Historical change and future scenarios of sea level rise in Macau and adjacent waters

Against a background of climate change, Macau is very exposed to sea level rise (SLR) because of its low elevation, small size, and ongoing land reclamation. Therefore, we evaluate sea level changes in Macau, both historical and, especially, possible future scenarios, aiming to provide knowledge and a framework to help accommodate and protect against future SLR. Sea level in Macau is now rising at an accelerated rate: 1.35 mm yr^-1 over 1925–2010 and jumping to 4.2 mm yr^-1 over 1970–2010, which outpaces the rise in global mean sea level. In addition, vertical land movement in Macau contributes little to local sea level change. In the future, the rate of SLR in Macau will be about 20% higher than the global average, as a consequence of a greater local warming tendency and strengthened northward winds. Specifically, the sea level is projected to rise 8–12, 22–51 and 35–118 cm by 2020, 2060 and 2100, respectively, depending on the emissions scenario and climate sensitivity. Under the +8.5 W m^-2 Representative Concentration Pathway (RCP8.5) scenario the increase in sea level by 2100 will reach 65–118 cm—double that under RCP2.6. Moreover, the SLR will accelerate under RCP6.0 and RCP8.5, while remaining at a moderate and steady rate under RCP4.5 and RCP2.6. The key source of uncertainty stems from the emissions scenario and climate sensitivity, among which the discrepancies in SLR are small during the first half of the 21st century but begin to diverge thereafter.