Rainless Periods Research Articles

Streamflow diurnal fluctuation and driving mechanism of headwater stream in a semi-humid mountainous region

Diurnal fluctuation in streamflow during rainless periods provides valuable signals for the calibration of hydrological models and comprehension of hydrological processes. Previous research has primarily focused on this phenomenon in the context of single-factor analysis in the Mediterranean, Maritime, and Alpine climates of Middle Europe and Western US. This study is based on the Xitaizi Experimental Watershed (XEW), a typical mountainous headwater watershed situated in the semi-humid monsoon North China Plain. Seven years of high-frequency observation data were used to investigate the characteristics of streamflow diurnal fluctuation, its driving mechanisms, and the propagation pathways of these fluctuation signals through hillslope-riparian-stream. The results are as follows: (1) Streamflow exhibits diurnal fluctuation during rainless periods throughout the year, with variations up to 36% of the daily mean and distinct patterns in rainy (peak at night) and dry seasons (peak in the afternoon). Choosing the proper timing for daily discharge observation can reduce bias due to fluctuations. (2) In rainy seasons, the impact of discharge fluctuation is significant, particularly in years with lower discharge. Meanwhile, the soil moisture in both the hillslope and the riparian zone, and the groundwater level in the riparian zone exhibit a daytime decline and a nighttime rise. The groundwater level in the hillslope fluctuates with a lag time of approximately 6 to 9 hours. (3) Numerical simulations and cross-correlation analysis demonstrate that the dominant driving mechanism of diurnal fluctuations in rainy seasons is the diurnal evapotranspiration variation in the riparian zone, while the influence of aquifer hydraulic conductivity is insignificant.

Observed characteristics and projected future changes of extreme consecutive dry days events of the growing season in Serbia

AbstractOne of the frequently used drought metrics in scientific research is the consecutive dry days (CDDs) because it effectively indicates short‐term droughts important to ecosystems and agriculture. CDDs are expected to increase in many parts of the world in the future. In Serbia, both the frequency and severity of droughts have increased in recent decades, with most droughts being caused by a lack of precipitation during the warmer months of the year and an increase in evapotranspiration due to higher temperatures. In this study, the frequency and duration of extreme CDDs in the growing season in Serbia were analysed for the past (1950–2019) and the future (2020–2100) period. The Threshold Level Method over precipitation data series was used to analyse CDD events, where extreme CDDs are defined as at least 15 consecutive days without precipitation. In contrast to the original definition of the CDD as the maximum number of consecutive days with precipitation less than 1 mm, here we defined the threshold that is more suitable for agriculture because field crops can experience water stress after 15 days of no rainfall or irrigation. An approach for modelling the stochastic process of extreme CDDs based on the Zelenhasić–Todorović (ZT) method was applied in this research. The ZT method was modified by selecting a different distribution function for modelling the durations of the longest CDD events, enabling a more reliable calculation of probabilities of occurrences. According to the results, future droughts in Serbia are likely to be more frequent and severe than those in the past. The duration of the longest CDDs in a growing season will be extended in the future, lasting up to 62 days with a 10‐year return period and up to 94 days with a 100‐year return period. Results indicate a worsening of drought conditions, especially in the eastern and northern parts of Serbia. The results can help decision‐makers adapt agricultural strategies to climate change by providing information on the expected durations of extreme rainless periods in future growing seasons. Although the analysis was performed in Serbia, it can be applied to any other region.

