Humid Subtropical Research Articles

Smallholder farmers expand production area of the perennial crop enset as a climate coping strategy in a drought‐prone indigenous agrisystem

Societal Impact StatementClimate resilient crops will become increasingly important, especially in regions where smallholder farmers are vulnerable to climate extremes. Enset, a multipurpose perennial staple crop consumed by over 20 million people in Ethiopia, purportedly provides food security during periods of drought. Here, we find evidence that frequent severe drought events led to an increase in enset production area. This is consistent with a broader pattern whereby farmers preferentially cultivate perennial and storable crops after long‐term drought events, providing an example of adaptation to fluctuations in climate through crop choice in indigenous agrisystems.SummarySmallholder farms in the semiarid and subhumid tropics are particularly vulnerable to increased climate variability. Indigenous agrisystems that have co‐evolved with climate variability may have developed resilience strategies. In the Southwest Ethiopian Highlands, agrisystems are dominated by the multipurpose perennial staple enset (Ensete ventricosum), characterised by flexible harvest timing, high yield, long storage, and putative drought tolerance, earning it the name ‘the tree against hunger’.We tested three hypotheses using crop production area and climate data. First, that enset production area is greatest in the most drought‐prone locations. Second, that farmers respond to drought events by increasing enset production area. And third, that drought encourages shifts in agrisystem composition more widely towards perennial or storable crops.We found that regions with a higher severe drought frequency are associated with significantly higher proportion of enset production. Similarly, the Standardised Precipitation Evapotranspiration Index of the previous 3 years is significantly negatively correlated with enset production area time series, suggesting that prior drier conditions led farmers to increase the land under enset production. Regarding other crops, storage crops roots and tubers were also preferentially selected after long‐term drought over annual crops, indicating their capacity for longer‐term resilience.Promoting the production of crops such as perennials, which have more extensive and established root systems, may be a strategy to ensure food security during drought or climate variability. These results indicate the potential of farmer's resilience strategies to improve food security in a changing climate.

Intensification and diversification of pasturelands in Brazil: Patterns and driving factors in the soil carbon stocks

The extensive system of pasture management in Brazil can reduce soil C stocks and increase CO2 emissions to the atmosphere. However, the adoption of sustainable management systems can change these conditions and enact modern practices of natural resource management as defined by the concept of ecosystem services. A field study was therefore carried out to assess the effects of adopting more intensive and diversified systems of pasture management on the quality and stocks of soil C. Treatments included fertilized pasture (FP), integrated crop-livestock (ICL), and integrated livestock-forest (ILF) and were compared to conventional management systems (CS) under different soil and climate conditions (tropical humid, subtropical dry and subtropical humid). Soil carbon stocks and soil organic matter (SOM) fractions were determined in the top one-meter layer. With the SOM fractions, we calculated the C lability (LI), pool (CPI) and management (CMI) indices. The results showed that adopting ICL systems under the conditions of a tropical humid and subtropical humid climate produced increases in soil C stocks of 0.75 Mg ha−1 yr−1 (P < 0.01) and 0.15 Mg ha−1 yr−1 (P < 0.05), respectively, relative to the CS. Similarly, the conversion of a CS to FP (tropical humid climate) and ILF (subtropical dry climate) led to increases in soil C stocks of 2 and 0.55 Mg ha−1 yr−1 (P < 0.05), respectively. In general, the adoption of more intensive and diversified systems of pasture management can also afford increases in the LI, CPI and CMI indices. These results can serve as a scientific basis for government initiatives that focus on recovering degraded pastures in Brazil through the use of more sustainable management systems and can also help to sequester more C in soils.

