Aug 8, 2007
Artificial snow drains mountain resources
As mountaintop temperatures rise and natural snow formation is reduced and delayed, winter ski resorts are increasingly turning to artificial snow production. But that could put water supplies and ecosystems under stress in fragile areas where an influx of tourists is already stretching resources.
Artificial snow-making takes place during autumn and winter when natural water resources are limited, causing conflicts with drinking water. What's more, the snow production process loses an estimated 30% of the water consumed for good through evaporation.
High-altitude mountain basins are usually small in size and lie above the un-saturated zone so surface water, as well as groundwater, is scarce. Water loss through abstraction and evaporation in winter has immediate effects on these limited water volumes, especially on mountain streams whose discharge is reduced by between 40 - 70% and which can easily run dry.
As temperatures rise considerably at high altitudes, artificial snow producers will be confronted with a reduced snow season along with rainfall instead of snowfall and stronger snowmelt, both of natural and artificial snow. This trend will pressurize snow producers to fabricate more and more snow in a losing battle against global warming. In future, as the economic pressure of climate change and winter tourism augments, municipalities, water agencies and environmental ministries will have to develop integrated water management concepts as well as considering alternative, less costly methods of attracting tourism that better harmonize and optimize available natural resources.
It's commonly believed that all the water extracted from nature for artificial snow production is given back. People assume that the only difference from natural snow formation is that the artificial process is slower and water is given back at a later stage, so it's not harmful to nature. This assumption is wrong from a scientific viewpoint since the notion of slowing down the water cycle and concentrating it at the surface alone implies that more water is lost on the way than usual.
A clear differentiation needs to be made between the natural water cycle and that modified for the production of artificial snow. My estimations based on long-term experimental measurements of the evaporation of water, evapotranspiration of plants and sublimation of snow in Europe's Alps and Morocco's High Atlas indicate that approximately 30 % of the water transformed into artificial snow is permanently lost to the area. The evaporated water is transported into the atmosphere and, depending on atmospheric conditions, it may be carried into the next basin or into the next country. This evaporation figure is supported by the French Ministry for Equipment, Transport, Housing and Tourism who assume 30% water loss and the French Water Agencies who assume as much as 50% water loss when taxing water. These are very large water losses for the amount of water that's available in the sub-basins concerned.
In addition, the arrival of snowfall is shifting. Snow is less likely to fall in December and can be delayed until January or later. Since the time of weakest stream discharge coincides with the most intense water abstraction for winter tourists - the Alps see around 70 million tourists - and greatest artificial snow production, mountain streams may lose nearly all their winter discharge and virtually dry up (see figure). Although the cumulative effects in larger basins further downstream may be less dramatic, the local effects are considerable, potentially causing conflicts with drinking water and loss of aquatic ecology.
The water loss associated with artificial snow production across the whole of the Alps is equivalent to the annual water consumption of a city of 500,000 inhabitants or a whole day of discharge from a large Alpine river. Although natural snow also evaporates and sublimates, artificial snow originates partially from groundwater and from water concentrated artificially at the surface so that these artificial-snow-related losses are irreversible.
By their very nature, the uppermost parts of mountain catchments do not store or produce water in large quantities, especially in the winter. The hydrology here is very complex, with large, virtually arid scree fields, whose flow is sub-surface and thus protected from evaporation, occurring right next to small stagnating zones such as swamps and streams. Groundwater is limited since aquifers are fractured and dispersed into many small niches, and so capable of storing much less water than the large porous aquifers commonly associated with the plains.
In these small sub-basins naturally scarce water supplies can no longer keep pace with the growing demand for water to increase the temporal and spatial extent of artificial snow surfaces. Water is extracted on a more and more permanent basis from a combination of sources - streams, small snow water storage reservoirs, hydroelectric dam reservoirs, groundwater, springs, drinking water networks - and has to be transported over increasingly long distances to meet the needs of artificial snow production. This transport includes not only interbasin transfers but also pumping water from lower basins, where it's more plentiful, to upper basins.
