The South African rainfall enhancement programme: 1997-2001

Abstract

This paper provides a summary of the South African Rainfall Enhancement Programme (SAREP) that was conducted in the Limpopo Province of South Africa. SAREP included an operational cloud-seeding campaign based on the South African developed hygroscopic flare-seeding technology which ran from December 1997 to the end of December 2000. In addition, a radar-based storm climatology was compiled using data collected during the period October 2000 to April 2001. During the cloud-seeding campaign 95 storms were seeded of which 37 were selected for treatment early in their lifetimes. This subset allowed a ‘time of origin\' analysis to quantify the seeding effect on radar-estimated rainfall. The Thunderstorm Identification Tracking Analyses and Nowcasting (TITAN) software was upgraded as part of SAREP for such an analysis. It was found that seeded storms on average produced twice the radar-determined rainfall that their controls produced. The cost for the additional rainfall was determined to be about R0.04/m3.
The radar-based storm climatology for the 10 000km2 target area was compiled using storm lifetime of 15 min and
30 dBZ radar reflectivity as the TITAN storm-tracking thresholds. It was found that more than 2 000 of these radar storm tracks affected the target area during the 7 months from October 2000 to April 2001. By comparing these radar storm tracks with those that were seeded, it was possible to identify the 290 radar storm tracks that could have been regarded as legitimate candidates for seeding. Based on the preliminary findings of this study, it is suggested that if 75 of the legitimate candidate storms in the specific target area are seeded, a marked (~10%) increase in area rainfall over the target area could be realised. This would have considerable socio-economic benefits. It is recommended that further development of this technology should remain a high priority in an integrated water resource management plan for South Africa.

Water SA Vol.31 (3) 2005: pp.291-298