The Impact of Beaver Dams on the Dynamic of Groundwater Levels at Łąki Soleckie

Areas excluded from agricultural production are susceptible to the presence of beaver families. The most significant changes occur during the initial period, when agricultural utilization is abandoned and beavers establish their presence on the land. During this period, some parcels remain uncultivated, while agricultural activities persist in neighboring areas. This situation is accompanied by the destruction of beaver dams, especially during periods of abundant water resources, and notably during intensive fieldwork. The article presents field studies aimed at determining the extent to which constructed and operational beaver dams contribute to changes in groundwater levels in drained peatland areas. In order to protect and sustainably use peat soils, it is necessary to maintain their high moisture content by ensuring a high groundwater level elevation. This can be achieved through the use of existing damming structures in the area (levees, weirs). Beaver dams can also serve a similar function, blocking the outflow of water from peat lands by raising the water level and consequently retaining it naturally. The specific objective was to develop principles for verifying factors influencing the effects of beaver dam construction on groundwater levels in fields within their range of influence. The water table levels within the study area during rainless periods were influenced by water levels in ditches, dependent on beaver activity in the nearby river. Beaver activities, manifested through dam construction, were influenced by periodic water resources in the river, defined by the cumulative monthly precipitation. Factors affecting groundwater levels in rainless periods on the plots also included the distance from the river cross-section and the permeability of soils expressed by the filtration coefficient of the active layer. Beaver dams had the greatest impact on stabilizing the water table in the soil profile closest to the river.

Role of Rain in the Spore Dispersal of Fungal Pathogens Associated with Grapevine Trunk Diseases.

Grapevine trunk diseases are caused by a complex of fungi that belong to different taxa, which produce different spore types and have different spore dispersal mechanisms. It is commonly accepted that rainfall plays a key role in spore dispersal, but there is conflicting information in the literature on the relationship between rain and spore trapping in aerobiology studies. We conducted a systematic literature review, extracted quantitative data from published papers, and used the pooled data for Bayesian analysis of the effect of rain on spore trapping. We selected 17 papers covering 95 studies and 8,778 trapping periods, concerning a total of 26 fungal taxa causing Botryosphaeria dieback (BD), Esca complex (EC), and Eutypa dieback (ED). Results confirmed the role of rain in the spore dispersal of these fungi but revealed differences among the different fungi. Rain was a good predictor of spore trapping for ED (AUROC = 0.820) and BD (0.766) but not for the ascomycetes involved in EC (0.569) and not for the only basidiomycetes, Fomitiporella viticola, studied as for spore discharge (AUROC not significant). Prediction of spore trapping was more accurate for negative prognosis than for positive prognosis; a rain cutoff of ≥0.2 mm provided an overall accuracy of ≥0.61 for correct prognoses. Spores trapped in rainless periods accounted for only <10% of the total spores. Our analysis had some drawbacks, which were mainly caused by knowledge gaps and limited data availability; these drawbacks are discussed to facilitate further research.

Revealing temporal variation of baseflow and its underlying causes in the source region of the Yangtze River (China)

Abstract Baseflow plays a crucial role in sustaining the alpine ecosystem during rainless or cold periods. Despite its importance, information on how and why baseflow has changed in the source region of the Yangtze River (SRYR) is sparse. In our study, statistical analysis and the elastic coefficient method were used to identify the dynamic characteristics of baseflow and the underlying causes. The results show that monthly baseflow contributed 62–97% of runoff with a mean value of 75%, and they followed remarkable increasing trends from 1957 to 2020. The contributions of precipitation, temperature, evapotranspiration, and ecological conservation programs (ECPs) on baseflow variations were 86, 53, −15, and −24%, respectively. However, their contributions differed across months. During the warm months of May to September, precipitation played a dominant role, followed by evapotranspiration. In contrast, during other colder months, temperature was dominant; meanwhile, the effect of precipitation was almost absent. Moreover, climatic change had a hysteretic effect on baseflow variation, with a maximum lag time of 10 months. Our results highlighted critical roles of both precipitation and temperature, and indicated that climate change, rather than ECPs, dominated the variation in baseflow in the SRYR.

