Temperature Tw Research Articles

Aquatic environment impacts of floating photovoltaic and implications for climate change challenges

With the aggravation of global warming and the increasing demand for energy, the development of renewable energy is imminent. Floating photovoltaic (FPV) is a new form of renewable energy generation. However, the impact of FPV on the aquatic environment is still unclear. By long-term empirical monitoring and data analysis, this paper reveals the shading effect of large-scale FPV power station on aquatic environment for the first time. The results show that: (1) Compared with the non-photovoltaic (NP) zone, FPV only significantly reduces the concentration of dissolved oxygen in the photovoltaic (P) zone. (2) The concentration of chlorophyll a, nitrate nitrogen and total phosphorus increase, while pH and ammonia nitrogen decrease. FPV only causes an effect of the same order of magnitude as the initial concentration, and has no significant adverse effects on the nutritional status of the water body at a coverage ratio less than 50%. (3) FPV has a cooling effect on the water body during the daytime and a thermal insulation effect at night, with the most pronounced impact on peak water temperature (Tw). The heating and cooling process of Tw in P zone usually lags behind the NP zone by 1–3 h. The diurnal fluctuation and vertical difference of Tw as well as the stability of water body are reduced under the shading of FPV, alleviating the influence of climate change on Tw and water body stratification. (4) If 10% of the water area larger than 1 km2 in China are used to develop FPV, more than 900 million tons of CO2 emissions can be reduced, and about 5 billion m3 water can be saved, which is significant in the context of climate change. In general, this paper provides a reference for the future aquatic environmental impact assessment of FPV and the formulation of related policies.

Experimental Investigation on the Flow Boiling of Two Microchannel Heat Sinks Connected in Parallel and Series for Cooling of Multiple Heat Sources.

Cooling methods for multiple heat sources with high heat flux have rarely been reported, but such situations threaten the stable operation of electronic devices. Therefore, in this paper, the use of two microchannel heat sinks is proposed, with and without grooves, labeled Type A and Type B, respectively. Experimental investigations on the flow boiling of two microchannel heat sinks connected in parallel and in series are carried out under different mass fluxes. In addition, a high-speed camera is used to observe flow patterns in the microchannels. The cold plate wall temperature (Tw), heat transfer coefficient (HTC), and pressure drop (PD) are obtained with the use of two microchannel heat sinks. The flow patterns of the bubbly flow and elongated bubbles in the microchannels are observed. The results of the analysis indicated that the Tw, HTC, and PD of the two microchannel heat sinks connected in parallel were degraded, especially when using the Type A-B parallel connection. Compared to the use of a single heat sink, the maximum decrease in HTC was 9.44 kW/(m2K) for Type A heat sinks connected in parallel, which represents a decrease of 45.95%. The influence of the series connection on the Tw, HTC, and PD of the two heat sinks is obvious. The Type A-A series connection exerted the greatest positive effect on the performance of the two heat sinks, especially in the case of the postposition heat sink. The maximum increase in HTC was 12.77 kW/(m2K) for the postposition Type A heat sink, representing an increase of 72.88%. These results could provide a reference for a two-phase flow-cooling complex for multiple heat sources with high heat flux.

Warming of the Willamette River, 1850–present: the effects of climate change and river system alterations

