Air Temperature Research Articles

Expert elicitation of state shifts and divergent sensitivities to climate warming across northern ecosystems

Northern regions are warming faster than the rest of the globe. It is difficult to predict ecosystem responses to warming because the thermal sensitivity of their biophysical components varies. Here, we present an analysis of the authors’ expert judgment regarding the sensitivity of six ecosystem components – permafrost, peatlands, lakes, snowpack, vegetation, and endothermic vertebrates – across northern landscapes ranging from boreal to polar biomes. We identified 28 discontinuous component states across a 3700 km latitudinal gradient in northeastern North America and quantified sensitivity as the transition time from an initial to a contrasting state following a theoretical step change increase in mean annual air temperature of 5 °C. We infer that multiple interconnected state shifts are likely to occur within a narrow subarctic latitudinal band at timescales of 10 to more than 100 years, and response times decrease with latitude. Response times differ between components and across latitudes, which is likely to impair the integrity of ecosystems.

Modelling of Indoor Air Quality and Thermal Comfort in Passive Buildings Subjected to External Warm Climate Conditions

Air renewal rate is an important parameter for both indoor air quality and thermal comfort. However, to improve indoor thermal comfort, the air renewal rate to be used, in general, will depend on the outdoor air temperature values. This article presents the modelling of indoor air quality and thermal comfort for occupants of a passive building subject to a climate with warm conditions. The ventilation and shading strategies implemented for the interior spaces are then considered, as well as the use of an underground space for storing cooled air. The indoor air quality is evaluated using the carbon dioxide concentration, and thermal comfort is evaluated using the Predicted Mean Vote index. The geometry of the passive building, with complex topology, is generated using a numerical model. The simulation is performed by Building Thermal Response software, considering the building’s geometry and materials, ventilation, and occupancy, among others. The building studied is a circular auditorium. The auditorium is divided into four semi-circular auditoriums and a central circular space, with vertical glazed windows and horizontal shading devices on its entire outer surface. Typical summer conditions existing in a Mediterranean-type environment were considered. In this work, two cases were simulated: in Case 1, the occupation is verified in the central space and the four semi-circular auditoriums and all spaces are considered as one; in Case 2, the occupation is verified only in each semi-circular auditorium and each one works independently. For both cases, three strategies were applied: A, without shading and geothermal devices; B, with a geothermal device and without a shading device; and C, with both shading and geothermal devices. The airflow rate contributes to improving indoor air quality throughout the day and thermal comfort for occupants, especially in the morning. The geothermal and shading devices improve the thermal comfort level, mainly in the afternoon.

Seasonal Variations in the Thermal Stratification Responses and Water Quality of the Paldang Lake

We evaluated the thermal and chemical stratifications of Paldang Lake using Schmidt’s stability index (SSI) and the chemical stratification index (IC-i) with weekly data from 2013 to 2022. The temporal trends of stratification were analyzed alongside correlations with meteorological, hydrological, and water quality variables. Thermal stratification intensified with rising air temperature and sunshine duration, while hydrological factors like discharge and retention time affected SSI during periods with less than five days of water retention. During summer, fewer occurrences of intense rainfall or early rainfall before August led to stronger stratification. In fall, nutrient influx from external sources during summer stimulated algal growth, increasing Chlorophyll-α (Chl-α) concentrations. Summer rainfall had a significant impact on the strength and duration of stratification in Paldang Lake. Annual rainfall patterns and subsequent changes in discharge were key factors affecting the physical environment of the lake, which in turn determined water quality and the extent of algal blooms. We provide insights into the seasonal stratification and water quality variations in temperate river-type reservoirs like Paldang Lake. SSI and IC-i from this research can be applied to understand stratification and mixing dynamics in other lakes.