Pushing the limits of C3 intrinsic water use efficiency in Mediterranean semiarid steppes: Responses of a drought‐avoider perennial grass to climate aridification

Abstract Intrinsic water use efficiency (WUEi) reflects the trade‐off between photosynthetic carbon gain and water loss through stomatal conductance and is key for understanding dryland plant responses to climate change. Stipa tenacissima is a perennial tussock C3 grass with an opportunistic, drought‐avoiding water use strategy that dominates arid and semiarid steppes across the western Mediterranean region. However, its ecophysiological responses to aridification and woody shrub encroachment, a major land‐use change in drylands worldwide, are not well‐understood. We investigated the variations in leaf stable isotopes (δ18O, δ13C, δ15N), nutrient concentrations (N, P, K), and culm water content and isotopic composition (δ18O, δ2H) of paired pure‐grass and shrub‐encroached S. tenacissima steppes along a 350 km aridity gradient in Spain (10 sites, 160 individuals). Culm water isotopes revealed that S. tenacissima is a shallow‐rooted grass that depends heavily on recent rainwater for water uptake, which may render it vulnerable to increasingly irregular rainfall combined with faster topsoil drying under climate warming and aridification. With increasing aridity, S. tenacissima enhanced leaf‐level WUEi through more stringent stomatal regulation of plant water flux and carbon assimilation (higher δ13C and δ18O), reaching exceptionally high δ13C values (−23‰ to −21‰) at the most arid steppes. Foliar N concentration was remarkably low across sites regardless of woody shrub encroachment, evidencing severe water and N co‐limitation of photosynthesis and productivity. Shrub encroachment decreased leaf P and K but did not affect S. tenacissima water status. Perennial grass cover decreased markedly with both declining winter rainfall and shrub encroachment suggesting population‐level rather than individual‐level responses of S. tenacissima to these changes. The fundamental physiological constraints of photosynthetic C3 metabolism combined with low foliar N content may hamper the ability of S. tenacissima and other drought‐avoider species with shallow roots to achieve further adaptive improvements in WUEi under increasing climatic stress. A drought‐avoiding water use strategy based on early stomatal closure and photosynthesis suppression during prolonged rainless periods may thus compromise the capacity of semiarid S. tenacissima steppes to maintain perennial grass cover, sustain productivity and cope with ongoing climate aridification at the drier parts of their current distribution. Read the free Plain Language Summary for this article on the Journal blog.

Old-growth forest versus generalist lichens: Sensitivity to prolonged desiccation stress and photosynthesis reactivation rate upon rehydration

ABSTRACT Most epiphytic lichens demonstrate high specificity to a habitat type, and sensitive hygrophilous species usually find shelter only in close-to-natural forest complexes. Some of them are considered as old-growth forest and/or long ecological continuity indicators. To evaluate general links between the narrow ecological range and physiological traits, two distinct sets of model lichens, i.e., old-growth forest (Cetrelia cetrarioides (Duby) W.L. Culb. & C.F. Culb., Lobaria pulmonaria (L.) Hoffm., Menegazzia terebrata (Hoffm.) A. Massal.), and generalist (Flavoparmelia caperata (L.) Hale, Hypogymnia physodes (L.) Nyl., Parmelia sulcata Taylor) ones, were examined in terms of sensitivity to long-term desiccation stress (1-, 2-, and 3-month) and photosynthesis activation rate upon rehydration. Desiccation tolerance and response rate to rehydration are specific to a given ecological set of lichens rather than to a particular species. Noticeable delayed and prompt recovery of high photosynthetic activity of photosystem II (PSII) characterize these sets, respectively. At the same time, although a decrease in the potential quantum yield of PSII in lichen thalli with a relative water content (RWC) at the level of 25% was observed, the efficiency remained at a very high level for all species, regardless of habitat preferences. Among the examined lichens, the fluorescence emission parameters for F. caperata were the fastest toward equilibrium upon rehydration, both after a shorter and a longer period of desiccation stress. In contrast to generalist lichens, retrieving of photosynthesis after 3-month desiccation failed in old-growth forest lichens. In the long term, prolonged rainless periods and unfavorable water balance in the environment predicted in the future may have a severely limiting effect on hygrophilous lichens during growing season (also in the sense of species associations) and, at the same time, promote the development of generalists.

