VIPOS (Vaal Dam Integrated Precipitation Observing System)—Using radar and gauges for rainfall estimation over an important catchment in South Africa

Apart from the use of radar information in a quantitative sense in cloud seeding experiments in South Africa and the work by the CSIR in the 1970s and 1980s on hail storms (and Doppler applications), the Vaal dam catchment Integrated Precipitation Observing System (VIPOS) represents a first in South Africa. During the record floods in the Vaal dam catchment in February 1996 the advantage of radar’s high spatial and temporal resolution data under these conditions became clear. Furthermore, the comparison between the radar estimated rainfall during this event and that measured by a dense raingauge network was excellent. Against the background of the dwindling number of reporting raingauges in South Africa an opportunity was seen in developing a system that uses the combination of conventional raingauge information and modern remote sensing rainfall estimation by radar. The Vaal dam catchment, with its high socio-economic profile became an obvious candidate for such a system. At the inception of the project in 1998 the following aims were stated:

To develop an integrated precipitation observing system for the Vaal dam catchment by:

∙ Further exploiting the capabilities of the MRL-5 dual-wavelength (S-and X-band) radar and related infrastructure at Bethlehem for refinement of the radar-based techniques for areal rainfall measurement.

∙ Transferring refined radar-rainfall measurement technology to other (C-band) radar installations potentially contributing to overall coverage of the Vaal dam catchment, testing the technology and making necessary adaptations.

∙ Locating and calibrating other potentially useful rainfall-measuring devices in the Vaal dam catchment and linking them, together with the radar installations, into a fully integrated precipitation observing system, specifically for hydrological applications.

∙ Developing appropriate software and communication systems needed to underpin the precipitation observing system and ensure operational reliability within the water resources management context.

∙ Design a spatial database in which data from the observing system, appropriately processed, can be stored and from which it can be withdrawn in near-real time for hydrological and modelling purposes.

∙ Ensuring the long-term sustainability of the observing system through the training and transfer of scientific and technical expertise.

This paper will described the step-wise manner in which these aims were accomplished in the past 3 years.