The southern African region is in close proximity to the South Atlantic Anomaly, a region between Africa and South America where the geomagnetic field is significantly weaker than at other comparable latitudes and is decreasing strongly. Between 2005 and 2009 very dense annual magnetic repeat station surveys were conducted in southern Africa within the framework of COMPASS (Comprehensive Magnetic Processes under the African Southern Sub-continent). This project aims at studying the regional geomagnetic field and particularly its evolutionary behaviour as part of the Inkaba yeAfrica cooperative project between Germany and South-Africa. We have modelled the magnetic field and its secular variation by means of two different techniques, one based on surface polynomials, the other on harmonic splines. Both approaches succeed in describing the characteristic time variations of the magnetic field components in this area. The rapid changes observed in the declination and vertical component during the period of investigation and revealed by the modelling results are of particular interest. Secular variation changes observed in the time-series of the Hermanus and the recently established Keetmanshoop magnetic observatories reveal the occurrence of a geomagnetic jerk in 2007.