Canopy Air Temperature Research Articles

Effects of Reduced Substrate Volumetric Water Contents on the Morphology and Physiology of Three Landscape Shrubs Grown in a Greenhouse

Reduced precipitation and increasing temperatures caused by climate change have escalated the irrigation requirements for maintaining the aesthetic quality of urban landscape plants. Many cities in the western United States now mandate the incorporation of drought-tolerant plants in new landscapes because of concerns regarding water scarcity. However, a knowledge gap persists regarding the drought tolerance of ornamental plant species commonly used in urban landscapes. The objectives of this study were to determine the effects of decreased volumetric water contents on the morphology, physiology, and plant growth of Rosa ×hybrida ‘Meibenbino’ (Petite Knock Out® rose), Salvia rosmarinus ‘Arp’ (‘Arp’ rosemary), and Vitex agnus-castus ‘SMVACBD’ (Blue Diddley® chaste tree). Twenty-four plants of each species were randomly assigned to an automated irrigation system, and the substrate volumetric water content was maintained at 0.40 or 0.20 m3⋅m−3 for 50 days. As the substrate volumetric water content declined, plants exhibited an increase in the proportion of visibly wilted and damaged leaves as well as chlorosis. Rose, rosemary, and vitex experienced up to a 30% decrease in the plant growth index [(height + width 1 + width 2)/3], whereas leaf dry weights (DWs) decreased by 84%, 66%, and 58%, respectively. Landscape plants in this study acclimated to drought stress by reducing the total leaf area, developing small leaves, increasing the root-to-shoot ratio, and decreasing stomatal conductance. However, stomatal closure also led to increases in leaf temperatures because of limited transpirational cooling efficiency. For the rosemary, trichome density on the adaxial surface increased as the substrate volumetric water content decreased. The trichome density might be regulated by turgor-pressure-driven cell expansion because the trichome density decreased with the increased leaf width. Rose was sensitive to decreased substrate water availability, resulting in severe growth reduction with a high leaf–air temperature difference. Rosemary maintained better visual quality than that of rose, but the low root-to-shoot ratio resulted in a high leaf-air temperature difference. Vitex, which had the highest root-to-shoot ratio, exhibited the lowest canopy–air temperature and lower growth reduction. Overall, under the experimental conditions, S. rosmarinus ‘Arp’ and V. agnus-castus ‘SMVACBD’ showed better tolerance to drought stress compared with that of R. ×hybrida ‘SMVACBD’.

Synergistic deployment of green infrastructure and reflective pavements for mitigation of UHI within urban blocks

Urbanisation is increasing globally, leading to the Urban Heat Island (UHI) effect, where urban areas experience higher temperatures than nearby rural regions. Mitigating UHI is a significant challenge with far-reaching implications. Green Infrastructure (GI) and reflective pavements have been shown to be effective for UHI mitigation, but extensive use of each can be impractical. By synergistically combining the benefits of both strategies, we can potentially achieve more effective UHI mitigation. Additionally, optimizing their configuration in relation to the surrounding urban morphology can also play a crucial role. This study explored the optimal distribution and configuration of GI and reflective pavements to maximise the cooling effect and cost efficiency in a generic urban block consisting of a regular grid of 25 buildings. A computational fluid dynamics (CFD) based numerical model is developed by solving the steady Reynolds-Averaged Navier-Stokes (RANS) equations to study the impact of GI and reflective pavements on temperature distributions. The climate of Ahmedabad, India, a hot and dry city, was considered. Various configurations of GI and reflective pavements were evaluated, involving a large central park, smaller distributed parks and converting only part of the roads into reflective ones. The findings indicated that the presence of a large central park and partial use of reflective pavements on only half the roads could reduce peak canopy air temperature by 0.16–0.33 °C, with a significantly higher benefit-to-cost ratio as compared to other configurations. These insights contribute to urban design by offering evidence-based solutions for temperature management, promoting sustainability, and enhancing urban quality of life.

