Search

Rising surface air temperatures, coupled with delays in the onset of austral summer rains and increased fuel load have amplified forest fire risk over southern Africa. This study investigates interactions between climate change and fire risk in South Africa's northern savanna biome. We employ the CCAM model to simulate the reference climate and project future forest fire risk on the savanna. An ensemble of six CMIP5 GCMs were downscaled to 8 km to project climate change in the far-future (2080 to 2099) under RCP8.5 emission scenario. The models were validated using ERA5-Land reanalyses whilst future projections focused on the 10th, 50th and 90th percentiles. The frequency of high fire risk days was calculated using a McArthur Forest Fire Danger Index (FFDI) which links meteorological variables to fire danger. The ensemble simulated widespread temperature rises of between 4.5 and 6 °C across the savanna, whilst rainfall is projected to decline by up to 20 mm/month, with corresponding decreases in minimum relative humidity. Heat wave days are projected to increase to above 8 days per annum, whilst soil moisture deficiency increases by above 50 mm on the savanna. Consequently, mean annual high fire danger days are projected to reach a peak frequency of 25 days in October, with an autumnal secondary peak. Spatially, greater increases in high FFDI days were projected over the western savanna extending toward neighbouring Botswana. This study contributes to understanding fire risk under unprecedented temperature rises which appear to be modulating fire intensity in the study region. [ABSTRACT FROM AUTHOR]

Pronounced subsidence leading to summer drought over southern Africa causes warmer than average surface air temperatures or even heatwave (HW) conditions. We investigated the occurrence of HWs during the summer drought over South Africa based on station data and the ECMWF ERA5 reanalyses. Temperature observations from the South African Weather Service were analyzed for seasonality and long-term trends (1981–2020) as background to the occurrence and variability of HWs. We focused on three severe El Niño Southern Oscillation (ENSO)-induced drought seasons, i.e., 1982/83, 1991/92, and 2015/16, to investigate HW characteristics. While 1997/98 was among the strongest El Niño seasons, the impacts were not as severe because it coincided with an intense Angola low, which allowed for rain-bearing cloud bands to form. Results showed that the hottest months were spread across the austral summer season from December to February. Regions experiencing high mean maximum temperatures and high HW frequencies exhibited a strong ENSO signal, with record HWs occurring during 2015/16. The establishment and persistence of a middle-level high-pressure system over Botswana/Namibia (Botswana High) appears to trigger the longest-lasting HWs during drought seasons. The Botswana high is usually coupled with a near-surface continental heat low and/or tropical warm air advection towards the affected region. It was also found that intense ENSO-induced drought events coincided with high HW frequency over South Africa, such as during 1982/83, 1991/92, and the recent 2015/16 events. The results of this study contribute to understanding drought and heat wave dynamics in a region experiencing rapid warming as a result of climate change. [ABSTRACT FROM AUTHOR]