Water Stewardship Information Sources
| ID | 1316 |
|---|---|
| Citation | Nelitz, M, Wieckowski, K, Porter, M, Bryan, K, Poulsen, F and D Carr. 2009. Evaluating the vulnerability of freshwater fish habitats to climate change in the Cariboo-Chilcotin: Part I - Summary of technical methods. Prepared for Fraser Salmon and Watersheds Program. |
| Organization | Fraser Basin Council |
| URL | http://www.thinksalmon.com/reports/PartI-MethodsReport_090314.pdf |
| Abstract/Description or Keywords | Over the next century in British Columbia climate induced changes in precipitation and air temperature are expected to be variable by region and season (Rodenhuis et al. 2007; Pike et al. 2008a). The general trend is for increasing air temperatures across the province with the largest increases projected in the north and during the winter. In regards to changes in precipitation the general pattern is for drier conditions in the south and during the summer, with northern latitudes projected to receive more precipitation. In the Cariboo-Chilcotin by the 2050s average annual air temperatures and average annual precipitation are both predicted to increase from 2.0-2.5 ﾰC and 5-20% respectively, although in some locations summer precipitation is expected to decrease by as much as 5% (Dawson et al. 2008). Based on historic observations (Leith and Whitfield 1998; Whitfiled and Cannon 2000; Zhang et al. 2001) and future projections (Leung and Qian 2003; Whitfield et al. 2003; Merritt et al. 2006) these kinds of changes in climate are expected to lead to noticeable changes in watershed hydrology as mediated by changes in snow pack accumulation, patterns of snowmelt, and glacier cover among other factors. The magnitude and direction of streamflow changes in a watershed will vary according to the dominant pattern of runoff. Watersheds in the Cariboo-Chilcotin are generally snowmelt-dominated which tend to have peak flows in the spring, low flows in the late summer and fall - due to low precipitation and dwindling snowpack - and low flows through the winter due to cold conditions that lead to precipitation accumulating as snowpack (Eaton and Moore 2007). In the future, these types of watersheds are anticipated to see shifts in runoff patterns that more closely mimic mixed hydrologic regimes (rainfall-snowmelt patterns) where periods of snow accumulation are reduced and peak flows start earlier in the spring (Pike et al. 2008b). Less is known about expected water temperature changes across freshwater systems in B.C. though stream and lake temperatures are generally expected to rise as a result of increasing air temperatures and changes in surface water and groundwater flows (Tyedmers and Ward 2001; Pike et al. 2008b). The Fraser River is the most well studied basin for water temperatures where historic analyses have shown increases in maximum water temperatures of approximately 1.8 ﾰC over the last 50 years at Hell's Gate (Foreman et al. 2001; Morrison et al. 2002; Farrell et al. 2008) and climate change models estimate up to an additional 2 ﾰC of warming by 2080 (Morrison et al. 2002). Given the known relationship between air and water temperatures in smaller streams (Stefan and Preud'homme 1993; Scholz 2001; Moore 2006; Nelitz et al. 2007b; 2008) increasing thermal regimes can also be expected in tributary and headwater systems. The biological implications of climate-induced changes in physical environments are significant as alterations in the timing / magnitude of streamflow and stream thermal regimes are fundamentally linked to behavioural and physiological responses of life stages of freshwater dependent fish species, such as Pacific salmon (Nelitz et al. 2007a) and bull trout (Dunham et al. 2003). In snowmelt-dominated systems overall mean annual flow is expected to increase though an earlier spring freshet may extend the period of summer low flows, thus constraining availability of summer rearing habitats. Streams in headwater areas will likely be affected most negatively by this change. Historically, these areas provided some of the most suitable habitat conditions which may become inaccessible if flows are reduced or unusable as cool-water refugia if warming occurs. Additionally, low flow conditions may coincide and exacerbate stream warming during periods of peak summer air temperature which can create thermal barriers to adult and juvenile migration, increase physiological stress and mortality of adults and juveniles, and alter the thermal suitability of rearing conditions (Irvine 2004; Nelitz et al. 2007a; Bisson 2008). Ultimately, the effects of temperature on individuals can lead to shifts in species distributions (Dunham et al. 2001) and fish community structure (Wehrly et al 2003; Nelitz et al. 2008). Alternatively, restoration actions can mitigate the effects of climate change by restoring freshwater supplies to mitigate against low summer flows during adult migration and spawning or by adjusting harvest rates to account for poor ocean productivity or in-river conditions. Given our general understanding of the adverse effects of climate change and contributing role of human actions in both positive and negative ways, it is critical that we develop strategies to help freshwater fish species cope (see range of strategies in Nelitz et al. 2007a). Developing intelligent coping strategies, however, requires that we make decisions using detailed information so we know what to do, where and when so as to avoid wasting precious time, money, and people's energy. Evaluating the vulnerability of freshwater habitats to climate change is a critical first step to providing decision makers with that detailed information (Spittlehouse and Stewart 2003) and is consistent with previously identified priorities for improving management of B.C.'s freshwater habitats in the context of climate change (Tyedmers and Ward 2001). This technical report describes the methods used to assess the vulnerability of freshwater habitats - changes in summer stream flows and water temperature - across the Cariboo-Chilcotin. It is the first study of its kind for this region and represents a pilot application of an approach for assessing vulnerability. The hope is that these methods could eventually be applied more broadly to assess other vulnerable regions in B.C. Results from this evaluation are presented in the second part of this report (Nelitz et al. 2009) and three species-specific habitat outlook papers (Porter and Nelitz 2009a; Porter and Nelitz 2009b; Nelitz and Porter 2009). The intention is that these results can eventually help regional decision makers understand potential vulnerabilities of freshwater habitats. Additional efforts are needed to help regional decision makers use this information and decide what actions to pursue today that will benefit human communities, freshwater habitats, and fish populations of the Cariboo-Chilcotin in the future. |
| Information Type | report |
| Regional Watershed | Fraser |
| Sub-watershed if known | Bridge, Seton, Stein |
| Aquifer # | |
| Comments | |
| Project status | complete |
| Contact Name | Marc Nelitz |
| Contact Email | [email protected] |