DIFFERENT TILLAGE REGIMES' EFFECT ON SOIL-WATER PHYSICAL AND AGROCHEMICAL PROPERTIES UNDER THE ENVIRONMENTAL CONDITIONS OF SOUTH EAST KAZAKHSTAN

For improvement and rational use of rainfed lands, a study on the influence of different tillage methods proceeded on the soil-water physical relationship and soil agrochemical properties in Southeast Kazakhstan. In the arable soil layer (0–30 cm), the soil density during the studied crop’s life from sowing to harvesting, enhanced to a medium compacted state with the traditional method of tillage (1.28–1.29 g/cm3), slightly higher with the minimum tillage (1.30–1.31 g/cm3), and the highest with zero tillage (1.32–1.33 g/cm3). Tillage with better crumbling, dissolution, and superior ingestion of plant vestiges in the cultivated soil layer contributed to a slight decrease in soil density, both with traditional and minimum tillage regimes. Given the least rainfall in summer, there was a decline in the productive moisture reserves in the soil with customary tillage (15.9–34.5 mm). However, the soil moisture enhanced gradually with reduced tillage, i.e., minimal tillage (20.7–36.7 mm) and zero tillage (29.8–54.8 mm). The nitrate nitrogen content in the soil also decreased from the initial state to the cultivated crops’ harvest, and a significant decrease emerged with zero tillage. The prolonged rainless period, accompanied by a decline in relative air humidity, soil moisture, and temperature increases, affected plants’ physiological processes and, eventually, the studied crops’ yield. In the studied crops, on average, acquiring the highest yield of 1.76 t/ha was with minimal tillage. Based on two-way analysis of variance (ANOVA), the contributed share of the crops in the grain yield formation was according to crop season, ranging from 0.73% to 2.89%, and the soil cultivation methods’ share was 83.3%–93.8%. The grain yield formation has a greater dependence on the tillage regimes, although that reliance might vary in association with weather conditions during the crop life. In rainfed conditions of Southeast Kazakhstan, zero tillage results in a significant reduction in nitrate nitrogen compared with conventional and minimum tillage. Therefore, with no tillage, more nitrogen fertilizer is necessary than usual plowing and the application of potash fertilizers, regardless of tillage methods.

Hydrological responses to litter density on runoff-infiltration patterns and water conservation in Pinus tabuliformis plantation

Leaf litter alters the distribution of rainfall and thus affect evapotranspiration and soil water storage (SWS), especially in areas with deep soil layers. Few studies have characterized the hydrological responses to leaf litter density in afforested ecosystems. Ten runoff plots of five litter masses, 0, 0.6, 0.9, 1.2 and 1.8 kg/m2 (referred to as 0LM, 0.6LM, 0.9LM, 1.2LM and 1.8LM, respectively), were established in a Pinus tabuliformis plantation to investigate the compound effects of litter density and rainfall on runoff generation, throughfall infiltration and water conservation in the rainy season of 2020–2021. The runoff coefficient (ɑ) was 0–0.80 mm/mm during rainfall events. With the exception of litter density, runoff generation was further affected by wind speed and rainfall intensity, especially during small rainfall events. In general, the runoff yield (R) was 51.8%, 63.8% and 83.9% lower in 0.6LM, 1.2LM and 1.8LM, respectively, than in bare soil. Higher litter density and greater throughfall (P) promoted the infiltration of P to deeper soil layers, and the wetting depth of 1.8LM increased from the 0–20 cm soil layer during small rainfalls to the 0–50 cm soil layer during large rainfall events in 2021. Moreover, thick litter had greater capacity in throughfall interception (I), partially contributed to the negative values of SWS during small rainfall events and rainless periods. A total of 0–8.7% of P was consumed in I, and 26.4%, 33.1%, 38.5%, and 40.2% of P contributed to SWS in 0LM, 0.6LM, 1.2LM, and 1.8LM, respectively. With the exception of the R/P of 1.2LM, which was a little higher than that of 1.8LM, the water conservation capacity of 1.2LM was similar to that of 1.8LM. This study may enhance our understanding of the eco-hydrological function of litter and will aid the sustainable and ecological management of plantations in Chinese Loess Plateau.

