It’s that time of year. Technically, it’s still winter in Colorado, but the snow is melting and the temperature is rising. Snowmelt has always been an interesting phenomenon, especially in the state of Colorado. Is there a correlation between snowmelt onset and annual rainfall? What about between snowmelt onset and river temperature? How does streamflow timing play into that? Does flux radiation have to do with it? Going back as far as 1978, scientists have been studying the effect of snowmelt on the climate, but what about the effect of climate on snowmelt? In the past 12 years, Colorado’s snow has been melting at a faster rate, vanishing earlier and earlier each year. How will this change the mountains, the habits of skiers and hikers, native animals and fish in our rivers, and anyone else who relies on snow?
So, what exactly is snowmelt? Snowmelt is essentially the surface runoff of melted snow. Snowmelt can be water or ice. In many parts of the world, water produced by snowmelt is an important part of the annual water cycle. This is true in Colorado. Some parts of Colorado are very dry and depend on the mountain’s snowmelt to sustain the environment. On the other hand, some parts of Colorado – like the Colorado River and the Arkansas River – are not dry, but still depend on the runoff to keep the water flowing to tributaries.
If there is not enough snowmelt, or if the snow melts too slowly, it can cause a lack of runoff into smaller tributaries and even major rivers, affecting the water cycle that relies on the amount of rainfall and snowfall. Contrary to this are the effects of an overabundance of snowmelt or snow that melts too rapidly, which can cause flooding in areas of Colorado with specific and sensitive ecosystems. Another way snowmelt can be dangerous for the climate of Colorado is the refreezing process. If snow melts and then freezes again, ice can accumulate in areas where it is necessary for the water or river to flow.
The science behind melting is fairly simple, but it is interesting to study. The science of snowmelt depends on the atmosphere’s temperature and release (or removal) of heat. Ground heat is the heat below the ground. Whether it is 10 degrees on the top of a mountain or -50 degrees, there is still ground heat. The ground heat acts as the energy supply for the ground to conduct with the snow. Radiation, as in the heat from the sun, is the energy supply delivered to the snow through the air. Once each of these temperatures—ground heat and air temperature—reaches a certain level in the atmosphere, the snow begins to melt.
The onset of snowmelt in any given climate is marked by a melt-date. The rate of warming in the past 12 years was greater than in the last 1,000 years, according to a study done in 2007 by the Intergovernmental Panel on Climate Change (IPCC). This means if the air is warming faster and faster each year, the melt-date is arriving earlier and earlier.
According to the U.S. Geological Survey, the onset of snowmelt, or the melt-date, in Central Colorado (Denver) in 1983 was April 26. In 1988, the melt-date was April 30. In 1993, the melt-date was April 19. In 1998, the melt-date was April 1. In 2003, the melt-date was March 28, and in 2008 the melt-date was March 10. This data means that in each trend studied in each of those years—snowmelt onset, rainfall, and snowfall—the slopes have been trending down each year; the snowmelt is melting earlier and earlier. It has been mapped out that, in Colorado, the snowmelt is earlier by half a day each year. Half a day is insignificant even when only looking at the past few years, but what about the past 30? For the past 28 years, snowmelt has arrived earlier and earlier every year.
If the trends continue to drop, winters will be consistently shorter, winter climates will change, and ecosystems that rely on heavy snowfall may not be able to adapt. On the other hand, with the snowmelt arriving earlier and earlier, rivers may run dry or become solely dependent on rainfall to sustain their ecosystems.
Isn’t rain more important for rivers, one might ask? According to USGS, “as much as 75 percent of water supplies in the western states are derived from snowmelt.” In March of 2000, the Colorado River streamflow was 1,200 cubic feet per second at the melt-date. During August, the month with the most amount of contributing storms on average, streamflow was only 75 cubic feet per second. Imagine rivers only relying on rain; streamflow in a river like the Colorado River would be slowed to the speed of honey, and the streamflow of tributaries would probably stop altogether.
In the next 30 to 50 years, the melt-date could evolve to two or three weeks earlier than the current date. This means that the mountains could melt early, animal migration and hibernation patterns could change, and fish in smaller tributary rivers could die off in the rivers that did not receive enough snowmelt. People may argue differently, but all the ecosystems in Colorado depend on snowmelt. Rain or no rain, the snowmelt is what keeps ecosystems and rivers alive.