The effects on drinking water supplies are most serious in the months of January and February, particularly when resources are sapped directly for snow production or where pressure is particularly high due to intense tourism. The first conflicts between drinking water and the production of artificial snow have arisen in mountain communes built on specific hydro-geological systems such as karst.
All these artificial snow-related manoeuvres are dangerous in the long run since they sap water sources that serve as stores for the winter or spring prior to snowmelt and redirect flow pathways to the surface that would otherwise form interflow at the subsurface. Turning the water cycle inside out in this way creates discontinuities in flow and disconnects classical temporal and spatial links between the surface and groundwater.
Since water can be permanently transferred to practically any destination with the support of power and pipeline infrastructure and this development is not sufficiently monitored and controlled, future trends will all take a common course of augmenting water and power consumption. The increasing amounts of artificial snow that ski and tourism operators are forced to produce under warmer atmospheric conditions will be increasingly difficult to make and will increasingly melt away. This vicious cycle will force snow producers to consume larger and larger amounts of water and more and more energy at increasingly higher production costs.
The larger the amount of water transferred to the surface, the more likely it is to evaporate under the warmer and drier atmospheric conditions of the future. Water loss by evaporation from artificial snow is the cumulative result of 1) moving water from groundwater reservoirs to the surface, 2) building high altitude reservoirs to store water for snow production and keeping these ice-free during the winter, 3) crystallizing ice during snow production and 4) stagnating water on the snow cover at lower altitudes.
High altitude reservoirs have impermeable plastic linings and artificially large exposed water surfaces, so they are more likely to heat up and evaporate water than streams or swamps protected by vegetation and rocks and linked to the groundwater. It's estimated that several centimetres of water are lost by evaporation from such reservoirs during the season.
During snow production, frozen water is commonly expelled through hoses at a height of up to 10 m into the air (see photo). Evaporative cooling allows the heavier ice crystals to condense and fall as artificial snow to the ground. Thus evaporation forms part of the process and water loss is inevitable at heights where wind velocities are three times higher than at ground level. This process is not comparable to natural snowfall; it is more like irrigation, yet nearly three times more water intensive, consuming up to 4700 cubic metres of water per hectare.
What's more, since the temperature of artificial snow is closer to freezing than natural snow, which is generally at -4°C, it can frequently melt and refreeze during the day. The resulting molten water lying on impermeable snow cover forms another ideal source for evaporation. Direct loss of snow into the atmosphere by sublimation at subzero temperatures is also likely to increase under these conditions. It must not be forgotten that it is precisely these atmospherically unfavourable conditions that prevent snow from falling or persisting as a permanent cover in the first place.
Another hydrological aspect not yet taken into account is the change in water routing caused by highly impermeable artificial snow surfaces that persist for roughly four weeks longer than the surrounding natural snow or snow-free surfaces. In those altitudes subject to rainfall, ski pistes covered by artificial snow are more likely to transfer water over the surface than bare slopes and there's a higher chance they'll cause rapid and peaky discharge by artificially linking up runoff pathways.
In addition, the laying of pipelines for water transport changes the hydrological pathways of subsurface flow. Since pipelines are inserted in a downslope direction, they will allow the preferential and faster drainage of water. Research results from Switzerland's Institut fur Schnee und Lawinenforschung (SLF) show that roughly 30% higher discharge is produced downhill from artificial snow than is created downslope from naturally snow-free surfaces. So when water is "given back" to nature at the end of the season, the discharge is more intensive - even if by then considerable quantities have been lost - and constrained to the surface.
As the climate warms, lift and ski operators will be faced with higher costs of artificial snow production. To keep up with these increasing costs, lift prices are likely to increase beyond the present levels. Should temperatures increase as predicted, snow production may soon become a pitfall for investors in the ski industry. That means that monitoring and regulation as well as control of the expansion of artificial snow surfaces is needed in addition to integrated watershed management to avoid water conflicts. Improved understanding of mountain water balance and resource management is also necessary. And managers involved in the ski and tourism industry should be warned about the profitability of artificial snow infrastructure. In future, cost-benefit analysis based on multiple scenarios will be needed to justify future investments better.
About the author
Carmen de Jong is a mountain hydrologist and professor and research director of The Mountain Institute of the University of Savoy, France.