| Citation |
Murdock, T.Q., J. Fraser, and C. Pearce, editors, 2007. Preliminary Analysis of Climate Variability and Change in the Canadian Columbia River Basin: Focus on Water Resources 2006. Pacific Climate Impacts Consortium, University of Victoria, Victoria BC, 57 pp. |
| Abstract/Description or Keywords |
Earth’s climate is maintained through radiation balance of solar heating and infrared cooling, moderated through the effects of clouds and trace gases, and the present temperatures at the surface of the Earth where we live are sustained through the action of a greenhouse effect. There is a scientific consensus that increases of trace gases including carbon dioxide have already increased the mean temperature of the Earth system of land, oceans, and ice. Moreover, this warming process is expected to accelerate, not only because of the continued accumulation of carbon dioxide, but also because of positive feedbacks from changes that have already occurred. Subsequently, the social, economic, and biological responses to these changes will be large and will include unexpected consequences. Although the Columbia River Basin (CRB) is only a small fraction of the globe, this basin is extraordinarily important as a fresh water resource for agriculture, fisheries, power-generation, First Nations, and urban users in the Pacific Northwest. The mountain snowpack and glaciers of the CRB are critical, since 30% of the annual flow is derived from these natural storage resources. Moreover, this resource is shared between Canada and the United States. The critical issues of water resources management in the Pacific Northwest have been identified in several studies over the past 10 years. Climate impacts on the CRB may be inferred, and some differentiation between the northern and southern portions of the basin can be estimated. _ A small increase in the average temperature may cause profound changes in runoff by increasing the frequency of melt events (even) without addition increases in precipitation. _ The sensitivity of snowpack and glacier water storage to increased temperatures is greater where winter temperature is near freezing (to the south and at lower elevations). _ The effect of warmer temperatures is to shift the timing of the runoff freshet to earlier in the spring, thus depleting the storage that would have been available for the later summer season. This pattern is independent of any seasonal precipitation changes. _ The changes in the water storage capacity of the CRB and timing of the runoff have serious consequences for the competing interests of water resources. These changes are expected to become greater in the coming decades, posing a serious challenge to water managers and users. The historical observations of temperature and precipitation at five stations within the Canadian watershed of the CRB were evaluated for this report. The results are, over a 90-year historical record: _ Annual temperature trend increased by 1.4°C, somewhat greater than the trend for Pacific Northwest. _ Annual precipitation increased by +26% (+32% rainfall; -6% snowfall). Furthermore, climate projections from an ensemble of Global Climate Models were evaluated for the Canadian portion of the CRB. The results are: _ increased annual temperature for the 2020s, 2050s, and 2080s of 1.3°C, 2.6°C, and 4.3°C, respectively. _ increased annual precipitation for the 2020s, 2050s, and 2080s of 2%, 3%, and 7%, respectively but drier summers. The impacts of these observed changes and projections on water resources of the CRB are a matter of considerable concern: Glaciers and Snowpack _ All glaciers within the CRB have experienced a net loss in area during the past 15 years (ending in 2000). The average loss was -16%, and some small glaciers have retreated up to -60%. This is consistent with the reduction of glaciers worldwide. _ A reduction in snowpack in the Canadian portion of the CRB of -4% and -12% for the 2020s and 2040s, respectively. Recent projections of snowpack inferred from hydrological modeling for the US sector of the CRB indicate extraordinary losses of snowpack of -21% and -35% for the 2020s and 2040s, respectively. This projection also implies continued erosion of glacier mass and area. Streamflow and Soil moisture _ Hydrological models of streamflow at selected sites (Waneta and Mica) indicate a shift to early runoff and late summer reductions in streamflow. _ For the entire CRB, reductions in peak streamflow of 20% have been projected. These declines could result in severe reductions in power generation and power deficits throughout the summer season. _ Increased summer temperatures, low summer precipitation, and low runoff in the CRB would increase drought potential. In addition to global climate change and warmer average temperatures, the CRB and the Pacific Northwest are also exposed to the variability of the Pacific Decadal Oscillation and the Pacific North American oscillation that carries El NiĖo and La NiĖa influences from the tropics. These sources of climate variability may reinforce the impacts of climate change, or may introduce additional impacts that have not yet been described. Therefore, the uncertainty of the future climate must be balanced with the available evidence that has been assembled. Several next steps are recommended for monitoring and documenting the inevitable changes that will occur in the CRB, including: _ Monitoring of the water resources of the CRB. _ Repeated applications of Global Climate Models and hydrological models to refine current understanding and revise the projections. _ Study the storage capacity of the CRB watersheds _ Document past changes in human water use/consumption and develop potential scenarios of future use _ Quantify risks of spring flooding, hydropower deficits in the summer, and threat of low water for salmon in the fall _ A collective effort to prepare communities and industry for change _ Begin a dialogue to understand the risks and adaptive capacity to hydrologic changes _ Develop flexibility; prepare for surprises _ Consult seasonal climate predictions for yearly planning, and climate change projections for long-range planning |