СКЛАДОВІ РАДІАЦІЙНОГО РЕЖИМУ СОНЯЧНОЇ РАДІАЦІЇ ПРИ ПОСУХАХ ЗА 1991-2020 РР. В УКРАЇНІ

Changes in the components of the radiation regime of solar radiation during periods of intense droughts and their comparison with average values for 1991-2020 in Ukraine are given. Drought is a complex and dangerous natural phenomenon caused by the anticyclonic nature of the atmospheric circulation, the long-term transformation of slow-moving air masses over large areas. A complex of dynamic processes leads to its development. They are facilitated by an increased supply of short-wave radiation, high air temperature, a rainless period, and a lack of moisture in the air and soil. The archive of measurements of the meteorological and actinometric network of observations of the Borys Sreznevskiy CGO of the SES of Ukraine was used. A database of observations of individual components of the radiation regime of solar radiation and a catalog of droughts has been created. Droughts of different intensity and duration during the growing seasons for 1991-2020 were determined. The change in atmospheric circulation led to an increase in clear and cloudless weather, changes in the arrival of components of the radiation regime of solar radiation to the substratum. The biggest changes were in the warm period. In 1991-2020, relative to 1961-1990, the duration of sunshine, direct and total solar radiation increased during the year, and diffuse radiation decreased. During 1991-2020, droughts were observed for 22 years, including 17 growing seasons throughout the territory. They differed in types (air, air-ground, ground), duration, distribution. Prerequisites for the development of droughts were observed in some cold periods. In particular, droughts. observed in November, February-March. In the warm period, intense droughts were observed for short periods of time (less than a month) in some areas and powerful, long-lasting ones in the prevailing area. In certain months of the growing season during droughts, significant deviations of individual components of solar radiation compared to the average for 1991-2020 were observed throughout the country. Usually, during dry periods, the duration of sunshine and direct solar radiation increased significantly, diffuse radiation decreased, so the total radiation did not always increase. An increase in individual components of the radiation regime led to an increase in the total radiation balance and albedo of the underlying surface. The research is part of the monitoring of climate anomalies. They are necessary for solving applied problems of adapting agricultural production to permanent and long-term droughts in a large area.

Perspective method for construction of drying and watering network for growing potatoes

In the Central region of the Russian Federation, precipitation is uneven both during the growing season of plants and during the calendar year. Therefore, to obtain sustainable yields and ensure the optimal water-air balance of the soil, agro-reclamation measures are required, including the organization of additional irrigation. During the winter period, a significant amount of snow accumulates, which during the melting period does not have time to soak into the soil, forming surface runoff. The construction of a drainage and water supply network will make it possible to accumulate excess moisture in reservoirs to moisten the soil during the rainless period. The joint use of the drainage network and the drip irrigation system is recommended. Using such a system will allow at the estimated time to supply or divert water to a specific area, removing excess moisture from the soil by drainage to storage tanks and then directing irrigation water to the drip irrigation system during the dry period. The calculation of the irrigation rate, taking into account the semi-elliptical shape of the humidification contour, showed that the required volume of water could be accumulated in special storage tanks. Drip tape laying can be carried out mechanized using a special stacker based on a ridge former.

