Trends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers

TitleTrends and abrupt changes in 104 years of ice cover and water temperature in a dimictic lake in response to air temperature, wind speed, and water clarity drivers
Publication TypeJournal Article
Year of Publication2016
AuthorsMagee, Madeline R., Wu Chin H., Robertson Dale M., Lathrop Richard C., and Hamilton David P.
JournalHydrology and Earth System Sciences
Pagination1681 - 1702
Date PublishedMay-03-2016
Keywordsdimictic ice, ice cover, temperature trends

The one-dimensional hydrodynamic ice model, DYRESM-WQ-I, was modified to simulate ice cover and thermal structure of dimictic Lake Mendota, Wisconsin, USA, over a continuous 104-year period (1911–2014). The model results were then used to examine the drivers of changes in ice cover and water temperature, focusing on the responses to shifts in air temperature, wind speed, and water clarity at multiyear timescales. Observations of the drivers include a change in the trend of warming air tem- peratures from 0.081 ◦ C per decade before 1981 to 0.334 ◦ C per decade thereafter, as well as a shift in mean wind speed from 4.44 m s−1 before 1994 to 3.74 m s−1 thereafter. Obser- vations show that Lake Mendota has experienced significant changes in ice cover: later ice-on date(9.0 days later per cen- tury), earlier ice-off date (12.3 days per century), decreasing ice cover duration (21.3 days per century), while model simu- lations indicate a change in maximum ice thickness (12.7 cm decrease per century). Model simulations also show changes in the lake thermal regime of earlier stratification onset (12.3 days per century), later fall turnover (14.6 days per cen- tury), longer stratification duration (26.8 days per century), and decreasing summer hypolimnetic temperatures (−1.4 ◦C per century). Correlation analysis of lake variables and driv- ing variables revealed ice cover variables, stratification on- set, epilimnetic temperature, and hypolimnetic temperature were most closely correlated with air temperature, whereas freeze-over water temperature, hypolimnetic heating, and fall turnover date were more closely correlated with wind speed.

Each lake variable (i.e., ice-on and ice-off dates, ice cover duration, maximum ice thickness, freeze-over water tem- perature, stratification onset, fall turnover date, stratification duration, epilimnion temperature, hypolimnion temperature, and hypolimnetic heating) was averaged for the three pe- riods (1911–1980, 1981–1993, and 1994–2014) delineated by abrupt changes in air temperature and wind speed. Aver- age summer hypolimnetic temperature and fall turnover date exhibit significant differences between the third period and the first two periods. Changes in ice cover (ice-on and ice- off dates, ice cover duration, and maximum ice thickness) exhibit an abrupt change after 1994, which was related in part to the warm El Niño winter of 1997–1998. Under-ice water temperature, freeze-over water temperature, hypolim- netic temperature, fall turnover date, and stratification dura- tion demonstrate a significant difference in the third period (1994–2014), when air temperature was warmest and wind speeds decreased rather abruptly. The trends in ice cover and water temperature demonstrate responses to both long-term and abrupt changes in meteorological conditions that can be complemented with numerical modeling to better understand how these variables will respond in a future climate. 

Short TitleHydrol. Earth Syst. Sci.