Heat transfer and electromagnetic property investigation on the hot air quartz fiber/PTFE capillary/epoxy resin anti/de‐icing composites

AbstractTo achieve the wave‐transparent and anti/de‐icing requirements of electromagnetic functional structural components on the windward surface of the aircraft, the PTFE capillary hot air tubes were pre‐buried inside the quartz fiber cloth and the hot air anti/de‐icing quartz fiber/PTFE capillary/epoxy resin (QF/PTFE/EP) composite components was prepared to that met the wave‐transparent performance. A multi‐field coupled numerical finite element simulation model was established, and the anti/de‐icing performance of the QF/PTFE/EP composite with different built‐in tube diameters were investigated by combining experiments and simulations under different hot air temperatures and pressures. The feasibility of hot air anti/de‐icing was verified through anti/de‐icing experiments and numerical simulation. The electromagnetic transmittance of the prepared hot air anti/de‐icing QF/PTFE/EP composite components was tested to characterize the effect on the stealth performance of the aircraft under the service environment. The experimental results demonstrated that with 5 mm tube pitch and hot air of 60°C ± 1°C, the surface temperature of the component with three tube diameters could reach more than 10°C. Furthermore, the decrease in the transmittance of the hot air anti/de‐icing QF/PTFE/EP composite components caused by different incidence angles and two polarization modes was less than 3%.Highlights The hot air QF/PTFE/EP anti/de‐icing composite components were fabricated. The heat transfer, anti/de‐icing, and electromagnetic transmittance performance of the hot air QF/PTFE/EP anti/de‐icing QF/PTFE/EP components were investigated. The experimental and simulation results verified the hot air anti/de‐icing QF/PTFE/EP components met the requirement of aircraft anti/de‐icing and wave transmission.

Design, modeling and cost analysis of 8.79 MW solar photovoltaic power plant at National University of Sciences and Technology (NUST), Islamabad, Pakistan

Climate change, as a critical global concern, has fueled our efforts to address it through different strategies. In response to the critical worldwide issue of climate change, we suggested a Photovoltaic (PV) system at the National University of Sciences and Technology (NUST) in Islamabad, Pakistan (latitude: 33.724530 N, longitude: 73.046869, terrain elevation: 552 m). Islamabad is located in a region blessed with enormous solar resources, boasting a daily horizontal solar irradiance of 1503.45 kWh/m2 and an average daily solar irradiance of 5.89 kWh/m2, with an exceptional solar fraction of 98.99%. The ambient air temperature, averaging 23.21 °C, reaches its maximum in June and its minimum in December. Our research thoroughly evaluates the system’s performance, accounting for various losses and utilizing modern PVsyst software. Over the course of 18 years, our PV system is expected to save 75,478.60 tons of CO2, the equivalent of planting 348,754 teak trees. Furthermore, the cost of energy generation is an affordable 0.0141 US $/kWh, much lower than traditional rates, including the Sherif cost of 0.028$/kWh. Along with the performance research, we conducted a detailed cost analysis, projecting the starting cost and cash flow, and discovered that the plant would be in surplus within 12 years of installation. Our system is positioned to generate 11,270,771 kWh/year with a respectable performance ratio (PR) of 76.2% and a Capacity Utilization Factor (CUF) of 16%. Our findings not only highlight the potential of renewable energy but also provide important insights for future sustainable energy programs.

Real-Time Indoor Environmental Quality (IEQ) Monitoring Using an IoT-Based Wireless Sensing Network

In recent years, our time spent indoors has risen to around 90% and to maintain an occupant’s comfort and well-being, Indoor Environmental Quality (IEQ) is monitored. Concerned with inhabitant’s satisfaction and health, the adoption of smart solutions for IEQ monitoring and improvement has expanded. The solution this study explores is an occupant-centric approach involving the implementation of an Internet of Things (IoT) IEQ sensing network in a prominent office skyscraper in Hong Kong. Over the course of 15 months, real-time IEQ data were collected from 12 locations within the building. The data were collected at 1-min time intervals and consisted of readings of indoor air temperature, radiant temperature, relative humidity, air velocity, carbon dioxide (CO2), particulate matter (PM10 and PM2.5), horizontal illuminance levels, and sound pressure levels, which served as the basis of the assessment made about the qualities of thermal comfort, indoor air quality (IAQ), aural comfort, and visual comfort. Compared to traditional periodic surveys, this IoT-based sensing network captured instantaneous environmental variations, providing valuable insights into the indoor environment’s spatial characterization and temporal dynamics. This smart solution also assisted facility management in terms of identifying sources of discomfort and developing effective mitigation strategies accordingly. This study presents an occupant-centric approach to improve occupant comfort and energy efficiency within office buildings. By customizing the built environment to enhance occupants’ well-being, comfort, and productivity, an emphasis is placed on a more personalized and occupant-focused design strategy. This approach integrates technical design with human experience, highlighting the importance of real-time physical and subjective surveys for achieving optimal results.