Abstract. Using archival research methods, we recovered and combined data from multiple sources to produce a unique, 140-year record of daily water temperature (Tw) in the lower Willamette River, Oregon (1881–1890, 1941–present). Additional daily weather and river flow records from the 1850s onwards are used to develop and validate a statistical regression model of Tw for 1850–2020. The model simulates the time-lagged response of Tw to air temperature and river flow and is calibrated for three distinct time periods: the late 19th, mid-20th, and early 21st centuries. Results show that Tw has trended upwards at 1.1 ∘C per century since the mid-19th century, with the largest shift in January and February (1.3 ∘C per century) and the smallest in May and June (∼ 0.8 ∘C per century). The duration that the river exceeds the ecologically important threshold of 20 ∘C has increased by about 20 d since the 1800s, to about 60 d yr−1. Moreover, cold-water days below 2 ∘C have virtually disappeared, and the river no longer freezes. Since 1900, changes are primarily correlated with increases in air temperature (Tw increase of 0.81 ± 0.25 ∘C) but also occur due to alterations in the river system such as depth increases from reservoirs (0.34 ± 0.12 ∘C). Managed release of water affects Tw seasonally, with an average reduction of up to 0.56 ∘C estimated for September. River system changes have decreased variability (σ) in daily minimum Tw by 0.44 ∘C, increased thermal memory, reduced interannual variability, and reduced the response to short-term meteorological forcing (e.g., heat waves). These changes fundamentally alter the response of Tw to climate change, posing additional stressors on fauna.

A thermodynamics-based versatile evapotranspiration estimation method of minimum data requirement for water resources investigations

A recent, two-parameter version of the thermodynamically derived complementary relationship (CR) of evaporation has been tested on a monthly basis at 124 FLUXNET stations around the globe. Local, station-by-station calibration explained 91% (R2) of the variance in eddy-covariance (EC) obtained latent-heat fluxes with the same Nash-Sutcliffe efficiency (NSE) value. When the dimensionless Priestley-Taylor parameter (α) was expressed as a universal function (f) of the estimated wet-environment air temperature (Tw), station-by-station calibration of the single dimensionless parameter, b (accounting for moisture advection), yielded an R2 value of 87% and NSE of 86%. Global calibration (all stations at once) of the two-parameter CR version yielded R2 = 82% and NSE = 81%, while the single-parameter version produced R2 = 81% and NSE = 79%. With a representative value (between the locally calibrated mode and mean) of b set equal to two, the thus, calibration-free CR still maintained an R2 of 80% and NSE of 78%, which is significantly better than Morton’s calibration-free WREVAP model (i.e., 71% and 55%, respectively). The advantage of the current CR model is that it can be employed in a fully calibration-free mode, similar to WREVAP, yet with available EC measurements or water-balance derived latent-heat fluxes the single [b, when α = f(Tw) is chosen] or two parameters (α and b) of the model can be easily calibrated within the respective 1 – 1.32 and 1 – 10 intervals, for further improved performance.

Outdoor Thermal Environment Regulation of Urban Green and Blue Infrastructure on Various Types of Pedestrian Walkways

Urban green and blue infrastructure (GBI) is effective in urban heat mitigation. However, the diurnal variations in the thermal regulation of GBI on different types of urban pedestrian walkways in the subtropical humid climate zone are unclear. Based on traverse measurements in January 2022, this study investigates how outdoor air temperature (Ta) and wet-bulb temperature (Tw) at the pedestrian level are affected by various urban morphology and GBI characteristics in the central urbanized area of Guangzhou (China). Six building-related, three vegetation-related, and three water-related parameters were applied in the analyses. Results show that green infrastructure (GI) has the strongest cooling effect (Pearson’s coefficient r = −0.33~−0.54) on Ta on cloudy evenings and the weakest cooling effect (r = −0.22~−0.32) on clear evenings. Blue infrastructure (BI) exhibits the highest correlations with the cooling effect for Ta on clear afternoons (r = −0.35~−0.51) and weaker, but more consistent, correlations throughout cloudy days (r = −0.23~−0.43). Strong correlations between GI and Tw cooling are observed in the morning and evening on clear days (r = −0.13~−0.48), while BI exhibits the strongest correlation with Tw cooling on clear afternoons (r = −0.13~−0.37). In addition, both GI and BI show a greater cooling effect on both Ta and Tw in low-rise areas compared to high-rise areas. Compared to the individual GI or BI, the integrated GBI has a higher cooling intensity for both Ta and Tw in high-rise areas. However, the cooling potential of integrated GBI is slightly lower for both Ta and Tw during noon and afternoon in low-rise areas. The findings of this study give insights into urban GBI planning and design of specific urban microclimate regulation strategies.

