Evaluation of the Impacts of Regional Atmosphere-Ocean Coupling on the Historical Precipation over the Cabo Verde Archipelago

Abstract

Accurate climate information at the appropriate spatial and temporal resolution is crucial for developing and providing tailored climate services for small islands. Dynamical downscaling of global climate models is commonly used to produce regional climate change data. However, deficiencies in the integration of atmosphere-ocean interactions can be an important source of bias to the model’s precipitation, especially for small islands in tropical regions. In this study, we evaluate the impact of a regional atmosphere-ocean coupling model on the simulation of precipitation over Cabo Verde archipelago. We compare simulations from a coupled model (ROM) and an uncoupled model (REMO) at a spatial resolution of 0.22° × 0.22°. Models were driven with the ERA-INTERIM reanalysis. To evaluate their results the CHIRPS data was used as the observational reference. The analyses were focused on the ability to simulate the seasonal and spatial patterns of rainfall, which were assessed using the Added Value (AV) metric. We also examined the models for reproducing annual precipitation anomalies and long-term droughts. The results showed that both models can adequately simulate the seasonal cycle of precipitation and the spatial heterogeneity of rainfall among the sub-regions. However, during the rainy season (ASO), ROM performs better in simulating precipitation amounts, especially during the peak of the season (September) when REMO overestimate rainfall. As a consequence, positive AV was found over all islands during the rainy season. For the interannual variability of anomalies, coupled performed better for the entire country and the southern islands, and models did not perform well for the northern and eastern islands. For the long-term drought, somehow both models managed to simulate consistently the alternation of dry and wet conditions between the 1980’s and 1990’s for Cabo Verde and the southern islands. Still, afterward, they lacked consistency among them and against observation. These results suggest the benefits of using a coupled atmosphere-ocean model to simulate precipitation over the Cabo Verde archipelago, particularly over the Southern Islands.