Why do the Sahara and Kalahari deserts have very dry climates?

The Sahara and Kalahari deserts experience very dry climates primarily due to their location within subtropical regions dominated by stable, high-pressure atmospheric cells.123

Atmospheric Circulation

These deserts are situated in areas where dry air masses descend from the upper atmosphere. This process is part of the Hadley cell circulation: air rises near the Equator, loses its moisture as rain, and then moves toward the subtropics. As this air descends, it becomes compressed and warmer, which significantly lowers its relative humidity and prevents the formation of precipitation.2

Additional Influencing Factors

• Continental Tropical Air Masses: The Sahara is heavily influenced by a hot, dry continental tropical air mass that dominates the region, suppressing rainfall.3
• Ocean Currents: Along the western coasts of Africa, cold ocean currents—such as the Benguela Current—chill the air above them. This cooling effect stabilizes the air, preventing the convectional rainfall that might otherwise occur, and contributes to the arid conditions of adjacent coastal areas.341
• Topography and Drainage: In the Kalahari, the lack of surface water is further exacerbated by deep sands that allow rain to drain instantly, creating an edaphic (soil-based) drought.56