Structural Uncertainty in the Sensitivity of Urban Temperatures to Anthropogenic Heat Flux

AbstractOne key source of uncertainty for weather and climate models is structural uncertainty arising from the fact that these models must simplify or approximate complex physical, chemical, and biological processes that occur in the real world. However, structural uncertainty is rarely examined in the context of simulated effects of anthropogenic heat flux in cities. Using the Weather Research and Forecasting (WRF) model coupled with a single‐layer urban canopy model, it is found that the sensitivity of urban canopy air temperature to anthropogenic heat flux can differ by an order of magnitude depending on how anthropogenic heat flux is released to the urban environment. Moreover, varying model structures through changing the treatment of roof‐air interaction and the parameterization of convective heat transfer between the canopy air and the atmosphere can affect the sensitivity of urban canopy air temperature by a factor of 4. Urban surface temperature and 2‐m air temperature are less sensitive to the methods of anthropogenic heat flux release and the examined model structural variants than urban canopy air temperature, but their sensitivities to anthropogenic heat flux can still vary by as much as a factor of 4 for surface temperature and 2 for 2‐m air temperature. Our study recommends using temperature sensitivity instead of temperature response to understand how various physical processes (and their representations in numerical models) modulate the simulated effects of anthropogenic heat flux.

Utilizing Infrared Thermometry to Assess the Crop Water Stress Index of Wheat Genotypes in Arid Regions under Varying Irrigation Regimes

Researchers are depending more than ever on remote sensing techniques to monitor and assess the agricultural water status, as well as to estimate crop water usage or crop actual evapotranspiration. In the current work, normal and stressed baselines for irrigated wheat genotypes were developed in an arid part of the Sohag governorate, Egypt, using infrared thermometry in conjunction with weather parameters. The experiment was carried out in a randomized complete block design in the normal and drought stress conditions based on three replicates using ten bread wheat genotypes (G1–G10), including five accessions, under drought stress. A standard Class-A-Pan in the experimental field provided the daily evaporation measurements (mm/day), which was multiplied by a pan factor of 0.8 and 0.4 for normal and stressed conditions, respectively. The relationship between the vapor pressure deficit (VPD) and canopy-air temperature differences (Tc − Ta) was plotted under upper (fully stressed) and lower baseline (normal) equations. Accordingly, the crop water stress indexes (CWSIs) for the stressed and normal baselines for wheat genotypes were developed. Additionally, the intercept (b) and the slope (a) of the lower baseline equation were computed for different genotypes. The results indicate that, before applying irrigation water, the CWSI values were high in both growing seasons and under all irrigation regimes. After that, the CWSI values declined. G10 underwent stress treatment, which produced the greatest CWSI (0.975). Conversely, the G6 condition that received well-watered irrigation yielded the lowest result (−0.007). When compared to a well-watered one, the CWSI values indicated a trend toward rising stress. There existed an inverse link between the CWSI and grain yield (GY); that is, a lower CWSI resulted in better plant water conditions and a higher GY. Under standard conditions, the wheat’s highest GY was recorded in G2, 8.36 Ton/ha and a WCSI of 0.481. In contrast, the CWSI result for the stress treatment was 0.883, indicating a minimum GY of 5.25 Ton/ha. The Water Use Efficiency (WUE) results demonstrated that the stress irrigation regime produced a greater WUE value than the usual one. This study makes a significant contribution by investigating the techniques that would allow CWSI to be used to estimate irrigation requirements, in addition to determining the irrigation time.

Determination of threshold crop water stress index for sub-surface drip irrigated maize-wheat cropping sequence in semi-arid region of Punjab