Evaluating geostatistical methods along with semi-destructive analysis for forensic provenancing organic-rich soils in humid subtropical climate

When no samples are available for direct comparisons during a criminal investigation, forensic scientists must resort to georeferenced soil databases in order to find the source of a single questioned evidence. To this end, several authors addressed many methods to infer the origin of soil samples, such as establishing search range intervals or defining statistical similarities. However, little is currently known about the efficiency of these methods when it comes to organic-rich and deep weathered subtropical soils. Therefore, this study attempts to contribute to this subject by evaluating the predictability of a soil database built in a 100 km² area in the Curitiba Metropolitan Region, Brazil, where 232 topsoil (<5 cm), 14 validation, and 38 subsoil samples (B horizon) were collected. To determine their physical, chemical, and colorimetric features, samples were subjected to magnetic susceptibility analysis, gamma-ray spectrometry, color analysis, pXRF, and ATR-FTIR. Two prediction methods were selected: search range intervals (SR) and n-dimensional Euclidean distances (ED). After the descriptive and multivariate statistical analyses, geostatistical models were generated for the 28 obtained variables using the empirical Bayesian kriging (EBK) with regression prediction method, where geological and airborne geophysical data were used as explanatory matrix. For the ED provenancing method, dissimilarity values were calculated and interpolated by applying the inverse distance weighting (IDW) approach. Findings, while preliminary, suggest that magnetic susceptibility, lightness, Fe, Mn, Cu, Ni, and the light elements group (LE) may be the most significant variables to discriminate parent rock and to correlate with subsurface data. The SR method managed to correctly predict the origin of 4 of 14 validation samples, reducing up to 97.5% of the original area. The ED method, on the other hand, accurately estimated the provenance of 8 out of 14 samples, excluding up to 63.4% of the area. Despite the limitations and errors inherent to semi-destructive analyses, the moderate chemical weathering, and the high organic matter content, overall soil provenancing results were suitable, demonstrating that spatial variability of topsoils developed under humid subtropical environments can be modeled and used in forensic contexts, as long as the right methods are applied.

Effect of the envelope structure on the indoor thermal environment of low-energy residential building in humid subtropical climate: In case of brick–timber vernacular dwelling in China

The brick–timber structure plays a crucial role in creating a comfort indoor thermal environment for low-energy vernacular dwellings. Herein, the thermal environment of the dwelling was studied by DesignBuilder software and evaluated using Adaptive Predicted Mean Vote (APMV) index. These results revealed that the indoor damp and cold feelings intensified in winter, and the mountain as a natural wind barrier weakened the attack of the prevailing wind in winter. These results leaded that the wind speed of the tested room was lower than 0.1 m/s. The thermal comfort satisfactory days in a year accounts for 56.2%, and the overall level of indoor thermal environment was low in the rest of the year, especially in winter. The simple structure of the exterior envelope and the single material were the main reasons for the poor indoor thermal environment of naturally ventilated buildings. Therefore, optimization strategies such as increasing the insulation materials of the envelope and adopting insulating glass windows were proposed. Compared to that before the retrofitting, the overall thermal environment grade of the vernacular dwelling has been improved by 4.7% (grade I), -0.3% (grade II) and -4.3% (grade III), respectively. The poor thermal performance and airtightness of the envelope easily lead to the negative effect of outdoor cold, heat and water vapor entering the house, which affects the thermal environment grade. These conclusions provided a reference for the optimization of the thermal environment of existing low-energy vernacular dwellings in subtropical humid climate areas. • Poor indoor thermal environment in winter in low-energy buildings. • Building airtightness is as important as the thermal performance of the envelope. • Buildings in humid subtropical climates should be well protected from moisture. • The height of surrounding buildings influences wind speed and shading

