Synoptic situations in Africa south of the equator linked to wet events in Namibia; a case study with the February 2008 flood episode

Namibia is one of the water stressed regions in sub-Saharan Africa, with an erratic rainfall pattern. This study investigates synoptic situations that can be favorable for wet events in Namibia. Obliquely rotated principal component analysis applied to the T-mode matrix (variable is time series and observation is grid points) of sea level pressure data set from NCEP-NCAR was used to characterize the modes of large-scale atmospheric circulation variability in Africa south of the equator, in the form of circulation types (CTs). 18 CTs were classified and the linkage of the CTs to wet events in Namibia showed that during austral summer and early austral autumn when sea surface temperature (SST) is warm at the southwest Indian ocean and continental heating is active on the southern African landmasses, stronger (weaker) anticyclonic circulation at the South Indian Ocean high-pressure (South Atlantic Ocean high-pressure) can be associated with enhanced low-level moisture advection by southeast (southwest) winds to Namibia, resulting in wet events in most regions in Namibia. Also, enhanced moisture uptake in the Mozambique Channel might compensate for a relatively weaker moisture advection rate by the South Indian Ocean high-pressure, so that enhanced rainfall can still be expected in Namibia under this scenario. During the early February 2008 flood episode in parts of Namibia, enhanced moisture uptake in the Mozambique Channel coupled with strong southeast winds advecting abundant moisture to Namibia was found to have contributed to the flood.