Assessing climate-related fire danger across the central Grassland Biome of South Africa
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Date
2020-01
Authors
Steyn, Abraham Stephanus (Stephan)
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
The grasslands of the South African interior plateau are subject to seasonal wildfires that occasionally inflict serious damage to livestock production systems and infrastructure. Recent and future projected changes in the climate imply long-term changes in the fire regime, which may pose challenges to fire managers and exceed the current suppression capacity. The aim of this study was thus to assess historical and future fire danger across the central grassland biome of South Africa. Both actual observed fires (i.e. total burned area obtained through satellite remote sensing) and climatological fire danger (i.e. fire danger indices calculated from reanalysis climate data) were considered over the historical period (1981 – 2010). Self-organizing map (SOM) analysis was also used to identify the 850 hPa synoptic weather patterns related to increased climatological fire danger over the historical period, while projections from six ensemble members were used in evaluating climate-related fire danger under the A2 scenario over three future periods (i.e. 2011 – 2040, 2041 – 2070 and 2071 – 2100). Results showed that enhanced rainfall during the antecedent mid-summer season lead to increased burning due to higher fuel loads. There was a large inter-annual variability in the total burned area, ranging from 478 000 to 1.6 million ha per annum, with a significant decreasing trend of about 34 000 ha per annum over the historical period. This was in contrast to the significant increase in climatological fire danger, particularly during the last decade. Climatological fire danger was shown to be considerably higher in the south-western part of the central grassland, where extreme days occurred on 5 – 9 days during the fire season. SOM analysis revealed that very dangerous fire conditions were mostly associated with the warm, dry and windy conditions typically experienced to the east of a well-developed frontal trough over the subcontinent. Projections from various ensemble members did not support a continued increase in climate-related fire danger over the current climate epoch and had broadly inconsistent spatial patterns of change in very dangerous occurrences. The bulk of the ensemble members projected relatively small changes in fire danger over the southern Highveld, while the largest increases occurred in the north-west. An increase of between 5 – 15 very dangerous days was predicted for the near-future climate epoch, and 5 – 45 days for the distant future epoch (double these values for FFDI under MIROC3.2). The pattern and magnitude of change generally corresponded to different degrees of warming. The shift towards higher fire danger seemed to be more prominent from mid-century onwards. The projections from two ensemble members, CSIRO Mk3.5 and GFDL-CM2.1, differed considerably from the others. They predicted a decrease of between 5 – 15 very dangerous days over the central and southern parts of the study area for the current and near-future climate epochs, and decreases of less than 5 days for the distant future epoch. Discrepancies among future climate scenarios and unrepresented processes (e.g. vegetation dynamics), contribute to uncertainty about the accuracy of these predictions. Nonetheless, the results of this study underscore the potentially large impacts of climate change on the central grassland biome.
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Keywords
Thesis (Ph.D. (Agrometeorology))--University of the Free State, 2020, Climate change, Fire danger index, Future projections, SOM analysis, Grassland biomes, Burned areas, Climatological fire danger, Self-Organizing Map (SOM)