Snowmelt

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Timelapse of Snowmelt over Okanagan Lake in British Columbia

In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many parts of the world, in some cases contributing high fractions of the annual runoff in a watershed. Predicting snowmelt runoff from a drainage basin may be a part of designing water control projects. Rapid snowmelt can cause flooding. If the snowmelt is then frozen, very dangerous conditions and accidents can occur, introducing the need for salt to melt the ice.

Contents

Vegetation gives off heat, resulting in this circular snowmelt pattern. Vegetation Induced Circular Snowmelt.jpg
Vegetation gives off heat, resulting in this circular snowmelt pattern.

There are several energy fluxes involved in the melting of snow. [2] These fluxes can act in opposing directions, that is either delivering heat to or removing heat from the snowpack. Ground heat flux is the energy delivered to the snowpack from the soil below by conduction. Radiation inputs to the snowpack include net shortwave (solar radiation including visible and ultraviolet light) and longwave (infrared) radiation. Net shortwave radiation is the difference in energy received from the sun and that reflected by the snowpack because of the snowpack albedo. Longwave radiation is received by the snowpack from many sources, including ozone, carbon dioxide, and water vapor present in all levels of the atmosphere. Longwave radiation is also emitted by the snowpack in the form near–black-body radiation, where snow has an emissivity between 0.97 and 1.0. [3] Generally the net longwave radiation term is negative, meaning a net loss of energy from the snowpack. Latent temperature flux is the energy removed from or delivered to the snowpack which accompanies the mass transfers of evaporation, sublimation, or condensation. Sensible heat flux is the heat flux due to convection between the air and snowpack.

Thaw circles around tree trunks

Tree trunks absorbing sunlight become warmer than the air and cause earlier melting of snow around them. The snow does not melt slower gradually with distance from the trunk, but rather creates a wall surrounding snow-free ground around it. According to some of sources, North American spring ephermal plants like spring beauty (Claytonia caroliniana), trout lily (Erythronium americanum) and red trillium (Trillium erectum L.) benefit from such thaw circles. They can emerge earlier inside these circles, what gives them more time before development of tree canopy foliage cutting off significant portion of the light. They perform nearly all of their yearly photosynthesis during this period. [4]

Evergreen trees tend to produce larger thaw circles than deciduous trees. This involves largely a different mechanism and spring ephemeral plants don't occur there. [4]

The snow melts earlier in forest also for example on microtopographic mounds (small elevations) or in wet places like edges of creeks or in seeps. These microsites affect distribution of many herbs too. [4]

Historical cases

In northern Alaska, the melt-date has advanced by 8 days since the mid-1960s. Decreased snowfall in winter followed by warmer spring conditions seems to be the cause for the advance. [5] In Europe, the 2012 heat wave has especially been anomalous at higher altitudes. For the first time on record, some of the highest Alpine peaks in Europe were snow-free. Although it would seem that the two were related, the question of how much of this is due to climate change firmly remains a center of debate. [6]

Snowmelt flowing into lake at Okanagan Mountain Provincial Park

Increased water runoff due to snowmelt was a cause of many famous floods. One well-known example is the Red River Flood of 1997, when the Red River of the North in the Red River Valley of the United States and Canada flooded. Flooding in the Red River Valley is augmented by the fact that the river flows north through Winnipeg, Manitoba and into Lake Winnipeg. As snow in Minnesota, North Dakota, and South Dakota begins to melt and flow into the Red River, the presence of downstream ice can act as a dam and force upstream water to rise. Colder temperatures downstream can also potentially lead to freezing of water as it flows north, thus augmenting the ice dam problem. Some areas in British Columbia are also prone to snowmelt flooding as well. [7]

Scholarly conversation

The date of annual melt is of great interest as a potential indicator of climate change. In order to determine whether the earlier disappearance of spring snow cover in northern Alaska is related to global warming versus an appearance of a more natural, continual cycle of the climate, further study and monitoring is necessary. [8]

Large year-to-year variability complicates the picture and furthers the debate. Inter-annual variability of springtime snow pack comes largely from variability of winter month precipitation which is in turn related to the variability of key patterns of atmospheric circulation.