A thorough understanding of how crops respond to water stress is essential for effective irrigation management under changing climate conditions and declining water resources. Amongst the various methods of irrigation, crop water stress index (CWSI)-based irrigation is popular due to its non-invasive techniques that require less data and can precisely indicate the severity of crop water deficiency. The present study focuses on establishing the upper- and lower-baselines of canopy-air temperature difference (Tc-Ta) for the estimation of the CWSI and to determine the CWSI threshold for maize and wheat crops. The upper- and lower-baseline of (Tc-Ta) was established using the relationship between (Tc-Ta) and vapor pressure deficit (VPD) for different irrigation treatments such as 60 %ETc, 70 %ETc, 80 %ETc, 90 %ETc, and 100 %ETc with irrigation interval of 1-day, 2-days, and 3-days. The study showed that the baselines varied with the growth stages of the crop and with irrigation treatments and reached the maximum in Anthesis and Silking growth stage for wheat and maize, respectively. The threshold of CWSI was estimated by developing a relationship between the normalized values of grain yield (GY) and irrigation water productivity (WPI). For the Rabi wheat, a quadratic correlation was identified between CWSI and WPI (r2 = 0.89), and GY (r2 = 0.93). Similarly, for Kharif maize, a quadratic relationship was noted between CWSI and both WPI (r2 = 0.75) and GY (r2 = 0.85). From the study, it was found that the CWSI thresholds of Rabi wheat and Kharif maize are 0.29 and 0.31, respectively. Based on the study, it can be concluded that by utilizing the thresholds for a winter wheat-summer maize cropping system, high GY and WPI can be achieved.

Infrared thermometry-based stress indices as indicators of yield performance and seasonal evapotranspiration in potato plants grown under different moisture and potassium regimes

As the demand for food continues to rise and water availability challenges intensify, the delicate equilibrium between efficient water usage and sustainable agricultural production has become increasingly pivotal. Recognizing the significance of water stress monitoring and nutrient management in the country's agricultural landscape, two years of field trials (2018–2019 and 2019–2020) were conducted at the Regional Research Station, Bidhan Chandra Krishi Viswavidyalaya, Gayeshpur, Nadia, to demonstrate the efficiency of canopy temperature-based indices for monitoring crop water stress in potato (cv. Kufri Jyoti) under varied irrigation (IW:CPE = 0.4, 0.8, 1.2 and 1.6) and potassium doses (K2O @ 100, 150 and 200 kg ha−1). The seasonal evapotranspiration of potato plants ranged from 121.0 mm to 320.9 mm during the crop growth period, and it exhibited a quadratic relationship with both the total dry biomass and the tuber yield. In 2019–2020, the highest water use efficiency (WUE) of 12.74 kg m−3 was obtained from the application of IW; CPE= 1.20 with the application of K2O @ 200 kg ha−1. In the following year, the highest WUE of 9.78 kg m−3 was obtained from irrigation at IW:CPE= 1.60, along with K2O application @ 200 kg ha−1. During a major part of the growth period, the canopy air temperature difference (CATD) was greater in the treatments in which irrigation was applied at IW:CPE = 0.4 and 0.8 than in those in which irrigation was applied at higher levels, i.e., IW:CPE = 1.2 and 1.6, implying the effectiveness of CATD as a stress indicator. The stress indices, stress degree days (SDD) and crop water stress index (CWSI) accumulated over the crop growing season showed decreasing trends with increasing irrigation and potassium doses. Both the accumulated SDD and accumulated CWSI showed a strong inverse relationship with tuber yield. The significant linear relationship between tuber yield and the seasonal accumulation of both infrared thermometry-based stress indices (i.e., SDD and CWSI) may help to predict crop yield in response to seasonal moisture stress and thus aid in strategic crop planning under the limited availability of irrigation.

Precise Drought Threshold Monitoring in Winter Wheat Using the Unmanned Aerial Vehicle Thermal Method

Accurate monitoring of crop drought thresholds at different growth periods is crucial for drought monitoring. In this study, the canopy temperature (Tc) of winter wheat (‘Weilong 169’ variety) during the three main growth periods was extracted from high-resolution thermal and multispectral images taken by a complete unmanned aerial vehicle (UAV) system. Canopy-air temperature difference (ΔT) and statistic Crop Water Stress Index (CWSIsi) indicators were constructed based on Tc. Combined experiment data from the field and drought thresholds for the ΔT and CWSIsi indicators for different drought levels at three main growth periods were monitored. The results showed a strong correlation between the Tc extracted using the NDVI-OTSU method and ground-truth temperature, with an R2 value of 0.94. The CWSIsi was more stable than the ΔT index in monitoring the drought level affecting winter wheat. The threshold ranges of the CWSIsi for different drought levels of winter wheat at three main growth periods were as follows: the jointing–heading period, where the threshold ranges for normal, mild drought, moderate drought, and severe drought are <0.30, 0.30–0.42, 0.42–0.48, and >0.48, respectively; the heading–filling period, where the threshold ranges for normal, and mild, moderate, and severe drought are <0.33, 0.33–0.47, 0.44–0.53, and >0.53, respectively; and the filling–maturation period, where the threshold ranges for normal, mild drought, moderate drought, and severe drought are <0.41, 0.41–0.54, 0.54–0.59, and >0.59, respectively. The UAV thermal threshold method system can improve the accuracy of crop drought monitoring and has considerable potential in crop drought disaster identification.

