Spatiotemporal Variability and Multiscale Drivers of Extreme Rainfall in KwaZulu-Natal, South Africa

Extreme rainfall events are a major driver of flooding and associated socio-economic impacts in eastern South Africa, where interactions between tropical and mid-latitude circulation systems strongly influence rainfall variability. This study investigated atmospheric drivers of extreme rainfall over KwaZulu-Natal during the 1990–2020 period. Daily and monthly rainfall data from the South African Weather Service were analyzed using spatiotemporal statistical techniques, while atmospheric circulation patterns were examined using NCEP/NCAR and ERA5 reanalysis datasets. The spatiotemporal statistical analysis in this study was implemented using a combination of station-based rainfall analysis, anomaly analysis, composite analysis, and correlation techniques to explicitly quantify spatial patterns and temporal variability. In the context of this study, short duration refers to extreme rainfall events occurring over synoptic timescales, typically lasting from approximately 1 to 3 days (24–72 h). Composite analysis, anomaly diagnostics, and case studies were applied using outgoing longwave radiation, sea-level pressure, geopotential height, wind vectors, and relative humidity fields. Tropical-temperate troughs (TTTs) are also shown to play a significant role, contributing to widespread high-intensity rainfall events. These systems enhance moisture transport and convergence, creating favourable conditions for persistent and spatially extensive precipitation. The results reveal a pronounced west–east rainfall gradient, with enhanced extremes along the eastern escarpment, and show that extreme rainfall is primarily associated with short-duration, high-intensity events. Cut-off lows were identified independently from rainfall using their characteristic circulation and thermal structure. A total of 24 COL events were identified, of which 20 (83.3%) were associated with maximum 24 h rainfall ≥ 50 mm and four (16.7%) produced lower rainfall. COLs occurred throughout the year, with the highest frequency during JJA (45.8%), followed by SON (33.3%). The ENSO-rainfall relationship was strongest during DJF, when the regional rainfall index was significantly negatively correlated with Niño 3.4 anomalies (r = −0.447, p = 0.013), indicating reduced summer rainfall during warmer Niño 3.4 conditions.