Dehydrated Food Waste and Leftover for Trench Composting

The growing global population has a persistently negative impact on the economy and ecology due to food waste. This topic has recently received much attention from around the world. For both homes and the food processing industry, recycling food waste is crucial to waste management. This study aims to show how dehydrated food scraps and leftovers can be used as raw materials for trench compost to enhance soil quality and reduce leachate and greenhouse gas emissions. The results showed that the pre-treatment and air temperature significantly affected the finished trench compost products’ EC, pH, and nutrient content. Pretreated dried leftover at 80°C after trench compost was found to have the highest value of CNH, S (36.53%), and micronutrients (0.103404%) when compared to micronutrients in the final product of pre-treatment dried leftover at 80<i>℃</i> after trench compost that was (0.057273%). Dehydrated leftovers from trench compost were thought to have nutrient content that would improve soil quality, slow decomposition, and reduce odor, thus enabling more frequent trash collection.

Application of GIS for Monitoring Firefly Population Abundance (Pteroptyx tener) and the Influence of Abiotic Factors

This study focuses on the <i>Pteroptyx tener</i> species in the Sepetang River, Malaysia, aiming to evaluate the firefly’s abundance and explore its correlation with various biotic and abiotic parameters. The study was conducted over six months, from November 2021 to April 2022, utilizing Geographic Information System (GIS) software to apply hotspot mapping and Inverse Distance Weighting (IDW) analysis to elucidate the spatial distribution of firefly populations. A total of 111,615 individuals were recorded, with a particular focus on this firefly species’ presence on their display trees. Hotspot analysis showed that Station 6, located at the mouth of a river with dense mangroves, hosted 55,723 fireflies (50.01%). In contrast, Stations 9 and 10, near ponds and shrimp settlements, recorded 517–723 fireflies (0.65% and 0.46%). Pearson’s correlation coefficient (r) unveiled a statistically significant positive correlation (r = 0.88, p < 0.05) between wind speed and the abundance of firefly populations within the Sepetang River. However, no statistically significant correlation (p > 0.05) was found between firefly abundance and various other abiotic parameters, including relative humidity (RH), air temperature, tide level, pH, electrical conductivity (EC), salinity, total dissolved solids (TDS), and water clarity. Thus, the results revealed the preference for fireflies due to the availability of vegetation, wind speed and minimal disturbance in this area. In conclusion, this study’s information significantly adds to our understanding of these interesting insects and their complicated relationships in nature. It underscores the importance of preserving their habitats and ecosystems.

Quantifying the potential of evidence-based planting-pattern for reducing the outdoor thermal stress from a bio-meteorological perspective in tropical conditions of Indian cities.

The impact of declined natural greenery and increased built surfaces exacerbates heat stress in urban areas causing limited usage of outdoor spaces. Greenery strategies such as trees are capable of mitigating outdoor thermal stress gain because of their phytological properties. While urban greenery guidelines have suggested the ad-hoc procedure of tree planting-schemes based on aesthetic-value, soil-water preservation etc., understanding of their morphological character help in regulating extreme thermal condition. Hence, this study aims to investigate the most efficient planting pattern based on canopies densities and trees clusters for reducing the outdoor thermal stress from bio-meteorological perspective.It initiates with the measurement of the site's morphological and meteorological attributes in existing commercial market of Bhopal City which has a humid sub-tropical climate (Aw, Koppen climate categorization). Furthermore, it leads to the development of 4-different iterated clusters incorporating moderate to high-density canopies and their overlaps pattern to estimate reduction potential in outdoors using field surveys and validated simulation model. The reduction potential in terms of magnitude and duration of thermal stress is quantified across 3-thermal variables i.e., air temperature, mean radiant temperature and universal thermal climate index. Results indicate highly-dense canopies are more effective in reducing greater magnitude of thermal stress along longer duration. Also overlapped planting pattern within the same canopy density does not make significant difference in stress reduction as compared to the changing the densities. This study will help planners and landscape architects to adopt evidence-based planting-pattern strategies for improving outdoor microclimate.

