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The role of groundwater (GW) discharge on surface water (SW) quantity, quality and temperature is known to be important. Moreover, the effect of GW contributions to river thermal budgets is critical in natural rivers considering that water temperature plays a vital role in fish survival during extreme heat events. The identification of zones with GW input in rivers can, thus, help river management plans. However, detecting these zones at the watershed scale can be a challenge. This work combines thermal infrared (TIR) imagery of rivers and water sampling for radon measurements for better documentation of GW in rivers. The Sainte-Marguerite and Berard Rivers, both located in Quebec, Canada, are known for their abundance of salmonids. Their water temperature profiles were plotted using TIR imagery, and five cooling zones in the Berard River and two for the Sainte-Marguerite River were identified in which notable GW–SW exchange was the suspected cause. Radon concentrations measured within the cooling zones showed clear GW contribution to SW. TIR imagery is an effective and fast way to identify GW seepage at the watershed scale. Radon can be used as a complementary natural tracer of GW in rivers at finer scales. The combination of both methods was shown to be reliable for the identification of GW in rivers. This can help for a better anticipation of GW effects in management plans to deal with extreme heat waves that are predicted to occur more frequently under future climate change scenarios. [ABSTRACT FROM AUTHOR]

• Shade from riparian tree planting can moderate high river temperature. • However, process-based modelling shows that location of tree planting is important. • Optimal temperature reductions achieved through tree planting in upstream reaches. • Low water volumes/high residence times maximise effect of reduced solar radiation. • Results provide useful guidance for climate change adaptation in rivers. Climate change is increasing river temperature globally, altering the thermal suitability for iconic cold-water adapted fishes. In regions with low tree cover, the impacts of projected climate change on river temperature will be particularly pronounced due to limited shading of the channel. Reforestation of the riparian corridor is thus increasingly being used to shade rivers and offset projected increases in water temperature. However, tree planting can be expensive and logistically challenging, meaning that there is a need to develop guidance to prioritise tree planting where it can deliver greatest benefits. In this study, we use a process-based stream temperature model to simulate the likely effects of a real-world tree planting scheme recently implemented on the Baddoch Burn, a tributary of the Aberdeenshire Dee, Scotland. Our results show that, when mature, ∼3 km of recent tree planting will increase effective shading in the lower reaches of the Burn from 22% to 47%, delivering a ∼1.5 °C decrease in maximum summer stream temperature in comparison to the present-day baseline. We subsequently systematically simulate riparian tree planting in different locations and configurations to determine how and where riparian planting produces and optimal stream temperature response. Our results highlight that different spatial configurations of planting (in terms of length, number, location upstream and spacing between planting zones) can have a considerable impact on stream temperature outcomes, but optimal temperature reductions are generally achieved through planting longer and/or more numerous strips of woodland in upstream reaches, where effective shade is maximised (due to reduced channel width) and where water volumes and residence times mean that impact of reduced solar radiation is greatest. Our investigation not only highlights the extent to which a real-world tree planting scheme will likely deliver summer stream temperature reductions, but also underscores the importance of planting configuration for delivering a temperature reduction in a desired location. Overall, our results provide useful information for river managers and practitioners to develop appropriate riparian shading schemes to combat climate change-driven stream temperature warming. [ABSTRACT FROM AUTHOR]

Riparian tree planting is increasingly being used as a strategy to shade river corridors and offset the impact of climate change on river temperature. Because the circumstances under which tree planting generates the greatest impact are still largely unknown, researchers are increasingly using process‐based models to simulate the impacts of tree planting (or felling) on river temperature. However, the high‐resolution data on existing riparian tree cover needed to parameterise these models can be difficult to obtain, especially in data‐sparse areas. In this paper, we compare the performance of a river temperature model parameterised with a range of different tree cover datasets, to assess whether tree cover data extracted from readily available GIS databases or coarser (i.e., 2–5 m) digital elevation products are able to generate river temperature simulations approaching the accuracy of higher resolution structure from motion (SfM) or LiDAR. Our results show that model performance for simulations incorporating these data is generally degraded in relation to LiDAR/SfM inputs and that tree cover data from "alternative" sources can lead to unexpected temperature model outcomes. We subsequently use our model to simulate the addition/removal of riparian tree cover from alongside the river channel. Simulations indicate that the vast majority of the "shading effect" is generated by tree cover within the 5‐m zone immediately adjacent to the river channel, a key finding with regards to developing efficient riparian tree planting strategies. These results further emphasise the importance of incorporating the highest possible resolution tree cover data when running tree planting/clearcutting scenario simulations. [ABSTRACT FROM AUTHOR]

