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Whatcom County Climate Action Plan:
Summary of Observed Trends and
Projected Climate Change Impacts
JANUARY 2020
INTRODUCTION
This document provides an overview of observed and projected climate changes relevant to Whatcom County. This overview is intended to provide the County with a foundation to understand and plan for anticipated climate impacts to assets, operations, and community services. The document focuses on the main drivers of climate change impacts, including changes in temperature, precipitation, hydrology, and sea level rise, as well as selected resulting impacts of wildfire and air quality. Additional secondary impacts are considered in the separate vulnerability assessments specific to identified focus areas.
This document provides the latest available climate science information from academic literature, research organizations, and institutions. Key sources of information consulted for this summary include the following:
SCALE RESOURCE NATIONAL •^ Fifth National Climate Assessment^ Synthesis Report , Intergovernmental Panel on Climate Change, 2014.
WASHINGTON
STATE
- Projected Sea Level Rise for Washington State , prepared by Washington Sea Grant, CIG, University of Oregon, University of Washington, and U.S. Geological Survey, 2018.
- Implications of 21 st^ Century Climate Change for the Hydrology of Washington State , by Elsner et al. , 2010.
PUGET SOUND
- State of Knowledge: Climate Change in Puget Sound , prepared by University of Washington Climate Impacts Group (CIG), 2015 (referenced in this document as SOK).
WHATCOM
COUNTY
- Modeling the Effects of Forecasted Climate Change and Glacier Recession on Late Summer Streamflow in the Upper Nooksack River Basin , by Murphy, 2016.
- Modeling the Effects of Climate Change on Stream Temperature in the Nooksack River Basin , by Truitt, 2018.
- Nooksack Indian Tribe Natural Resources Climate Change Vulnerability Assessment , Morgan and Krosby, CIG, 2017.
- South Fork Nooksack River Watershed Conservation Plan, Nooksack Indian Tribe Natural Resources Department, 2017.
- Community Research Project , Whatcom County Climate Impact Advisory Committee,
This document begins with an executive summary of key findings about future conditions. Following the summary is a brief overview of the science, methods, and geographic scales of climate change projections and their application to decision-making. The document then presents the observed trends and projected changes in climate for temperature, precipitation, hydrology, sea level rise and storm surge, wildfire, and air quality. In each of these sections, key findings are shown in blue boxes, followed by more detailed and technical information.
EXECUTIVE SUMMARY
Temperature
- By the 2050s, the average year in Washington will likely be warmer than the hottest year of the 1900s, based on a business-as-usual emissions scenario (RCP 8.5), which is the highest emissions scenario typically used in climate change projections.
- By the 2050s, average annual temperatures in Puget Sound are projected to increase by 4.2 °F to 5.5 °F under low- and high-emissions scenarios, respectively, compared to the 1970-1999 average of 46.5 °F. By 2100, they are projected to be 5.5 °F to 9.1 °F warmer under low- and high-emissions scenarios, respectively.
- By 2080 under a high-emissions scenario, Bellingham’s climate is projected to feel like Seattle’s climate today, which is typically warmer and drier than Bellingham historically has experienced.
- By the 2050s, under a low-emissions scenario, projections indicate at least 1 to 2 days per year in Whatcom County and at least 2 to 3 days per year in Bellingham specifically when the heat index is above 90 °F, compared to zero days historically (1971-2000). By 2100, under a high-emissions scenario, those numbers are projected to rise to as many as 11 days per year in Whatcom County and 20 days in Bellingham.
Precipitation
- Average annual precipitation in Puget Sound is projected to increase by 4% to 5% by the 2050s under low- and high-emissions scenarios, respectively, and another 2% by the 2080s under both emissions scenarios (relative to the 1970-1999 average).
- Wetter conditions are anticipated in spring, fall, and winter, while summer will likely continue to get drier and warmer in Puget Sound. By the 2050s, summer precipitation is projected to decrease by 50% under a high-emissions scenario.
- Under a high-emissions scenario, heavy precipitation events west of the Cascades are projected to increase in intensity by 22% by the 2080s—meaning they will have 22% more rain. Meanwhile, those rain events will become more frequent, occurring five more days per year by the 2080s.
Hydrology
- Mountains draining into Puget Sound are projected to have 29% less snowpack by the 2040s.