Projecting future forest microclimate using a land surface model

The forest understory experiences temperature variations that are dampened compared to adjacent open areas, allowing the development of a forest microclimate and associated ecological conditions. It is however unclear to what extent forests will maintain this buffering effect under increasing global warming. Providing reliable projections of future forest microclimates is therefore crucial to anticipate climate change impacts on forest biodiversity, and to identify corresponding conservation strategies. Recent empirical studies suggest that the buffering of air temperature extremes in forest understory compared to open land could increase with global warming, albeit at a slower rate than macroclimate temperatures. Here, we investigate the trend of this temperature buffering effect in a high-emission global warming scenario, using the process-based Land Surface Model CLM5.1. We find biome-dependant buffering trends with strongest values in tropical forests where buffering increases for every degree of global warming by 0.1 ∘C for maximum soil temperature, and by 0.2 ∘C for maximum canopy air temperature. In boreal regions, forest microclimate exhibits a strong seasonality and the effect of global warming is more uncertain. Thus, our results highlight the importance of tropical forest canopies in particular, in maintaining hospitable conditions for understory species while increasing their climate debt under global warming. Our research also illustrates the potential and limitations of Land Surface Models to simulate forest microclimate, and calls for further collaborations between Earth system modelers and ecologists to jointly question climate and biosphere dynamics.

Effects of Deficit Irrigation on Canopy Temperature Dynamics and Physiology of Landscape Groundcovers

Identifying the irrigation-induced cooling effects from a particular plant species used for urban groundcovers while optimizing the rates of irrigation applications is important in regions with hot and dry summers. A 2-year (2020–21) study was conducted in Riverside, CA, USA, to evaluate the effect of irrigation rates on the canopy temperature dynamics of 10 urban groundcovers. Four reference evapotranspiration (ETo)-based irrigation treatments (20%, 40%, 60%, and 80% ETo) and 10 groundcovers were laid in a randomized complete block design and replicated three times. The effect of irrigation rates on the difference between canopy–air temperature (ΔT), leaf area index (LAI), and stomatal conductance (gs) were evaluated. All response variables were collected between May and October 2020 and 2021. The crop water stress index for five groundcovers was also computed. The ΔT was affected (P < 0.05) by irrigation rates, and groundcovers, including Rhagodia spinescens and Baccharis × ‘Starn Thompson’, maintained the canopy temperature less than the ambient air temperature for all irrigation rates imposed. For most of the groundcovers, the ΔT yielded a strong relationship with LAI (r = –0.41 to –0.73), and gs (r = –0.35 to –0.60). Crop water stress index also showed a strong correlation to normalized difference vegetation index (r = 0.42 to –0.72) and gs (r = –0.57 to –0.64). Irrigation-included cooling was evident in most groundcovers irrigated at higher rates; however, Rhagodia spinescens and Baccharis × ‘Starn Thompson’ were found to perform well in cooling ability and maintaining the canopy growth as evidenced by LAI. Our study showed that proper plant selection and irrigation management could help maintain green spaces and mitigate the urban heat island effect while conserving irrigation water.

