The Tihamah (“hot lands”) form a very arid and flat coastal plain. Despite the aridity, the presence of many lagoons makes this region very marshy and a suitable breeding ground for malarial mosquitoes. There are also extensive crescent-shaped sand dunes. The evaporation in the Tihama is so great that streams from the highlands never reach the sea, but they do contribute to extensive groundwater reserves; today these are heavily exploited for agricultural use.

The Tihamah ends abruptly at the escarpment of the western highlands. This area, now heavily terraced to meet the demand for food, receives the highest rainfall in Arabia, rapidly increasing from 100 mm (4 inches) per year to about 760 mm (30 inches) in Ta’izz and over 1,000 mm (40 inches) in Ibb. Agriculture here is very diverse, with such crops as sorghum dominating, but cotton and many fruit trees are also grown, with mangoes being the most valuable. Temperatures are hot in the day but fall dramatically at night. There are perennial streams in the highlands but these never reach the sea because of high evaporation in the Tihama.