Precipitation Patterns in Cape Verde Islands: Santiago Island Case Study

Abstract

The Cape Verde archipelago is located between 14 。 N - 18 。 N and 22 。 W - 28 。 W in the Atlantic Ocean. Previous studies associated Cape Verde’s rainfall regime with ITCZ and African squall lines. This hypothesis is revisited here using rainfall time series of the 4 Santiago Island station network of Cape Verde National Institute of Meteorology and Geophysics. Rainfall monthly totals are standardized to produce indices in the 1981-2009 period. Time section plots of zonal and meridional wind components anomalies are made using reanalysis data from ESRL/PSD/NOAA website. Daily outgoing long wave radiation and sea level pressure time section plots are also made as proxies for weather systems propagation. Results show that Santiago presents a seasonal rainfall regime characterized by dry (November-June) and wet (July-October) seasons, with short transition period. In general, rainfall totals increase with altitude. Weather systems within a wet year rainy season were associated with positive anomalies of zonal and meridional wind components of relative short duration, while negative anomalies dominated in dry years. These results suggest that winds coming from southwestern quadrant over warm Atlantic Ocean, associated with frontal systems traveling eastward, are the rain-producing events in wet years, not ITCZ or African squall lines. Winds coming from the northeastern quadrant produce dry years. Apparently, decadal-long wet periods are related to PDO cold phase. In the current PDO cold phase, there is only one year (2002) slightly dry. Considering that each PDO phases lasts 25 to 30 years and the current PDO cold phase started in 1999, it is possible that wet years predominate in the next 10 to 15 years.