Climate change in the Arctic is expected to have a major impact on stream ecosystems, affecting hydrological and thermal regimes. Although temperature is important to a range of in‐stream processes, previous Arctic stream temperature research is limited—focused on glacierised headwaters in summer—with limited attention to snowmelt streams and winter. This is the first high‐resolution study on stream temperature in north‐east Greenland (Zackenberg). Data were collected from five streams from September 2013 to September 2015 (24 months). During the winter, streams were largely frozen solid and water temperature variability low. Spring ice‐off date occurred simultaneously across all streams, but 11 days earlier in 2014 compared with 2015 due to thicker snow insulation. During summer, water temperature was highly variable and exhibited a strong relationship with meteorological variables, particularly incoming shortwave radiation and air temperature. Mean summer water temperature in these snowmelt streams was high compared with streams studied previously in Svalbard, yet was lower in Swedish Lapland, as was expected given latitude. With global warning, Arctic stream thermal variability may be less in summer and increased during the winter due to higher summer air temperature and elevated winter precipitation, and the spring and autumn ice‐on and ice‐off dates may extend the flowing water season—in turn affecting stream productivity and diversity. [ABSTRACT FROM AUTHOR]

Climatic warming will increase river temperature globally, with consequences for cold water-adapted organisms. In regions with low forest cover, elevated river temperature is often associated with a lack of bankside shading. Consequently, river managers have advocated riparian tree planting as a strategy to reduce temperature extremes. However, the effect of riparian shading on river temperature varies substantially between locations. Process-based models can elucidate the relative importance of woodland and other factors driving river temperature and thus improve understanding of spatial variability of the effect of shading, but characterising the spatial distribution and height of riparian tree cover necessary to parameterise these models remains a significant challenge. Here, we document a novel approach that combines Structure-from-Motion (SfM) photogrammetry acquired from a drone to characterise the riparian canopy with a process based temperature model (Heat Source) to simulate the effects of tree shading on river temperature. Our approach was applied in the Girnock Burn, a tributary of the Aberdeenshire Dee, Scotland. Results show that SfM approximates true canopy elevation with a good degree of accuracy (R2 = 0.96) and reveals notable spatial heterogeneity in shading. When these data were incorporated into a process-based temperature model, it was possible to simulate river temperatures with a similarly-high level of accuracy (RMSE <0.7 °C) to a model parameterised using 'conventional' LiDAR tree height data. We subsequently demonstrate the utility of our approach for quantifying the magnitude of shading effects on stream temperature by comparing simulated temperatures against another model from which all riparian woodland has been removed. Our findings highlight drone-based SfM as an effective tool for characterising riparian shading and improving river temperature models. This research provides valuable insights into the effects of riparian woodland on river temperature and the potential of bankside tree planting for climate change adaptation. Unlabelled Image • Riparian shading can moderate river temperature extremes, but data needed to model this effect can be difficult to obtain • We combine Structure-from-Motion (SfM) photogrammetry with river temperature modelling to simulate the effect of tree shading • Our approach simulates river temperature with a high degree of accuracy and can help better understand thermal processes in rivers [ABSTRACT FROM AUTHOR]

Climate change is altering river temperature regimes, modifying the dynamics of temperature‐sensitive fishes. The ability to map river temperature is therefore important for understanding the impacts of future warming. Thermal infrared (TIR) remote sensing has proven effective for river temperature mapping, but TIR surveys of rivers remain expensive. Recent drone‐based TIR systems present a potential solution to this problem. However, information regarding the utility of these miniaturised systems for surveying rivers is limited. Here, we present the results of several drone‐based TIR surveys conducted with a view to understanding their suitability for characterising river temperature heterogeneity. We find that drone‐based TIR data are able to clearly reveal the location and extent of discrete thermal inputs to rivers, but thermal imagery suffers from temperature drift‐induced bias, which prevents the extraction of accurate temperature data. Statistical analysis of the causes of this drift reveals that drone flight characteristics and environmental conditions at the time of acquisition explain ~66% of the variance in TIR sensor drift. These results shed important light on the factors influencing drone‐based TIR data quality and suggest that further technological development is required to enable the extraction of robust river temperature data. Nonetheless, this technology represents a promising approach for augmenting in situ sensor capabilities and improved quantification of advective inputs to rivers at intermediate spatial scales between point measurements and "conventional" airborne or satellite remote sensing. [ABSTRACT FROM AUTHOR]

Climate change is likely to increase summer temperatures in many river environments, raising concerns that this will reduce their thermal suitability for a range of freshwater fish species. As a result, river managers have pursued riparian tree planting due to its ability to moderate stream temperatures by providing shading. However, little is known about the relative ability of different riparian forest types to moderate stream temperatures. Further research is therefore necessary to inform best-practise riparian tree planting strategies. This article contrasts stream temperature and energy fluxes under three riparian vegetation types common to Europe: open grassland terrain (OS), semi-natural deciduous woodland (SNS), and commercial conifer plantation (CS). Data was recorded over the course of a year by weather stations installed in each of the vegetation types. Mean daily stream temperature was generally warmest at OS and coolest at CS. Energy gains at all sites were dominated by shortwave radiation, whereas losses where principally due to longwave and latent heat flux. The magnitude of shortwave radiation received at the water surface was strongly dependent upon vegetation type, with OS and SNS woodland sites receiving approximately 6 × and 4 × (respectively) the incoming solar radiation of CS. Although CS lost less energy through longwave or latent fluxes than the other sites, net surface heat flux was ordered OS > SNS > CS, mirroring the stream temperature results. These findings demonstrate that energy fluxes at the air-water interface vary substantially between different riparian forest types and that stream temperature response to bankside vegetation depends upon the type of vegetation present. These results present new insights into the conditions under which riparian vegetation shading is optimal for the reduction of surface heat fluxes and have important implications for the development of ‘best-practice’ tree planting strategies to moderate summer temperature extremes in rivers. [ABSTRACT FROM AUTHOR]