Assimilation apparatus of evergreen vines in humid subtropics of Russia

In the article, the research results on the morphophysiological parameters of the assimilation apparatus of evergreen vines in the humid subtropics of Russia are presented. Тhe endemic species to subtropical regions of East Asia, including Trachelospermum asiaticum (Siebold &amp; Zucc.) Nakai, Trachelospermum jasminoides (Lindl.) Lem., Trachelospermum liukiuense Hatus., Clematis armandii Franch., Kadsura japonica (L.) Dunal and Akebia quinata (Houtt.) Decne. were studied. Morphological traits (the area and thickness of the leaf blade), physiological traits (the content of dry substances and the main photosynthetic pigments in the leaves) and the integral parameter (the specific surface density of the leaf) were studied in dynamics by standard methods in plant physiology. It was established that evergreen vines exhibit specific and seasonal differences in the dynamics of morphophysiological parameters of the assimilation apparatus, while the variation in these parameters directly depends on the hydrothermal conditions of cultivation. Such morphological traits as the area and thickness of the leaf blade depend on the temperature and relative humidity of the air, respectively, while physiological and such integral parameters as the specific surface density of the leaf depend on the relative humidity of the air. Тhe dynamic changes in a number of morphophysiological properties of plants underlying the adaptability of exotic species along with correlative relationships between abiotic stress factors and the physiological state of plants allow a group of promising evergreen vines for ornamental gardening in a humid subtropical climate to be defined. Here, among the representatives of the genus Trachelospermum , T. asiaticum exhibits great adaptive potential. In landscaping of the coast, however, the less stable species T. jasminoides is are widely found. Less common in landscape construction C. armandii, A. quinata and uncommon in the region K. japonica must be placed factoring in the microclimatic characteristics of the landscaping object and the environmental requirements for the vines.

Xin’anjiang Nested Experimental Watershed (XAJ-NEW) for Understanding Multiscale Water Cycle: Scientific Objectives and Experimental Design

• Designed a five-tier nested experimental watershed for multi-scale water cycle study. • Hydrological processes exhibit a spatiotemporal scaling effect. • Canopy leaf density has an exponential effect on rainfall interception. • Surface runoff serves as a major component of total runoff in the humid zone. This paper presents the background, scientific objectives, experimental design, and preliminary achievements of the Xin’anjiang nested experimental watershed (XAJ-NEW), implemented in 2017 in eastern China, which has a subtropical humid monsoon climate and a total area of 2674 km 2 . The scientific objectives of the XAJ-NEW include building a comprehensive, multiscale, and nested hydrometeorological monitoring and experimental program, strengthening the observation of the water cycle, discovering the spatiotemporal scaling effects of hydrological processes, and revealing the mechanisms controlling runoff generation and partitioning in a typical humid, hilly area. After two years of operation, preliminary results indicated scale-dependent variability in key hydrometeorological processes and variables such as precipitation, runoff, groundwater, and soil moisture. The effects of canopy interception and runoff partitioning between the surface and subsurface were also identified. Continuous operation of this program can further reveal the mechanisms controlling runoff generation and partitioning, discover the spatiotemporal scaling effects of hydrological processes, and understand the impacts of climate change on hydrological processes. These findings provide new insights into understanding multiscale hydrological processes and their responses to meteorological forcings, improving model parameterization schemes, and enhancing weather and climate forecast skills.

Agronomic performance of Arabica coffee cultivars in the subtropical humid environment of Vale do Ribeira Paulista, Brazil

This research is related to the evaluation of vegetative growth parameters, initial yield and incidence of pests and diseases of twelve Arabica coffee cultivars submitted to the subtropical humidity environment of Vale do Ribeira Paulista, Brazil. The experiment was performed in the Experimental Campus of the UNESP in Registro, in a randomized block design, with three replications. Stem diameter, number of plagiotropic branches, plant height, number of internodes of plagiotropic branches, length of the first plagiotropic branch, incidence of brown eye spot and phoma leaf spot on coffee leaves, infestation by leaf miner and the yield of cultivars were evaluated. The results obtained allowed to conclude that: i) cultivars Catuaí Amarelo IAC 62, Catuaí Vermelho IAC 99 and Mundo Novo IAC 379-1 were higher than the others, with yield above the national average in 2020 and percentage of flat beans below 10%; ii) all cultivars evaluated showed a similar level of increment of variables that indicate plant growth and reproductive development; iii) the cultivation environment is favorable to infestation by the leaf miner and unfavorable to the incidence of rust; iv) The prevailing climatic conditions in the Vale do Ribeira Paulista is suitable for the production of Arabica coffee.

