Okanagan Basin

The Okanagan basin is located in the southern interior of British Columbia, Canada, situated around Okanagan Lake (Figure 1). The surface area of the basin is 8200 km2 (Cohen and Kulkarni, 2001). The Okanagan has a dry continental climate, because the valley sits in the rain shadow of the Coast and Cascade Mountain ranges. The semiarid climate receives approximately 30 cm of precipitation each year, of which 85% is lost through evapotranspiration from local lakes. The

Cascade Hydrology
Figure 1 Okanagan and Columbia River basins.

hydrology of the basin is largely snow dominated, with much of the water that enters the lakes and Okanagan River originating from high-elevation regions (Cohen and Neale, 2003). The quality of water from these is generally good, but outbreaks of both Giardia and Cryptosporidium have occurred in valley communities (Cohen and Kulkarni, 2001).

The Okanagan region has become the most prominent location for 90% of soft fruit orchards and 95% of vineyards in British Columbia. The arid Okanagan summers are beneficial for fruit development but provide insufficient moisture, so irrigation is steadily used to support the growing crops. The region's extensive natural resources also contribute to its thriving tourism industry (Cohen and Kulkarni, 2001).

The Okanagan River flows south from British Columbia into Washington State, where it eventually meets the main stem of the Columbia River. The Columbia has been the subject of detailed case studies on the implications of climate change for water resources and water management (Hamlet and Lettenmaier, 1999; Miles et al., 2000; Mote et al., 1999).

The Okanagan basin presents an interesting forum for exploring water allocation and licensing given its semiarid climate; its growing population, which has nearly doubled since the 1970s (Embley et al., 2001); and the importance of irrigation to the regional economy. The drought of 2003 exposed some vulnerability in the Okanagan basin, as illustrated by the emergence of local water conflicts (Moorhouse, 2003) and the implementation of emergency conservation measures (Watershed News, 2003a, 2003b).

There are more than 4000 active water licenses in the Okanagan basin, representing approximately 1 billion m3 of allocated water on 980 streams for both consumptive and in-stream uses. Around 45% is allocated for consumptive purposes, where water is removed from the source. Approximately two-thirds are allocated for the purposes of "irrigation" and "irrigation local authority." A majority of streams within this basin are already fully allocated.

Since 1997, a number of studies have been initiated on climate change, climate impacts, and adaptation within the Okanagan region (Cohen and Kulkarni, 2001; Cohen and

Neale, 2003; Cohen et al., 2000; Cohen et al., 2004; Merritt and Alila, 2004; Neilsen et al., 2001; Shepherd, 2004. The climate change scenario for the 2050s that appears to be emerging is as follows:

• A warming, relative to the 1961-90 baseline, of 1.5-4°C in winter with precipitation increases on the order of 5-25%; for summer, a warming of roughly 2-4°C and precipitation changes ranging from almost no change to a 35% decrease

• An earlier spring freshet of around 4 weeks, with reductions of annual and freshet flow volumes; for example, annual volumes for the Ellis reservoir near Penticton decline 20-35%

• An increase in crop water demand, due to warmer growing conditions, of 20-35% for the region as a whole; estimated increases of 20-40% for Oliver, near Osoyoos (D. Nielsen, personal communication)

This combination of a longer and warmer growing season, reduced water supply, and increased crop water demand represents a new average state for Okanagan water resources for the 2050s, and this suggests an increase in the frequency and severity of dry years with conditions likely to be considered as drought. This scenario does not assume any particular adaptation strategy, nor does it assume any changes in management practices in agriculture or among other regional bodies (municipalities, water agencies, fisheries interests, etc.). It does establish a "what if" context for consideration of possible options for adaptation.

A number of demand-side and supply-side options can be considered, including additional withdrawals directly from Okanagan Lake and the Okanagan River to augment withdrawals from the tributary streams and groundwater. Costs vary widely; from CAN$500 to CAN$3400 per acre-foot, and no single option would appear to be sufficient (see Cohen and Neale, 2003).

Previous discussions with regional stakeholders (see Cohen and Kulkarni, 2001) revealed no clear preference. Increased storage in upstream areas, buying back some exist ing water licenses, metering, and public efforts to reduce demand for water (e.g., through xeriscaping residential areas) are ideas that appear to have some support. There has been some recent experience with instituting metering in the city of Kelowna and in the Southeast Kelowna Irrigation District (Shepherd, 2004). Plans are underway for a new round of dialogue exercises with regional interests to consider how an adaptation portfolio might be developed and implemented (Cohen and Neale, 2003).

It is also conceivable that changes to operating rules could become part of an adaptation strategy to address the climate change scenario being considered here. Flow near the transboundary border is controlled by the Zosel Dam, built on the U.S. side just south of Osoyoos Lake and regulated by the IJC's Osoyoos Lake Board of Control. The Penticton Lake Dam controls outflows from Okanagan Lake. And several key reservoirs (such as Ellis reservoir) provide storage in the upstream areas.

This case represents an important opportunity to explore climate change adaptation in a proactive manner and in the context of ongoing planning processes that are a normal part of regional and local governance.

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