Canopy Air Research Articles

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.

The emission of CO from tropical rainforest soils

Abstract. Soil carbon monoxide (CO) fluxes represent a net balance between biological soil CO uptake and abiotic soil and (senescent) plant CO production. Studies largely from temperate and boreal forests indicate that soils serve as a net sink for CO, but uncertainty remains about the role of tropical rainforest soils to date. Here we report the first direct measurements of soil CO fluxes in a tropical rainforest and compare them with estimates of net ecosystem CO fluxes derived from accumulation of CO at night under stable atmospheric conditions. Furthermore, we used laboratory experiments to demonstrate the importance of temperature on net soil CO fluxes. Net soil surface CO fluxes ranged from −0.19 to 3.36 nmol m−2 s−1, averaging ∼1 nmol CO m−2 s−1. Fluxes varied with season and topographic location, with the highest fluxes measured in the dry season in a seasonally inundated valley. Ecosystem CO fluxes estimated from nocturnal canopy air profiles, which showed CO mixing ratios that consistently decreased with height, ranged between 0.3 and 2.0 nmol CO m−2 s−1. A canopy layer budget method, using the nocturnal increase in CO, estimated similar flux magnitudes (1.1 to 2.3 nmol CO m−2 s−1). In the wet season, a greater valley ecosystem CO production was observed in comparison to measured soil valley CO fluxes, suggesting a contribution of the valley stream to overall CO emissions. Laboratory incubations demonstrated a clear increase in CO production with temperature that was also observed in field fluxes, though high correlations between soil temperature and moisture limit our ability to interpret the field relationship. At a common temperature (25 °C), expected plateau and valley senescent-leaf CO production was small (0.012 and 0.002 nmol CO m−2 s−1) in comparison to expected soil material CO emissions (∼ 0.9 nmol CO m−2 s−1). Based on our field and laboratory observations, we expect that tropical rainforest ecosystems are a net source of CO, with thermal-degradation-induced soil emissions likely being the main contributor to ecosystem CO emissions. Extrapolating our first observation-based tropical rainforest soil emission estimate of ∼ 1 nmol m−2 s−1, global tropical rainforest soil emissions of ∼ 16.0 Tg CO yr−1 are estimated. Nevertheless, total ecosystem CO emissions might be higher, since valley streams and inundated areas might represent local CO emission hot spots. To further improve tropical forest ecosystem CO emission estimates, more in situ tropical forest soil and ecosystem CO flux measurements are essential.

Effects of dust controls on respirable coal mine dust composition and particle sizes: case studies on auxiliary scrubbers and canopy air curtain

Control of dust in underground coal mines is critical for mitigating both safety and health hazards. For decades, the National Institute of Occupational Safety and Health (NIOSH) has led research to evaluate the effectiveness of various dust control technologies in coal mines. Recent studies have included the evaluation of auxiliary scrubbers to reduce respirable dust downstream of active mining and the use of canopy air curtains (CACs) to reduce respirable dust in key operator positions. While detailed dust characterization was not a focus of such studies, this is a growing area of interest. Using preserved filter samples from three previous NIOSH studies, the current work aims to explore the effect of two different scrubbers (one wet and one dry) and a roof bolter CAC on respirable dust composition and particle size distribution. For this, the preserved filter samples were analyzed by thermogravimetric analysis and/or scanning electron microscopy with energy dispersive X-ray. Results indicate that dust composition was not appreciably affected by either scrubber or the CAC. However, the wet scrubber and CAC appeared to decrease the overall particle size distribution. Such an effect of the dry scrubber was not consistently observed, but this is probably related to the particular sampling location downstream of the scrubber which allowed for significant mixing of the scrubber exhaust and other return air. Aside from the insights gained with respect to the three specific dust control case studies revisited here, this work demonstrates the value of preserved dust samples for follow-up investigation more broadly.

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.

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.

