Vegetation change in response to climate extremes in Limpopo Province, South Africa

Abstract

An increase in the level of greenhouse gases (GHGs) in the atmosphere, combined with climatic variability, is likely to bring about extreme climate events, such as tropical storms, heat waves, floods, and droughts. In addition, a small change in the variance and mean of climate parameters might result in a strong shift in the intensity and frequency of extreme climatic events. The climatic conditions over southern Africa are highly variable and, and as such, southern Africa region becomes highly vulnerable to changes in extreme climatic conditions. Changes in climate extremes exert much pressure on the vegetation cover, thereby threatening the ecological stability of an area. This study analysed changes in vegetation cover and responses to extreme climate and weather events in the Limpopo Province, South Africa. The specific objectives of the study are to determine the nature of climate extremes from 2000 to 2017; to examine vegetation change in the study area, and analyse vegetation responses and sensitivity to climate extremes. In order to achieve these objectives, various quantitative techniques were employed. Extreme climate characterisation was done using GPCP precipitation, maximum temperature, and standardized precipitation evapotranspiration index (SPEI), whilst MODIS satellite was used for land use/ land cover change and vegetation response. To analyse vegetation response to extreme weather events, MODIS vegetation indices i.e. NDVI, EVI, and LSWI were used to analyse vegetation conditions and sensitivity in relation to extreme climatic events. Using the interannual rainfall variability and anomalies, seasons with abnormal rainfall patterns were chosen and analysed. Season with anomalous heavy rainfall occurred in 1999/00 and 2005/06 over Limpopo Province, whilst the anomalous low rainfall occurred during the summer season (DJF) in 2002/03 and 2015/16. Over the region, heavy rainfall was observed to be negatively associated with maximum temperatures (r = -0.66). Severely dry or drought conditions were associated with very poor vegetation conditions due to excessive temperatures and increased evaporation rate resulting in land surface water loss (LSWI < 0) and vegetation stress, meanwhile, heavy rainfall had a strong association with good vegetation conditions. However, vegetation tends to lag by one month from heavy rainfall. Using the Pearson moment correlation coefficient, the vegetation conditions (NDVI and EVI) were correlated with Land Surface Water Index (LSWI) and climate variables i.e. GPCP precipitation and maximum temperatures, with correlation coefficient of LSWI against GPCP, Tmax, NDVI, and EVI (r = 0.83, r = -0.78, r = 0.73, r = 0.87 respectively), NDVI and EVI against GPCP precipitation and Tmax (r = 0.31, r = -0.70, r = 0.53, and r = -0.73 respectively). The study shows a link between extreme weather events i.e. drought/ floods conditions and vegetation conditions. The findings of the study could serve as a scientific baseline data for better understanding the effects of drought and floods in relation to vegetation for sustainable management of the ecosystems. With enough details or information about the vegetation, it can be possible to generate policies and launch programs to save ecosystems and the environment. Foresters, biodiversity officers, and policymakers could also find the information important in the formulation of policies, and programs that require development planning.