Significance of Snow-melt Processes in Freshwater

Describe the processes of snowmelt and examine their significance for the freshwater environment.

Snow melt is an integral component of the hydrological cycle for many catchments across the Northern hemisphere where snow accumulation is greater and therefore the subsequent melting has a more important role in the hydrological cycle of these areas (Aygun, Kinnard, and Campeau, 2020). Over several months, winter precipitation is gathered into a snowpack which is subsequently melted in a shorter time during the spring snowmelt. This shorter snowmelt period contributes to the catchment`s runoff, with snowpacks creating large amounts of meltwater that is subsequently flowed, by overland or subsurface flow, into lakes or rivers in the catchment (USGS, 2019). This process plays a crucial role in hydrological forecasting, in mid to high-latitude areas of the world, which forecasts the spatial and temporal progress of snowpacks, the melting rate, the melt waters impact, and flood forecasting (Aygun, Kinnard, and Campeau, 2020). Although, in many parts of the world this process is under threat due to rising air temperatures which is decreasing snow accumulation and melt and is resulting in snow melting earlier. These changes have consequences for the hydrological cycle, and the freshwater environment and could also result in increased floods in affected areas (Anderson and Shepard, 2013). This essay will explain the processes of snowmelt through two examples, one in the Cairngorm mountains of Scotland and the other in the mountainous areas of Central Europe, and will also showcase their significance to the freshwater in their catchments. It will also explain the possible consequences of climate change on snowmelt and the effects that it will have on freshwater environments.

Snowmelt is a contributing factor in the runoff of catchment in areas where climate permits high accumulation of snow to create snowpacks. These snowpacks are generated over several months in winter and are usually found in mountainous and mid-to-high latitude areas. The subsequent melting of these snowpacks is experienced in the spring-melting period due to Energy inputs (solar energy). These inputs result in changes to the structure of the snowpack over time and the warming of ice to 0 degrees Celsius (Holko, Gorbachova, and Kostka, 2011). Further inputs of solar energy and air temperature result in the melting of snow into meltwater outflow. This meltwater contributes to the basin`s runoff, in which higher levels of runoff can be achieved (Holko, Gorbachova, and Kostka, 2011). This process can be observed in both central Europe and the Cairngorm mountains of Scotland. This will be explained in greater depth within this essay.

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The case study of the processes of Snowmelt in Central Europe examines the phenomena of snowmelt experienced in the Carpathian Mountains in north Slovakia, which can be categorized into three phases. The first phase in the small runoff event is in relation to the melting of snowpacks in the mountain valleys brought on by precipitation. Although snow from the mountain valleys is subsequently melted the snow on the mountains stays intact (Holko, Gorbachova, and Kostka, 2011). This stage is usually initiated at the end of March or the start of April. The second stage results in no change to the snowpack at the start of April as colder air masses from high latitudes prevent the snowpack from melting (Holko, Gorbachova, and Kostka, 2011). The third stage initiates the subsequent melting of the snowpacks on the mountains. This stage usually starts in the 3rd week of April, if during this time, rainfall is experienced alongside snowmelt, runoff usually is increased resulting in annual runoff maxima values for the catchment. If rainfall is not occurring and contributing to the process of snowmelt then diurnal runoff oscillations take place with respect to melting snowpacks (Holko, Gorbachova, and Kostka, 2011). Variations in air and surface temperatures influenced by solar radiation are shown to be higher in the daytime and lower at night, leaving a delayed response to snow melting. With the Carpathian Mountains show higher runoff values at night and minimum values at midday. This variance in temperatures, therefore, leads to the delayed response of the discharge of snowmelt (Holko, Gorbachova, and Kostka, 2011). This means that discharge is variable with time and can be longer or shorter due to characteristics such as catchment size. Figure 1 illustrates the increased runoff experienced in the 3rd week of April with low values of precipitation and high levels of air temperature. The graph illustrates that increased runoff is mainly attributed to the process of snowmelt.

This subsequent increase in runoff at this time of year flows into the Danube basin. Snowmelt has a significant influence on the Danube runoff regime, especially in the areas of the Alps and the Carpathian Mountains which give higher levels of runoff in late April due to the snowmelt (Holko, Gorbachova, and Kostka, 2011). In the event of rainfall during the snow melt period floods can be a threat due to the increased runoff values of these areas.

A similar process of snow melting can be seen in the second example of the basin Feshie in the eastern highlands of Scotland, with the British uplands and especially Scottish Highlands experiencing a mass accumulation of snow in winter months which results in snowpacks being present in many mid to high latitude areas within these catchments (Ferguson, 1984). The case study conducted by F.I. Ferguson describes the runoff from the basin in relation to snowmelt from 1979-1980. The Feshie river flows into the larger Spey river that flows off the western edge of the Cairngorm mountains (Ferguson, 1984). Ferguson illustrates the importance of snowmelt in the basin's hydrological cycle as there is a recurrence of diurnal oscillation in the streamflow, occurring at night. The snowy cold winter from 1978-79 accounted to be the cause of generating the large snow accumulation for the snowpack and diurnal oscillations experienced in the streamflow starting on April 10th, 1979, and lasting up until June (Ferguson, 1984). Ferguson makes a link between diurnal peak discharges and maximum air temperature during the day (Ferguson, 1984). This can be represented in Figure 2, which shows discharge flows peaking on days with higher air temperatures, resulting from the increased melting of snow.

