Circulation patterns linked to extreme wet and dry conditions in Mozambique, relationship with climatic modes, and changes since 1961

Abstract This study investigates circulation types (CTs) in Africa south of the equator that can be associated with extreme wet and dry conditions in Mozambique; the relationship between the CTs and climatic modes in the south Indian Ocean; and changes in the frequency of occurrence of the CTs since 1961. Obliquely rotated principal component analysis applied to sea level pressure field from NCEP-NACR for the 1961-2020 period was used to derive physically interpretable CTs. At the synoptic scale, widespread rainfall in Mozambique was found to be related to widespread cyclonic activity on the Mozambique landmass and in the southwest Indian Ocean, coupled with abundant onshore moisture advection by southeast winds. On average, this circulation type (CT) was found to be significantly related to the positive phase of the Indian Ocean Dipole and the El Niño climatic modes, which both favor anomalous warming of the (western) tropical Indian Ocean. The aforementioned climatic modes equally constrain the annual frequency of occurrence of the CT, possibly due to the anomalous deepening of cyclonic activity in the southwest Indian Ocean during their active periods. Since 1961 the frequency of occurrence and days of persistence of the aforementioned CT has increased, suggesting a possible increase in the vulnerability of the hydroclimate of Mozambique. Extreme dry conditions in Mozambique can be related to widespread anticyclonic activity on the Mozambique landmass and the southwest Indian Ocean, coupled with the weakening of onshore moisture advection.