Effects of ENSO-Induced Precipitation on Lowveld Ecosystems, South Africa

Studies that investigate how climatic variables impact plant growth and development in response to aperiodic climatic fluctuations are mostly undertaken at continental or biome scale with fewer investigations at finer bioregion scale, particularly for South African ecosystems. Vegetation canopies in South African savanna systems depend on the effective availability of soil moisture in the topsoil, which is influenced by factors including inter-annual precipitation variability and edaphic factors. The El Niño-Southern Oscillation (ENSO) is a major driver of precipitation variability and often is a leading cause of floods and droughts in southern Africa. To the extent that ENSO teleconnections can be potentially disruptive for natural and managed environments, and therefore for societies, detailed fine scale ENSO studies are increasingly relevant in heterogenous savanna landscapes. The Bushbuckridge municipality covers ~16,800 km2 of predominantly water constrained semi-arid savanna in the South African lowveld bioregion that lies to the south of Kruger National Park. Rainfall in the study area increases east to west along a topographic gradient and exhibits significant interannual variability. We performed a lagged spatial cross-correlation analysis between sea surface temperature in the Niño 3.4 region of the Eastern Pacific Ocean (using the ONI record) and CHIRPS 0.05° monthly gridded precipitation for the last 40 years to provide a comprehensive view of the times at which ENSO exerts maximum influence on the rainfall across the municipality. We also investigated the extent delayed precipitation fluctuations associated with ENSO may induce subsequent excesses or deficits of plant productivity defined by monthly standardised anomalies of the Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) retrieved from the Multiangle Imaging SpectroRadiometer (MISR) instrument onboard the NASA Terra platform for the last 20 years. The results indicate that biomass accumulation is controlled by the sequence, duration and relative strengths of the El Niño and La Niña events and moderated by the physical properties of the ecosystem. The findings are relevant for assisting local authorities in enacting policies and practices that may reduce the impacts of hazards or help recovery efforts.