Trend analysis of long-term rainfall data in the Upper Karoo of South Africa

Abstract

Rainfall and stocking densities are key drivers of vegetation functioning and productivity in semi-arid regions. Below-average rainfall is of particular importance in the agricultural sector as it limits fodder availability for livestock in the short term, and can influence potential agricultural productivity through inducing the mortality of palatable perennial plant species in the long term. Changes in rainfall trends are not equal for all regions and must be quantified locally to sustainably manage natural grazing resources. The Upper Karoo has experienced considerable fluctuations in rainfall for many thousands of years, with relatively wetter and drier phases. This study analysed farm records from the past eight decades at eight sites in the Upper Karoo. The aim was to provide detailed and comparable descriptions to generate a more general understanding of rainfall at a spatial scale over this entire bioregion and to assess recent farming conditions within a historical rainfall context. A steadily increasing trend in rainfall of approximately 10 mm per decade has been observed in the Upper Karoo over the past eight decades, and the 30-year period from 1989 to 2018 was generally characterised by above-average rainfall. Presently, the farming conditions are more favourable compared to historical rainfall recorded before the year 1989.

Keywords:

• grazing
• precipitation
• climate
• SPI
• trend

ACKNOWLEDGEMENTS

The authors would like to thank the following individuals that made the long-term rainfall data records available and for their continued perseverance to collect this valuable information. Mr W.H. Hollander, Mr G.W. (Godfrey) Hollander, Miss G. Harms (Grootmeestersklip), Mr W. Olivier (Springfontein), Mr T. Buys (Biesieslaagte - DALRRD, Northern Cape), Mr P. Roux (Biega), Dr A.P. Marais (Klipplaat), Miss Anna Clarke (Taaibosfontein), and Mr S.P. van der Walt (Hughdale). The authors also thank the Editor-in-Chief and two anonymous reviewers for providing helpful comments to improve the manuscript.