Trifoliate Orange-Related Rootstocks Enhance the Horticultural Performance of ‘Shamouti’ Sweet Orange under Humid Subtropical Condition

The narrow genetic pool for both scions and rootstocks used in the Brazilian orchards makes the citrus industry vulnerable to biotic and abiotic threats. Orchard diversification by using different scion–rootstock combinations is an efficient measure to promote citrus protection, through increasing the level of genetic diversity. In this paper, we report the horticultural performance of the mid-season ‘Shamouti’ sweet orange grafted on five different rootstocks (‘Rangpur’ lime, ‘Swingle’ citrumelo, ‘C-13′ citrange, and ‘Cleopatra’ and ‘Sunki’ mandarins) in a long-term experiment (2007–2017) under the Brazilian humid subtropical condition. ‘Shamouti’ trees were assessed for vegetative growth, yield, and fruit quality. Additionally, a study was performed to estimate tree density and yield for new plantings. Trees grafted on ‘Swingle’ and ‘C-13′ rootstocks were less vigorous and more productive, with cumulative yields of &gt;480 kg per tree, allowing high-density plantings (363–337 trees·ha−1). Trees on ‘Cleopatra’, ‘Sunki’, and ‘Rangpur’ were the most vigorous among the tested rootstocks, with tree heights &gt; 4.20 m. However, they took longer to establish in the field, evidenced by their growth progress. These combinations also displayed the lowest tree density estimation (≤311 trees·ha−1). Trees on ‘Cleopatra’ exhibited the lowest cumulative yield (255 kg per tree). Although some significant differences were found for fruit quality, all rootstock combinations produced fruit of suitable quality, attending the commercial grading. Our findings evidence the potential of the trifoliate orange-related rootstocks ‘C-13′ and ‘Swingle’ to be used as promising rootstocks for ‘Shamouti’ cultivation in the humid subtropics, promoting genetic diversification and enhancing yield and tree density in new orchards.

Ecohydrology of coastal aquifers in humid environments and implications of a drying climate

AbstractCoastal groundwater‐dependent ecosystems (GDEs), such as wetlands, estuaries and mangrove forests, are globally important habitats that promote biodiversity, provide climate regulation and serve as refugia for plant and animal communities. However, global warming, coastal development and over‐abstraction threaten the availability and quality of groundwater in coastal aquifers and, by extension, the ecohydrological function of dependent ecosystems. Because ecohydrological knowledge of coastal groundwater is disparate across disciplines and habitat types, we begin by summarising the physiochemical, biological and hydrological processes supported by groundwater across coastal watersheds. Groundwater makes a significant but poorly recognised contribution to the function and resilience of coastal ecosystems and will play an essential role in climate change mitigation and adaptation. This review then explores how critical ecosystem processes supported by groundwater will be affected in areas of the humid subtropics that are expected to be impacted by climatic drying. Where rainfall is predicted to decrease, reduced groundwater recharge will interrupt the hydrology of coastal GDEs, while anthropogenic pressures, such as land‐use intensification and pollution, will diminish the quality of remaining groundwater. The challenges of managing groundwater for multiple purposes under climate change predictions are highlighted. To improve the management of coastal GDEs, research should be aimed at developing robust conceptual models of coastal groundwater systems that quantify biophysical linkages with ecological communities across relevant spatiotemporal scales.

Green roofs in the humid subtropics: The role of environmental and design factors on stormwater retention and peak reduction

Numerous factors affecting the hydrological performance of green roofs vary by climate and region. But meteorological factors have received relatively little attention, while no empirical research has focused on a quantified assessment of design and environmental factors on retention and peak reduction in humid subtropical climates. In this study, the hydrological performance of green roofs with designed substrates and vegetation was monitored in a humid subtropical climate. The influence of design and environmental factors was quantitatively assessed by ANOVA and regression. Results showed that substrates based on shale and perlite performed best in combination with grasses or forbs. The order of factors influencing retention was rainfall depth > relative humidity > substrate > antecedent volumetric water content > mean intensity. As for peak reduction, the order was rainfall depth > substrate > mean intensity. These findings suggest that the role of design factors is limited compared to environmental factors. However, the peak reduction or retention of runoff on a green roof can still be improved by adjusting the materials and relative proportions of the substrates. The key factors and optimal design features identified in this study may help promote the application of green roofs in humid subtropics.

