Defining river thermal sensitivity as a function of climate

Abstract

Water temperature is increasingly acknowledged as a key variable for the sustainable management of lotic environments. Thermal variability in rivers dictates in large part the ecosystem functions of these water bodies. River thermal sensitivity (TS), defined in this work as the value of the regression slope between water and air temperature (Tair) measurements, is often used to determine how river temperature regime is expected to vary as climate evolves. This study proposes a method to contextualize climate conditions during the river temperature-monitoring period in order to define a common basis to compare TS values calculated for different stations distributed across various climatic regions in the province of Québec (Canada). Nine climate classes were defined based on Tair and precipitation. Annual climate conditions were classified according to their anomalies compared to a reference period .For the reference climate class ("Normal-Normal" conditions), results indicate contrasted summer TS values between Québec rivers and within rivers. Furthermore, observed summer TS variations between climate classes underline the need to account for climate conditions when studying spatial variations in river thermal sensitivity. Climate contextualization also allows us to study the potential role of previous conditions. Rivers were grouped according to their drainage basins characteristics to examine spatial variability in TS for the chosen reference climate conditions. River slope, station elevation and geographic location partly explained TS spatial variability.Useful proxies are needed to describe the relative contribution of groundwater to river temperature and to potentially improve the group classification results.climate, river, river thermal sensitivity, temperature | INTRODUCTIONClimate change induces shifts in the thermal regime of rivers worldwide (Wanders, Vliet, Wada, Bierkens, & Beek, 2019) and these changes will likely increase water temperature mean, maximum and variance in many rivers around the world (van Vliet et al., 2013). This will alter the thermal habitat of many lotic aquatic organisms. For instance, Daufresne and Boët (2007) conducted a meta-analysis of fish communities in large French rivers and concluded that warmer river water temperatures in recent decades induced a significant increase in the proportion of warm water species and species richness. Heino, Virkkala, and Toivonen (2009) described spatial shifts in the spatial range of numerous aquatic species with cold-water species being more affected than warm-water species. Markovic et al. (2014) analyzed the biodiversity of freshwater organisms in Europe under different climate change scenarios and envisaged that as much as 77% of rare species could lose over 90% of their current spatial range. Even though, these scenarios vary from one river system to another. Given that the largest air temperature increases have occurred and will continue to occur at mid to high latitudes (IPCC, 2002), northern rivers are being exposed to larger increase...

Empirical stream thermal sensitivities cluster on the landscape according to geology and climate

“…Viewing thermal sensitivity as a continuous parameter adds novel insights to our understanding of river basin functioning. Studies have highlighted the importance of annual shifts in the processes that drive heat budgets as well as the non-stationarity of the resulting statistical relationships (Arismendi et al 2014, Boyer et al 2021. Our clustering analysis overcomes these issues by using a varying coefficient model that treats thermal sensitivity as a continuous function through time, rather than a series of discrete summary metrics, and allows clustering based on the entirety of average annual patterns.…”

“…Additionally, identification of particularly insensitive portions of the river could help to better constrain areas where coldwater patches exist that may be used as refuges for coldwater fish (Snyder et al 2020). This process-based approach will be particularly important as non-stationary relationships caused by climate change make it unreliable to use past regressions built under historical climate conditions (Boyer et al 2021). Furthermore, as longer, more spatially extensive air and water temperature time series become available (Isaak et al 2017), we can begin to ask questions about 1) the spatial extent of different thermal sensitivity regimes, 2) how interannual variability shifts with climate conditions and geographic context, and 3) detect changes in the external drivers of thermal sensitivities.…”

Stream groundwater inputs generate fine‐scale variation in brook trout phenology and growth across a warming landscape

“…Rates of warming observed in groundwater‐dominated streams also were much slower than rainfall‐dominated streams (Table 2; Figure 4), suggesting that future temperature differences among streams may widen if this pattern persists. However, stream temperature records in Cape Race contained multiple gaps that are likely to have prevented this study from capturing the full range of conditions, as recent hydrological studies recommend using at least 5 years of continuous stream temperature data to characterise thermal sensitivity (Boyer et al., 2021; Daigle et al., 2019). Additionally, we did not account for temporal autocorrelation or non‐stationarity in air–stream temperature relationships, which will change in the future if climate change impacts the recharge, routing and depth of groundwater (Arismendi et al., 2014; Hare et al., 2021).…”

“…Responses to warming are particularly complex in freshwater environments, which can exhibit vastly different thermal sensitivity, defined as the expected change in water temperature for every 1° increase in air temperature (Boyer et al., 2021). For example, boreal streams in southwestern Alaska varying in elevation, slope and contribution of snowmelt to streamflow displayed >5‐fold differences in thermal sensitivity during summer months (Lisi et al., 2015).…”

Rising summer river water temperature across Canada: spatial patterns and hydroclimatic controls

“…However, previous studies on river temperature variability and change over Canada have been limited to basin-scale or regional assessments (e.g. Daigle et al 2019, Islam et al 2019, Boyer et al 2021, Shrestha and Pesklevits 2023a.…”