Quality control procedures for sub-hourly rainfall data: An investigation in different spatio-temporal scales in Brazil

• 1st automatic quality control on sub-hourly scale applied to Brazil rainfall dataset. • An automatic procedure that does not use a reference quality-controlled dataset. • Rainfall properties were used to spatially identify malfunctioning gauges. • 93.6% of high-quality and 78.6% of poor-quality gauges were correctly identified. There has been an increase in the intensity of rainfall extreme events. These events have a high contribution to hazards in urban areas, such as flash flooding, and landslides, which lead to social, economic, and environmental damage. Sub-hourly rainfall information has a critical role in the assessment of such natural disasters. However, precipitation gauge networks in developing countries still lack high-quality data. This study presents a new automatic quality control procedure (A-QCP) for sub-hourly rainfall data in Brazil, analysing 7 years (2014–2020) of tipping bucket rain gauge (TBRG) data from over 3,000 gauges per year provided by CEMADEN’s (Brazilian National Centre for Monitoring and Early Warnings of Natural Disasters) rain gauge network as a case study. The A-QCP developed separately examines each year through a series of single-gauge tests in which each station was considered independently, going through procedures to assess possible equipment malfunctions through data analysis like long rainless periods or with constant tips due to clogging, spurious rainfall peaks, and long periods of missing data. Then, nearest neighbour analysis was performed through spatial outlier detection using Local Moran’s Index. The performance of the method was evaluated through a confusion matrix, which compared the procedures’ results with a reference dataset created using visual and independent analyses. After the application of the proposed A-QCP to the whole database, the results show that the procedure was able to correctly identify 78.6 % of faulty rain gauges for the whole period, with less than 8 % of functioning rain gauges removed from the final High-Quality database. It was also noted that the best performing filters were the first ones applied, showing that the procedure works best on the identification of gross errors, with diminished efficiency in finding malfunctions after the sequential removal of Poor-Quality rain gauges.

Quality of first flush of rainwater from urban area: short review

As a result of changes in social, economic, and political relations, undesirable phenomena are created that have an adverse effect on the urban environment. Surface runoff represents one of several risks to environmental policy, causing the major problem in urban agglomerations. In an urbanized area, it causes an increased runoff volume and the flood peak. Also, it affects increasing the contamination of urban rainwater. The significant problem of surface runoff formation in urban river basins is the accumulation of pollutants on the surface of paved areas during the rainless period. In the case of the formation of surface runoff, these substances come into movement. It is assumed that the most polluted rainwater is in the initial phase of runoff formation. However, not all authors agree with the statement. In some literature, this phenomenon is termed the first flush. Given the above facts, the study focuses on surface runoff characteristics in terms of its quality and quantity in the initial phase of surface runoff formatting. The study aims to summarize and compare the results of several studies to evaluate the first rainwater flush in an urbanized area.

Air pollutant removal by four sidewalk tree species in the largest city in Taiwan.

Air pollutants pose risks to human health, especially in densely populated cities. We compared the interception of suspended particles and metal elements by four sidewalk tree species with different leaf surface wettability (based on contact angle), leaf area, and phenology in Taipei, Taiwan. Suspended particles were enriched 2.0-2.5 times in throughfall relative to rainfall due to wash-off of suspended particles deposited on leaf surfaces during rainless periods. The enrichment in throughfall was greater in tree species with larger leaf areas. Despite greater concentrations of suspended particles in rainfall during the low-leaf-area period, enrichment was greater in the high-leaf-area period, indicating that leaf area was a key factor affecting canopy interception of pollutants. Throughfall enrichment of suspended particles positively correlated with water quantity, indicating that air pollutants intercepted by tree canopies were not fully washed off by rainfall. Annually, ∼830g of suspended particles were intercepted and washed off from one tree canopy, with a crown area of 42 m2 . Scaling up, a rough estimate of 72.7 Mg of suspended particles were intercepted annually by the 90,000 sidewalk trees in Taipei City. Copper, chromium, and aluminum were enriched in throughfall compared with rainfall. However, lead was depleted in throughfall, indicating greater interception than wash-off. Based on our results, leaf area and length of foliated period are key characteristics affecting canopy interception of particulate matter and associated metal elements, whereas leaf surface wettability is of secondary importance.