The impact of climate change on Arctic rivers is expected to be severe. There is therefore a need for greater understanding of Arctic river temperature processes. This study quantifies the spatio-temporal variability of water temperatures in the Kårsa River, Sweden. Water temperature was monitored over two summers within the main proglacial channel and within braids fed by different sources. Longitudinal and lateral temperature patterns were assessed in relation to prevailing hydro-meteorology. Temperature metrics in the main channel increased with distance downstream but were moderated by a large lake, while temperatures in the braids were dependent upon channel source. The high temperature standard deviation and inter-site differences within the braids highlight the importance of braided channels for creating thermal habitat heterogeneity. Temperatures were dependent on hydro-meteorological conditions, with sensitivity to air temperature maximized during cooler, rainy conditions. These results shed new light on Arctic river temperature patterns and their controlling processes. [ABSTRACT FROM PUBLISHER]

Water temperature governs the distribution and behaviour of fish. Riverine salmonids use discrete cold water patches, termed thermal refuges, when stream temperature exceeds their thermal tolerances. Currently, little is known about the mechanisms driving the spatial distribution of thermal refuges, particularly at large scales. Given the threat posed by climate warming to salmon populations in Europe and North America, thermal refuges are increasingly important for salmonids during summer. In this study, we used airborne thermal infrared (TIR) imagery to characterise the spatial distribution of thermal refuges from ~ 700 km of rivers in an eastern Canada salmon watershed. Thermal refuges were classified into a range of categories, and those identified as being driven by groundwater processes were observed to be both the most abundant and most spatially variable. Spatial analysis was used to assemble a range of landscape metrics that were tested for associations with the spatial distribution of groundwater-driven refuges. Associations between landscape metrics and the individual occurrence of thermal refuges were assessed using Jacobs' selectivity index. Results showed that the occurrence of groundwater thermal refuges was significantly associated with high values of channel curvature and close proximity of incoming tributary valleys ( X 2 p < 0.05, df = 9). Regression was used to assess correlations between landscape metrics and the density of thermal refuges (number per river km). Channel confinement was found to correlate strongly with the density of groundwater thermal refuges using a quadratic model (R 2 = 0.83, p < 0.05). Our study is the first to quantify the relationship between the spatial distribution of groundwater thermal refuges and landscape hydromorphology throughout a riverscape. This information can be used to aid conservation efforts and manage critical thermal habitats in rivers and streams. [ABSTRACT FROM AUTHOR]

Abstract: In response to high summer river temperatures, salmonids avoid heat stress by making use of discrete units of cold water termed thermal refuges. Although recent research has documented how their spatial arrangement within a river affects salmonid distribution and behaviour, no information is currently available concerning temporal variation in the abundance and types of thermal refuges. In this study, a FLIR SC660 thermal infrared imaging camera (640×480 pixels, NETD <30mK, 7.5–13μm) mounted on a helicopter platform was used to acquire thermal imagery of an Atlantic salmon river in Québec, Canada on six occasions between 2009 and 2011, with a view to characterising temporal variability in thermal refuges and broader scale water temperature complexity. Thermal refuges detected from TIR imagery were classified into a series of process-based categories, revealing notable inter-survey variability in the absolute counts of each refuge type. Downstream temperature complexity, quantified as the standard deviation of derivatives taken of temperature long profiles of each survey, was highly temporally variable, exposing the presence of several warm and cool reaches which varied in magnitude between surveys. Data from local meteorological and discharge logging stations was used to examine whether hydrometeorological conditions could account for observed temporal variability trends. Temporal variability in the absolute counts of lateral groundwater seeps, the most frequently observed thermal refuge class, was shown to correlate strongly with long duration hydrometeorological metrics such as seasonal mean discharge (R2 =0.94, p <0.01). Conversely, thermal refuges resulting from cold water tributaries were more temporally stable and exhibited a weaker correlation with hydrometeorological metrics. Downstream temperature complexity was shown to correlate best with short duration metrics such as cumulative precipitation depth within a 5-day period prior to each survey (R2 =0.90, p <0.01). This study is the first of its kind to link thermal refuge dynamics to hydrometeorological conditions and may offer valuable insights into how changing climatic regimes could influence these important cold water units in the future. [Copyright &y& Elsevier]