Effect of wall temperature in streamwise supersonic corner flow

The interaction between corner flow and heat transfer is very common in the internal and external flow of hypersonic vehicle surface, but it is not clear how the wall thermal boundary condition affects the supersonic corner flow boundary layer. In the present study, the Reynolds stress model is used to solve the Reynolds-averaged Navier–Stokes equations. The results show that when the symmetrical wall temperature Tw is less than or equal to the recovery temperature Taw, the mean velocity profile in the corner zone is similar to the plate zone, and the temperature is higher in the corner zone. At heating wall condition of Tw>Taw, both velocity and temperature profile of outer corner boundary layer are different from that in the plate zone. The near-wall temperature distribution increases relatively, and the temperature profile is no longer similar to the law of the wall when Tw rises. Along the spanwise wall, the deviation of the velocity–temperature quadratic curve and the generalized Reynolds analogy (GRA) relation is within 10%. In the supersonic corner flow, the velocity–temperature relation under non-adiabatic wall condition satisfies the GRA relation. The effect of wall temperature on corner boundary layer velocity and temperature is significant. It is necessary to consider wall thermal boundary condition in the supersonic corner flow boundary layer analysis.

Experimental analysis of heat transfer characteristics of static water pool under low pressure vaporization

Low pressure vaporization (LPV) is considered a promising method for rapid cooling and a significant rate of water vaporization. This article presents an experimental investigation for the detailed heat and mass characterization of a static water pool exposed to low pressure conditions. An LPV experimental setup has been fabricated in the lab to investigate the effect of process parameters like initial temperature (Tw,0), initial vacuum tank pressure (Pv,0), and the water pool height (Hw,0) on the non-equilibrium fraction (NEF) and heat transfer coefficient (hv). Results shows that NEF initially increased to a high value and then tediously dropped. The final value of NEF decreased with decreasing the initial vacuum tank pressure and initial water pool height inside the flash chamber. A maximum value of the hv existed with the rise of the degree of superheat (ΔT) of liquid. It is found that with an increase of the degree of superheat by 13.44 °C, the value of hv is enhanced by 67%, and the NEF decreased by 46.7%, respectively.

Local hydrothermal characteristics and temperature uniformity improvement of microchannel heat sink with non-uniformly distributed grooves

In order to improve the temperature uniformity of bottom walls, a novel design of microchannel heat sink with From-Sparse-To-Dense embowed grooves (MC-FSTD) was proposed as well as a comparative one with From-Dense-To-Sparse embowed grooves (MC-FDTS). The local hydrothermal characteristics and temperature distribution variance of bottom wall of microchannel heat sinks were numerically investigated for Reynolds number (Re) ranging from 100 to 800. The results showed that the denser grooves led to lower flow velocity, lower local friction factor and higher local pressure as well as the lower bottom wall temperature (Tw) and higher local Nusselt number (Nuz). The local Nusselt number and the bottom wall temperature of MC-FSTD were 2.17 times higher and 9.1K lower than that of MC-SC at z = 10 mm, respectively. MC-FSTD also had the most uniform temperature of the bottom wall and the corresponding temperature variance was 6.42 times lower than that of MC-SC at Re = 795.38. The heat transfer entropy generation rate and the total entropy generation rate of MC-FSTD were also the lowest with an acceptable friction entropy generation rate. Finally, the effects of the decreasing magnitude (Li) of the distance between two adjacent grooves on the local hydrothermal characteristics and temperature uniformity of MC-FSTD were explored and the total entropy generation rate was further reduced to 5.22 × 10−4 W/K at Li = 0.015 mm and Re = 795.38.