Impact of hail-netting on Vitis vinifera L. canopy microclimate, leaf gas exchange, fruit quality, and yield in a semi-arid environment

Hail events have the potential to destroy grapevine shoots, reduce yield, and inflict economic loss upon growers. As a result, many grape growers have adopted the use of hail-netting to mitigate potential vine damage. Although hail-netting has been observed to prevent hail damage, Texas High Plains grape growers have expressed concerns regarding effects hail-netting may have on vine canopy microclimate, grapevine health, fruit maturity, fruit quality and yield. Therefore, over three growing seasons (2018 – 2020), field-grown vines (Vitis vinifera L. ‘Malbec’ and ‘Pinot gris’) were exposed to hail-netting, or grown without hail-netting. Each growing season canopy microclimate, leaf gas exchange, fruit maturity, yield parameters, and vegetative growth were monitored. Netting reduced canopy air and leaf temperature and decreased canopy vapour pressure deficit. By modifying light infiltration and leaf temperature, hail-netting altered leaf gas exchange. In addition, gas exchange differences were found between cultivars. Although fruit pH and total acidity were not different at harvest, fruit maturity measurements revealed total soluble solid development was influenced by netting and cultivar. Vine cluster numbers were greater for vines without netting and yield parameters were generally lower for ‘Malbec’ vines. Pruning weights indicate decreased vegetative growth for hail-netting and ‘Pinot gris’ vines. Results suggest grape-growers' use of hail-netting may allow growers to achieve fruit production goals. However, when using hail-netting, growers should consider possible management modifications due to changes in vine physiology, fruit maturation, and harvest schedules.

Impact of hail-netting on Vitis vinifera L. canopy microclimate, leaf gas exchange, fruit quality, and yield in a semi-arid environment

Hail events have the potential to destroy grapevine shoots, reduce yield, and inflict economic loss upon growers. As a result, many grape growers have adopted the use of hail-netting to mitigate potential vine damage. Although hail-netting has been observed to prevent hail damage, Texas High Plains grape growers have expressed concerns regarding effects hail-netting may have on vine canopy microclimate, grapevine health, fruit maturity, fruit quality and yield. Therefore, over three growing seasons (2018 – 2020), field-grown vines (Vitis viniferaL. ‘Malbec’ and ‘Pinot gris’) were exposed to hail-netting, or grown without hail-netting. Each growing season canopy microclimate, leaf gas exchange, fruit maturity, yield parameters, and vegetative growth were monitored. Netting reduced canopy air and leaf temperature and decreased canopy vapour pressure deficit. By modifying light infiltration and leaf temperature, hail-netting altered leaf gas exchange. In addition, gas exchange differences were found between cultivars. Although fruit pH and total acidity were not different at harvest, fruit maturity measurements revealed total soluble solid development was influenced by netting and cultivar. Vine cluster numbers were greater for vines without netting and yield parameters were generally lower for ‘Malbec’ vines. Pruning weights indicate decreased vegetative growth for hail-netting and ‘Pinot gris’ vines. Results suggest grape-growers' use of hail-netting may allow growers to achieve fruit production goals. However, when using hail-netting, growers should consider possible management modifications due to changes in vine physiology, fruit maturation, and harvest schedules.

Deciphering the sensitivity of urban canopy air temperature to anthropogenic heat flux with a forcing-feedback framework

The sensitivity of urban canopy air temperature () to anthropogenic heat flux () is known to vary with space and time, but the key factors controlling such spatiotemporal variabilities remain elusive. To quantify the contributions of different physical processes to the magnitude and variability of (where represents a change), we develop a forcing-feedback framework based on the energy budget of air within the urban canopy layer and apply it to diagnosing simulated by the Community Land Model Urban over the contiguous United States (CONUS). In summer, the median is around 0.01 over the CONUS. Besides the direct effect of on , there are important feedbacks through changes in the surface temperature, the atmosphere–canopy air heat conductance (), and the surface–canopy air heat conductance. The positive and negative feedbacks nearly cancel each other out and is mostly controlled by the direct effect in summer. In winter, becomes stronger, with the median value increased by about 20% due to weakened negative feedback associated with . The spatial and temporal (both seasonal and diurnal) variability of as well as the nonlinear response of to are strongly related to the variability of , highlighting the importance of correctly parameterizing convective heat transfer in urban canopy models.

Exogenous application of spermidine and methyl jasmonate can mitigate salt stress in fenugreek (Trigonella foenum-graecum L.)

