Rainfall across much of the continent is variable and unpredictable, both between and within years. High seasonal variability compounds these effects, causing droughts and floods. Some 220 million people are annually exposed to drought in Africa. And more than 1.5 million were affected by floods in 2007. Runoff is extraordinarily low—only half of that in Australia, North America, Europe, and Asia, despite similar levels of average precipitation.
This pronounced hydrological variability is expected to increase with climate change. The greatest impact is anticipated in the semiarid margins of the Sahara and the central part of southern Africa.
The macroeconomic impacts of hydrological variability are considerable. For example, water-related shocks depress Mozambique’s gross domestic product growth by more than one percentage point each year. In Zambia, variability of rainfall lowers the country’s agricultural growth by one percentage point each year and will cost the country $4.3 billion in lost GDP over 10 years. Because rain-fed subsistence agriculture is the dominant livelihood, droughts and floods significantly affect food security across the region.
Hydroclimatic variability in Africa (percent change)