Water – Forever on the move

What is water?

Water means different things to different people. It has unique physical and chemical properties; you can freeze it, melt it, evaporate it, heat it, and combine it.

Normally, water is a liquid substance made of molecules containing one atom of oxygen and two atoms of hydrogen (H₂O). Pure water has no colour, no taste, no smell; it turns to a solid at 0°C and a vapour at 100°C at standard mean sea level pressure. Its density is 1 gram per cubic centimetre (1 g/cm³), and it is an extremely good solvent.

All life depends on water. It makes up over one half of the human body. A person can live without food for more than a month, but can live for only a few days without water. All living things, from the tiniest insect to the tallest tree, need water to survive.

Where did all the water in the oceans, lakes, rivers, and under the ground come from?

There are a number of theories that try to answer this question. Some scientists believe that water was here from the start; some think it came later, from comets. Many scientists believe that 4.5 billion years ago, when the earth was being formed, its primitive atmosphere contained many poisonous substances. Among the chemicals present at the time were the basic constituents needed to form water.

Over time, the earth cooled and a mass of molten lava became the soils and bedrock we know today. This process began when water was formed in the atmosphere and fell to the ground as rain. The rain continued for many, many years. While the earth cooled from the falling rain, forces from within created vast land masses and oceans. Many scientists believe that life itself began in these oceans and, over the years, evolved and adapted to dry land.

What is the hydrologic cycle?

From the beginning of time when water first appeared, it has been constant in quantity and continuously in motion. Little has been added or lost over the years. The same water molecules have been transferred time and time again from the oceans and the land surface into the atmosphere by evaporation, dropped on the land as precipitation, and transferred back to the sea by rivers and groundwater. This endless circulation is known as the "hydrologic cycle". At any instant, about 5 litres out of every 100 000 litres is in motion. 

Over time, major cyclic changes in climatic processes have produced deserts and ice cover across entire continents. Today, regional short-term fluctuations in the order of days, months, or a few years in the hydrologic cycle result in droughts and floods.

Is water related to climate?

Water and climate are intimately related. It is obvious, from a water resource perspective, how the climate of a region to a large extent determines the water supply in that region based on the precipitation available and on the evaporation loss. Perhaps less obvious is the role of water in climate. Large water bodies, such as the oceans and the Great Lakes, have a moderating effect on the local climate because they act as a large source and sink for heat. Regions near these water bodies generally have milder winters and cooler summers than would be the case if the nearby water body did not exist.

Water has a basic role in the climate system through the hydrologic cycle. The evaporation of water into the atmosphere requires an enormous amount of energy, which ultimately comes from the sun. The sun's heat is trapped in the earth's atmosphere by greenhouse gases, the most plentiful of which by far is water vapour. When water vapour in the atmosphere condenses to precipitation, this energy is released into the atmosphere. Fresh water can mediate climate change to some degree because it is stored on the landscape as lakes, snow covers, glaciers, wetlands, and rivers, and is a store of latent energy. Thus water acts as an energy transfer and storage medium for the climate system.

The water cycle is also a key process upon which other cycles operate. For example one needs to properly understand the water cycle in order to address many of the chemical cycles in the atmosphere.

Most scientists are predicting extensive climate change. How would this affect water resources?

We have all experienced the natural variability in climate from time to time in the form of cool summers, warm winters, and droughts. It is now believed that changes to the atmospheric composition may result in unprecedented changes in the global climate within the next 100 years. The increasing concentrations of "greenhouse" gases, such as carbon dioxide (from the burning of coal, oil, and gas for industry and energy production, and from large-scale deforestation) and methane (from rice paddies, wetlands, and livestock), trap heat near the earth's surface. As a result, the global mean temperature is expected to increase, with resulting changes in climate being more pronounced in the northern latitudes, which include much of Canada.

Because of the intimate relationship between climate and the hydrologic cycle, changes in the climatic regimes would directly affect the average annual water flow, its annual variability, and its seasonal distribution. For example, greater climatic variability would mean changing the frequency of extreme weather events and increasing the incidences of dry and wet year sequences. Water supplies would become more uncertain as a result of this combined with increased summer evapotranspiration, reduced snowpacks, and unknown water use responses to climate change. Current design criteria for hydrologically related infrastructures such as dams, culverts, urban sewage capacities, wharves, channels, docks, and dykes, as well as for zoning, flow allocation, dam management, and flood damage reduction efforts, may prove to be inadequate under future climatic conditions.

