Are they driven by precipitation or evaporation?
Lake Level Trends In recent years, the lakes of northern Wisconsin have undergone a pronounced drop in water level. An example of this is shown in Figure 1, which graphs the water level of Sparkling Lake (in Vilas County) from 1984-2007. Over this time period, the lake level typically varied over a range of about 60 cm (2 feet), with high lake levels in the mid 1980s and 1990s and low levels at other times. On top of this variation is a long-term trend toward lower water levels, with an average downward trend of about 16 cm per decade (the straight line in Figure 1). Much of this downward trend began after 1997, when lake levels dropped by 107 cm (42 inches) to their current record low level in 2007. This dramatic 10-year drop is probably what stands out most in the eyes of northern Wisconsin residents. A natural question to ask is “Why?” Have we simply been receiving less rain? Less runoff from snow? More evaporation from the lakes? There are many possible contributing factors, and we