Interfacial heat transfer and boiling transition of the droplets on superheated surface with Leidenfrost effects

This study, a novel three-dimensional (3D) method is developed to address the Leidenfrost effect issues with a focus on the synergies of droplet velocity (v) and surface temperature (Tw). Here, we proposed a 3D computational fluid dynamics numerical simulation that combines a VOF model and an amended evaporation model and performed high-speed video testing for capturing vapor dynamics details and distinguish anisotropic heat transfer on a high-temperature surface near the Leidenfrost point. The results revealed that the law of the dynamic Leidenfrost point (TDLT) was predominated by changes in the thickness and shape of the vapor layer. Additionally, coexistence of v and Tw produced a vapor layer, instantly disentangling the boiling state and initiating a gradual change from contact boiling to film boiling, with v affecting the boiling state transition and delaying buildup of the vapor layer aggregation. We determined the empirical correlation of TDLT with the Weber number (We) as follows: TDLT=376.65+84.45×We0.22. Moreover, the high Tw promoted vapor layer formation, thereby decreasing the heat transfer efficiency, whereas the large v inhibited vapor layer formation and enhanced interfacial heat transfer. These findings contribute to a better understanding of the theoretical basis for inhibiting the Leidenfrost effect.

Performance of single slope solar still with various operation parameters—An experimental, statistical, and CFD simulation approach toward optimality

Potable water is a basic need in various aspects of daily life. The conversion of brackish water to potable water through conventional sources is costly and environmental issues are associated. In this regard, solar energy is a preference over fossil fuel or another energy source because of its cost and environment. Therefore, solar still is very popular, but the performance still must be improved to meet our potable water demand. In the present work, the productivity of the still is tested with various operational parameters such as glass plate inclination 27°, 28°, and 29°, and basin heat absorption capacity was also observed with sand, clay sand, and granite for water yield. Water yielding is also affected by water depth in basing investigated as 2, 3, and 4 cm for productivity. Performance of still with various operation parameters was analyzed by using RSM (response surface methodology). The process optimization to get maximum output was analyzed through the RSM technique to save time and effort for experiments. After analysis, a better yield of 630 mL may be obtained with clay sand at 27° glass inclination and 2 cm water depth. The analyzed optimum parameters were validated through experimental data. This optimum condition was also verified by CFD analysis by using ANSYS Fluent v17, in which glass temperature ( TG) and water temperature ( Tw) variation was noted, and water yielding was found proportional to the heat transfer coefficient. The economy of the operation was calculated as 2.87 Rs/liter best price of yielded distilled water with clay sand.

Increased heat risk in wet climate induced by urban humid heat.

Cities are generally warmer than their adjacent rural land, a phenomenon known as the urban heat island (UHI). Often accompanying the UHI effect is another phenomenon called the urban dry island (UDI), whereby the humidity of urban land is lower than that of the surrounding rural land1-3. The UHI exacerbates heat stress on urban residents4,5, whereas the UDI may instead provide relief because the human body can cope with hot conditions better at lower humidity through perspiration6,7. The relative balance between the UHI and the UDI-as measured by changes in the wet-bulb temperature (Tw)-is a key yet largely unknown determinant of human heat stress in urban climates. Here we show that Tw is reduced in cities in dry and moderately wet climates, where the UDI more than offsets the UHI, but increased in wet climates (summer precipitation of more than 570 millimetres). Our results arise from analysis of urban and rural weather station data across the world and calculations with an urban climate model. In wet climates, the urban daytime Tw is 0.17 ± 0.14 degrees Celsius (mean ± 1 standard deviation) higher than rural Tw in the summer, primarily because of a weaker dynamic mixing in urban air. This Tw increment is small, but because of the high background Tw in wet climates, it is enough to cause two to six extra dangerous heat-stress days per summer for urban residents under current climate conditions. The risk of extreme humid heat is projected to increase in the future, and these urban effects may further amplify the risk.