Extreme rainless periods in Pannonian Basin

AbstractThis paper analyses extreme meteorological droughts in the territory of the Pannonian Basin in central and southeastern Europe. Droughts are treated from an agricultural perspective as periods of consecutive days with very little or no rainfall at all. By using data from the historical period 1981–2010, time intervals longer than 20 days with less than 3 mm per day during the growing season April–September are examined to determine theoretical and empirical distributions of their number and durations. Related discrete stochastic process of extremes is analysed by the Zelenhasic–Todorovic (ZT) method, successfully applied in hydrology and meteorology (e.g., peak flows, low flows, meteorological droughts, etc.). The method is applied to 52 locations across Pannonia Basin. At each location, the Poisson distribution is determined for the number of droughts, exponential distribution for the duration of droughts, and double exponential distribution for the duration of the (annually) longest droughts. To validate the quality of modelling and the results obtained, standard statistical goodness of fit tests are used. Historical data from the period 1981–2010 indicate that the central and northern part of Hungary and the entire territory of Vojvodina Province in the north of Serbia experienced the longest droughts, on average 55–60 days. In statistical terms, across Pannonia Basin once in 100 years drought may occur with an average duration of 56 days. Theoretically longest 100‐year droughts could be expected in the northern part of Hungary (up to 70 days), the eastern part of Romania (up to 68 days), and Serbia (up to 69 days). The 2‐year droughts are on the average duration of 3 weeks. Generated maps of the longest droughts in the basin may help to reduce agricultural risks due to global warming and other negative impacts of climate change.

Вплив екстремальних погодних умов вегетаційного періоду на ріст і розвиток горіха чорного (Juglans nigra L.) у зоні Полісся

Distinctive features of the morphometric indicators of the vegetative organs of Juglans nigra by years of research were determined. It was established that the seasonal rhythm of the development of research objects is consistent with the natural and climatic conditions of the introduction area. During the years of research, the weather conditions for black walnut vegetation were extreme. On average, over three years of research, May was the wettest month - 61.80 mm. Quantitative parameters of the leaf blade: length, width of a compound leaf, the number of leaves and their area were strongly correlated with the weather conditions of the growing season of the research years, while no positive correlation was found in the structural changes of the growth of the leaf surface and their number relative to the height of the plant during the three years of observations. In 2019, the following factors negatively affected the formation of the black walnut leaf blade (significantly reducing its parameters): a winter with little snow, insignificant precipitation during the growing season, a long rainless period in the summer months, high temperatures and low air humidity during the growing season. However, during the period of research, young and adult plants of black walnut successfully passed the dry growing seasons, among them no dried trees that fell from the plantations were found. The plants showed adaptive properties to the negative impact of the hot and dry growing season of 2019 in the research area. According to the results of the research, a conclusion was made about the success of the introduction of black walnut in the conditions of the Polissia zone of Ukraine.

Analysis of varietal diversity, decorativeness and peculiarities of growth and development of cultivars Dahlia cultorum Thorsrud & Reisaeter in the collection of the biostationary of Bila Tserkva NAU

