Minimum temperatures and frost at Grootfontein in the eastern Karoo, South Africa, over 98 years

Abstract

Minimum temperatures and frost are ecologically and agriculturally important parameters as they can cause mortality in plants and livestock, shape the position of biome boundaries, influence the lifecycles of pests and diseases, and influence the availability and quality of livestock feed. This study examines minimum temperature data from 1916 to 2014 for a site on the Nama-Karoo/Grassland biome ecotone. Temperatures of at least −6 °C occur almost every year, while temperatures of below −10 °C occurred in 15 of the years on record. Temperature data did not exhibit a random pattern, but rather showed the period from 1935 to 1960 to be particularly cold in terms of absolute minimum temperatures, the probability of occurrence of frost and the duration of the dormant (frost) season. The results provide a platform for interpretation for ecological and agricultural processes that have been recorded in several long-term trials at Grootfontein. The patterns of variation in the data indicate that short (c. 50-year) temperature datasets may give misleading indications in trends in temperature, and for an empirically-based interpretation of climate change, long-term datasets of approximately a hundred years are needed.

Keywords:

• climate change
• freeze
• dormant season
• growing season
• semi-arid

ACKNOWLEDGEMENTS

We thank the South African Weather Service and the ARC Institute for Soil, Climate and Water (Infruitec Campus) for supplying the data for this study. Two anonymous reviewers allowed an earlier version to be substantially improved.