Decrease In Wind Speed Research Articles

Statistical characteristics and mechanism of the South Atlantic Ocean Dipole

AbstractThe statistical characteristics and mechanism of the South Atlantic Ocean Dipole (SAOD) from 1980 to 2021 are analysed using observational datasets. The spatial pattern of the sea surface temperature anomaly (SSTA) during SAOD is a dipole pattern oriented in the northeast‐southwest direction, and the intensity of the SSTA in the northeast pole (NEP) is stronger than that in the southwest pole (SWP). SAOD has a decadal variability of about 12 years during 1980–2007, along with obvious seasonal phase‐locking, with the anomaly pattern developing in boreal spring (March–May), peaking in summer (June–August) and decaying in autumn (September–November). For a positive SAOD event (positive SSTA in the NEP, negative in the SWP), positive SSTA in the NEP grows due to a decrease in wind speed and thus in latent heat flux loss in boreal spring, as well as an increase in shortwave radiation flux from boreal spring to summer. However, southwesterly wind anomalies drive cold water from high latitudes to the SWP in boreal spring and summer, coupled with strong wind speed anomalies enhancing the loss of latent heat flux, which contributes to a negative SSTA in the SWP. In addition, the intensity of the SSTA in the SWP is weaker than that in the NEP because of the contribution of smaller shortwave radiation flux, sensible heat flux and larger mixed layer depth in the SWP in summer. For a negative SAOD mode (negative SSTA in the NEP, positive in the SWP), the wind, shortwave radiation flux, sensible heat flux and mixed layer depth anomalies are the opposite of those under a positive SAOD event.

Contribution rates of climate variables to the change in reference evapotranspiration in northern Thailand from 1991 to 2019

AbstractHigher temperatures are expected to increase evaporation and reference evapotranspiration (ETo). However, a decrease in ETo has been observed in numerous regions worldwide. ETo is controlled by climate variables besides temperature; wind speed, air humidity, and radiation, which vary according to regional climatic conditions, may also be drivers. Few studies have quantified the sensitivity and contributions of climate variables to ETo change in tropical savanna climates. Long‐term (1991–2019) climate time series in northern Thailand was used to assess the trends in ETo and determine which climate variables exert the strongest control on ETo, during the rainy and non‐rainy season, as an example for the tropical savanna climate. Furthermore, this study used the proportion of contribution and sum of positive (negative) contribution and classified the results into five groups to analyse the change in ETo. This helped to determine the climate variable with the highest contribution. From this study, ETo was the most sensitive to the maximum temperature, followed by sunshine duration in both rainy and non‐rainy seasons. Furthermore, the variables that contributed the most to the long‐term change in ETo were sunshine duration and wind speed. The increase (decrease) in sunshine duration and wind speed contributed to the increase (decrease) in ETo in this area. Understanding ETo changes and determining whether ETo has a strong tendency to change are the basis for water resource planning and management in the region.

Why do algal blooms intensify under reduced nitrogen and fluctuating phosphorus conditions: The underappreciated role of non‐algal light attenuation

AbstractLight availability for phytoplankton in shallow lakes is closely related to non‐algal light attenuation (KdNALA, the fractional light absorption by non‐algal substances, such as suspended sediments); thus, significant changes in global wind speed in recent decades may have a profound effect on light availability and algal blooms in shallow lakes. Herein, the eutrophic shallow Lake Taihu was selected to investigate the long‐term dynamics of light availability and its effect on algal blooms. The results showed that KdNALA decreased from approximately 3.5 to 2.5 m−1 with decreasing wind speed from 2005 to 2021, indicating the significantly increased light availability for phytoplankton despite surface photosynthetically active radiation exhibiting limited variability during the study period. In addition, both experimental (i.e., in situ nutrient enrichment experiments) and statistical approaches (i.e., deviations of Trophic State Index subindices) indicated that phytoplankton growth was primarily light‐limited during the study period in Lake Taihu. Consequently, considerable increases in fraction of observed and maximal chlorophyll a yield at given nitrogen or phosphorus concentration were observed and were mostly related to decreasing KdNALA, which implied that decreasing KdNALA allowed phytoplankton utilize “unused nutrient‐capacity” until the additional algal‐turbidity induce further light limitation or nutrient limitation. As the effect of changes in global wind speed on KdNALA and algal growth received limited attention in the existing research, we revealed an underappreciated mechanism by which global changes in wind speed significantly affects algal biomass by influencing light availability, which may have profound effects on future algal bloom mitigation efforts in shallow lakes.