A study of the mountains in the western United States show a region wide decline in spring snow-pack since the mid-1900s, dominated by loss at low elevations where winter temperatures are near freezing. These losses are an indication of increased temperatures which lead to snow loss via some combination of increased regularity of rain versus snow and increased melting during winter months. These natural variations make it challenging to quantify trends with confidence, to deduce observed changes to predict future climate, or to clearly detect changes in snow-pack due to human impact on warming trends. [9]

See also

Related Research Articles

<span class="mw-page-title-main">Albedo</span> Ratio of how much light is reflected back from a body

Albedo is the fraction of sunlight that is diffusely reflected by a body. It is measured on a scale from 0 to 1. Surface albedo is defined as the ratio of radiosity Je to the irradiance Ee received by a surface. The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface. These factors vary with atmospheric composition, geographic location, and time.

<span class="mw-page-title-main">Greenhouse effect</span> Atmospheric phenomenon causing planetary warming

The greenhouse effect occurs when greenhouse gases in a planet's atmosphere insulate the planet from losing heat to space, raising its surface temperature. Surface heating can happen from an internal heat source as in the case of Jupiter, or from its host star as in the case of the Earth. In the case of Earth, the Sun emits shortwave radiation (sunlight) that passes through greenhouse gases to heat the Earth's surface. In response, the Earth's surface emits longwave radiation that is mostly absorbed by greenhouse gases. The absorption of longwave radiation prevents it from reaching space, reducing the rate at which the Earth can cool off.

<span class="mw-page-title-main">Snow</span> Precipitation in the form of ice crystal flakes

Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.

<span class="mw-page-title-main">Cryosphere</span> Earths surface where water is frozen

The cryosphere is an umbrella term for those portions of Earth's surface where water is in solid form. This includes sea ice, ice on lakes or rivers, snow, glaciers, ice caps, ice sheets, and frozen ground. Thus, there is a overlap with the hydrosphere. The cryosphere is an integral part of the global climate system. It also has important feedbacks on the climate system. These feedbacks come from the cryosphere's influence on surface energy and moisture fluxes, clouds, the water cycle, atmospheric and oceanic circulation.

<span class="mw-page-title-main">Earth's energy budget</span> Concept for energy flows to and from Earth

Earth's energy budget is the balance between the energy that Earth receives from the Sun and the energy the Earth loses back into outer space. Smaller energy sources, such as Earth's internal heat, are taken into consideration, but make a tiny contribution compared to solar energy. The energy budget also takes into account how energy moves through the climate system. The Sun heats the equatorial tropics more than the polar regions. Therefore, the amount of solar irradiance received by a certain region is unevenly distributed. As the energy seeks equilibrium across the planet, it drives interactions in Earth's climate system, i.e., Earth's water, ice, atmosphere, rocky crust, and all living things. The result is Earth's climate.

<span class="mw-page-title-main">Freshet</span> High water levels caused by melting snow and ice

The term freshet is most commonly used to describe a snowmelt, an annual high water event on rivers resulting from snow and river ice melting.

<span class="mw-page-title-main">Outgoing longwave radiation</span> Energy transfer mechanism which enables planetary cooling

In climate science, longwave radiation (LWR) is electromagnetic thermal radiation emitted by Earth's surface, atmosphere, and clouds. It is also referred to as terrestrial radiation. This radiation is in the infrared portion of the spectrum, but is distinct from the shortwave (SW) near-infrared radiation found in sunlight.

<span class="mw-page-title-main">Meltwater</span> Water released by the melting of snow or ice

Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found during early spring when snow packs and frozen rivers melt with rising temperatures, and in the ablation zone of glaciers where the rate of snow cover is reducing. Meltwater can be produced during volcanic eruptions, in a similar way in which the more dangerous lahars form. It can also be produced by the heat generated by the flow itself.

