Multiscale ENSO and Indian Ocean Dipole Controls on Drought Across Mainland SADC : A Meridional Teleconnection Dipole, Its Seasonal and Sectoral Structure and a Domain‐Gated Readiness Index

Abstract

ABSTRACT Drought is the dominant climatic hazard of the Southern African Development Community (SADC). We assess how the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) control drought across the SADC mainland using the Standardised Precipitation Evapotranspiration Index (SPEI) from ERA5. The analysis spans January 1950 to March 2026 across five accumulation scales on a 0.25°grid covering mainland SADC, including the Democratic Republic of the Congo and the southern part of Tanzania. Methods combine fixed‐lead correlation, split‐sample cross‐validation of lead selection, partial correlation, interaction regression, phase‐stratified composites, circulation composites at three levels, an independent check against CHIRPS rainfall and a within‐reanalysis consistency check against ERA5 soil moisture. Three results stand out. First, drought is organised by a meridional teleconnection dipole. The southern interior dries under El Niño while the northern tier shows the opposite sign, with the inversion near 12°–15° south. The pattern is field‐significant over nearly half of the domain, concentrated in both lobes and is reproduced by CHIRPS (pattern correlation 0.89) and by soil moisture (0.90). Second, ENSO dominates the unique linear signal and the IOD adds little independent variance. Compound El Niño and positive IOD seasons are the driest in the composites and show vertically coherent subsidence, with upper‐level convergence, mid‐level descent and low‐level divergence. The phase‐locked record is statistically underpowered to confirm a nonlinear interaction, so the compound signal is reported as consistent with enhanced risk rather than as an established effect. Third, coupling deepens with increasing accumulation scale, peaking at SPEI‐12 and strengthening through the rainy season. We translate these diagnostics into SCODP‐GATE, a domain‐gated readiness index that is skilful in the central interior, southern interior and western drylands and is not applied where the teleconnection is weak or reversed.