Confounding effects of harvesting on urban heat island intensity in a mid-sized city in Brazil

Urban heat island (UHI) studies have traditionally focused on the relative difference between air temperatures measured at an urban area and those at a rural location, taken as a reference. Whereas the influence of urban areas on UHI intensity has been abundantly explored, the impact of the choice of an adequate rural reference location, due to the frequent agricultural use of rural areas, still remains understudied. The issue of climate variability of rural areas is a determining factor for assessing UHI intensity. Brazil is the world's largest sugarcane producer, with a 33% share of the global market. Many mid-sized cities in the Brazilian state of São Paulo are located close to sugarcane fields, which all undergo the sugarcane growth cycle with defined pre-harvest and post-harvest stages. The aim of this study is to understand the interference of seasonal harvesting periods in sugarcane plantations on the development of UHI magnitudes in and around (at suburban locations) Piracicaba, located in the state of São Paulo, Brazil, at 22° 42′ 30“ S and 47° 38’ 01” W and characterized by Köppen-Geiger's Cfa, humid subtropical climate. We deployed a fully-equipped weather station at the site of a sugarcane crop at post- and pre-harvest and a small network of three weather stations provided with air temperature and humidity sensors in the city center and in suburban neighborhoods in Piracicaba. Pre-harvest showed the highest UHI intensities, though not confounding the analysis of intra-urban temperature differentiation patterns. Results stress the relevance of the choice of the baseline rural station in terms of temporal variability related to the sugarcane harvesting cycle.

Biodiagnostics of Resistance to the Copper (Cu) Pollution of Forest Soils at the Dry and Humid Subtropics in the Greater Caucasus Region

Forest ecosystems perform important forestry and ecological functions. However, mining and processing companies cause significant soil contamination by heavy metals, in particular, copper (Cu). The resistance of nine types and subtypes of forest soils of the dry and humid subtropics in the Greater Caucasus region to Cu contamination at concentrations of 100, 1000, and 10,000 mg/kg was evaluated for the first time following the most sensitive and informative biological (microbiological, biochemical, and phytotoxic) indicators via a laboratory simulation study. Contamination was simulated under laboratory conditions. The series of forest soils was established following their resistance to Cu pollution: brown leached soils (Haplic Cambisols Eutric) = brown typical soils (Haplic Cambisols Eutric) &gt; brown carbonate soils (Haplic Cambisols Eutric) = sod-carbonate typical soils (Rendzic Leptosols Eutric) ≥ yellow soils (Albic Luvisols Abruptic) ≥ leached sod-carbonate soils (Rendzic Leptosols Eutric) &gt; brown forest slightly unsaturated soils (Haplic Cambisols Eutric) &gt; acid brown forest soils (Haplic Cambisols Eutric) &gt; acid brown forest podzolized soils (Haplic Cambisols Eutric). Regional environmentally safe standards for the Cu content in forest soils of the dry and humid subtropics of the Greater Caucasus were proposed: for brown typical soils, brown leached soils, brown carbonate soils, brown forest slightly unsaturated soils, sod-carbonate typical soils, leached sod-carbonate soils, and yellow soils, the rMPC was 100 mg/kg; for acid brown forest soils and acid brown forest podzolized soils, the rMPC was 70 mg/kg.

Long-term tillage, residue management and crop rotation impacts on N2O and CH4 emissions from two contrasting soils in sub-humid Zimbabwe