Implementation of WRF‐Urban Asymmetric Convective Model (UACM) for Simulating Urban Fog Over Delhi, India

AbstractAccurate fog prediction in densely urbanized cities poses a challenge due to the complex influence of urban morphology on meteorological conditions in the urban roughness sublayer. This study implemented a coupled WRF‐Urban Asymmetric Convective Model (WRF‐UACM) for Delhi, India, integrating explicit urban physics with Sentinel‐updated USGS land‐use and urban morphological parameters derived from the UT‐GLOBUS dataset. When evaluated against the baseline Asymmetric Convective Model (WRF‐BACM) using Winter Fog Experiment (WiFEX) data, WRF‐UACM significantly improved urban meteorological variables such as diurnal variations in 10‐m wind speed, 2‐m air temperature (T2), and 2‐m relative humidity (RH2) during a fog event. UACM also demonstrates improved accuracy in simulating temperature and significantly reducing biases for wind speed and daytime RH2 under clear sky conditions. UACM reproduced the nighttime urban heat island effect within the city, showing realistic diurnal heating and cooling patterns that are important for accurate fog onset and duration. UACM effectively predicts the onset, evolution, and dissipation of fog, aligning well with observed data and satellite imagery. Compared to WRF‐BACM, WRF‐UACM reduces the cold bias soon after sunset, thus improving the fog onset error by ∼3 hr. This study highlights the UACM's potential to improve fog prediction and its application in operational settings. With further investigation into different fog types, the UACM can provide crucial insights for preventive measures and reducing disruptions in urban areas.

Anthropogenic Exacerbation in Dry‐Hot Probability and Consequential Record‐Shattering Droughts in the Middle and Lower Reaches of the Yangtze River

AbstractIn the year 2019, the middle and lower reaches of the Yangtze River (MLRYR) experienced an unprecedented summer‐autumn drought (SAD) driven by dry‐hot conditions [high near‐surface air temperatures (T) and low precipitation (P)], causing substantial agricultural and economic losses. However, the influence of anthropogenic climate change (ACC) on these dry‐hot conditions and their impacts on SAD occurrences remains uncertain. Here, both observations and simulations show that an ACC‐driven T increase led to the greater likelihood of dry‐hot conditions from August to November 1901–2020 in MLRYR. Using the self‐calibrating Palmer drought index (scPDSI) to assess SAD severity, we find an increasing likelihood of SAD occurrence (from 33.3% in 1901–2000 to 85.7% in 2001–2020) in MLRYR associated with more frequent dry‐hot conditions. Under a business‐as‐usual scenario, future dry‐hot association is projected to be stronger, with exceptional dry‐hot conditions to increase by +10% per century. ACC‐induced increase in dry‐hot conditions would elevate the likelihood of SAD events like the 2019 event from 1.59% (1961–2020) to 17.82% (2041–2100). Therefore, effective measures are needed in MLRYR to adapt to increasing dry‐hot conditions and associated SAD occurrences under anthropogenic warming.

Highest Occurring Vascular Plants from Ladakh Provide Wood Anatomical Evidence for a Thermal Limitation of Cell Wall Lignification.

