The wettest places on the planet are found in the tropics -- as well as some of the dryest. Lush jungles are supported by heavy rains, including the awesome power of the monsoons in some areas. Parched, baked sand and rock make up some of the most famous deserts in the world. In between are the savannas and steppes that receive more moderate amounts of rain.
Humid tropical climates -- category A -- are further distinguished by adding single lower-case letters, describing typical rainfall. There are four subcategories: f indicates a location that is rainy year-round, m designates a place that receives monsoon rains, s describes a region with a dry summer and a rainy winter, and w is just the reverse, with dry winter and rainy summer.
Dry climates -- category B -- are divided into two subcategories, BS for steppe and BW for desert. In the tropics, average monthly temperatures never fall below freezing, so h, meaning heiss (German for "hot"), is appended. In a few deserts that get little moisture other than frequent fog, however, n is appended instead.
By Dave Bryant, copyright 2002