The respective contribution of conservation agriculture (CA) principles (no-tillage, permanent soil cover/mulch and crop rotations) on greenhouse gas (GHG) emissions is still unclear. This study was conducted at two long-term experimental sites established in 2013 in Zimbabwe, on an abruptic Lixisol at Domboshava Training Center (DTC) and on a xanthic Ferralsol at the University of Zimbabwe Farm (UZF). The purpose of the study was to unravel the individual and combined effects of tillage, mulching and rotation on N2O and CH4 emissions in low nitrogen (N) input maize-based cropping systems (< 60 kg N ha−1) and to compare emissions within maize rows and between maize rows. We hypothesised that integrating no tillage, mulch and cereal-legume rotation would enhance N2O emissions. Six treatments, replicated four times were investigated: conventional tillage, conventional tillage with rotation, no-tillage, no-tillage with mulch, no-tillage with rotation, no-tillage with mulch and rotation. The main crop was maize (Zea mays L.) and treatments with rotation included cowpea (Vigna unguiculate L. Walp.). Gas samples were regularly collected using the static chamber method in the maize row and inter-row spaces during the 2019/20 and 2020/21 cropping seasons and during the 2020/21 dry season. Soil moisture and mineral N were measured in the 0–20 cm soil depth. In 2019/20, cumulative total N2O emissions were significantly higher in mulch treatments at DTC, while at UZF N2O emissions were higher with cowpea rotation. Cumulative total N2O emissions ranged from 215 to 496 g N2O-N ha−1 yr−1 and from 226 to 395 g N2O-N ha−1 yr−1, at DTC and UZF, respectively. In 2020/21, N2O emissions were much lower and no differences were found between treatments on both sites (145 to 179 g N2O-N ha−1 yr−1 and 83 to 136 g N2O-N ha−1 yr−1 at DTC and UZF, respectively). A significant relationship was found between soil nitrate and daily N2O emissions. At UZF, highest N2O emissions were observed at a water-filled pore space of 60–70%. There were no significant differences in yield-scaled N2O emissions between treatments at both sites for the two seasons. DTC was a net source of CH4 (694 g CH4-C ha−1 yr−1 on average), while UZF was a net sink of CH4 (−494 g CH4-C ha−1 yr−1 on average). No evidence was found for in situ CH4 production at DTC, and an external source is most likely. Our study indicates that for low N input cropping systems in the sub-humid tropics, N loss through N2O is low.

Climatic water balance forecasting with machine learning and deep learning models over Bangladesh

AbstractUnderstanding the impact of input variables on black‐box machine learning and deep learning models is necessary. Therefore, this study proposed SHapley Additive exPlanations (SHAP) values to address the problem of the interpretability of the output of the support vector machine (SVM), random forest (RF), convolutional neural network (CNN), and long short‐term memory (LSTM) models to forecast climatic water balance (CWB) within 1–3 months lead‐time. The current study uses two Koppen–Geiger climate zones over Bangladesh: the humid subtropical climate with dry winter and hot summer (Cwa) and the tropical climate (Af‐Am). Monthly antecedent CWB, potential evapotranspiration (PET), convective available potential energy (CAPE), relative humidity (RH), air temperature (TEM), El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and North Atlantic oscillation (NAO) are used as the inputs to the proposed model. SHAP values show that CWB (current month) for both climate zones has the maximum impact on the prediction. The effects of atmospheric variables and ocean–atmospheric teleconnections on CWB forecasts over Bangladesh are low. Forecasting results show that the SVM model shows the best performance for CWB forecasts in the Cwa and Af‐Am climate zones in terms of antecedent CWB as input. And this model effectively decreases the negative effect of increasing forecast lead‐time. Since the proposed model can predict CWB in 3‐months lead‐time, it would help policy‐makers and practitioners to reduce the drought and flood impacts in the future by adopting better preparedness plans.

A year-assessment of the suitability of a green façade to improve thermal performance of an affordable housing