The effects of climate change on the quality of water would modify the stress on aquatic life and cause new cleanup problems. For example, unusually low water levels – which can impair navigation, stimulate the growth of noxious nearshore weeds, and increase the probability of summer fish kills due to anoxia (lack of oxygen) – would require increased dredging activities, thus harming bottom-dwelling organisms and contaminating surrounding waters. Further, low flows will decrease the dilution of effluents resulting in increased contamination levels in receiving waters.

How would climate change affect water resources in the North?

Most scenarios of climate change based on a doubling of atmospheric carbon dioxide predict significant warming in the Far North. For example, the Canadian Climate Centre model estimates an increase of from 4°C to 10°C in winter and from 2°C to 4°C in summer, with the smaller increases in the Yukon. Higher temperatures would, by the year 2100, probably lead to longer periods of open water, extending inland and marine navigation seasons. However, later summer/fall river levels would likely decline as runoff is expected to remain relatively constant, although spread over a larger period. Higher temperatures would also cause some areas of permafrost (permanently frozen ground) to melt, resulting in erosion or "slumping" and the degradation of critical wetland and fish spawning habitats due to the increased transport and deposition of suspended sediment in rivers. The melting of permafrost would also affect the stability of docks, highways, tailings ponds, pipelines, and buildings. It would also drastically alter surface-water and groundwater hydrology as well as related wildlife habitats.

Changes in precipitation due to climate change, have not been so well defined by models, but experience from recent mild winters in some parts of the North suggests that snowfall may increase, while summer precipitation may not change. While greater winter precipitation may increase spring breakup flows, higher summer evaporation is likely to decrease mean annual flows for many northern rivers and to cause drier summers, making forests more vulnerable to fire.

It is anticipated that climate induced stresses on forests and taiga will all but eliminate the southern arctic ecozone from the mainland. This area is presently the major summer range and calving grounds for Canada's largest caribou herds as well as habitat for bear, wolf, moose, arctic ground squirrels, and lemmings. It is a major breeding and nesting ground for a variety of migratory birds including yellow-billed, arctic, and red-throated loons, tundra swans, snow geese, oldsquaws, gyrfalcons, ptarmigans, and snowy owls. It is home to Canada's Inuit and includes the Queen Maud Gulf lowlands, an internationally recognized waterfowl area. Reduced duration and extent of nearshore sea ice threatens the survival of Canada's polar bears, particularly in Hudson Bay, where bears are having difficulty surviving longer periods of summer open water without access to their prime source of food (seals on sea ice). Studies of possible impacts of increasing ocean temperatures for a scenario of doubling the atmospheric carbon dioxide indicate that all salmon species may be eliminated from the north Pacific due to their inability to withstand warmer sea temperatures.

Water also occurs as forms of precipitation such as freezing rain and wet snow. These generally occur within specific storms but they can have long-lasting impacts. This includes the devastation of trees and structures. It can also include, for example, the covering of the surface by ice so that wintering animals, like deer or caribou, are unable to reach their food supply. Whether these forms of precipitation may or may not change in occurrence, severity, or location are also quite important from a climate point of view.

Both the continued relevance of traditional knowledge and the persistence of Aboriginal cultures are also at risk. Aboriginal peoples' culture is much more sensitive to environmental degradation because many live, at least in part, in closer connection to the land than non-Aboriginal people. Where environmental damage or change restricts access to traditional foods, traditional hunting, fishing, or gathering areas, or to traditional spiritual places, the impact can be loss of Aboriginal culture.

The potential impacts of climate change scenarios on the Mackenzie River basin were assessed and reported in the Mackenzie Basin Impact Study. The Mackenzie basin is one of five basins worldwide that is being assessed under the Global Energy and Water Cycle Experiment (GEWEX). Visit the following Web site for information on the Mackenzie Basin GEWEX Study (MAGS). 

