Ask NRRI

"How does the far below average amount of snow this winter affect Minnesota water resources? "

Water resources scientist
Rich Axler answers:

Article was originally posted in early, 2012.

A bunch of things happen when we get so little snow in fall and early winter. One is that wildfire danger increases which is really unusual for this time of year. Another is that without the insulating effect of snow, the frost depth increases and so when night time lows get back to normal (i.e. subzero) ground heave and freezing water can wreak havoc on municipal water lines and on individual on-site sewage treatment systems ("septics") in rural areas. Duluth Public Works Department has already had to deal with numerous water line breaks. The bedrock, electrolysis within the soils (which corrodes pipes), and hillside slope are all factors that lead to pipe failure, and lack of snow cover just worsens problems typical for this time of year. When the ground freezes deeper than "normal" ground water may be forced to come to the surface and cause ice build-up in places that normally don’t have water/ice issues and is a big problem if ice accumulates on a sidewalk, driveway or roadway.

Snow cover also insulates septic tanks and their leach fields. In the winters from 2000-2003 we had a similar situation and an NRRI/St. Louis County survey indicated freezing related problems with more than 50 percent of county septic systems during one of these snow free periods. Frozen systems require septic tanks to be pumped out more often and home owners are forced to greatly reduce water use, as every drop that enters the tank needs to be pumped out and disposed of in a proper fashion. This can be costly if the system is frozen for an extended time. Frost depth affects wells and home waterlines also. On the plus side, there can be reduced inputs of de-icing salts and sand to water bodies which reduces road and lot maintenance costs for everyone. But one of the hardest scenarios on water quality can be a lot of small snow events because road crews are out applying product constantly.

The effects on lakes and streams obviously include less water overall, but can also lead to thicker ice cover if temperatures are normal because of reduced insulation by snow. In small streams, shallow lakes and wetlands the extra ice acts to reduce liquid water volume which can lead to low oxygen and reduced habitat if the water freezes to the bottom. When streams freeze solid, they trap fish and other critters, resulting in winter kills. Minnesota DNR fisheries biologists worry that we may have the "perfect storm’ for streams freezing to the bottom because we had drought conditions in the fall with very low flows, and now have little snow for insulation. With even normal temperatures, stream fish will likely suffer. These ’bottlenecks’ are important in determining stream carrying capacity which is highly variable from year to year. Most streams don’t freeze to the bottom for their entire length, but in years shaping up like this, resident fish populations can be reduced by 50 percent or more. Of course, this winter we are also experiencing above-normal air temperatures which has delayed ice cover on streams, and led to thinner than normal ice cover on ponds and lakes. Without snow cover, more light can penetrate resulting in increased photosynthesis by algae and plants which releases oxygen which may prevent winterkill in shallow, more productive systems — good for traditional fish lakes, bad for marginal lakes/ponds used by aquaculture folks for rearing minnows, walleye and musky. Shoreland plants are another important component of aquatic ecosystems and frost depth can be a big problem for plants that are at or near their thermal tolerances within their plant hardiness zone.

There are likely other subtle effects when weather is far outside the "normal" range of variation and we’ll have to see how the weather "behaves" during the rest of the winter. The most dramatic trends in Minnesota’s weather over the past 15 years or so have been in the increased winter temperatures recorded around the state, particularly the average daily low temperatures.

Note: This analysis benefited from thoughtful comments from Todd Carlson and Chris Kleist (City of Duluth Stormwater Utility), Don Schreiner (MN DNR Lake Superior Area Fisheries Manager), and Jerry Henneck and Lucinda Johnson (NRRI).