Fenugreek (Trigonella foenum-graecum L.) has long been cultivated as both culinary and medicinal plant. The objective of this study was to investigate the effect of plant growth regulators such as spermidine (Spd) and methyl jasmonate (MeJA) on morpho-physiological and biochemical properties of fenugreek under saline conditions. A replicated greenhouse experiment in completely randomized block design was conducted with two levels of salinity (0.5 dS/m as control and 6 dS/m), three levels of spermidine (0, 1, 2 mM) and methyl jasmonate (0, 100, 200 µM), respectively. The results showed that salinity elevation reduced the leaf relative water content, leaf water potential, canopy-air temperature difference, photochemistry efficiency of photosystem II, and water-use efficiency of fenugreek. In contrast, salinity increased leaf thickness,greenness index, canopy temperature, leaf Na+, ash contents, malondialdehyde, other aldehydes, and electrolyte leakage. Moreover, Salinity stress reduced the amount of photosynthetic pigments, chlorophyll a/b ratio, total soluble protein, K+, maximum fluorescence, and K+/Na+ ratio in leaves. Elevation of water salinity, however, resulted in an increase in the activity of antioxidant enzymes (except superoxide dismutase), proline, and minimum fluorescence. When fenugreek was treated with 1 mM spermidine and/or 100 µM methyl jasmonate, the adverse effects of salinity stress were significantly mitigated, while the effects of these plant growth regulators on mitigating salinity stress were less pronounced at higher concentrations (2 mM spermidine and/or 200 µM methyl jasmonate). The current study suggests the application of 1 mM spermidine and/or 100 µM methyl jasmonate during the vegetative growth stage mitigating the adverse effects of salinity with an associated improvement in plant growth under moderate salinity (about 6 dS/m) when used for irrigation.

Physiological and Canopy Temperature Responses to Drought of Four Penstemon Species

Available water for urban landscape irrigation is likely to become more limited because of inadequate precipitation and the ever-increasing water demand of a growing population. Recent droughts in the western United States have also increased the demand for low-water-use landscapes in urban areas. Penstemon species (beardtongues) are ornamental perennials commonly grown in low-water-use landscapes, but their drought tolerance has not been widely investigated. The objectives of this study were to determine the effects of water availability on the morphology, physiology, and canopy temperature of Penstemon barbatus (Cav.) Roth ‘Novapenblu’ (Rock Candy Blue® penstemon), P. digitalis Nutt. ex Sims ‘TNPENDB’ (Dakota™ Burgundy beardtongue), P. ×mexicali Mitch. ‘P007S’ (Pikes Peak Purple® penstemon), and P. strictus Benth. (Rocky Mountain penstemon). Twenty-four plants of each penstemon species were randomly assigned to blocks in an automated irrigation system, and the substrate volumetric water content was maintained at 0.15 or 0.35 m3⋅m−3 for 50 days. The decreased substrate volumetric water content resulted in a decreased aesthetic appearance of the four penstemon species because of the increased numbers of visibly wilted leaves and chlorosis. Plant growth index [(height + (width 1 + width 2)/2)/2], shoot number, shoot dry weight, leaf size, and total leaf area also decreased as the substrate volumetric water content decreased, but the root-to-shoot ratio and leaf thickness increased. Photosynthesis decreased, stomatal resistance increased, and warmer canopy temperatures were observed when plants were dehydrated. Additionally, as substrate volumetric water content decreased, the leaf reflectance of P. barbatus and P. strictus increased. Penstemon digitalis, which had the highest canopy–air temperature difference, was sensitive to drought stress, exhibiting a large proportion of visibly wilted leaves. Penstemon ×mexicali, which had the lowest root-to-shoot ratio, had the lowest shoot water content of the species studied and more than 65% of leaves visibly wilted when experiencing drought stress. Penstemon barbatus and P. strictus, native to arid regions, exhibited lower canopy–air temperature differences and better aesthetic quality than the other two species. Under the conditions of this study, Penstemon barbatus and P. strictus exhibited better drought tolerance than P. digitalis and P. ×mexicali.

