Synopsis of temperature data collected in the Garden Route National Park over 20 years
TWENTY YEARS OF CLIMATE DATA HAS INCREASED THE UNDERSTANDING OF HOW CHANGING CLIMATES IMPACT ON THE INDIGENOUS FORESTS OF THE SOUTHERN CAPE
For the past 20 years, small dataloggers log climate data hourly at two stations in the Garden Route (Photo: Johan Baard).
Poor availability of temperature data resulted in the deployment of temperature loggers in the Southern Afromontane Forests of the Garden Route National Park in the early 2000s. Loggers were placed at Groenkop (6 km east of George) and Harkerville forests (11 km east of Knysna) and the first data recorded in 2001. These sites, both around 240 m above mean sea level, are 6.2 km and 4.5 km from the ocean, respectively. Onset Hobo temperature and relative humidity loggers (model H08-003-02) were used until 2017, with Hobo UX100-003 loggers used thereafter.
Initially loggers were plagued by technical and logistical problems that resulted in data gaps. Problems included batteries failing, software failures, theft and damage. The newer Hobo UX100-003 loggers seem to be much more reliable and battery-efficient, which resulted in little data loss for the last ten years. Initially data were recorded three-hourly, then two-hourly and since 2017, on the hour.
Various statistics are obtained and patterns emerge from recorded relative humidity and temperature data. For example, Harkerville has both higher and lower temperatures recorded than Groenkop. One degree Celsius frequency tables show a range for Harkerville of 0.5⁰C – 44.9⁰C (n = 101 361) and for Groenkop of 1.6⁰C – 38.2⁰C (n = 99 624). Extreme temperatures are rare; for Harkerville, only 326 (0.3%) records are above 34⁰C and only 887 (0.9%) are below 5⁰C. At Groenkop, less than 0.3% of records were in the extreme ranges of <5⁰C or >34⁰C. The winter mean monthly minimum (June-July) at Harkerville over 18 years is 2.6⁰C but is significantly higher at 5.6⁰C at Groenkop. Conversely, mean monthly maximum in Harkerville is 36.2⁰C for December and January, while at Groenkop it is 30.1⁰C for the same months. The hottest winter record for Harkerville was 30.1⁰C in July 2019 and at Groenkop 31.1⁰C in June 2013, possibly due to berg wind conditions. At both sites the minimum summer temperature is just below 10⁰C. The five year periods of 2008-2012, 2013-2017 and 2018-2022 had average maximums recorded of 32.9⁰C, 33.3⁰C, 31.7⁰C at Harkerville and 27.2⁰C, 27.8⁰C, 28.5⁰C at Groenkop.
These long-term datasets continue to grow and add value to diverse projects and our understanding of changing climates and their impact on the indigenous forests of the southern Cape. Relative humidity and temperature data have been used in various published articles and for legal cases related to wildfires.
This article was originally published in the 2022/2023 Research Report.
