The Tundra biome, a vast, treeless plain located in the high latitudes of the Arctic and on high mountain peaks globally, is defined by its extremely cold temperatures and permanently frozen subsoil. This environment is often mistakenly imagined as a landscape of endless, deep snow, but it is actually a harsh, dry cold environment. The defining characteristic that prevents the growth of trees is the low temperature, which leads to a short growing season and the presence of permafrost. The amount of water that enters this biome annually is surprisingly low, a factor that profoundly shapes the unique hydrology of this seemingly snowy world.
Annual Precipitation Totals
The Tundra is considered a type of cold desert due to its minimal moisture input. The average annual precipitation across the entire biome is a remarkably low range, typically falling between 150 and 250 millimeters (6 to 10 inches) of water equivalent per year. This total includes all forms of moisture, such as rain, snow, and ice, once melted down into a liquid measurement. For context, many of the world’s hot, sandy deserts receive comparable or even greater amounts of precipitation annually.
The Importance of Frozen Precipitation
The vast majority of the Tundra’s scant annual precipitation arrives in the form of snow or ice, rather than liquid rain. This precipitation falls slowly over the long, dark winter months, often being redistributed by persistent, high winds into deep snowdrifts. The cold air physics explain the low totals because absolute humidity is significantly lower in frigid air compared to warm air. Simply put, air at sub-zero temperatures has a minimal capacity to hold water vapor, limiting the amount that can condense and fall as precipitation. The resulting snowpack, while often extensive and long-lasting, represents a relatively small volume of water once melted.
How Permafrost Affects Water Retention
Despite the Tundra receiving desert-like precipitation totals, the landscape often appears boggy, wet, and saturated during the brief summer. This is explained by the presence of permafrost, the layer of ground that remains permanently frozen for at least two consecutive years. This impermeable frozen layer acts as a barrier, preventing water from draining deeper into the ground. As the top layer of soil, known as the active layer, thaws during the summer, the meltwater from the snowpack and any summer rainfall are trapped above the permafrost. This retention creates widespread surface saturation, leading to the formation of numerous shallow lakes, ponds, and wetlands across the Tundra landscape.
Regional Differences in Tundra Rainfall
The general precipitation average of 150 to 250 millimeters masks variations across the three main Tundra types: Arctic, Antarctic, and Alpine. The Antarctic Tundra, primarily found on islands and the Antarctic Peninsula, is typically the driest, with some areas receiving extremely low amounts of moisture. The Arctic Tundra, which spans the northern regions of North America, Europe, and Asia, represents the biome’s average. Alpine Tundra, located on high mountains worldwide above the tree line, often receives slightly higher total precipitation than its Arctic counterpart. This increase is due to orographic lift, where mountains force moisture-laden air to rise and cool, generating more snowfall on the peaks compared to the surrounding lowlands.