Effect of Maize and Chickpea Intercropping under the Different Row Ratios on Air Temperature and Vapoure Pressure Profile in Crop Canopy

An experiment was laid out to study the effect of maize and chickpea intercropping under the different row ratios on air temperature and vapoure pressure profile in crop canopy at Agronomy farm, Bansilal Amritlal College of Agriculture, Anand Agricultural University, Anand (Gujarat), India during the rabi season of the year 2021-2022. The soil of the experimental field was loamy sand. The experiment was laid out in a randomized block design with six treatments replicated four times. The treatments details are T1: Sole maize, T2: Sole chickpea, T3: Maize paired row, T4: Maize + chickpea (1: 1), T5: Maize + chickpea (1 : 2), T6: Maize + chickpea (2 : 2). During the early crop growth inversion profile of air temperature was observed because crops canopy was short. Air temperature was lowest at ground level, with increase in height air temperature increase. At upper canopy air temperature is lower than lower canopy because active transpiration by the dense foliage at upper canopy lower down the air temperature. During the early crop growth lapse profile of vapour pressure was observed. Highest value of vapour pressure was observed at the ground, but with an increase in height vapour pressure decreased. In the case of within crop canopy, strong gradient of vapour pressure was observed in upper crop canopy and weak gradient at lower crop canopy.

Modeling urban canopy air temperature at city-block scale based on urban 3D morphology parameters– A study in Tianjin, North China

Urban 3D morphology significantly influences the outdoor thermal environment. Understanding the influence of urban expansion in both horizontal and vertical landscapes helps the canopy urban heat island (CUHI) effect mitigation. However, the microscale numerical CUHI models are difficult to be applied for large-area CUHI effect studies. On the other hand, the mesoscale CUHI models make a wider study area workable but lost some of the model accuracies. To perform a large-area study on the CUHI effect with relatively light computing costs and fine accuracy, this paper builds a canopy air temperature predicting model at city-block scale with urban 3D morphology parameters including building coverage ratio (BCR), grass coverage ratio (GCR) and the mean value of building height (BH) to obtain the citywide block-mean 2-m temperature (T2M). The model accuracy was validated through RMSEs and comparison with the mereological station data. The proposed model shows an RMSE of 0.286 straight °C and an R-square of 0.83. Using the validated model, Tianjin with an area of 647 km 2 was performed to investigate the effects of vertical landscape on the canopy air temperature under different scenarios between 2010 and 2016, including the changes in landcover and building heights. It finds that a 40% increase in BCR may lead to the highest canopy air temperature, and the increase of BH may lead to an increase in the canopy air temperature in low-rise and high-rise building areas, but there is an opposite trend in multi-story and mid-rise building areas.

Applicability of the crop water stress index based on canopy–air temperature differences for monitoring water status in a cork oak plantation, northern China

The crop water stress index based on canopy–air temperature differences (CWSIdT) is an appropriate index for monitoring the water status of croplands but is rarely used to evaluate the water status of forest ecosystems. In this study, we selected a cork oak plantation in the lithoid mountain area of northern China as the research object and observed the canopy temperature (Tc), actual evapotranspiration (ETa), and meteorological factors of the plantation continuously and synchronously during the period of canopy closure (May–September) in 2020 and 2021. Taking the crop water stress index based on the ratio of ETa to potential evapotranspiration (CWSIet) as a standard, the applicability of CWSIdT for detecting water status in the plantation was evaluated. The results showed that, under well-watered conditions, the canopy–air temperature differences (dT) and the canopy surface transpiration rate were both controlled by the net radiation received by the canopy surface (Rnc), and the warming effect of Rnc masked the cooling effect of latent heat on dT, resulting in a failure establishment of the non-water-stressed baseline in the plantation. Therefore, the empirical CWSIdT (CWSIdTe) is not suitable for evaluating the water status in this plantation. However, the theoretical CWSIdT (CWSIdTt), based on the energy balance and Penman–Monteith equation, captured daily variations in the water status in our plantation and showed a significant linear correlation with the measured relative available water content in the root zone (R2 = 0.59, P < 0.01) and CWSIet (R2 = 0.75, P < 0.01). The CWSIdTt showed an upward trend during the day, and midday (13:00−14:00) was the optimal time to measure dT for detecting the daily water status of the plantation. The CWSIdTt provides an effective, sensitive, and non-contact method of assessing daily water status changes in the cork oak plantation.

