combines satellite records with a tide gauge, measurements of land movement and flood maps. Decisions should consider several time horizons because a road, hospital or drainage system may last for decades. One projection is not a promise; several scenarios help planners test choices against a range of plausible futures. Local adaptation needs global trends and local measurements. Using several records also helps a community update its plan when land movement, storms or new observations change the local picture.