Factors controlling the changes in surface water temperature in the Ebro River Basin

Study regionThe Ebro River Basin, northeast Spain. Study focusThe work analyzes the evolution of water temperature (Tw) in the Ebro River and its main tributaries, its annual cycle and its trends, as well as the effects of various natural and anthropogenic factors on them. New hydrological insights for the regionStations located downstream of nuclear power plants showed an anomalous increase in Tw not consistent with the river section where they are located, with higher values in the lower-flow months (August to December). The stations affected by the main reservoirs along the Ebro River showed a lower annual temperature range and the stations located in large irrigation systems showed a lower summer temperature compared to other stations with similar climatic conditions. Finally, there was a significant annual increase in Tw at all stations (mean ∆Tw=0.05 °C/year), except those located at the head of the tributaries. These trends were higher for the stations downstream of the Ascó nuclear power plant (∆Tw > 0.08 °C/year). Seasonally, the spring months showed the greatest changes, with higher increases at the stations downstream of Ascó (∆Tw ≥ 0.10 °C/year). The increase in air temperature associated with global warming and the decrease in flows associated with the increase in water consumption resulted in an increase in the temperature of the river.

Theoretical profiles of two-phase transcritical laminar boundary layer near the Widom line

Boundary layers can be defined as sub-, trans-, and supercritical regime according to whether their temperature profiles cross the Widom line. The transcritical boundary layers which contain liquid and supercritical phases are hard to solve. In this paper, adiabatic flat plate laminar boundary layers of supercritical carbon dioxide (SCO2) are preliminarily explored by the self-similar solution. We analyze the difference of boundary layer profiles at 8 MPa - inflow pressure by varying inflow temperature Te and Mach number Ma. The influence of Te and Ma on the velocity profiles exhibits complex diversity at three boundary layer regimes. Compared with subcritical and supercritical boundary layers, transcritical boundary layers with smaller skin friction coefficients are the most special, and they include the “sub-layer”. Notably, there is no transcritical boundary layer when Te increases to pseudo-critical temperature Tpc at small Ma. The wall temperature Tw of transcritical boundary layers may be greater than inflow total temperature T0 at larger Ma.

Phase transitions and droplet shapes above a wetting stripe

We consider fluid adsorption on a planar wall patterned by a single stripe of width L of a wet material imbedded within a partially wet surface. If L were infinite we suppose that the wall would exhibit a first-order wetting transition at temperature Tw, and an associated line of pre-wetting transitions extending off bulk-coexistence. For finite widths L, we a) determine the finite-size scaling shift of the wetting temperature Tw(L), b) derive an equation, analogous to the Kelvin equation for capillary condensation, for the shift of the pre-wetting line but involving boundary tensions and a boundary contact angle and c) highlight the scaling and conformally invariant properties of condensed liquid drops lying above the stripe at bulk coexistence. We point out analogies between these predictions and those for capillary condensation and criticality in a parallel plate geometry and test them against numerical results obtained from a microscopic non-local classical density functional theory.

Improvement of thermal performance and energy efficiency of micro-thermophotovoltaic with the dual-inlet combustor at appropriate equivalence ratio

Micro-thermophotovoltaic is facing challenge caused by small size, large area-volume proportion and heat loss ratio, reducing the burning stability and output power. So, the dual-inlet combustors with exit-step and porous medium are proposed for micro-thermophotovoltaic system. Effects of equivalence ratio, exit-step and porous medium setting on combustion characteristic and thermal performance are conducted and analyzed. Results demonstrate that 1% air in the second-inlet is conducive to releasing heat of combustion and optimizing wall temperature distribution, where the total equivalence ratio of H2/air keeps 1.0. Furthermore, the exit-step with applicable length and channel height can generate heat recirculation and enhance working performance of micro-combustor, while the employment of porous medium can further enhance heat transmission of gas-wall and boost the radiation temperature Tw. Combustor CP13 with porosity ε = 0.85 obtains the highest average Tw of 1273.9 K at mf = 3.376 × 10-5 kg/s. With the increase of mf, system efficiency of the combustor with porous medium is increased, while that with exit-step reaches the maximum at mf = 4.501 × 10-5 kg/s. The highest output electrical power and efficiency are appeared in combustor CP15 with ε = 0.95 at mf = 5.626 × 10-5 kg/s, that is, 4.2 W and 2.2%.

