Assessment of vegetation density trends in response to long-term climate change impacts in Western South Africa (1962–2022) using SPEI and NDVI time series

Western South Africa is highly vulnerable to climate change due to its arid and semi-arid conditions, shaped by the region’s complex meteorology. This study investigated long-term patterns of rainfall, temperature variability, and drought dynamics in western South Africa from 1962 to 2022, with an emphasis on their implications for vegetation density. Meteorological data from the South African Weather Service and the Global Surface Summary of the Day were used to compute multi-timescale Standardized Precipitation and Evapotranspiration Index (SPEI), while Normalized Difference Vegetation Index (NDVI) time series (1992–2022) were derived from Landsat and MODIS satellite imagery processed on Google Earth Engine and ArcGIS. The findings reveal a significant and sustained decline in rainfall, particularly after 2000, accompanied by rising temperatures and an increase in drought frequency, duration, and severity. Notably, a single, prolonged drought from 2014 to 2022—lasting 7.5 years—marked the most severe event during the 60-year period. This drought had a region-wide impact on vegetation, with NDVI anomalies showing widespread vegetation browning in the western sub-region and relative vegetation greening in the eastern. This indicates that the impact was more pronounced in the western than in the eastern sub-region. While NDVI was positively correlated with rainfall (r = 0.37) and negatively with temperature (r = − 0.32), the modest strength of these relationships suggests that non-climatic factors may also influence vegetation cover. The study highlights the need for further investigation into the roles of land use, soil properties, and anthropogenic pressures in shaping vegetation responses to climate change.