Yemen can be divided geographically into four main regions: the coastal plains in the west, the western highlands, the eastern highlands, and the Rub' al Khali in the east. The Tihāmah ("hot lands" or "hot earth") form a very arid and flat coastal plain along Yemen's entire Red Sea coastline. Despite the aridity, the presence of many lagoons makes this region very marshy and a suitable breeding ground for malaria mosquitos. Extensive crescent-shaped sand dunes are present. The evaporation in the Tihamah 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. Near the village of Madar about  north of Sana'a, dinosaur footprints were found, indicating that the area was once a muddy flat. 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  per year to about  in Taiz and over  in Ibb. Temperatures are warm in the day but fall dramatically at night. Perennial streams occur in the highlands, but these never reach the sea because of high evaporation in the Tihamah.