Assessment of the Current Trophic Status of the Southern Baikal Littoral Zone

Eutrophication is a major ecological problem and affects and endangers freshwater bodies, making assessment of the trophic status of water bodies crucial for their restoration and sustainable use. Lake Baikal is affected by a number of environmental stressors, including coastal eutrophication. Daily measurements of concentrations of nutrients, dissolved oxygen (DO), chlorophyll-a (Chl-a), weekly measurements of algae abundance and biomass in the open water season in June-December 2020, and measurements of concentrations of nutrients at 2–7-day intervals in June-October 2021 were made in the littoral of the South Baikal for the first time. It was shown that nitrate and phosphate concentrations decreased by July-August, their minimum content was maintained until September, concentrations began to increase in October and reached a maximum in December. The maximum abundance and biomass of algae and chlorophyll concentrations were only observed in early July. Storm situations increased the content of nitrogen, phosphorus and DO in water, the duration of their influence was not more than 2 days. A correlation matrix revealed significant positive correlations of NO3−-DO, phosphate (SPR)-NO3−, SRP-DO and biomass-Chl-a and strong negative correlations between water temperature (Tw)-DO, Tw-NO3−, Tw-total nitrogen (TN) and Tw-SRP. Based on SRP and NO3− concentrations and TN:TP ratios, it was concluded that algal development was limited to nitrogen and phosphorus in summer. The trophic status of the Southern Baikal littoral zone was assessed using classifications based on TN, TP, NO3−, SRP, Chl-a content and algal biomass, as well as the Carlson index (TSI) and probabilistic assessment. The results of assessments using different methods of trophic status determination showed that the Baikal littoral zone in the study area belongs to the oligotrophic type with minor elements of mesotrophy. According to the saprobity index, water purity of littoral waters varies within the oligosaprobic and β-mesosaprobic zones and corresponded to quality classes II and III (clean and moderate purity); the system demonstrates a high capacity for self-purification.

Emergent Scaling of Dissolved Oxygen (DO) in Freshwater Streams Across Contiguous USA

AbstractDissolved oxygen (DO) indicates the overall stream water quality and ecosystem health. We investigated emergent scaling of DO with the dominant environmental drivers in freshwater (non‐coastal) streams across the contiguous United States. Available data of monthly to quarterly sampling frequencies during 1998–2015 were obtained for 86 U.S. streams. Data analytics indicated water temperature (Tw) and pH (a proxy of carbon dioxide) dominating the key environmental process components of DO concentrations in the freshwater streams. The “climatic” process component (comprising Tw and net radiation) had, respectively, ∼3 and ∼9 times stronger control on DO than the “biogeochemical” (total nitrogen, total phosphorus, pH, and specific conductivity) and “hydro‐atmospheric” exchange (stream flow and atmospheric pressure) components. The predominant climatic control on stream DO was linked to the high extent of vegetated land (on average ∼53%) and steep slope (∼10%) in the draining watersheds, despite the notable presence of agricultural land (∼35%). An emergent power law scaling relationship was then developed to acceptably predict DO (mg/l) based on Tw (K) and pH, with the approximate exponents of −15/2 and 1/2, respectively (Nash‐Sutcliffe Efficiency = 0.72–0.73). The scaling law demonstrated the underlying organizing principles such as the depletion of stream DO due to reduced dissolution and increased metabolic respiration with the increasing temperature and nutrients. The scaling law was persistent across the various U.S. streams, representing gradients in climate, hydrology, biogeochemistry, and land use/cover. The findings would help understand and manage water quality and ecosystem health in freshwater streams across the United States and beyond.