Early-age shrinkage behavior of cement-fly ash paste under wind speeds: A study using BSE-IA and MIP techniques

While laboratory studies have shown that fly ash (FA) can reduce shrinkage in cement-based materials in the absence of wind, its impact on cement-based materials under wind speed conditions has not been extensively studied. This research investigates the influence of FA on the early-age shrinkage of cement paste under various wind speeds. The corresponding changes in pore structure were tested using mercury intrusion porosimetry (MIP) and backscattered electron image analysis (BSE-IA). The results show that under wind speed conditions, FA is not effective in reducing early-age shrinkage of cement paste. In fact, high levels of FA content can increase shrinkage values under wind speed conditions. Both wind speed and FA increase water evaporation, but they have different impact times. Although both wind speed and FA decrease mesopore content below 50 nm and increase water evaporation, they have opposite effects on early-age shrinkage. This suggests that mesopore content and water evaporation alone cannot fully characterize the change trend of early drying shrinkage. The two-factor parameter rs, which combines water evaporation and MIP-based pore size distribution, can effectively characterize drying shrinkage trends under the combined effects of wind speed and FA. BSE-IA can intuitively characterize pore size distribution above 200 nm, while the results of MIP underestimate the distribution of large capillary pores. Therefore, the current rs obtained based on MIP may be smaller than the actual value. With the advancement of testing technology in the future, rs can be further optimized.

Experimental study on wind characteristics and prediction of mean wind profile over complex heterogeneous terrain

This study investigates the impact of complex heterogeneous terrain on mean wind speed and turbulence intensity, highlighting the significance of terrain configuration in the wind loading on buildings and airflow over urban areas. Extensive wind tunnel tests were conducted for 60 different roughness configurations, obtained by processing aerial images across the United States. The study makes two main contributions. First, a model was proposed to predict mean wind profiles, using the morphological information of complex heterogeneous terrain. The Deaves and Harris model was utilized along with a novel algorithm for the automatic characterization of roughness transitions. The proposed model exhibited less than 2% average prediction error compared to the measured wind speed. Second, the study investigated the impact of terrain complexity on near-surface wind characteristics. By comparing the experimental results with those obtained from a homogeneous terrain with a similar roughness length, we quantified the potential errors that may arise when assuming a homogeneous terrain for wind speed assessment. It was observed that increasing variability in roughness length led to a decrease in mean wind speed and an increase in turbulence intensity. The influence of terrain complexity, however, was found to be secondary compared to roughness length. Consequently, the relationships between terrain complexity and wind characteristics were quantified, and a simplified model was proposed.

Long-Term Trends of Astroclimatic Parameters above the Terskol Observatory

Astroclimatic conditions characterize the quality of an astronomical site. The Terskol Observatory was founded over 42 years ago in 1980. The astronomical site (coordinates 43°16′29″ N, 42°30′03″ E) is located about 10 km from Mt. Elbrus in the northern Caucasus Mountains. The paper presents the results of an analysis of long-term variations from 1980 to 2022 of astroclimatic parameters such as total cloud cover, precipitable water vapor, and wind speed at a level of 200 hPa above the Terskol Observatory using atmospheric ERA5 Reanalysis data from the European Center for Medium-Range Weather Forecast. The probability distributions and seasonal variations of the astroclimatic parameters are also presented. Long-term trends of the astroclimatic parameters are studied with statistically significant trend analysis methods using the Mann–Kendall test and the Sen’s slope test to estimate the magnitude of the changes. The results show non-significant decreases of annual average 200-hPa wind speed and increases in precipitable water vapor, but significant (99 per cent confidence level) long-term decreasing of total cloud cover above the Terskol Observatory.

