As noted in the previous GeoCurrents post on the “deserts” of Colombia, Colombia is usually considered to be the world’s rainiest country, receiving some 127 inches (3249 mm) of precipitation annually, averaged over the entire country. Learning this fact inspired me to make a map of average annual precipitation by country, which is posted below.
The result is, admittedly, a terrible precipitation map, as patterns of rain and snow obviously do not follow national borders. French Guiana, for example, is a very rainy place, getting on average around 114 inches (2,900 mm) per year, yet on my map it is depicted as relatively dry. It is portrayed in this manner because it is an integral part of France and is mapped accordingly. But although this is a poor way of mapping precipitation, it moderately significant as a political map of a major aspect of physical geography.
On this map, much more of the world is depicted as drier than average (brown) than as wetter than average (green). This is simply because many of the world’s rainiest countries are small while many of its driest ones are large. São Tomé and Príncipe, for example, ranks second, Solomon Islands fourth, Panama fifth, Costa Rica sixth, Samoa seventh, and Brunei ninth. Some rainy island countries, such as the Maldives, are too small to appear on the map. In contrast, the three countries receiving the least precipitation, Egypt, Libya, and Saudi Arabia, are relatively large, as are seventh-placed Algeria and eighth-placed Mauritania. At any rate, there are as many countries falling into the green categories as into the brown ones. Those in the middle of the spectrum are mapped in a neutral shade of grey.
It might be surprising that several heavily forested countries, such as Russia, Finland, and Canada, are significantly drier than average. But as they are also relatively cold, they have low levels of average annual evaporation and transpiration, allowing forest vegetation. Yakutsk, in central Siberia, receives only 9.3 inches/235 mm of precipitation annually, yet lies in the taiga (boreal forest) biome. Fairbanks, Alaska gets just a little more (11.7 inches/296 mm) and is also in a largely forested area.