The urban green infrastructure has been increasingly used for sustainable design and resilient cities. Despite its many benefits, such as aesthetic enhancement, improvement of the physical and mental health of residents, especially for vulnerable youth and elderly people, or creating opportunities for social cohesion and climate regulation, green infrastructure has not been used in low-income housing in subtropical Brazil, where the temperature can reach over 40 °C along the summer. This study evaluated a full-scale, low-cost green façade over a year to assess its effect on the thermal performance of an eco-friendly affordable housing located in humid subtropical climate. Aiming to be eco-friendly and keep its cost low, the house was built with materials such as unplastered hollow soil-cement bricks, not having very good thermal performance. The Wisteria floribunda, a deciduous vine, was used in the green façade installed on a west-facing wall, adjacent to a bare wall, which was also evaluated enabling to establish the thermal difference between the shaded wall and the bare wall. In the winter, the shaded and bare walls' amplitudes were remarkably close, due to leaf shedding, a desirable feature to improve temperatures within the house. The benefits of the green façade were clearer during spring and summer when the external surface temperature of the shaded wall was reduced by up to 9 °C compared to the bare wall, and its thermal amplitude varied by 8.4 °C, while the amplitude of the bare wall was more than double this value. The plant layer diminished the heat flux through the external wall by up to 22.3 W/m2 during the summer, and 8 W/m2 during the winter. These results show the potential of a low-cost green façade to improve the thermal comfort of green affordable housing projects.

Storage variability controls seasonal runoff generation in catchments at the threshold between energy and water limitation

AbstractAnnual water balance calculations may elide intra‐annual variability in runoff generation, which could limit understanding of the similarities and differences between water‐ and energy‐limited catchments. This may be especially important in comparisons between catchments close to the threshold between water‐ and energy‐limitation. For this study, we examined runoff generation as a function of catchment storage in four watersheds, with focus on two that exist close to these thresholds, to identify how year‐to‐year variability in storage that results in intra‐annual variations of runoff generation efficiency. Specifically, we focused on one energy‐limited catchment in the humid subtropics and one water‐limited catchment in a Mediterranean climate. We used measured and calculated daily water balance components to calculate variations in the relative magnitude of daily storage. We isolated precipitation events to draw connections between storage and runoff generation at intra‐annual scales and compared our findings to the same metrics in two intensely energy‐limited landscapes. We observed distinct stages in daily storage across water years in watersheds at the threshold, where systems experienced wet‐up, plateau, and dry‐down stages. During the wet‐up, precipitation was partitioned to storage and runoff ratios (RR) were low. In the plateau, storage was filled and precipitation was partitioned to runoff, causing high RRs. During the dry‐down, storage decreased as precipitation was partitioned to evapotranspiration and runoff, causing low RRs. The critical role of evapotranspiration during the growing season resulted in relatively higher RRs during the wet‐up than during the dry‐down for a given storage value. Thus, the same storage amount was partitioned to evapotranspiration or runoff differently throughout the year, depending on the storage stage. Despite their different positions on opposite sides of the threshold, the similarity between the two focus catchments suggests a potential characteristic behaviour of systems at the threshold common to both humid and semi‐arid landscapes.

Effect of mulching materials on soil temperature and horticultural attributes in pear (Pyrus pyrifoila (Burm.) Nakai) under humid subtropical climate of Punjab

ABSTRACT- The effect of mulching materials on soil temperature and horticultural attributes in pear under subtropics of northwestern India was studied for years 2018 and 2019. Different mulches such as paddy straw mulch (PSM), white polythene mulch (WPM) and black polythene mulch (BPM) were applied underneath the canopies of ‘Patharnakh’ pear trees during second week of April. The weedy check (control) and manual weeding plots were kept to compare the relative effects of different mulching materials. The observations on soil temperature were noted at weekly interval while the quality parameters of pear fruit were recorded at harvest. Among the time intervals of soil temperatures, the higher soil temperature was observed with the WPM mulch followed by BPM while the minimum soil temperature was recorded with PSM. The WPM treatment showed soil warming effect from 16th to 28th standard meteorological week (SMW) during both the years of investigation. Different mulches significantly influenced the fruit yield and quality attributes of Patharnakh pear. The maximum fruit weight and fruit yield was observed in PSM, while minimum in control as weedy check. The internal quality of pear fruits in terms of total soluble solids was better in PSM and WPM as compared to fruits from control plants. It can be summarized that the readily available soil moisture and optimum soil temperature conditions during fruit development period improves fruit size particularly under PSM and WPM.&#x0D; Key words: Soil temperature, mulches, management practices, pear, fruit attributes.