Analysis of Dry-Wet Changes and the Driving Factors in Mainland China under Climate Change

Evaluation of changes in dry-wet climate is crucial in the context of global climate change to ensure regional water resources, ecosystem stability, and socio-economic development. Long-term daily meteorological data, including temperature, precipitation, relative humidity, wind speed, sunshine duration, and air pressure data from 1680 stations across mainland China from 1971 to 2019, were collected to investigate the temporal and spatial variations in aridity index (AI), precipitation (P), reference evapotranspiration (ET0), and the underlying driving climatic factors. Results indicated that the Northwest, Northeast, and Huang-Huai regions were undergoing significant wetting processes, while the Southwest and Southeast China were undergoing significant drying processes. The changing AI was mainly decided by the changing trends of ET0. For most regions, ET0 has undergone significant increases. The average increasing rate over mainland China was 3.76 mm/10a. Stations with decreasing trends were mainly located in the Tibet Plateau, Huang-Huai, and northern Northeast China. Trends in ET0 were negatively affected by the increasing changes in relative humidity and positively affected by the decreasing changes in wind speed and sunshine duration and the increasing changes in air temperature. Wind speed and relative humidity were found to be the main dominant factors driving the changes in ET0, and their contribution varied with regions. Huang-Huai and northern Northeast China showed a significant downward trend in ET0, mainly driven by the decrease in wind speed, while the increase in relative humidity was the primary contributor to the significant upward trends in ET0 across all other regions in China.

Potential Impacts of Climate Change on Renewable Energy and Storage Requirements for Grid Reliability and Resource Adequacy

Abstract This paper provides a study of the potential impacts of climate change on intermittent renewable energy resources and storage requirements for grid reliability and resource adequacy. Climate change models and available regional data were first evaluated to determine uncertainty and potential changes in solar irradiance, temperature, and wind speed within a specific U.S. southwest service area as a case study. These changes were then implemented in solar and wind energy models to determine impacts on renewable energy resources. Results for the extreme climate change scenario show that the projected wind power may decrease by ∼13% due to projected decreases in wind speed. Projected solar power may decrease by ∼4% due to decreases in irradiance and increases in temperature. Uncertainty in these climate-induced changes in wind and solar resources was accommodated in probabilistic models assuming uniform distributions in the annual reductions in solar and wind resources. Uncertainty in battery storage performance was also evaluated based on increased temperature, capacity fade, and degradation in round-trip efficiency. The hourly energy balance among electrical load, generation, and storage was calculated throughout the year. The annual loss of load expectation (LOLE) was found to increase from ∼0 days/year to a median value of ∼2 days/year due to potential reductions in renewable energy resources caused by climate change and decreased battery performance. Significantly increased battery storage was required to reduce the LOLE to desired values of 0.2 days/year.

MODIS observations reveal decrease in lake suspended particulate matter across China over the past two decades

Variations in the concentrations and distribution of suspended particulate matter (SPM) of lakes can be used to show the responses of lake environment to climate and landscape change. However, the shifts and trends of SPM and potential drivers have not been well investigated across large spatial and temporal dimensions. This study developed a robust machine learning model to generate SPM time series in 269 lakes across China larger than 30 km2 from 2002 to 2021 using MODIS/Aqua imagery. The support vector regression model showed satisfactory performance on SPM retrievals over four orders of magnitude (0.1–1000 mg L−1) (mean absolute percentage error = 26%). The model performance was shown to be insensitive to changes in environmental and observing conditions (e.g., aerosol type and thickness, viewing geometry), based on a radiative transfer simulation model. The long-term MODIS record showed a spatial pattern of lower SPM in the western lakes compared to the shallow lakes of east China. Importantly, the SPM showed a significant decrease in the 21st century (average rate of change of −0.2 mg L−1/decade). The interannual variations in SPM were aggregated into five categories, ranging from lakes with continuous changing patterns to those with reversed changing patterns. The driving factors behind the changing patterns vary between different climate zones and ecoregions. A warmer and wetter climate was associated with decreasing SPM in western lakes, while the decrease in wind speed and reduced possibility of soil erosion were the primary drivers of progressively lower SPM in the eastern shallow lakes. These results not only show a comprehensive picture of the SPM dynamics of lakes in China but also provide new insights into the complex mechanisms that drive SPM spatiotemporal dynamics.