- The Nooksack River basin is anticipated to transition from being a mixed snow and rain-dominant system to a rain-dominant system in the future. By the 2080s, peak streamflow in the Nooksack River is projected to shift approximately 27 days earlier in the year, under a moderate-emissions scenario (compared to the 1970-1999 average).
- Flooding in the Nooksack River is expected to become more intense and frequent. Under a moderate emissions scenario, streamflow in the Nooksack River during a 100-year flood event (1% probability) is projected to increase by 27% by the 2080s.
- Under a moderate emissions scenario, summer minimum streamflow in the Nooksack River is projected to decrease by 27% by the 2080s relative to the 1970-1999 average, and summertime stream temperatures are projected to increase, reaching levels that exceed the thermal tolerance of most fish species.
Sea Level Rise and Storm Surge
- By 2100, relative sea level rise in the Bellingham area is projected to be between 1.5 (likely range of 0.9-2.1 feet) and 1.9 feet (likely range of 1.3-2.7 feet) with a 50% likelihood of exceeding those values under low- and high-emissions scenarios, respectively.
- Puget Sound coastlines, including Whatcom County, are expected to experience increased storm surge and high tide flooding due to sea level rise.
Wildfire
- By the 2050s, Western Washington is projected to have 12 more days annually with very high fire danger compared to the 1971-2000 average.
- By 2100, the period of time between wildfires in the North Cascade ecoregion will shorten by a factor of 2.2 to 2.5 under low- and high-emissions scenarios, respectively [39].
- The median area burned annually from wildfire across the Northwest is projected to increase by 0. million hectares by the 2080s compared to 1980-2006 [40].
Air Quality
- In the future, Whatcom County’s air quality is likely to decline during periods of increased wildfire activity in the Pacific Northwest, especially during the summer and early fall.
- Warmer temperatures and increases in ozone pollution may reduce Whatcom County’s air quality.
Figure 1. Greenhouse gas concentrations by RCP and greenhouse gas type—carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 0) [2].
It is difficult to verify which model most accurately matches future conditions. However, it is worth noting that observed increases in GHG emissions over the past 15 to 20 years align most closely with those projected in the higher-emissions scenarios, such as RCPs 6.0 and 8.5 [5].
The IPCC’s recent report urges cities and countries to take rapid action to keep global warming below 1.5 °C in the 21 st^ century [6]. The latest IPCC global climate change synthesis report indicates that RCP 2.6 is the only pathway that is likely to keep global warming below 2 °C. To achieve this goal, substantial net negative emissions are required—meaning that carbon must be removed from the atmosphere (see Table 2) [7].
To reduce GHG emissions, it can be useful to aim for a low-emissions trajectory like RCP 2.6 when setting emissions reduction targets and planning mitigation strategies. However, when preparing for climate change impacts and planning resilience strategies, it is important to prepare for more severe conditions projected in high-emissions scenarios that are unlikely to limit warming to 2 °C. Given this, in this report we use RCPs 4.5 and 8.5 to provide a low and high projection of future emissions, which is aligned with common practices in national and regional climate projection reports.
Table 2. Key characteristics of the scenarios assessed in the IPCC Synthesis Report (2014). Adapted from Table 3. in report.
Corresponding RCPs
Likelihood of staying below a specific temperature level over the 21st^ century (relative to 1850-1900) 1.5 °C 2 °C 3 °C 4 °C RCP 2.6 <50%
RCP 4. <50%
50% RCP 6.0 <50% RCP 8.5 <50%
Geographic Scale
Global climate models used to generate projections of future climate impacts simulate changes at broad geographic scales or resolutions, with about 50 to 100 miles between one “pixel” or grid cell to the next. At this scale, the projections are not representative of local-scale patterns in weather and climate. “Downscaling” refers to taking the coarse resolution projections from global climate models and applying them to a smaller geographic scale, achieving a level of detail that is more relevant to local management and decision-making. The increased resolution from downscaling is usually about 5 to 10 miles from one grid cell to the next; this is a 10-fold increase compared to global climate models. However, climate modeling results generally become less accurate at a smaller geographic scale, especially at the sub-regional level. Downscaling is also costly. As a result, it is uncommon to have climate projections at the city or county level.