Long-term drought effects on the thermal sensitivity of Amazon forest trees.

The continued functioning of tropical forests under climate change depends on their resilience to drought and heat. However, there is little understanding of how tropical forests will respond to combinations of these stresses, and no field studies to date have explicitly evaluated whether sustained drought alters sensitivity to temperature. We measured the temperature response of net photosynthesis, foliar respiration and the maximum quantum efficiency of photosystem II (Fv /Fm ) of eight hyper-dominant Amazonian tree species at the world's longest-running tropical forest drought experiment, to investigate the effect of drought on forest thermal sensitivity. Despite a 0.6°C-2°Cincrease in canopy air temperatures following long-term drought, no change in overall thermal sensitivity of net photosynthesis or respiration was observed. However, photosystem II tolerance to extreme-heat damage (T50 ) was reduced from 50.0 ± 0.3°C to 48.5 ± 0.3°Cunder drought. Our results suggest that long-term reductions in precipitation, as projected across much of Amazonia by climate models, are unlikely to greatly alter the response of tropical forests to rising mean temperatures but may increase the risk of leaf thermal damage during heatwaves.

The Impact of Anthropogenic Disturbance to the Canopy Microclimate of Tropical Forests in the Southern Western Ghats, India

Anthropogenic disturbances are a pressing driver of forest degradation and are known to affect the microclimate within forests. Most organisms experience the microclimate and hence, associated changes may drive species communities in rainforests. However, such knowledge remains limited in the case of forest canopies, especially in south Asia. We aimed to identify differences in the temperature and light intensity, and beetles and vascular epiphytes in the canopy between old-growth and secondary forests. Using sensors, we recorded two key microclimatic variables, the air temperature, and light intensity, in the crowns of 36 Cullenia exarillata A. Robyns trees. We sampled beetles (morphospecies) and vascular epiphytes (genera) in the crowns. We provide evidence that canopies of secondary forest stands (intensively logged 60 years ago) (1) continue to show higher canopy air temperatures and light intensity, and (2) have higher beetle abundance (individuals), richness (morphospecies), and diversity but lower vascular epiphyte abundance (individuals), richness (genera), and diversity as compared to primary forest stands. We also show that the beetle communities differ (with greater beta diversity in the primary forest), but the vascular epiphyte communities were similar between the two forest types. We hope that this information begins to bridge the gap in understanding the role of microclimate in driving species communities and the ecology of human-modified forests.

How Soil Covers Can Affect the Dynamics of Temperature, Soil Moisture, and Productivity of Creeping Fresh Market Tomatoes?

The aim was to evaluate the influence of soil covers on the dynamics of soil temperature and moisture, canopy air temperature, and yield of creeping fresh market tomatoes. The experiment was carried out in randomized blocks design, using the tomato cultivar Thaise, with 5 treatments, 4 replications, with different soil covers: a) Uncovered soil (conventional planting); b) Mulching (double-sided plastic film - black and white); c) Sorghum; d) Sudan grass and e) Pearl millet), cultivated in Tangará da Serra, Mato Grosso, Brazil. Soil temperature was monitored at depths of 5, 10, 20, and 30 cm and in the crop canopy, using thermocouple sensors of the type "K". Soil moisture was monitored in the 0 to 30 cm layer, using of time-domain reflectometry (TDR) probes. Soil temperature and moisture were evaluated throughout the cycle and, in the end, the total and commercial yield of tomato crop. Soil covers have a positive influence on soil temperature and moisture in the cultivation of creeping fresh market tomatoes so that soil cover with mulching provides the highest soil temperature in the early stages of development and covers with mulching and pearl millet provide the highest values of soil moisture. The highest total and commercial yield of tomato were in the soil cover with mulching, with 110.71 and 75.93 t ha-1, respectively, presenting ideal ranges of temperature and soil moisture, so that the other treatments do not differ from each other, with the average total yield of 91.45 t ha-1.