Effects of Climate Change on Water Resources in the Columbia River Basin

Introduction

A 9th order river, the Columbia is the fifth largest river in North America in terms of its discharge and basal area. Located in the Pacific Northwest, with the river's basin encompassing parts of the province of British Columbia, the states of Washington, Oregon, Nevada, Utah, Idaho, Wyoming and Montana, it drains an average of 7,730 m3/s within an area of 724,025 km2 (Stanford and Hauer, 2005). The Columbia River receives the majority of its massive discharge from 12 of 39 primary tributaries; Flathead River, Methow River, Spokane River, Yakima River, Snake River, Clearwater River, Salmon River, Owyhee River, Grande Ronde River, John Day River, Cowlitz River, and Willamette River [see figure 1].

The Columbia is a very important water resource for human consumption and activity in British Columbia and above states mentioned; activities include dams for flood control and hydroelectric power, irrigation, navigation, and water consumption by cities and other municipalities. With the increasing threat of global climate change, the delicate balance of the hydrologic cycle will be disrupted (Leith and Whitfield, 1998; Barnett et.al, 2004; Hamlet and Lettenmaier, 1999). This paper discusses the present and future climatic variability within the Columbia basin; how this impacts the hydrologic cycle of the river system and; what effects the modified hydrologic cycle has on the water resources of this economically important waterway.

Climate

The Columbia River watershed is in several climatic zones which greatly influence the amount of water each tributary contributes to the main stem of the Columbia. These areas range from cool mountain regions of the Rocky Mountains and upper regions of the Cascade Range to the hot semi-arid region of eastern Washington, eastern Oregon, southern Idaho, and northern Nevada (National Oceanic and Atmospheric Administration, 2006). The river have has very defined low and high flow periods because it is strongly dominated by winter snow accumulation and spring melt; low period in the autumn and winter months and a high peak period from snow melt in the spring and early summer (Hamlet and Lettenmaier). Because the Columbia is dominated by snow melt, most of the hydrologically significant precipitation falls in the winter months between October and March in the upper and mid regions of the watershed and dominated by rainfall in the lower reaches of the watershed due to warmer climate of the Pacific coast (Hamlet and Lettenmaier).

Within the last 50 years climate change has been evident, affecting every corner of the planet, some places more than others. The Pacific Northwest region, which encompasses the Columbia watershed have been experiencing climate changes moderately for the past 50 years (Environment Canada, 2000 and National Oceanic and Atmospheric Administration). Within the next 50 years, winter temperatures are expected to increase by an average of 3 to 5 degrees C (Environment Canada). With such a large increase in temperatures it will surely affect the watershed in terms of the volume of water, timing and the duration of high and low periods (Hamlet and Lettenmaier).

With increased temperatures, snowfall that falls right now will start falling as rain, giving a shorter winter. No only will there be less snowfall to melt, but the snowfall that has fallen with melt much faster, and increased temperatures will also allow for increased evaporation.

The Hydrologic Process

As mentioned above, the Columbia River system is strongly dominated by winter snow accumulation and spring melt, thus giving periods of high and low periods of flow. With the river's headwaters beginning in the Rocky Mountains of British Columbia, a large percentage of flow come from glaciers and high snowfall in the snow-dominated ranges of southeast British Columbia; snow-dominated meaning the river obtaining most of its discharge from melt water of snow or ice (Geological Survey of Canada, 2001). In this region discharge peaks in the late spring early summer and decreases to its lowest levels in the autumn and spring [see figure 2]. Any precipitation in the summer is usually either infiltrates the soil or is returned to the atmosphere through either direct evaporation from the soil, forest canopies, or the litter layer of the forest, and transpiration from plants (Hamlet and Lettenmaier).

The Columbia progresses southward through the much warmer and drier interior plateaus of eastern Washington and other states around its boundaries, where the volume of the river still increases by spring melts. As the Columbia River moves towards the Pacific Ocean, the river's discharge is increased more by rainfall or snow-rain mix from the Cascade Range where air temperatures are warm enough for precipitation to fall as rain. These rain-dominated mountains are the source of the river's winter discharge which occurs from early autumn to early spring on the last 300 kilometers of the river (Hamlet and Lettenmaier). The Columbia River is mostly dependent on winter storms to accumulate snow in the northern mountains for melt in the spring, and rainfall on the coastal mountains (Geological Survey of Canada).

Types of Water Resources

Within the Columbia River basin, like all waterways, several activities take place that require the water resource that the Columbia provides; hydropower, agriculture, and recreation.

The Columbia is the most dammed river in North America, hydroelectric dams were built by both Canada, the United States, and jointly. These dams are very sensible to the rate of streamflow that the Columbia obtains which is found using the Energy Content Curve (ECC) which is calculated for major storage dams based on forecasts of spring runoff, allocates the releases of water for hydroelectric production (Hamlet and Lettenmaier). Agriculture is relatively small in comparison to the large international hydroelectric projects; nevertheless it is still a large part of the economy on both sides of the border. The withdraw of water from the main stem of the Columbia is relatively small compared to some of the major tributaries such as the Snake River where irrigation withdrawals are much larger relative to the annual flow (Hamlet and Lettenmaier; Leung and Wigmosta, 1999). Due the construction of dams along the Columbia River, large reservoirs were created. These "man made lakes" have been used for decades for recreational purposes have allowed for a variety of activities from swimming to fishing. It is important to note that on top of hydroelectric dams that were built along the Columbia River, several

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