Johannesburg Rainfall: 760 mm Annual Average, Summer-Concentrated

Johannesburg receives ~760 mm (30 in) mean annual precipitation — moderate for a subtropical highland climate (1,750 m elevation).

Seasonal Pattern

• Summer (Oct–Mar): 80% of annual rain. Afternoon thunderstorms — intense, brief, often hail.
• Winter (Apr–Sep): Dry, sunny, cold nights (0–5°C). Rare frontal rain.
• Peak months: Nov, Dec, Jan (100–130 mm each).
• Driest: Jun, Jul (<5 mm).

Variability

• ENSO influence: El Niño → drier; La Niña → wetter (flood risk).
• 2021–22: 1,100 mm (La Niña); 2015–16: 450 mm (El Niño + drought).

Urban Impact

• Stormwater system overwhelmed → flash floods (Alexandra, Soweto low-lying).
• Acid mine drainage + sewage overflows contaminate Jukskei/Klip rivers.
• Water security: Rand Water (Vaal Dam) supplies 98% — rainfall in catchment matters more than local.

Joburg's rain comes in bursts — the city must catch, clean, and store it.