As an evolutionary achievement of almost all terrestrial plants, lignin biosynthesis is essential for various mechanical and physiological processes. Possible effects of plant cell wall lignification on large-scale vegetation distribution are, however, not yet fully understood. Here, we present double-stained, wood anatomical stem measurements of 207 perennial herbs (Potentilla pamirica Wolf), which were collected between 5550 and 5850 m asl on the north-western Tibetan Plateau in Ladakh, India. We also measured changes in situ root zone and surface air temperatures along the sampling gradient and applied piecewise structural equation models to assess direct and indirect relationships between the age and size of plants, the degree of cell wall lignification in their stems, and the elevation at which they were growing. Based on the world's highest-occurring vascular plants, the Pamir Cinquefoils, we demonstrate that the amount of lignin in the secondary cell walls decreases significantly with increasing elevation (r = -0.73; p < 0.01). Since elevation is a proxy for temperature, our findings suggest a thermal constrain on lignin biosynthesis at the cold range limit of woody plant growth.

Evaluating the tradeoffs between water conservation, aesthetic value, evaporative cooling and CO2 emissions in St. augustinegrass and buffalograss

Urban lawns comprise a significant portion of urban greenery and provide several ecosystem services. Nevertheless, maintaining lawns comes with significant water costs in semi-arid inland southern California, as they require consistent irrigation to stay healthy and productive. The main objective of this study was to evaluate the effect of a wide range of irrigation rates and frequencies applied autonomously by a smart ET-based controller on the aesthetic value, cooling potential, and CO2 efflux of two warm-season turfgrass species. For three years, we studied the responses of Buffalograss and St. Augustinegrass to six irrigation rates and two irrigation frequencies in Riverside, California. Under historical average climate conditions, the minimum irrigation rate for Buffalograss was 93 % ETo, and for St. Augustinegrass, it was 74 % ETo. Under projected future climate conditions, the estimated minimum irrigation rate for Buffalograss did not change, but for St. Augustinegrass, it increased by 4 % and 7 % in 2100 under low emission (RCP 4.5) and high emission (RCP 8.5) scenarios, respectively. On average, canopy minus air temperature in Buffalograss was 6.2 ℃, and in St. Augustinegrass, it was 1.1 ℃. The average CO2 efflux in Buffalograss was 122.3 µg CO2-C m−2 s−1, and in St. Augustinegrass, it was 182.8 µg CO2-C m−2 s−1. Our results showed that turfgrass aesthetic values, cooling potential, and CO2 efflux diminished as the irrigation rate decreased, but at different rates for each turfgrass species.

Design and performance analysis of a coupled burner for the Solid Oxide Fuel Cell system

The Solid Oxide Fuel Cell (SOFC) system is characterized by high energy conversion efficiency and low emissions. The energy supply and recovery of the SOFC system are facilitated through the ignition burner and the off-gas burner, respectively. This study proposes a coupled design of the ignition burner and the off-gas burner to reduce the burner volume, thereby enhancing the power density of the SOFC system. The ignition burner employs radially opposed jet combustion with fully premixed natural gas, while the off-gas burner uses swirl diffusion combustion with the anode off gas. When the premixed gas and lean anode off gas are unable to sustain the flame, catalytic combustion is initiated. Simulation and experiment methods are utilized to analyze the performance of the coupled burner in this paper. The results indicate that uniform mixing is achieved with a high swirl number (s1 = 2.6) for the premixed gas, and the maximum excess air coefficient for stable flame combustion at 400 °C is 2.47. As the temperature of the cathode off gas increases, the flameout boundary for the premixed gas gradually increases; conversely, with increasing burner power, the flameout boundary gradually decreases. The intersection cooling effect of mixed air and circumferential high-temperature flue gas is effective, and the flame does not exceed the tolerance temperature of the catalytic carrier. The diffusion combustion of anode off gas with a swirl number (s2 = 0.5) exhibits great gas mixing uniformity without a high-temperature core region. When transitioning from flame to catalytic combustion with premixed natural gas and anode off gas, there is a temperature lag of approximately 60 s. The isotropic cylindrical cordierite catalytic carrier with a 400 mesh and a coating of 60 g/ft3 Pt0.1Pd0.5 achieves stable catalytic combustion in an environment with preheated air temperatures ranging from 400 to 600 °C and H2 concentrations of 0.25–2.91 %.