In this report, we most often use downscaled projections for the Puget Sound region (see Figure 2) created by the University of Washington’s Climate Impacts Group (CIG). We also use some projections for Washington State or the Pacific Northwest more broadly to provide context and confirm the accuracy of downscaled projections. We use downscaled projections at the sub-regional level (Whatcom County, Bellingham, and Nooksack River) for changes in high-heat days, changes in streamflow, and sea level rise. Sub-regional downscaled projections were not available for other changes. In each section, the descriptions progress from larger to smaller geographic scales, beginning with the Pacific Northwest and the Puget Sound region and then scaling down to Whatcom County and Bellingham, where data are available.
Climate Variability and Climate Change
The climate in the Puget Sound region is complex and diverse with natural variability. Climate variability refers to the changes in climate that range over many time and space scales. Climate variability in Puget Sound is partially due to the year-to-year and decade-to-decade Pacific Ocean trends. These include the El Niño- Southern Oscillation (ENSO), also known as El Niño/La Niña, and the Pacific Decadal Oscillation (PDO) [8].
Figure 2. Puget Sound region used for many downscaled projections in this report [9].
<33%
65%
region’s frost-free season, also known as the growing season, increased by 30 days between 1920 and 2014 [12].
Table 3. Observed annual and seasonal trends in temperature for Puget Sound and Bellingham. All trends are significant. Note that data in this table was drawn from two separate sources that did not provide the exact same type of information for the two different spatial scales, as indicated by “N/A” [10] [12] [11].
Time Period/Season Temperature Change Puget Sound, 1895-
Temperature Change Bellingham, 1895- Annual +1.3 °F (+ 0 .7 to +1.9 °F) +2.8 °F Fall (Sept/Oct/Nov) + 0 .12 °F/decade (+.07 to +.17 °F) + 0 .21 °F/decade Winter (Dec/Jan/Feb) + 0 .13 °F/decade (+.02 to +.24 °F) + 0 .18 °F/decade Spring (Mar/Apr/May) No significant change + 0 .2 2 °F/decade Summer (June/July/Aug) + 0 .13 °F/decade (+.07 to +.19 °F) + 0. 31 °F/decade Frost-Free Season +30 days (+18 to +41 days) N/A
Figure 4. Annual average temperature for Bellingham, 1895-2018 [11].
Projected future changes
- By the mid-21 st^ century, the average year in Washington will be warmer than the hottest year of the 20 th^ century under a high-emissions scenario [13].
- By the mid-21 st^ century, average annual temperatures in Puget Sound are projected to increase by 4.2 °F to 5.5 °F under low- and high-emissions scenarios, respectively, compared to the average annual temperature between 1970-1999 of 46.5 °F (see Figure 5). By 2100, they are projected to be 5.5 °F to 9.1 °F warmer under low- and high-emissions scenarios, respectively [13].
- By the mid-century, projections indicate 1 to 2 days per year in Whatcom County and 2 to 3 days per year in Bellingham when the heat index is above 90 ° F. By 2100, those numbers are projected to rise to as many as 11 days per year in Whatcom County and 20 days in Bellingham [14].
Warming is projected to continue in Puget Sound for all emissions scenarios and all seasons, with summer seeing the largest temperature increases [15]. Until mid-century, the anticipated average temperature increases are relatively similar across all scenarios since most warming in these years is the result of greenhouse gas emissions already produced and changes that are already underway. After that time, additional warming will depend on the amount of emissions generated in the upcoming decades [9].
Figure 5. Projected changes in average annual and seasonal temperature for the Puget Sound region. All projected changes for the two time periods shown below (2040-2069 and 2070-2099) are relative to 46.5 °F, the average annual temperature for 1970-1999. Average seasonal temperature refers to the change in average temperature for a given season: summer (June through August) or winter (December through February). Both time periods include the low-emissions scenario (blue bar), and the high-emissions scenario (green bar). The hollow markers indicate the range of projected change. This figure was developed with data from CIG 2015 [9].
As temperatures rise, Whatcom County’s climate is projected to shift. By 2080, under a high-emissions scenario, the climate in Bellingham is projected to feel like the climate in Seattle [16]. For reference, the average summer in Seattle is 3 °F warmer and 30% drier than in Bellingham [16].
The frequency and strength of extreme heat events are projected to increase, especially nighttime heat events, while extreme cold events are projected to decrease relative to the 1970-1999 average. Compared to that period, the hottest days in the year for the Puget Sound region are expected to be 6.5 °F warmer and the coolest nights are projected to be 5.4 °F warmer by the 2050s (see Table 4) [9].
