Snowpack determines relative importance of climate factors driving summer lake warming

Abstract

Lake thermal regimes are frequently decoupled from rising air temperature trends in their watersheds because interactions among climate factors and local features affect net heat gain or loss. Although snowpack has been empirically linked to temperature and warming rates in mountain lakes, the mechanisms governing this relationship remain unclear and untested, despite predicted declines in mountain snow across the world. We quantified how snowpack and ice cover regulate lake warming in summer primarily by controlling when and how long lakes receive solar radiation, and we demonstrate the relative role of snowmelt on the lake heat budget. We contrast lake thermal responses between extremely wet and dry years and illustrate the increasing importance of other climate factors in the absence of snow. AbstractMountain lakes experience extreme interannual climate variation as well as rapidly warming air temperatures, making them ideal systems to understand lake-climate responses. Snowpack and water temperature are highly correlated in mountain lakes, but we lack a complete understanding of underlying mechanisms. Motivated by predicted declines in snowfall with future temperature increases, we investigated how surface heat fluxes and lake warming responded to variation in snowpack, ice-off, and summer weather patterns in a high elevation lake in the Sierra Nevada, California. Ice-off timing determined the phenology of lake exposure to solar radiation, and was the dominant mechanism linking snowpack to lake temperature. The relative importance of heat loss fluxes (longwave radiation, latent and sensible heat exchange) varied among wet and dry years. Declines in snowpack and ice cover in mountain systems will reduce variability in lake thermal responses and increase the responsiveness of lake warming to atmospheric forcing.

Ice Cover and Extreme Events Determine Dissolved Oxygen in a Placid Mountain Lake

“…Decreases in snowfall usually are greatest near the low-elevation margin of the snowpack and cause reductions in surface albedo and increases in absorbed solar radiation, further leading to elevation-dependent amplification of warming (Minder et al, 2018). In snow-dependent mountain lakes, the amount of spring snowmelt, ice-off timing, and duration of ice cover is strongly tied to the evolution of physical processes such as thermal stratification and mixing (Flaim et al, 2019;Preston et al, 2016;Sadro et al, 2019;Smits et al, 2020;Zhang et al, 2014). Furthermore, topography, especially as it determines the amount and timing of solar radiation impinging on a lake, can also be a major factor affecting the physics and biology of mountain lakes (Flaim et al, 2010(Flaim et al, , 2019Ptak et al, 2018;Sadro et al, 2011).…”

Predicting open-water thermal regimes of temperate North American lakes

“…J S had a robust relationship with spring mean air temperature, reflecting other models that describe the negative influence of this variable (Crossman et al 2016) Smits et al 2020). Changes in wind speed can have large effects on lake stratification dynamics, and outweigh the long-term effects of air temperature (Woolway et al 2017) and change the likelihood of stratification in small lakes (Martinsen et al 2019).…”

“…S4) corresponding to the date of peak land surface air temperature, described by (Gorham 1964), thus, they take longer to reach their maximum temperature leading to higher J M values, as represented by the positive effect of ln(area) on J M . We expected to see a positive relationship between J M and elevation, as lakes at relatively high elevations on a regional scale have been shown to reach their peak summer surface water temperatures at later dates than lower elevation lakes (Livingstone et al 2005), possibly due to delayed ice-off and increased snowpack at higher elevations (Smits et al 2020). We found that adding an elevation term improved the model, but the model coefficient had a negative sign which opposed the potential mechanistic relationship explained above, so we removed the elevation term from the ETM.…”

“…). The negative relationship with elevation may be due to high elevation lakes having greater snowpack than low elevation lakes, thus ice-off occurs later in the year and these lakes have less time to absorb solar radiation(Preston et al 2016;Smits et al 2020). As for the negative relationship with July mean wind speed, wind energy can stimulate mixing thus deepening the epilimnion as well as homogenizing and cooling the upper water column(Nõges et al 2011).…”

The extent and variability of storm‐induced temperature changes in lakes measured with long‐term and high‐frequency data

“…In stratified lakes, epilimnetic temperatures may decrease because of colder water from the hypolimnion mixing into the epilimnion (Znachor et al 2008; Umaña‐Villalobos 2014), upwelling, internal waves breaking at the shore, or heat flux at the lake surface altered by wind, rain, or changes in air temperature (e.g., Andreas et al 1995; Kasprzak et al 2017; Rooney et al 2018). However, the extent of temperature change from storm events also depends on a variety of environmental and lake characteristics (Padisák et al 1988; Kuha et al 2016; Andersen et al 2020), such as the frequency of storm events (Smits et al 2020), internal seiche dynamics (Woolway et al, 2018), lake mixing regime (Jennings et al 2012; Kuha et al 2016), and the ratio of the watershed area to the lake surface area (WA:SA) (Jennings et al 2012; Klug et al 2012). Therefore, what constitutes a storm and how storms may affect lake processes are highly variable, making comparisons across waterbodies difficult (Stockwell et al 2020).…”