Temperatures are more pleasant in Yemen than other arab countries due to high elevation. Rainfall is varied based on elevation. The highlands enjoy a temperate, rainy summer with an average high temperature of and a cool, moderately dry winter with temperatures occasionally dipping below . The climate of the Tihamah (western coastal plain) is tropical; temperatures occasionally exceed , and the humidity ranges from 50 to 70 percent. Rainfall, which comes in irregular heavy torrents, averages annually. In Aden the average temperature is in January and in June, but with highs often exceeding . Average annual rainfall is . The highest mountainous areas of southern Yemen receive from of rain a year. Some areas of the western highlands, most notably Ibb and Ta'izz, receive from about of rain each year. The capital, Sana'a, receives around a year, it is not uncommon for the northern and eastern sections of the country to receive no rain for five years or more. The Wadi Hadhramaut in the eastern part of Yemen is arid and hot, and the humidity ranges from 35 percent in June to 64 percent in January. Yemen has the most fertile land in the Arabian peninsula.