Experimental study and simulation of a solid desiccant cooling system installed in northern Algeria

An experimental investigation of a solid desiccant cooling system for a research laboratory on the Algerian coast has been carried out. The system utilized flat-plate solar collectors for regeneration and was evaluated through a combination of individual component characterization, system modeling (using TRNSYS), and experimental validation. The results obtained have been validated and show that the efficiency of the rotary heat exchanger reached 65 %, the evaporative humidifier efficiency reached 94 %, and the desiccant wheel achieved efficiencies of 73 % on the process side and 66 % on the regeneration side. This translates to a significant dehumidification effect, reducing absolute humidity in the treated air by 9 g/kg, for the supply air temperature effectively maintained at a comfortable 24 °C. The close agreement between the simulated and experimental COP values (1.13 and 1.08, respectively) validates the chosen approach and confirms the potential of this technology for energy-efficient building cooling in the hot and humid Mediterranean climate of northern Algeria.

Large-Scale Surface Air Temperature Bias in Summer over the CONUS and its Relationship to Tropical Central Pacific Convection in the UFS Prototype 8

Large-Scale Surface Air Temperature Bias in Summer over the CONUS and its Relationship to Tropical Central Pacific Convection in the UFS Prototype 8

Influence of view factors on outdoor thermal comfort of residential areas in hot-humid regions.

Sky View Factor (SVF) is commonly used to describe the impact of urban geometry on the urban thermal environment. Shading effects from plants and buildings also exert a considerable influence. To investigate the influence of view factors on outdoor thermal comfort in residential areas, we employed the Physiological Equivalent Temperature (PET) and view factors (SVF, TVF, BVF) as indicators to determine outdoor thermal comfort and the quantity of shaded spaces. Thermal measurements collected from 13 points in Guangzhou, China, Our findings revealed that high TVF points exhibited more stable air temperature throughout the daytime, with average temperature differentials ranging 0.4-1.9°C lower than other points. Air temperature demonstrated a positive correlation with SVF (R2 = 0.53), while exhibiting a negative correlation with TVF (R2 = 0.45). Additionally, shading provided by plants and buildings manifests heterogeneity. At similar SVF levels, points predominantly shaded by plants (TVF > BVF) showcased lower Mean Radiant Temperature (MRT) and PET compared to points shaded mainly by buildings (BVF > TVF). The maximum reduction in air temperature and PET reached 1.1°C and 1.2°C, respectively. BVF exerted greater influence earlier in the morning, as solar altitude angle rises, the average thermal parameters of sites with BVF > TVF escalated rapidly until eventually surpassing sites with TVF > BVF. Last, superior thermal conditions were only ensured under high shading conditions. When the effective shading ratio of plants and buildings diminished (SVF > 0.3), the microclimate of measurement points might be impacted by the long-wave radiation from the underlying surface.

Evaluating the performances of SVR and XGBoost for short-range forecasting of heatwaves across different temperature zones of India

This research aims to forecast maximum temperatures and the frequency of heatwave days across four different temperature zones (Zone 1, 2, 3 and 4) in India. These four zones are categorized based on the 30-year average maximum temperatures (T30AMT) during the summer months of April, May, and June (AMJ). Two Machine Learning (ML) algorithms eXtreme Gradient Boosting (XGBoost) and Support Vector Regression (SVR) are employed to achieve this goal. The study utilizes nine key atmospheric variables namely air temperature, geopotential height, relative humidity, U-wind, V-wind, soil moisture, solar radiation, sea surface temperature, and mean sea level pressure at a daily scale spanning from 1991 to 2020 for the months of March, April, May, and June as predictors. The India Meteorological Department daily maximum temperature data spanning from 1991 to 2020 for the months of AMJ serves as the predictands. ML models are developed using spatially averaged atmospheric variables and daily maximum temperature across the grids falling within each temperature zone. Results indicate that for a 7-day lead time, SVR outperforms XGBoost in Zone-1 (T30AMT > 38 °C) and Zone-2 (T30AMT: 35.01 °C–38 °C) by more accurately capturing peak temperatures during training and testing. Conversely, for a 15-day lead time in Zone-1, XGBoost better predicts temperature peaks in both phases. In Zone-3 (T30AMT: 30 °C–35 °C) and Zone-4 (T30AMT < 30 °C) for both lead times, the performance of both models decline, indicating models and input variables are more effective in predicting higher temperatures typical of Zone-1 and 2 but less so in Zone-3 and 4. In a nutshell, the study attempts to highlight the capability of advanced ML techniques combined with spatial climate data to enhance the prediction of extreme heatwave events. These insights can aid in heatwave preparedness, climate management, and adaptation strategies for different Indian temperature zones.