Experimental and numerical analysis of naturally ventilated PV-DSF in a humid subtropical climate

Photovoltaic double-skin façades (PV-DSFs) have great potential to simultaneously achieve power generation, thermal insulation and natural lighting when applied in buildings. Among them, crystalline silicon PV-DSF is one of the common types due to its high efficiency and mature technology. However, the alternate arrangement of opaque crystalline silicon and transparent glass in crystalline silicon PV-DSF complicates its heat transfer characteristics. Furthermore, the ventilation air cavity in crystalline silicon PV-DSF could induce a vertical convective heat transfer process. It is difficult to accurately predict the complex multidimensional heat transfer process in crystalline silicon PV-DSF by simplified 1-D or 2-D thermal models. Therefore, a comprehensive numerical model of PV-DSF including the optics, electricity and 3-D heat transfer sub-models is developed in this paper to estimate the annual electrical and thermal properties of PV-DSF in a humid subtropical climate. The effects of structure, orientation, air cavity depth and solar cell coverage on the overall performance of PV-DSF are analyzed. In comparison with single-glazed semi-transparent photovoltaic, PV-DSF provides a 30.4% reduction in heat gain and a 50.3% reduction in heat loss. The preferred installation orientation is due south for PV-DSF in a humid subtropical climate.

Allelopathy and Allelochemicals of Imperata cylindrica as an Invasive Plant Species.

Imperata cylindrica is native to Southeast Asia and East Africa and has become naturalized in humid tropics, subtropics and warmer temperate zones of the world. The species is one of the top ten worst weeds in the worlds and is listed among the world’s top 100 worst invasive alien species. It is an aggressive colonizer and forms large monospecific stands in several countries. Possible evidence of the allelopathy of I. cylindrica has been accumulated in the literature over three decades. The extracts, leachates, root exudates, decomposing residues and rhizosphere soil of I. cylindrica were found to suppress the germination and growth of several plant species, including woody plant species, and to reduce their rhizobium nodulation and mycorrhizal colonization. Several allelochemicals, such as fatty acids, terpenoids, simple phenolics, benzoic acids, phenolic acids, phenolic aldehydes, phenylpropanoids, flavonoids, quinones and alkaloids, were also found in the extracts, leachates, root exudates and/or growth medium of I. cylindrica. These observations suggest that allelochemicals may be synthesized in I. cylindrica and released into the rhizosphere soil and surrounding environments either by the leachates, root exudation or decomposition process of plant parts, and certain allelochemicals may contribute to the alteration of the microbial community, including rhizobia and mycorrhizal fungi, suppressing the regeneration process of native plant species through the inhibition of their germination and growth. Therefore, the allelopathy of I. cylindrica may support its invasiveness, naturalization and formation of large monospecific stands. This is the first review article focusing on the allelopathy of I. cylindrica.

CO2 dynamics in a small and old subtropical reservoir in East Asia: Environmental controls driving seasonal and spatial variability

Inland waters have been increasingly viewed as hotspots for greenhouse gas (GHG) emissions owing to their strong capability to intercept and mineralize carbon from the terrestrial environment. Although small waterbodies in humid subtropical climates have the potential to emit considerable amounts of GHG, their emission patterns have remained understudied. This study involved intensive measurements of carbon dioxide (CO2) emissions from a small reservoir and its upstream and downstream reaches located in subtropical Hong Kong. Our results revealed that a variety of metabolic, hydrological, and hydrochemical processes play a critical role in regulating its CO2 dynamics. The reservoir was an overall source of CO2 to the atmosphere with an average areal flux of 24.6 mmol m−2 d−1, and it occasionally functioned as a sink for atmospheric CO2 under intense solar radiation when primary productivity was high. This flux is on the low side relative to that of global (sub)tropical reservoirs, which was likely attributable to the prolonged history of the reservoir (>150 years) and the occasional undersaturation of CO2 in the water column. We also noticed pronounced differences in the underlying controls of CO2 dynamics between the reservoir and its upstream and downstream reaches, emphasizing the importance of taking into account the distinct characteristics of both lentic and lotic waters when evaluating catchment-scale CO2 fluxes.