Investigating Coastal Sea Level Variability of the Cape Verde Archipelago in the Face of Climate Change

Abstract

The coast which serves as an intermediary between land and the ocean is subject to variable sea level from a scale of seconds to centuries. This study quantifies the drivers for coastal sea level variability of Cape Verde. By making use of the only public available tide gauge at Palmeira, Sal (spanning March 2000 to December 2019), the relative contribution of tides, surges, surface waves and sea level changes driven by ocean currents (dynamic topography) are estimated. A spectra analysis revealed that the tides (M2, S2, etc.) contribute up to 815mm of the 1300 mm range in observed sea level variability. Further analyzing the sea level at Palmeira with the tidal signal removed (SLA_residual) reveals multiannual variability with a magnitude of about 212mm. Furthermore, identified event-like, short term surges and lows may add another 155mm, lasting a few hours. Operational wave and sea level products revealed that Cape Verde’s highest sea level variability is due to waves (averagely 1700mm and 4400mm in some instances) in temporal scale <12 seconds and were primarily wind driven. The long term trends for the study period were 2.238mm/year, 3.024mm/year and -0.156mm/year for the CMEMS reanalysis, satellite and tide gauge, respectively. The satellite based dynamical heights sea level anomaly had a range of 182 and 208mm when using the satellite and reanalysis datasets with strong connections to the region’s SST and wind stress curl. An extension of the tide gauge observational network for the Cape Verde region would help verify the operational products used here and thus help to create a spatial monitoring of the sea level in the Cape Verde region. Services such as the desalination-plants, local harbors, coastal businesses, etc. would benefit from such a network, for planning and operations.