The heat index is a measure of how hot the air feels when humidity is considered in addition to the actual air temperature. A heat index greater than 90 °F indicates that outdoor workers and others who experience prolonged exposure or strenuous outdoor activity are more susceptible to heat-related illnesses and should take extreme caution. A heat index in the around 102 °F or higher indicates dangerous conditions posing greater risk of heat-related illnesses. Whatcom County is projected to average two days per year with a heat index above 90 °F or higher by mid-century, and up to 11 days of 90 °F or higher by the end of the century if carbon emissions continue at their current rates (see Figure 6) [14]. Whatcom County is still projected to be one of the relatively cooler areas in the continental United States, with comparably fewer days when the heat
Table 4. Projected changes in Puget Sound region temperature extremes. All changes are relative to the average for 1970-1999. Temperature of hottest days represents the projected change in the 99th^ percentile of daily maximum temperature. Temperature of coolest nights represents the projected change in the 1st^ percentile of daily minimum temperature. (Table adapted from CIG 2015 SOK) [15].
Indicator 2040-2069 2070- Average RCP 4.5 RCP 8.5 Average RCP 4.5 RCP 8. Temperature of hottest days +6.5 °F^ +4.0 °F^ +10.2 °F^ +9.8 °F^ +5.3 °F^ +15.3 °F Temperature of coolest nights
+5.4 °F +1.3 °F +10.4 °F +8.3 °F +3.7 °F +14.6 °F
Heating degree days (dd) −1600 dd −2300 dd −1000 dd −2306 dd −3493 dd −1387 dd Cooling degree days +17 dd +5 dd +56 dd +52 dd +6 dd +200 dd Growing degree days +800 dd +500 dd +1300 dd +1280 dd +591 dd +2295 dd
Figure 6. Projected days per year when the heat index will exceed specific temperature thresholds in Whatcom County and Bellingham compared to a simulated historical annual average between 1971-2000. [14].
Precipitation
Observed changes to date
- Spring precipitation increased by 27% in the Puget Sound lowlands since the late 19 th^ century. All other seasons show no significant trends in precipitation [11].
- In the Bellingham area, average annual precipitation increased 19% since the late 19 th^ century. During that time, spring and fall precipitation both increased 3% and 3.5% per decade, respectively (see Figure 7 and Figure 9) [11].
- Modest increases in extreme precipitation events have been observed in Western Washington during the 20 th^ century [9].
- Since 1900, there have been 19 drought occurrences in Washington State [17].
The Puget Sound region has naturally variable precipitation patterns, causing fluctuations between wet and dry years, as well as between wet and dry decades [10]. In Bellingham, average annual precipitation increased by 19% between 1858 and 2018, or about 2% per decade (see Figure 7 [11].^1
Trends in seasonal precipitation (changes in total precipitation across the three months of each season from year to year) are typically insignificant; the exception is spring and fall precipitation in Bellingham. In Bellingham, spring (March through May) precipitation increased by nearly 29% between 1858 and 2018, or approximately 3% per decade [11]. During that timeframe, Bellingham also experienced a statistically significant increase in fall (September through November) precipitation by about 35%, or 3.5% per decade (see Figure 9) [11]. Historical records indicate that heavy rainfall events in Western Washington have increased modestly in both frequency and intensity over the 20 th^ century, but not all trends are statistically significant [9].
There have been 19 drought occurrences in Washington State since 1900. Within the past 10 years, Whatcom County has experienced impacts from drought. In 2010, the City of Bellingham implemented mandatory water use restrictions. The 2015 drought was primarily driven by low snowpack that accumulated during the winter of 2014-2015, as much of the precipitation fell as rain rather than snow due to above-average temperatures [17]. The snowpack acts as a water reservoir for Whatcom County and is an important water source for rivers, as lowland precipitation begins to decline in the late spring to early summer.
Figure 7. Historic average annual precipitation in Bellingham between 1858 and 2018. Trend line indicates a 1.9% change per decade [11].
(^1) Additional data is available for historic precipitation in Blaine and Clearbrook, but trends at those locations
are not significant and thus not presented in this report. The data for those sites can be accessed through the PNW Precipitation Trend Analysis Tool from the Office of the Washington State Climatologist.
- Under a high-emissions scenario, the intensity and frequency of heavy precipitation events west of the Cascades are projected to increase by the 2080s by 22% and five more days each year, respectively [9].^2
- Due to its reliance on lower elevation snowpack and precipitation, Whatcom County is vulnerable to drought effects such as those that occurred in 2014 and 2015 [17].