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<span class="mw-page-title-main">Snowpack</span> Compressed accumulation of snow

Snowpack is an accumulation of snow that compresses with time and melts seasonally, often at high elevation or high latitude. Snowpacks are an important water resource that feed streams and rivers as they melt, sometimes leading to flooding. Snowpacks provide water to down-slope communities for drinking and agriculture. High-latitude or high-elevation snowpacks contribute mass to glaciers in their accumulation zones, where annual snow deposition exceeds annual melting.

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The climate of the Arctic is characterized by long, cold winters and short, cool summers. There is a large amount of variability in climate across the Arctic, but all regions experience extremes of solar radiation in both summer and winter. Some parts of the Arctic are covered by ice year-round, and nearly all parts of the Arctic experience long periods with some form of ice on the surface.

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<span class="mw-page-title-main">Rotten ice</span> Melting or otherwise disintegrating ice on open water

Rotten ice is a loose term for ice that is melting or structurally disintegrating due to being honeycombed by liquid water, air, or contaminants trapped between the initial growth of ice crystals. It may appear transparent or splotchy grey, and it is generally found after spring or summer thaws, presenting a danger to those traveling or spending time in outdoor recreation. The increase of rotten ice vs. solid ice in the Arctic affects ocean-atmosphere heat transfer and year-to-year ice formation, as well as the lives of the Inuit, sea mammals such as walrus and polar bear, and the microorganisms that live inside the ice.

The Surface Heat Budget of the Arctic Ocean (SHEBA) study was a National Science Foundation-funded research project designed to quantify the heat transfer processes that occur between the ocean and the atmosphere over the course of a year in the Arctic Ocean, where the sun is above the horizon from spring through summer and below the horizon the rest of the time. The study was designed to provide data for use in global climate models, which scientists use to study global climate change.

<span class="mw-page-title-main">Snow science</span> Interdisciplinary field of hydrology, mechanics and meteorology

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References

  1. Ray, Claiborne C. (April 12, 2011). "When Trees Unfreeze". The New York Times, the New York Edition: D2. Retrieved December 11, 2017.
  2. Gray, D.M., Male, D. H. (1981). Handbook of Snow: Principles, Processes, Management, and Use. Pergamon Press. ISBN   978-1-932846-06-5.{{cite book}}: CS1 maint: multiple names: authors list (link)
  3. Kondratyev, K. Ya. (1969). "Radiation in the Atmosphere". Inter. Geophys. Ser. 12.
  4. 1 2 3 Vellend, Mark; Young, Amanda B.; Letendre, Gabriel; Rivest, Sébastien (November 15, 2017). "Thaw circles around tree trunks provide spring ephemeral plants with a big head start on the growing season" (PDF). Ecology. 98 (12). Ecological Society of America: 3224–3226. Bibcode:2017Ecol...98.3224V. doi:10.1002/ecy.2024. PMID   29141104 . Retrieved December 11, 2017.
  5. Stone, Robert (2002). "Earlier Spring Snowmelt in Northern Alaska as an Indicator of Climate Change". Journal of Geophysical Research. 107 (4089): ACL 10-1-ACL 10-13. Bibcode:2002JGRD..107.4089S. doi: 10.1029/2000jd000286 .
  6. Burt, Christopher. "Unprecedented Snow Melt and Heat in the European Alps". Weather Underground blog. Weather Underground. Archived from the original on 2019-03-24. Retrieved 4 October 2012.
  7. "Flooding Events in Canada - British Columbia". Environment and Climate Change Canada. Environment Canada. Retrieved 12 March 2017.
  8. Hoffman, David. "Earth System Research Laboratory". Climate Monitoring and Diagnostics Laboratory Summary Report No. 24. U.S. Department of Commerce. Retrieved 4 October 2012.
  9. Minder, Justin (2009). "The Sensitivity of Mountain Snowpack Accumulation to Climate Warming". Journal of Climate. 23 (10): 2634–650. doi: 10.1175/2009jcli3263.1 . S2CID   17326866.