Why is snow important in water resources?

Snow is precipitation in the form of ice crystals. When it falls to the ground and accumulates, it may be considered as water in storage. In Canada, about 36% of the total annual precipitation is in the form of snow. When the winter snowpack melts in the spring, it becomes a significant portion of the water available for streamflow. Because snow accumulates during periods when the evaporation loss is low, the relative contribution of its meltwaters to streamflow in some regions may be greater than the flow contributed by rainfall. Snow supplies at least one third of the water used for irrigation in the world and is an important contributor to hydropower reservoirs. The fact that snow acts as water storage over the winter and provides soil moisture recharge in the spring is of particular importance to agricultural productivity in some regions.

How do climate, snow, and ice affect the water resources in the North?

The cold northern climate slows down many processes in the hydrologic cycle. For example, in the Northwest Territories and Nunavut, where water bodies remain ice-covered for six to ten months of the year, there is little evaporation or precipitation occurring in winter due to the low moisture capacity of air at low temperatures. Runoff from winter snowfall is concentrated in the brief period of spring snowmelt, breakup, and flooding. Most of the highest streamflows in the Northwest Territories and Nunavut occur during spring runoff, except in the Mackenzie Mountains part of western Northwest Territories, where significant summer rainfall floods occur. Melting snow can also contribute to runoff for substantial parts of the summer – for example it takes about two months for snowmelt to make its way through the Mackenzie River system.

The Yukon has an appreciably different climate. There the ice cover lasts from five to eight months, most of the precipitation is in winter, and evaporation is high. The runoff in the Yukon comes from both snowmelt and glacial melt. Glacial melt causes the characteristic August high water levels in the western Yukon rivers that drain off high mountains. This high water period is critical to the local ecosystems.

What is a drought?

A drought is a sustained and regionally extensive occurrence of appreciably below-average natural water availability in the form of precipitation, streamflow, or groundwater. Droughts are natural events of varying duration that have occurred throughout history and they are part of the cyclical fluctuations of our planet's climate system.

Where do droughts occur?

Droughts can occur anywhere. However, regions with a semi-arid or arid climate, and only marginal annual precipitation to meet their water demands, are more vulnerable to droughts. In Canada, southern Saskatchewan and the interior valleys of British Columbia experience frequent droughts.

What causes floods?

Flooding is almost always a natural occurrence; an exception would be flooding due to the collapse of a dam. There are many conditions and variables that determine whether a lake or river overtops its banks or an ocean rises along its shores. The most common causes of flooding in Canada are water backing up behind ice jams and the rapid melting of heavy winter snow cover, particularly when accompanied by rainfall. Heavy rainfall by itself can also cause floods. On large lakes, severe storms can result in strong surges when sustained high winds from one direction push the water level up at one end of the lake. Flooding is worse if high tides occur at the same time.

Certain conditions affect only specific regions in Canada. For example, under-sea disturbances such as volcanic eruptions or earthquakes may result in catastrophic waves called "tsunamis" in the ocean coastal regions. In the glaciated areas of Canada, lakes dammed by glaciers (extensive bodies of land ice) may drain suddenly, resulting in glacier-outburst floods. These floods are called "jökulhlaups" and can be devastating to the local ecosystem as they can cause flood levels of up to 100 times greater than those of normal rain or snowmelt floods.

Is it true that you should not build close to a river because you might get flooded?

Generally, yes. It depends, however, on the characteristics of the river and the floodplain. In Canada, the floodplain is usually divided into two zones: the floodway and the flood fringe. Damage and risk to life are greatest in the floodway, where the water depths and velocities are the greatest. It is within these areas that you should not build, since you could expect to suffer considerable damage, not just once in a lifetime but time and time again. 
Within the flood fringe you may be able to build, providing that you undertake some protection measures such as adequate flood-proofing. 

How do you find out whether or not you are on a floodplain?

If you are considering buying property, be sure to consult with your municipal or regional office, provincial authorities, or Environment Canada offices in your region to determine whether flood risk maps have been produced for your area.

If maps are unavailable, talk to neighbours or local historians or check at local libraries or archives for records of past flooding.

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