Niwot Ridge LTER Climate

When compared to nearby lower elevations, Niwot Ridge is characterized by low temperatures throughout the year, increased solar radiation (and consequently higher levels of ultraviolet radiation), higher wind velocities, and an abbreviated growing season. Meteorological data have been collected since 1953 from a network of stations ranging in elevation from 2591 to 3743 m.

Annual mean temperature at 3743 m is -3.7 degrees Celsius. The January mean temperature is -13.2 degrees Celsius and the July mean is 8.2 degrees Celsius.

Mean annual precipitation is about 930 mm, of which one-third is used in evapotranspiration, the remainder leaving the system as runoff. Precipitation is highly variable temporally -- most occurs as snow during the winter and spring months and annual totals vary greatly from year to year. The interactions among wind, snow, and high relief result in a mosaic of snow-free and snow-accumulation areas with consequent wide variability in the amount and timing of meltwater release. Summer precipitation is also highly variable, both temporally and spatially, usually arriving in brief convective storms.

The headwaters of the three major rivers of the southwestern United States (the Arkansas, Colorado, and Rio Grande) are located in the Colorado Rockies. The mountain snowpacks provide most of the water used in human activities in the region; they are highly susceptible to the effects of global climate change if it leads to altered precipitation and/or wind patterns in these mountains. However, general circulation models usually have lower confidence for precipitation than for temperature prediction, and the extrapolation from low elevations to the alpine tundra adds further uncertainty. Thus, continued analysis of the long-term climate database at the Niwot Ridge site is important.

The record for atmospheric carbon dioxide concentration on Niwot Ridge is among the longest for continental North America.

The significance of snowpack, including patterns of deposition, the timing of snow, its depth and chemical composition, as well as its subsequent disappearence, continue to dominate the biological and biogeochemical questions addressed by Niwot Ridge LTER scientists. New research tools to investigate this variable include a subnivean laboratory, used to monitor biogeochemical processes within and below the snow, and a 60-m snowfence, used to modify the timing, amount, and duration of snow. Nitrogen enrichment studies are also being conducted as part of the recognition that enhanced atmospheric deposition of nitrogen has and is occurring in this region.