Sub-hourly water temperature data collected across the Nechako Watershed, 2019-2021.

Water temperature is actively being monitored along the regulated Nechako River and some of its unregulated tributaries in northern British Columbia (BC) to determine how climate variability, climate change and flow regulation influence water temperatures. The Nechako Watershed, located mainly in the sub-boreal spruce biogeoclimatic zone, spans 47,200 km2 in area [1]. The regional climate experiences a prominent seasonal cycle in air temperature and precipitation, with subfreezing temperatures and snow accumulating during winter. Waterways therefore experience extended near 0°C water/ice temperatures during the winter season. The accumulation of snow yields snowmelt-generated peaks in discharge during the spring freshet period in unregulated tributaries [2]. Regional studies on climate reveal recent warming trends that are anticipated to persist through the 21st century, with a projected mean air temperature increase of ∼2°C by the 2050's [3]. In response to warming air temperatures, regional water temperatures are also on the rise, with an average warming trend of 0.7°C from 1950 to 2015 [4]. Changing water temperatures are important in understanding ecological and environmental impacts on riverine systems, including aquatic species such as fish (e.g., sockeye salmon (Oncorhynchus nerka), rainbow trout (Oncorhynchus mykiss) and white sturgeon (Acipenser transmontanus), all endemic species to the Nechako Watershed), invertebrates, and micro-organisms. Managing water temperatures during the fish spawning season is crucial as elevated temperatures induce stress and affect reproduction success [5]. Starting with a pilot project in summer of 2019, we expanded in situ monitoring of water temperature to 29 sites; however, for the purposes of this paper, only data from 24 sites are included (some sites have limited data samples or loggers could not be retrieved in the field). Currently, 25 sites are fully operational and collecting data, all deployed to sample and record data at 15-minute intervals starting at the top of the hour. Site data collection occurs at minimum once annually (typically during summer/early fall), along with site and logger maintenance. Field notes are taken to identify any potential issues with data collection, such as loggers dewatering during low flows, duration of logger removal for data collection, and any other environmental concerns that should later be considered during data analysis. The assembled data are useful to build long-term time series of observed water temperatures within the Nechako Watershed and as a baseline for future projects. The data are also used to determine the effectiveness of the Summer Temperature Management Program at the Nechako Reservoir and Skins Lake Spillway [1]. Therefore, these data can be used in the future to better identify the optimal discharge from the reservoir to minimize ecological effects on the watershed.

Vanishing weekly hydropeaking cycles in American and Canadian rivers.

Sub-daily and weekly flow cycles termed 'hydropeaking' are common features in regulated rivers worldwide. Weekly flow periodicity arises from fluctuating electricity demand and production tied to socioeconomic activity, typically with higher consumption during weekdays followed by reductions on weekends. Here, we propose a weekly hydropeaking index to quantify the 1920-2019 intensity and prevalence of weekly hydropeaking cycles at 500 sites across the United States of America and Canada. A robust weekly hydropeaking signal exists at 1.8% of sites starting in 1920, peaking at 18.9% in 1963, and diminishing to 3.1% in 2019, marking a 21st century decline in weekly hydropeaking intensity. We propose this decline may be tied to recent, above-average precipitation, socioeconomic shifts, alternative energy production, and legislative and policy changes impacting water management in regulated systems. Vanishing weekly hydropeaking cycles may offset some of the prior deleterious ecohydrological impacts from hydropeaking in highly regulated rivers.

Associations of five food- and water-borne diseases with ecological zone, land use and aquifer type in a changing climate.

