The Saskatchewan River Sub-Basin (SSRSB) is subject to both floods and droughts. Floods and droughts are primarily natural events, although they can be modified, both positively and negatively, by human activity. These phenomena affect natural ecosystems and human settlement. Although the effects of smaller floods and droughts can be mitigated, there is always the risk of a flood event exceeding the design capacity of the infrastructure, or of a drought exceeding the coping range of aquatic ecosystems, individual water users or infrastructure.
Many urban communities in the basin are in river valleys. During spring runoff and intense summer rainstorms, these communities can be flooded. Although loss of life is rare in Canadian floods, financial and other losses associated with flooding are significant. Entire communities may be disrupted for lengthy periods following a flood.
The traditional approach to reducing flood damages was through construction of structural measures such as dams, dikes, and diversions. These measures are costly to build and maintain, and may lead to a false sense of security for floodplain residents. They may also have significant environmental consequences.
Current approaches tend to be non-structural: that is, the flood hazard in a community is determined, high risk property is identified, and zoning implemented to reduce the threat of flood damages. This often leads to floodplains being used for parks and other low- impact uses, rather than for homes and industries. Flood-risk areas have been determined for urban communities in the basin, and maps showing that risk are available from provincial authorities.
Rural areas of the basin are subject to flooding hazards, leading to losses in agricultural productivity and other economic losses. Damages can sometimes be reduced through operation of water infrastructure, but often adjustments to help upstream lands lead to flooding of downstream lands and vice versa.
Provincial governments produce flood forecasts and warnings so that emergency response personnel and the public can take appropriate action during a flood. Maintaining meteorological and hydrometric monitoring networks to support flood forecasting can be a problem.
Unlike other natural hazards that can affect the basin, drought is a slow-onset phenomenon. In fact, definitions of drought vary considerably and the precise beginning and end of a drought period may be difficult to determine. All droughts begin with a deficiency in precipitation extending over a significant length of time, known as a climatological drought. If this deficiency leads to lack of availability of soil water to support agricultural activities, an agricultural drought exists. With continuing precipitation deficits, streamflows, lakes, reservoirs, and aquifers may become depleted, leading to hydrological drought.
Finally, effects of meteorological, agricultural and hydrological droughts on human activity may affect human activity so significantly that we can speak of a socioeconomic drought. The economic impact of the 2001-2002 nation-wide drought in Canada, if taken as one event, would constitute the largest natural disaster in Canadian history.
Defining a drought requires consideration of three elements: intensity, duration and spatial coverage. In North America, the Palmer Drought Severity Index (PDSI) is frequently used to indicate the extent and severity of drought, and reconstructed PDSIs have been produced for many severe events over many decades. PDSI maps do not take into account water storage and supply factors and are, therefore, a better indication of climatological rather than hydrological drought.
Efforts have been made to produce indices of surface water availability based on precipitation, streamflow, reservoir storage, and so on. While useful, different drought indices will provide different results. In terms of informing the public and water users, a consistent approach is probably more important than a ‘right’ approach. Products from the Prairie Farm Rehabilitation Administration’s Drought Watch are good examples of this consistent approach.
The 20th century was climatologically benign compared to other recent centuries. While significant droughts have taken place, for example in the 1930s, they may not have been as severe as those of previous centuries. Examination of proxy climate data using tree ring reconstruction indicates, for example, that droughts of varying intensity may have persisted in the Cypress Hills (Alberta and Saskatchewan) for almost the entire 1688-1692, 1792-1804, and 1887-1896 periods.
Nonetheless, the 20th century featured three major prairie drought events. The first was during the period 1917-1926, the second during the 1930s, and the third during the 1980s. The 2001-02 drought was unusual for its broad spatial coverage and intensity. Farm income on the prairies was negative or zero for the first time in 25 years.
A return to the more extreme climates of previous centuries may raise the prospect of decadal droughts. Planning for a decadal drought in the entire North and South Saskatchewan River basin is very conservative. Consider, for example that in 1981, a very dry year in southern Saskatchewan, there was a significant flood threat on the North Saskatchewan River and flows in the Saskatchewan basin as a whole were well above normal.
Drought preparedness can be a difficult task because of the slow-onset nature of the problem and the lack of agreement on drought definitions and preparedness methodologies. Current approaches use risk management approaches to define the problem and to determine the public-policy response.
A drought-preparedness plan is much preferred to taking a crisis-management approach to drought response. Alberta’s Drought Risk Management Plan is an example of drought-preparedness planning.