Effects of Wind Barrier Porosity and Inclination on Wind Speed Reduction

Wind barriers play a vital role in protecting saplings until maturity when planted as vegetative windbreak forests. Most previous studies have focused on the porosity of wind barriers, but no studies have simultaneously examined the effects of the porosity and inclination, despite the potential of the inclination to decrease wind speed. We tested three wind barrier cases in wind tunnel experiments: (1) Case A (porosity of 0% with inclinations (90°, 80°, and 70°)), (2) Case B (porosity of 25% with inclinations (90°, 80°, and 70°)), and (3) Case C (porosity of 50% with inclinations (90°, 80°, and 70°)). The vertical and horizontal wind velocities were measured at three vertical and seven horizontal points behind the barriers. The results demonstrated a statistically significant decrease in the correlation between the distance and mean wind velocity for all cases, with up to a six-fold wind protection effect. The wind barrier with 0% porosity and a 90° inclination provided the highest degree of wind protection. However, the wind protection range was limited downwind, and recirculation of wind flow could occur in the leeward direction, potentially damaging saplings. A wind barrier with 50% porosity and 70° inclination sufficiently decreased the wind velocity and prevented recirculation of wind flow, demonstrating that both porosity and inclination considerably impacted the wind protection effect by reducing wind velocity. Our findings offer novel insights into the influence of wind barriers with varying porosities and inclinations and can provide valuable guidance for constructing efficient windbreak forests.

Multi-model ensemble projection of the global dust cycle by the end of 21st century using the Coupled Model Intercomparison Project version 6 data

Abstract. As a natural aerosol with the largest emissions on land, dust has important impacts on the atmospheric environment and climate systems. Both the emissions and transport of dust aerosols are tightly connected to meteorological conditions and as a result are confronted with strong modulations by the changing climate. Here, we project the changes in the global dust emissions and loading by the end of the 21st century, using an ensemble of model outputs from the Coupled Model Intercomparison Project version 6 (CMIP6) under four Shared Socioeconomic Pathways (SSPs). Based on the validations against site-level observations, we select 9 out of 14 models and estimate an ensemble global dust emissions of 2566 ± 1996 Tg a−1 (1 Tg = 1012 g) for the present day, in which 68 % is dry deposited and 31 % is wet deposited. Compared to 2005–2014, global dust emissions show varied responses, with a reduction of −5.6 ± 503 Tg a−1 under the SSP3–7.0 scenario but increased emissions up to 60.7 ± 542 Tg a−1 under the SSP5–8.5 scenario at 2090–2099. For all scenarios, the most significant increase in the dust emissions appears in North Africa (0.6 %–5.6 %) due to the combined effects of reduced precipitation but strengthened surface wind. In contrast, all scenarios show decreased emissions in the Taklimakan and Gobi deserts (−0.8 % to −11.9 %) because of the increased precipitation but decreased wind speed on a regional scale. The dust loading shows uniform increases over North Africa (1.6 %–13.5 %) and the downwind Atlantic, following the increased emissions but decreases over East Asia (−1.3 % to −10.5 %), and the downwind Pacific, partly due to enhanced local precipitation that promotes wet deposition. In total, global dust loading will increase by 2.0 %–12.5 % at the end of the 21st century under different climate scenarios, suggesting a likelihood of strengthened radiative and climatic perturbations by dust aerosols in a warmer climate.

Arctic polar vortex dynamics during winters 2014/2015 and 2020/2021

The dynamic barrier of the polar vortex contributes to lowering the temperature inside the vortex in the lower stratosphere and prevents the penetration of air masses into the vortex. The presence of a dynamic barrier during winter is one of the criteria determining the possibility of ozone depletion from late winter to spring. We considered the dynamics of the Arctic polar vortex in the winters of 2014/2015 and 2020/2021 at the 50, 30 and 10 hPa levels by the vortex delineation method using the geopotential. In early January 2015 and 2021, sudden stratospheric warmings were recorded as a result of the splitting (4 January 2015) and the significant displacement (5 January 2021) of the polar vortex. In both cases, the weakening of the dynamic barrier of the polar vortex was observed. The polar vortex is characterized by the presence of a dynamic barrier, when the wind speed along the entire edge of the vortex is more than 20, 24 and 30 m/s at the 50, 30 and 10 hPa levels, respectively. A decrease in the average wind speed along the vortex edge below 30, 36 and 45 m/s, at the 50, 30 and 10 hPa levels, respectively, usually indicates a local decrease in the wind speed below 20, 24 and 30 m/s at these levels, i.e., indirectly indicates a weakening of the dynamic barrier.