BACKGROUND: Food- and water-borne pathogens exhibit spatial heterogeneity, but attribution to specific environmental processes is lacking while anthropogenic climate change alters these processes. The goal of this study was to investigate ecology, land-use and health associations of these pathogens and to make future disease projections. METHODS: The rates of five acute gastrointestinal illnesses (AGIs) (campylobacteriosis, Verotoxin- producing Escherichia coli, salmonellosis, giardiasis and cryptosporidiosis) from 2000 to 2013 in British Columbia, Canada, were calculated across three environmental variables: ecological zone, land use, and aquifer type. A correlation analysis investigated relationships between 19 climatic factors and AGI. Mean annual temperature at the ecological zone scale was used in a univariate regression model to calculate annual relative AGI risk per 1 °C increase. Future cases attributable to climate change were estimated into the 2080s. FINDINGS: Each of the bacterial AGI rates was correlated with several annual temperature-related factors while the protozoan AGIs were not. In the regression model, combined relative risk for the three bacterial AGIs was 1.1 [95% CI: 1.02-1.21] for every 1 °C in mean annual temperature. Campylobacteriosis, salmonellosis and giardiasis rates were significantly higher (p < 0.05) in the urban land use class than in the rural one. In rural areas, bacteria and protozoan AGIs had significantly higher rates in the unconsolidated aquifers. Verotoxin-producing Escherichia coli rates were significantly higher in watersheds with more agricultural land, while rates of campylobacteriosis, salmonellosis and giardiasis were significantly lower in agricultural watersheds. Ecological zones with higher bacterial AGI rates were generally projected to expand in range by the 2080s. INTERPRETATION: These findings suggest that risk of AGI can vary across ecosystem, land use and aquifer type, and that warming temperatures may be associated with an increased risk of food-borne AGI. In addition, spatial patterns of these diseases are projected to shift under climate change.

Modelling the impacts of climate change on riverine thermal regimes in western Canada's largest Pacific watershed.

Quantification of climate change impacts on the thermal regimes of rivers in British Columbia (BC) is crucial given their importance to aquatic ecosystems. Using the Air2Stream model, we investigate the impact of both air temperature and streamflow changes on river water temperatures from 1950 to 2015 across BC's 234,000 km2 Fraser River Basin (FRB). Model results show the FRB's summer water temperatures rose by nearly 1.0 °C during 1950-2015 with 0.47 °C spread across 17 river sites. For most of these sites, such increases in average summer water temperature have doubled the number of days exceeding 20 °C, the water temperature that, if exceeded, potentially increases the physiological stress of salmon during migration. Furthermore, river sites, especially those in the upper and middle FRB, show significant associations between Pacific Ocean teleconnections and regional water temperatures. A multivariate linear regression analysis reveals that air temperature primarily controls simulated water temperatures in the FRB by capturing ~80% of its explained variance with secondary impacts through river discharge. Given such increases in river water temperature, salmon returning to spawn in the Fraser River and its tributaries are facing continued and increasing physical challenges now and potentially into the future.

Hydroclimatic Variability and Predictability: A Survey of Recent Research.

Recent research in large-scale hydroclimatic variability is surveyed, focusing on five topics: (i) variability in general, (ii) droughts, (iii) floods, (iv) land-atmosphere coupling, and (v) hydroclimatic prediction. Each surveyed topic is supplemented by illustrative examples of recent research, as presented at a 2016 symposium honoring the career of Professor Eric Wood. Taken together, the recent literature and the illustrative examples clearly show that current research into hydroclimatic variability is strong, vibrant, and multifaceted.

Impacts of a Rapidly Declining Mountain Snowpack on Streamflow Timing in Canada's Fraser River Basin.

With its headwaters in the water towers of the western Cordillera of North America, the Fraser River is one of the continent's mightiest rivers by annual flows, supplies vital freshwater resources to populous downstream locations, and sustains the world's largest stocks of sockeye salmon along with four other salmon species. Here we show the Variable Infiltration Capacity (VIC) model's ability to reproduce accurately observed trends in daily streamflow for the Fraser River's main stem and six of its major tributaries over 1949-2006 when air temperatures rose by 1.4 °C while annual precipitation amounts remained stable. Rapidly declining mountain snowpacks and earlier melt onsets result in a 10-day advance of the Fraser River's spring freshet with subsequent reductions in summer flows when up-river salmon migrations occur. Identification of the sub-basins driving the Fraser River's most significant changes provides a measure of seasonal predictability of future floods or droughts in a changing climate.