Impact of Uncertainties in Land Surface Processes on Subseasonal Predictability of Heat Waves Onset Over the Yangtze River Valley

AbstractLand surface processes are strongly associated with heat waves (HWs). However, how the uncertainties in land surface processes owing to inaccurate physical parameters influence subseasonal HW predictions has rarely been explored. To examine the impact of parameter errors of land surface processes on the uncertainty of subseasonal HW predictions, five strong and long‐lasting HW events over the middle and lower reaches of the Yangtze River are investigated. Based on the Weather Research and Forecasting model, the conditional nonlinear optimal perturbation related to parameters (CNOP‐P) approach is employed to address the aforementioned issues. Numerical results demonstrate that the CNOP‐P type errors of physical parameters cause large prediction errors for five HW event onsets. Two types of CNOP‐Ps are obtained for HW events, called the type‐1 CNOP‐P and the type‐2 CNOP‐P. The type‐1 (type‐2) CNOP‐P causes an approximately 3°C (2°C) warm (cold) bias during the HW period. Surface sensible and latent heat flux errors, especially flux exchange between vegetation canopy and canopy air, provide considerable uncertainty in subseasonal HW predictions. The type‐1 (type‐2) CNOP‐P exhibits an underestimation (overestimation) of transpiration. Furthermore, it should be noted that the type‐1 CNOP‐P results in a substantial difference in soil moisture, a phenomenon that is demonstrated to be challenging to observe in the type‐2 CNOP‐P. The results indicate that understanding vegetation‐atmosphere dynamics is crucial for improving subseasonal HW predictions. Jointly lowering soil‒atmosphere and vegetation‐atmosphere uncertainty can notably improve subseasonal HW prediction skills.

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.

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.

Optimization of urban design/retrofit scenarios using a computationally light standalone urban energy/climate model (SUECM) forced by ERA5 data

Standalone urban canopy models attempt to replace the full-fledged atmospheric representation with a simplified equivalent. In this study, we investigate the offline forcing of an offline Standalone Urban Energy/Climate Model (SUECM) by the fifth generation reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA5). The result is a computationally light numerical model of the urban canopy air that can be incorporated in a design optimization work flow. The model is applied to the city of Abu Dhabi (United Arab Emirates). The model’s accuracy is validated against measurements. The urban heat island (UHI) mitigation and building energy conservation potential of several urban design/retrofit scenarios is evaluated in comparison to business-as-usual. District cooling implementation is best overall with an estimated reduction of cooling electricity demand by more than 40% and of UHI intensity by more than 25%. Building-integrated vegetation systems (green roof/wall) are also effective mitigation/conservation measures; however, their positive impact must be weighed against the need for irrigation. Among the two other design/retrofit scenarios, cool surfaces are more effective in reducing UHI (−16%) while energy efficient buildings are to be preferred in case cooling energy demand reduction is prioritized (−25%). Based on the physical network representation principle, the model has been implemented in a graphical development and simulation environment, thereby simplifying specializations and future enhancements.

Attributing the Urban–Rural Contrast of Heat Stress Simulated by a Global Model

Abstract The two-resistance mechanism (TRM) attribution method, which was designed to analyze the urban–rural contrast of temperature, is improved to study the urban–rural contrast of heat stress. The improved method can be applied to diagnosing any heat stress index that is a function of temperature and humidity. As an example, in this study we use it to analyze the summertime urban–rural contrast of simplified wet bulb globe temperature (SWBGT) simulated by the Geophysical Fluid Dynamics Laboratory land model coupled with an urban canopy model. We find that the urban–rural contrast of SWBGT is primarily caused by the lack of evapotranspiration in urban areas during the daytime and the release of heat storage during the nighttime, with the urban–rural differences in aerodynamic features playing either positive or negative roles depending on the background climate. Compared to the magnitude of the urban–rural contrast of temperature, the magnitude of the urban–rural contrast of SWBGT is damped due to the moisture deficits in urban areas. We further find that the urban–rural contrast of 2-m air temperature/SWBGT is fundamentally different from that of canopy air temperature/SWBGT. Turbulent mixing in the surface layer leads to much smaller urban–rural contrasts of 2-m air temperature/SWBGT than their canopy air counterparts. Significance Statement Heat leads to serious public health concerns, but urban and rural areas have different levels of heat stress. Our study explains the magnitude and pattern of the simulated urban–rural contrast in heat stress at the global scale and improves an attribution method to quantify which biophysical processes are mostly responsible for the simulated urban–rural contrast in heat stress. We highlight two well-known causes of higher heat stress in cities: the lack of evapotranspiration and the stronger release of heat storage. Meanwhile, we draw attention to the vegetation types in rural areas, which determine the urban–rural difference in surface roughness and significantly affect the urban–rural difference in heat stress. Last, we find the urban–rural contrasts of 2-m air temperature/SWBGT are largely reduced relative to their canopy air counterparts due to the turbulent mixing effect.