The unprecedented 2022 extreme summer heatwaves increased harmful cyanobacteria blooms

Heatwaves are increasing and expected to intensify in coming decades with global warming. However, direct evidence and knowledge of the mechanisms of the effects of heatwaves on harmful cyanobacteria blooms are limited and unclear. In 2022, we measured chlorophyll-a (Chla) at 20-s intervals based on a novel ground-based proximal sensing system (GBPSs) in the shallow eutrophic Lake Taihu and combined in situ Chla measurements with meteorological data to explore the impacts of heatwaves on cyanobacterial blooms and the potential relevant mechanisms. We found that three unprecedented summer heatwaves (July 4–15, July 22–August 16, and August 18–23) lasting a total of 44 days were observed with average maximum air temperatures (MATs) of 38.1 ± 1.9 °C, 38.7 ± 1.9 °C, and 40.2 ± 2.1 °C, respectively, and that these heatwaves were characterized by high air temperature, strong PAR, low wind speed and rainfall. The daily Chla significantly increased with increasing MAT and photosynthetically active radiation (PAR) and decreasing wind speed, revealing a clear promotion effect on harmful cyanobacteria blooms from the heatwaves. Moreover, the combined effects of high temperature, strong PAR and low wind, enhanced the stability of the water column, the light availability and the phosphorus release from the sediment which ultimately boosted cyanobacteria blooms. The projected increase in heatwave occurrence under future climate change underscores the urgency of reducing nutrient input to eutrophic lakes to combat cyanobacteria growth and of improving early warning systems to ensure secure water management.

Wind-induced fragility of a group of three gable-roof buildings with different roof slope and building spacing

The influence of the roof slope, building spacing, building orientation and joint probability of wind speed and direction on the wind-induced fragility (WIF) of a group of three gable-roof buildings was investigated. The results show that wind interference effects on the WIF of buildings are significant. The dependency of the WIF of buildings with a small roof slope of 10° is nearly opposite from that with a large roof slope of 35°. When the roof slope is 10°, wind shielding effects make the WIF of the center and downstream buildings less than that of the isolated building, the WIF decreases with the decrease of building spacing, and the maximum increase of the minimum critical wind speed among all wind directions reaches 14.1%. When the roof slope is 35°, wind amplification effects make the WIF of the upstream and center buildings greater than that of the isolated building, the WIF increases with the decrease of building spacing, and the maximum decrease of the minimum critical wind speed is 7.2%. When the buildings are located in Fuzhou, the WIF reaches the minimum (it means the most favorable building arrangement) for buildings with a roof slope of 10°, and it reaches the maximum (it means the most unfavorable building arrangement) for buildings with a roof slope of 35° at the building orientation of about 30° with a small building spacing.

The Variability of Pan Evaporation over China during 1961–2020

Abstract The most basic features of climatological normals and variability are useful for describing observed or likely future climate fluctuations. Pan evaporation (Epan) is an important indicator of climate change; however, current research on Epan has focused on its change in mean rather than its variability. The variability of monthly Epan from 1961 to 2020 at 969 stations in China was analyzed using a theoretical framework that can distinguish changes in Epan variance between space and time. The Epan variance was decomposed into spatial and temporal components, and the temporal component was further decomposed into interannual and intra-annual components. The results show that the variance in Epan was mainly controlled by the temporal component. The time variance was mainly controlled by intra-annual variance, decreasing continuously in the first 30 years, and slightly increasing after the 1990s. This is mainly due to the fact that the decrease of wind speed and the increase of water vapor pressure deficit with the temperature increase offset each other and inhibit the variability of Epan. The variance decreased more in the northern region, whereas it exhibited a small decrease or slight increase in the southern region. The reduction in seasonality was dominated by spring, followed by summer. The differences in Epan variability in space and season were mainly caused by the differing rates of change in evaporation driving forces, such as a greater reduction in wind speed in the northern region and spring. Significance Statement The purpose of this study is to better understand how the variability of evaporation changes rather than in mean under climate change. This is important because the variability is useful to describe the observed or likely future fluctuations, and a small fluctuation may have large impacts on water practices, such as agricultural production. Our findings showed that the temporal and spatial variability of evaporation decreased due to its drivers offsetting each other. However, because the drivers are numerous and continuously changing under climate change, it is necessary to pay attention to its mean and variability for serving water resources practice.