Across the Puget Sound region, annual precipitation is projected to increase under both low- and high- emissions scenarios [9]. Projected changes in annual precipitation are small relative to year-to-year variability.
Most projections indicate an increase in precipitation intensity for the Puget Sound region for all seasons except for summer. Summer precipitation in the Puget Sound region is projected to decline approximately 22% for the 2050s compared to 1970-1999, for both low- and high-emissions scenarios (see Figure 11) [15]. Although some projections for fall, winter, and spring show ranges that project decreases in precipitation, the overall trend is upward [15]. The most pronounced increases for seasonal precipitation are in fall and winter under a high-emissions scenario. Fall precipitation is projected to increase between 5-6% by 2050 and between 10-12% by the 2080s, relative to 1970-1999 values. Winter precipitation is expected to increase approximately 10% by 2050 for both emissions scenarios and is projected to increase between 11-15% by 2080 under low- and high-emissions scenarios, respectively. By the 2050s, spring precipitation is projected to increase between 2.4-3.8% under low-and high-emissions scenarios, respectively. Spring precipitation is anticipated to have a smaller increase by the 2080s, with models projecting an increase of 1.6% under a low- emissions scenario and 2.5% under a high-emissions scenario, compared to 1970-1990 averages.
While models project decreases in summer precipitation, the overall trend in precipitation among the other seasons is upward.
The intensity and frequency of heavy precipitation events west of the Cascades are projected to increase by the 2080s. Under a high emissions scenario, the intensity of heavy precipitation events (24-hour precipitation events with a 1% likelihood of occurring) are projected to increase by 22%. Furthermore, these heavy precipitation events are expected to occur seven days per year compared to only two days a year historically (1970-1999 average) [9].
Projections are not available for changes in frequency or intensity of droughts in Whatcom County or Washington State. However, due to Whatcom County’s dependence on lower elevation snowpack and precipitation, the projected increases in temperature and projected decreases in summer precipitation could increase the county’s vulnerability to drought effects. Vulnerabilities are projected to include drought effects such as those that occurred in 2014 and 2015 [17]. The historical patterns of water supply and runoff are shifting, and it is likely that low stream flows and elevated water temperatures often associated with drought conditions will become more common [17]. In addition, the typical pattern of higher water use during the driest part of the year is often exacerbated during droughts, where hotter and drier weather increases water use above normal levels at a time when water availability is more restricted.
(^2) Heavy precipitation events are defined as 24-hour precipitation events that have a 1% likelihood of
occurring.
Figure 10. Projected change in annual Puget Sound precipitation. All changes are relative to the average for 1970-
- The average projected change is shown with the black dot, and the colored bars show the range of projected values from 10 climate models for both RCP 4.5 in blue and RCP 8.5 in green (Figure created using data from CIG 2015 SOK) [9].
Figure 11. Projected change in seasonal Puget Sound precipitation. All changes are relative to the average for 1970-1999. The average projected change is shown with the black dot, and the colored bars show the range of projected values from 10 climate models for both RCP 4.5 in blue and RCP 8.5 in green (Figure created using data from CIG 2015 SOK) [9].
Hydrology
Observed changes to date
- Puget Sound glacial numbers and volume are declining. Between 1900 and 2009, glacier area in the North Cascades declined by 56% [9].
indicate how the timing of peak streamflow has changed [19]. Historic mean peak flow between 1967 and 2017 has been 23,500 cubic feet per second (cfs) (see Figure 14) [19]. For reference, peak flow during the extreme flood event on November 11, 1990, was 48,200 cfs [19].
Projected future changes
- Snowpack for mountains draining into Puget Sound is projected to decrease by 29% by the 2040s [19].
- The Nooksack Valley basin is anticipated to transition from being a mixed snow and rain-dominant system to a rain-dominant system [9] [19]. By the 2080s, peak streamflow in the Nooksack River is projected to shift approximately 27 days earlier in the year compared to 1970-1999 [20].