Penerapan Analisis Data Panel Pada Suhu Udara Terhadap Perubahan Iklim Curah Hujan di Kota Padang

Climate is the average weather conditions that prevail over an extended period in a particular region. The complex climate system, comprising components such as the atmosphere, lithosphere, and biosphere, generates climate variations among different areas. Climate change has potential impacts such as changes in rainfall patterns, rising temperatures, and sea level rise. Extreme weather, prolonged droughts, and heatwaves can endanger both the environment and human beings.This article aims to assist in predicting future climate patterns to prepare for their impacts using panel data analysis. A panel data regression model is employed to assess the influence of rainfall and air temperature on climate change in Kota Padang from 2018 to 2022. The analysis reveals a significant influence of air temperature, estimated at 0.08, on climate change in Kota Padang during this period. These findings provide a basis for developing mitigation and adaptation strategies to address climate challenges in the region and offer valuable insights for government policies in facing future climate-related issues.

Temporal and spatial use of a freshwater lake by upstream and downstream migrating adult Atlantic salmon Salmo salar.

Atlantic salmon Salmo salar typically enter fresh water several months prior to spawning and just as pools can provide areas of refuge in river systems, lakes may also provide important refuge habitat during the spawning migration. Using acoustic telemetry we examined the spatial and temporal movements of wild and a ranched strain of Atlantic salmon in a freshwater lake where the main spawning areas were located upstream of the lake. Over the study period (2011-2014), returning adult wild salmon spent an average of 228 days in fresh water and 90% of that time in the lake. On entering the lake, most wild salmon moved quickly to the northern part of the lake, close to the main inflow, spending an average 76% of the time in this location. The average number of days wild fish were absent from the lake during the main spawning period varied between years, ranging from 10 to 26 days for females and 32 to 35 days for males. Seventy four per cent (17/23) of salmon spawners returned to the lake and two salmon subsequently died in the lake post-spawning. Atypically, two salmon were resident in the lake for the whole period in 2013/14. During the study, wild salmon were detected at depths within the top 5 m for 73% of the time. Median depths post-spawning were greater than in the pre-spawning period, when salmon were found to spend extensive periods at depths in excess of 10 m. In July 2013, when the lake was stratified, thermal regulation behaviour was observed in wild salmon, whereby salmon moved to cooler deeper water when water temperatures at 1 m exceeded 20°C. In contrast to wild salmon, the majority of ranch salmon returned to the traps downstream of the lake prior to the spawning period, which would be expected as they were released as smolts below the freshwater lake. Ranch fish spent an average 80% of the time in the vicinity of receivers in the south of the lake and an average 98% of the time within the top 5 m. However, two ranch females were resident in the lake until the following spring and one ranch female moved upstream into the river during the spawning period. Clearly, in this catchment the lake provides an important habitat for migrating adult salmon. In the context of climate change, where thermal and hydrological regimes in rivers are expected to change in response to changes in air temperature and precipitation patterns, the availability of deep lakes that stratify in the summer and cool water refuges in river systems is likely to play a key role in the sustenance and conservation of salmonid species. Information about the migration patterns of Atlantic salmon in undisturbed freshwater systems may also assist in resolving issues associated with fish passage in impacted rivers and inform management decisions.