Observing Tropical Cyclone Morphology Using RADARSAT-2 and Sentinel-1 Synthetic Aperture Radar Images

Abstract Since the 1960s, meteorological satellites have been able to monitor tropical cyclones and typhoons. Their images have been acquired by passive remote sensing instruments that operate in the visible and infrared bands, where they only display the cloud-top structure of tropical cyclones and make it a challenge to study the air–sea interaction near the sea surface. On the other hand, active remote sensors, such as spaceborne microwave scatterometers and synthetic aperture radars (SARs), can “see” through clouds and facilitate observations of the air–sea interaction processes. However, SAR acquires images and provides the wind field at a much higher resolution, where the eye of a tropical cyclone at surface level can be identified. The backscattered signals received by the SAR can be processed into a high-resolution image and calibrated to represent the normalized radar cross section (NRCS) of the sea surface. In this study, 33 RADARSAT-2 and 102 Sentinel-1 SAR images of Atlantic and Indian Ocean tropical cyclones and Pacific typhoons from 2016 to 2021, which display eye structure, have been statistically analyzed with ancillary tropical cyclone intensity information. To measure the size of the eye, a 34-kt (∼17 m s−1) contour is defined around it and the amount and size of pixels within the eye is utilized to provide its area in square kilometers. Additionally, an azimuthal wavenumber for each shape of the eye was assigned. Results showed that eye areas increase with decreasing wind speed and increasing wavenumber and demonstrate that SAR-derived data are useful for studying tropical cyclones at the air–sea interface and provide results of these behaviors closely to data derived from best track archives.

Effects of Mesoscale Eddies on the Intensity of Cyclones in the Mediterranean Sea

AbstractThe Mediterranean Sea is a relatively small basin with complex, unique topography and has long been considered a hot spot for cyclones. This sea is also characterized by intense mesoscale eddy activity. Although eddies are known to play important roles in cyclones in other regions, their effects on Mediterranean cyclones have not received much research attention. Here, we analyzed how warm‐core eddies (WCEs) and cold‐core eddies (CCEs) interact with Mediterranean cyclones. We considered eight Mediterranean cyclones: four that passed over WCEs and four that passed over CCEs. In general, we observed sudden drops in Mean Sea level (MSL) pressure and increased wind speeds over the WCEs and increased MSL pressure and decreased wind speeds above the CCEs. The temperature of the mixed layer decreased after a cyclone passed over an eddy, but this occurred to a lesser extent for CCEs. In contrast, mixed‐layer salinity decreased in the case of WCEs and increased in the case of CCEs. Larger amounts of precipitation were observed over WCEs, as compared to CCEs. The amount of precipitation associated with a WCE seemed to depend on the area and intensity of the eddy; larger, more intense eddies were associated with larger amounts of precipitation. Also, higher latent and sensible heat fluxes were observed over WCEs, as compared to CCEs, which could be responsible for the sudden increases in cyclone intensity. Interestingly, only one persistent WCE was found in the winter; whereas no persistent CCEs were found in the summer, calling for further case‐by‐case detailed investigation.

The Role of Vegetation on Urban Atmosphere of Three European Cities—Part 1: Evaluation of Vegetation Impact on Meteorological Conditions

This study quantifies the vegetation impact on urban meteorology by means of the numerical model WRF (Weather Research and Forecasting model). The assessment was made for two months: July and January. These were considered as representative for the summer and winter seasons, for the reference year 2015 in three European cities: Bologna, Milano, and Madrid. Two simulations at 1 km resolution were conducted over the cities with and without the actual urban vegetation, called VEG and NOVEG, respectively, in the model input. Then, the impact of vegetation was evaluated as the difference between the two simulations (VEG-NOVEG) for temperature, relative humidity, and wind speed fields. In general, we found that, as can be expected, urban vegetation tends to cool the atmosphere, enhance the humidity, and reduce the wind speed. However, in some cases, areas with the opposite behaviour exist, so that no a priori results can be attributed to the presence of urban vegetation. Moreover, even when major impact is confined around grid cells where urban vegetation is present, changes in meteorological quantities can be observed elsewhere in the city’s area. The magnitude of urban vegetation impact is higher in summer than in winter and it depends on the city’s morphological peculiarities, such as urban texture and vegetation types and distribution: average July temperature variations due to the presence of urban vegetation reach peaks of −0.8 °C in Milano, −0.6 °C Madrid, and −0.4 °C in Bologna, while in January, the values range between −0.3 and −0.1 °C. An average heating effect of ca. +0.2 °C is found in some parts of Madrid in January. For relative humidity, we found increments of 2%–3% in July and 0.5%–0.8% in January, while a decrease in wind speed was found between 0.1 and 0.5 m/s, with the highest occurring in Madrid during July.