- Heavy rainfall events are projected to become more intense. Regional models anticipate that heavy rainfall events in Western Washington will intensify by 22% by the 2080s [9]. Under a moderate (A1B) emissions scenario, streamflow in the Nooksack River during a 100-year flood event is projected to increase by 27% by the 2080s [19]. 5
- Summer minimum streamflow in the Nooksack River is projected to decrease by 27% by the 2080s relative to the 1970-1999 average, and summertime stream temperatures are projected to increase , reaching levels that exceed the thermal tolerance of most fish species [20].
As the climate warms, the Pacific Northwest is projected to continue to face decreased snowpack and changes to streamflow timing and seasonal minimums. One study found that glaciers in the Nooksack River basin are projected to recede by approximately 90% by 2100, at which time smaller glaciers are projected to disappear completely, under a low-emissions scenario [21]. These projections indicate a decline in both glacier area and volume, which will reduce the amount of ice melt that contributes to streamflow. In the Nooksack River, glacial melt makes a critical contribution to streamflow, so the projected glacial loss poses significant implications for aquatic ecosystems and critical species like salmon that rely on snow and glacier- fed water resource [22]. In the same study, projections indicate a 50% and 69% decline in snow water equivalent in the Middle Fork Nooksack Basin under a low- and high-emissions scenarios, respectively, by 2075 [21]. Another study projected a 33-45% decline in monthly median snow water equivalent by 2050 in the Middle Fork Nooksack Basin, which was the highest elevation studied [23]. Thus, lower elevation locations are projected to experience even faster rates of snow water equivalent decline. In addition, peak snow water equivalent is also projected to shift earlier in the year, from approximately April 1 to March or even earlier by the 2050s, but that may occur even sooner for lower elevation locations. This shift contributes to a shift in peak streamflow.
By the end of the 21 st^ century, based on a low-emissions scenario, the main form of precipitation in Puget Sound watersheds is expected to be rainfall [9]. The Nooksack River basin and other Puget Sound watersheds that are currently dominated by a mix of rain and snow in the winter are projected to become progressively more rain-dominant [9]. This transition to mostly rainfall precipitation is expected to lead to an increase in winter streamflow, an earlier peak streamflow, and a decline in summer streamflow [9] [24]. By the 2080s, peak streamflow in the Nooksack River is projected to shift earlier in the year, occurring 19 to 40 days earlier compared to 1970-1999, based on a moderate (A1B) greenhouse gas scenario [9].
(^5) The moderate (A1B) emissions scenario is most similar to RCP6.0. The A1B scenario is one of a suite of
scenarios commonly used in earlier climate change assessments (including IPCC reports). The new set of scenarios—, Representative Concentration Pathways (RCPs)—were developed for the 5 th^ IPCC Assessment Report are now the industry standard for climate change assessments.
Figure 12. Model projections of Puget Sound watersheds suggest a transition to largely rain-dominant basins by the 2080s [9].
Heavy rainfall events, or atmospheric river events, are projected to become more intense in the future, increasing the risk of flooding in the Puget Sound region, particularly at low elevations. With a shift to a rain- dominant basin, the Nooksack River will likely experience an increase in frequency and magnitude of floods [23]. Regional models anticipate that heavy rainfall events in Western Washington will intensify by 22% by the 2080s [9]. In the Nooksack River, the streamflow during a 100-year flood event is projected to increase by 27% (range of 9% to 60%) by the 2080s relative to the 1970-1999 average [19].The return period magnitude is also projected to shift in the future. For instance, the magnitude of a historical 10-year flood in the Nooksack River is projected to have a return internal of only 3 years by 2050 [23].
While winter streamflow is projected to increase, summer streamflow is projected to decrease as peak streamflow shifts to earlier in the year and as snowpack decreases. Summer minimum streamflow in the Nooksack River is projected to decrease by 27% (range of –38% to –13%) by the 2080s relative to the 1970- 1999 average [9]. Declining summer streamflows and increasing summertime air temperatures are expected to increase stream temperatures in the summer, reducing water quality in streams. By 2040, it is projected that 40 miles of the Nooksack River will exceed 64 °F, which is the thermal tolerance for adult salmon compared to zero miles in 2015 [25]. By the late 21 st^ century, one study found that the South Fork of the Nooksack River, which is at a lower elevation than the Middle Fork and North Fork, is projected to have an average of 115 days per year when the 7-day average of daily maximum stream temperature exceeds 60.8 °F, which is considered a threshold for protecting aquatic habitats [26]. During that same period, the higher- elevation Middle and North Fork basins are projected to have 35 and 23 days, respectively, when that threshold is exceeded.
