Climate change and fire regimes in Limpopo grasslands

Abstract

Wildfires are becoming more frequent due to increased fuel load, human activities and climate change and are some of the major hazards in the southern Africa region. The delay in the onset of the rainy season coupled with rising surface air temperatures have increased fire risk in the region. This study investigates the interactions between climate change and fire regimes in the grasslands of Limpopo, a region in northern South Africa. The study seeks to understand how the Conformal Cubic Atmospheric Model (CCAM) simulates the present-day fire season. The frequency of high fire risk days in the “present-day climate” and the future of fire risk under climate change are analysed using a fire danger index. The study employs the “McArthur Forest Fire Danger Index” which links rainfall, temperature and wind to fire danger. The CCAM model at a horizontal resolution of 8 km is forced with an ensemble of six “General Circulation Models” (GCMs) from phase 6 of the “Coupled Model Intercomparison Project” (CMIP6) to simulate climate change projections for the period 2021-2040, 2041-2060 and 2080-2099 against a historical baseline from 1961 to 1980. The models were validated using observational data comprising CRU ts4 gridded weather station data with spatial resolution of 0.5° × 0.5° and ARC-SA weather station data. Taylor diagram was used for model verification integrating standard deviation, correlation coefficient, and Root Mean Square Errors (RMSE). Future climate projections were analysed with focus on the 50th percentile. The models’ verification showed close variability, least RMSE and high correlation (>r=0.9) compared with CRU ts4. The 50th percentile future simulations projected extreme hot and dry conditions over much of the study area. Projected mean annual high fire danger days from near future (2021–2040) reached a peak (> 10–15 days) south of the grasslands, whilst the west region peaked (15–20 days) during September and October. During mid future (2041—2060), high fire danger days increased by a peak of 5 days and a further 5 days into the far future (2080–2099) during September and October. Results of this study contribute to an understanding of changing fire regimes in response to recent unprecedented temperature increases coupled with repeated heat waves, which appear to be modulating fire intensity in the study area.