Comparisons of the Urbanization Effect on Heat Stress Changes in Guangdong during Different Periods

While rapid urbanization promotes social and economic development, it exacerbates human outdoor thermal comfort, which increases the risks to human health. This paper uses four thermal comfort indices and multiple satellite observations to explore the urbanization effect on summer heat stress in Guangdong from 1979–2018, a coastal province of China. Two types of thermal comfort index are used here, namely the direct thermal comfort index (Heat Index, HI; Temperature–Humidity Index, THI; Discomfort Index, DI) and the physiological thermal comfort index (Universal Thermal Climate Index, UTCI). We compare the differences in the urbanization effects on the changes in the three direct thermal comfort indices (HI, THI, and DI) and a physiological thermal comfort index (UTCI). The results show that all four thermal comfort indices indicate an overall warming trend. Of them, urban sites show a higher warming trend than rural sites, indicating that heat stress changes are significantly influenced by urbanization from 1979–2018, which is consistent with the effect of urbanization on surface air temperature. However, except for the UTCI, this warming of direct thermal comfort indices affected by urbanization has become insignificant under the regional vegetation greening from 2004–2018 (also consistent with surface air temperature). This is primarily attributed to the different effects of wind speed on the physiological thermal comfort index in urban and rural areas: Decreasing wind speeds in urban areas lead to an increase in UTCI, while wind speeds in rural areas increase instead and decrease UTCI, thus widening the UTCI differences between urban and rural areas. Our results indicate that urbanization has a different effect on thermal comfort indices. When using the thermal comfort index, it is necessary to consider that different thermal comfort indices may bring different results. UTCI considers more factors that affect human heat perception, so it can better describe human outdoor thermal comfort. It also highlights the importance of urban ventilation and urban greenness in mitigating urban outdoor thermal comfort in the sustainable construction of future urbanization in coastal cities.

Comparing thermal conditions inside and outside lactating dairy cattle barns in Canada

The health, longevity, and performance of dairy cattle can be adversely affected by heat stress. This study evaluated the in-barn condition [i.e., temperature, relative humidity, and resulting temperature-humidity index (THI)] at 9 dairy barns with various climates and farm design-management combinations. Hourly and daily indoor and outdoor conditions were compared at each farm, including both mechanically and naturally ventilated barns. On-site conditions were compared with on-farm outdoor conditions, meteorological stations up to 125 km away, and NASA Power data. Canadian dairy cattle face periods of extreme cold and periods of high THI, dependent on the regional climate and season. The northernmost location (53°N) experienced about 75% fewer hours of THI >68 compared with the southernmost location (42°N). Milking parlors had higher THI than the rest of the barn during milking times. The THI conditions inside dairy barns were well correlated with THI conditions measured outside the barns. Naturally ventilated barns with metal roofs and without sprinklers fit a linear relationship (hourly and daily means) with a slope <1, indicating that in-barn THI exceeded outdoor THI more at lower THI and reached equality at higher THI. Mechanically ventilated barns fit nonlinear relationships, which showed the in-barn THI exceeded outdoor THI more at lower THI (e.g., 55-65) and approached equality at higher THI. In-barn THI exceedance was greater in the evening and overnight due to factors such as decreased wind speed and latent heat retention. Eight regression equations were developed (4 hourly, 4 daily) to predict in-barn conditions based on outdoor conditions, considering different barn designs and management systems. Correlations between in-barn and outdoor THI were best when using the on-site weather data from the study, but publicly available weather data from stations within 50 km provided reasonable estimates. Climate stations 75 to 125 km away and NASA Power ensemble data gave poorer fit statistics. For studies involving many dairy barns, the use of NASA Power data with equations for estimating average in-barn conditions in a population is likely appropriate especially when public stations have incomplete data. Results from this study show the importance of adapting recommendation on heat stress to the barn design and guide the selection of appropriate weather data depending on the aim of the study.