Remote sensing of dissolved CO2 concentrations in meso-eutrophic lakes using Sentinel-3 imagery

Satellite observation can significantly reduce the uncertainties in CO2 emission estimations compared to insufficient field data. However, big challenges remain in developing remote sensing-based models for mapping concentrations of dissolved carbon dioxide (cCO2) in lakes at regional or global scales. We developed a cCO2 estimation model using Sentinel-3-derived lake environmental variables and near-synchronous field cCO2 data from 16 lakes in the middle and lower reaches of the Yangtze and Huai River (ML_YHR) basins in Eastern China (N = 248). Stepwise quadratic polynomial regressions of several combinations of chlorophyll-a (Chl-a), water temperature (Tw), Secchi disk depth (ZSD), and photosynthetic active radiation (PAR)-related variables were tested and validated to select the best approach. The final model showed high performance in calibration and validation (R2 > 0.72, RMSE < 6.35 μmol L−1, MAPE < 30.31%). The model sensitivity analysis, based on Monte Carlo simulations, showed the model's estimated bias as <25% based on uncertainties of all input variables. Spatial and temporal dynamics of dissolved CO2 concentrations in 113 lakes (≥ 10 km2) in the ML_YHR basins were mapped from 2016 to 2021 using the Sentinel-3 data. The result showed that CO2 concentrations were low in the summer and autumn but high in the winter and spring with dramatic variations (e.g., mean coefficient of variation: 52.59%). The annual mean CO2 concentrations of lakes revealed that about 28% of the lakes acted as weak atmospheric CO2 sinks (14.96 ± 1.13 μmol L−1) while the rest were sources (19.22 ± 2.02 μmol L−1), compared with a mean concentration of CO2 atmospheric equilibrium (16.29 μmol L−1). CO2 concentrations decreased with increasing eutrophication and decreasing lake size (p < 0.05). This study advances current knowledge about CO2 emissions from emerging meso-eutrophic lakes and shows how satellite remote sensing can expand the spatiotemporal coverage of lake CO2.

Modelling spatial and temporal variability of water temperature across six rivers in Western Canada

AbstractIncreasing river water temperature in response to the warming climate is concerning for water quality and ecosystem health of rivers. This study provides an assessment of the spatio‐temporal variability of the ongoing and potential future river water temperature (Tw) change in western Canada. We use the air2stream model to reconstruct historical Tw dataset for 17 stations across six rivers, and employ the reconstructed Tw to analyze hydro‐climatic controls, trends, and sensitivities in relation to air temperature (Ta) and discharge. Results provide insights on the contrasting summer (July and August) Tw responses. While Tw is primarily Ta controlled for the northern rivers, discharge exerts increasing influence that approaches Ta control for the southern rivers. Trends in Tw are increasing and spatially varied, with significant increases and occurrences above the critical 18 and 20°C thresholds for the southern Fraser and Similkameen Rivers. A sensitivity analysis indicated 0.5–1.5°C Tw increases for a 2.0°C Ta increase, and 0.2–0.6°C Tw increases for a 20% summer discharge decline. Overall, the results provide critical information for understanding the river ecosystem health, such as cold‐water species habitat.

An Empirical Equation for Wet-Bulb Temperature Using Air Temperature and Relative Humidity

Climate change causes extreme heat and high humidity in some regions. The wet-bulb temperature (Tw) is a heat stress index, and the threshold is 35 °C. It is difficult to measure the value of Tw using a psychrometer, but the Tw value can be calculated using the air temperature and humidity. To provide accuracy for the Tw calculation, an empirical equation is established using regression analysis. This study defines the empirical equation as Tw=−4.391976+0.0198197RH+0.526359Td+0.00730271RH·Td+2.4315×10−4RH2−2.58101×10−5Td·RH2, where Td is the air temperature in °C and RH is the relative humidity in %. This equation applies to a temperature of 20~45 °C and RH of 40~99%. The fit is better than that for the Stull equation in this range. The prediction accuracy is 0.022 °C and there is no fixed pattern for the error distribution for the range of Td and RH. The measurement uncertainty for Tw values for thermometer and humidity sensors that are not calibrated is 1.4~2.2%. If these sensors are calibrated, the measurement uncertainty for Tw values is 0.16~0.28 °C. Therefore, well-calibrated sensors are necessary to enhance the accuracy of the Tw predictive equation.