Changes in plant nutrient status following combined elevated [CO2] and canopy warming in winter wheat.

Projected global climate change is a potential threat to nutrient utilization in agroecosystems. However, the combined effects of elevated [CO2] and canopy warming on plant nutrient concentrations and translocations are not well understood. Here we conducted an open-air field experiment to investigate the impact of factorial elevated [CO2] (up to 500 μmol mol-1) and canopy air warming (+2°C) on nutrient (N, P, and K) status during the wheat growing season in a winter wheat field. Compared to ambient conditions, soil nutrient status was generally unchanged under elevated [CO2] and canopy warming. In contrast, elevated [CO2] decreased K concentrations by 11.0% and 11.5% in plant shoot and root, respectively, but had no impact on N or P concentration. Canopy warming increased shoot N, P and K concentrations by 8.9%, 7.5% and 15.0%, but decreased root N, P, and K concentrations by 12.3%, 9.0% and 31.6%, respectively. Accordingly, canopy warming rather than elevated [CO2] increased respectively N, P and K transfer coefficients (defined as the ratio of nutrient concentrations in the shoot to root) by 22.2%, 27.9% and 84.3%, which illustrated that canopy warming played a more important role in nutrient translocation from belowground to aboveground than elevated [CO2]. These results suggested that the response of nutrient dynamics was more sensitive in plants than in soil under climate change.

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.

A portable sensor for the determination of tree canopy air quality

A low-cost portable sensor system has been developed and described to interrogate individual trees and quantify their impact on air quality (CO, NO2, PM2.5).

Simulating the Impacts of Drought and Warming in Summer and Autumn on the Productivity of Subtropical Coniferous Forests

The impacts of drought and/or warming on forests have received great attention in recent decades. Although the extreme drought and/or warming events significantly changed the forest demography and regional carbon cycle, the seasonality quantifying the impacts of these climate extremes with different severities on the productivity of subtropical coniferous forests remains poorly understood. This study evaluated the effects of seasonal drought and/or warming on the net primary productivity (NPP) of subtropical coniferous forests (i.e., Cunninghamia lanceolata and Pinus massoniana forests) from Hengyang–Shaoyang Basin in southern China using the Ecosystem Demography model, Version 2.2 (ED-2.2) and based on the datasets from forest inventory, meteorological reanalysis, and remotely sensed products. The results showed that the goodness of fit of the DBH-height allometric equations was better than that of the default in ED-2.2 after model calibration; the ED-2.2 model qualitatively captured the seasonality of NPP in the subtropical coniferous forests; and the mismatch between simulated annual NPP and MODIS-NPP (MOD17A3HGF) became smaller over time. The effect of seasonal drought on NPP was greater than that of warming; the decline rate of NPP gradually increased and decreased with time (from July to October) under the seasonal drought and warming scenarios, respectively; NPP decreased more seriously under the combined drought-warming scenario in October, with an average decrease of 31.72%, than the drought-only and warming-only scenarios; seasonal drought had an obvious legacy impact on productivity recovery of subtropical coniferous forests, but it was not the case for warming. With the increase in drought severity, the average values of soil available water and NPP together showed a downward trend. With the increase in warming severity, the average values of canopy air space temperature increased, but NPP decreased. Seasonal drought and/or warming limit forest production through decreasing soil moisture and/or increasing canopy air space temperature, which impact on plant photosynthesis and productivity, respectively. Our results highlight the significance of taking into account the impacts of seasonal warming and drought when evaluating the productivity of subtropical coniferous forests, as well as the significance of enhancing the resistance and resilience of forests to future, more severe global climate change.

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.