The above studies describe the process of snowmelt and how it affects the hydrological cycle in their respective catchments. The fundamental process is similar, although climate factors such as rainfall and air temperature can contribute to a higher amount of snow melt and subsequent increase in runoff.

A major disturbance to the hydrological cycle is the threat of climate change to the process of snowmelt. Snow accumulation and melt are very sensitive to climate change as the predicted changes in precipitation and air temperature in this medium to high-latitude areas result in a decrease in snow accumulation and seasonal melting, which will affect the increased runoff in the spring melting season for many catchments (Aygun, Kinnard and Campeau, 2020). Projected climate models in the western USA, show that global warming influences can change the timing of snowmelt peak runoff from the warmer months to the cooler months in catchments in the affected areas. This change in climate can affect water resources and the economies of these mid to high-latitude regions (Aygun, Kinnard, and Campeau, 2020). From the climate models, future snow accumulation and snowmelt are predicted to decrease, therefore decreasing winter snowpack and peak runoff flows in the spring. Although in certain areas this model predicts in a minority of continental locations an increase in mid-winter snow accumulation may be experienced. The decrease in snow accumulation in mid to high-latitude areas could give rise to more frequent rainfall events, rather than snow, which could contribute to higher flood potential for certain areas (Anderson and Shepherd, 2013). Spring snowmelt can also provide a positive cooling effect in freshwater rivers. This can be seen in the River Spey, which is the habitat for many species of fish, including salmon. The predicted rising river temperatures due to warming air temperatures are a threat to aquatic livelihood as increased river temperature can affect their reproduction, habitat, and other biological factors (Pohle, Helliwell et.al, 2019). The rising air temperatures also affect the snowpack accumulation, which will decrease the amount of snow accumulated in the pack and the snowmelt that is discharged to the river. The process of snowmelt alongside precipitation and discharge influences the intra-annual variability of this river temperature (Pohle, Helliwell et.al, 2019). The subsequent gradual loss of this factor in the hydrological cycle has consequences for the Spey river and its aquatic species.

The current and projected loss of winter snowpacks and spring snowmelt due to climate change highlights their critical role in the hydrological cycle of these areas and the effect they have on the freshwater environment. In the spring melting season, snowmelt is a crucial component in the runoff of a catchment, as in many cold regions the major contributor to streamflow in a catchments river is meltwater runoff. Therefore, the projected shift of seasonal snowmelt to colder months and the overall predicted future loss of this snowmelt have serious implications on freshwater environments and the contribution they provide to water supplies and water processes in a period of spring snowmelt(Aygun, Kinnard, and Campeau, 2020). This decrease in streamflow will have implications for other tributary rivers and the aquatic species that live in these freshwater environments. The process of snowmelt in these areas serves a significant role in freshwater environments through runoff and discharge contributing to streamflow and the influence of meltwater on river temperatures that help contribute to cooling in the spring season (Pohle, Helliwell et.al, 2019). This can be seen from the two examples where the snowmelt from the Carpathian Mountains contributes to a large discharge of meltwater to the basin of the Danube and the Feshie catchment contributing large runoff of meltwater to the Spey river contributing to its streamflow and river temperatures.

References

1. Andersen, TK and Shepherd, JM (2013) Floods in a changing climate. Geography Compass, 7, 95-115. DOI: https:doi.org10.1111gec3.12025
2. Aygün, O, Kinnard, C, Campeau, S (2020) Impacts of climate change on the hydrology of northern midlatitude cold regions. Progress in Physical Geography, 44, 338-375. DOI: 10.11770309133319878123
3. Ferguson, RI (1984) Magnitude and modeling of snowmelt runoff in the Cairngorm mountains, Scotland. Hydrological Sciences Journal, 29, 49-62. DOI: 10.108002626668409490921
4. Holko, L., Gorbachova, L and Kostka, Z (2011) Snow Hydrology in Central Europe. Geography Compass, 5, 200-218. DOI: 10.1111j.1749-8198.2011.00412.x
5. Pohle, I, Helliwell, R, Aube, C, Gibbs, S, Spencer, M, Spezia, L (2019) Citizen science evidence from the past century shows that Scottish rivers are warming. Science of the Total Environment, 659, 53-65. DOI: 10.1016j.scitotenv.2018.12.325
6. USGS, (2019) 'Snowmelt Runoff and the Water Cycle'. Available at: https:www.usgs.govspecial-topic water-science-school science snowmelt-runoff-and-water-cycle?qt-science_center_objects=0#qt-science_center_objectsFigure references
7. Ferguson, RI (1984) Magnitude and modeling of snowmelt runoff in the Cairngorm mountains, Scotland. Hydrological Sciences Journal, 29, 49-62. DOI: 10.108002626668409490921
8. Holko, L., Gorbachova, L and Kostka, Z (2011) Snow Hydrology in Central Europe. Geography Compass, 5, 200-218. DOI: 10.1111j.1749-8198.2011.00412.x