Aim. In order to identify promising cultivars of Dahlia cultorum for use in landscaping in Kyiv region, the analysis of the system of qualitative and quantitative indicators of cultivars of dahlias, the peculiarities of their growth and development in the absence of irrigation is conducted. Methods. To analyze the diversity of Dahlia cultorum cultivars at the biostationary of Bila Tserkva NAU, the classification developed by the American Society of Dahlia (ADS classification) was used. The cultivar assortment of dahlias was studied according to the descriptions of the catalog of the company “SontseSad”, which transferred 108 cultivars of Dahlia cultorum to Bila Tserkva NAU biostationary in 2014. Phenological rhythms of growth and development of dahlias were studied according to the methods of B. K. Shybniev, H. D. Yurkevych, and D. S. Holod. The increment of dahlias was measured during the period of active growth, the size of the flower — during the period of its full opening with the help of a measuring ruler on 5 specimens of each cultivar every decade. Results. Based on the analysis of the varietal composition of Dahlia cultorum collection of dahlia cultivars of Bila Tserkva NAU biostationary, it was found that the largest number of 36% belongs to the cultivar group of decorative dahlias, 12% — to cactus, 7% — to spherical and 1% to pompoms and anemones. The mixed cultivar of dahlias is 43.4%, among them the most numerous group of dahlias with dissected leaves “Deer antlers” — 48%, “Karma” — 19%, pot — 12%, French collection — 21%. According to the color spectrum, the collection is dominated by dahlias of red color — 29%, pink — 19%, yellow and orange — 16% each, violet — 12%, white color — 6%. Two-color cultivars amount to only 2%. Observations show that in May–June, due to the long and dry period and the lack of artificial irrigation, all cultivars of dahlias at Bila Tserkva NAU biostationary were marked by very slow growth. As of July 15, the height of dahlia bushes averaged 30–50 cm, which was significantly less than the size presented in the catalog of the magazine “SontseSad”. Conclusions. The collection of dahlias at Bila Tserkva NAU biostationary includes 108 cultivars belonging to seven main cultivar groups, including 11 cultivars from the new French collection. Early in the first decade of July, the cultivars ‘Islande’, ‘Maki’, ‘Sir Alf Ramsay’, ‘Mingus Alex’, ‘Glorie van Heemstede’ begin to bloom. Latest of all, in August, cultivars ‘Babylon Rose’, ‘Amanda’, ‘Aitara Bronwyn’, ’Karma Gold’, ‘Gallery Rembrandt’, ‘Lilac Time’, and ‘Star Spectacle’ began flowering. It is established that the period from the appearance of the bud to the opening of the flower in dahlia cultivars lasts 25-30 days. The first buds appeared in early July, but their peduncles were very short and such flowers were not suitable for cutting. In fact, the blooming central flower itself was 5-10 cm lower than the second-order buds around it, and therefore had a limited view from the inflorescence, which led to a loss of decorativeness in the cultivars ‘Romance’, ‘Candlelight’, and “Karma Bon Bini”. The duration of flowering of one dahlia flower in different cultivars ranged from 5 to 17 days. The longest period of blooming of one flower is 14-17 days in ‘Autumn Fairy’, ‘Nagano’, ‘Idylle’, ‘Babylon Brons’, ‘Duet’ cultivars. The shortest blooming period of one flower is 5-7 days for ‘Ellen Huston’, ‘Champs Elysees’, ‘ThykiYori No Shisha’, ‘Aspen’ cultivars. Due to the high air temperature and the long rainless period, the peak of flowering of dahlias in the conditions of Bila Tserkva NAU biostationary was at the beginning of September.

Vier Dekaden Weberknechtforschung mit dem 64. Band der ‚Tierwelt Deutschlands‘ – Rückblick, aktueller Stand und Ausblick

A short history of the Opiliones volume in ‘Die Tierwelt Deutschlands’ published by Martens (1978) is presented. The area under consideration comprises Central Europe expanded by large parts of Scandinavia, the British Isles, non-Mediterranean France, Benelux, the complete Alps and in the south-east those parts of Romania and Croatia whose fauna was sufficiently well known. Additions and changes which appeared since 1978 are highlighted: new species discovered in this area, taxonomic changes, important distributional records, as well as changes of faunal composition due to human-mediated influences and climate change are addressed. Perspectives for further research concern faunal inventory especially in the Southern Alps, ecological studies, control of faunal change dynamics and morphological-anatomical investigations. Originally, 113 species were documented for this area and 31 species have been newly discovered since. Of these, 22 species have their type locality in the area under consideration. Eight species had to be excluded from the list due to incorrect identifications, wrongly attributed locality indications and synonymies (Peltonychia postumicola, P. gabria, P. insignis, Ischyropsalis pyrenaea, I. helvetica, Leiobunum tiscae, Nelima nigripalpe, Opilio ravennae). The majority of the new species were discovered in isolated areas of the Southern Alps, largely congruent with Massifs de Refuge, i.e. zones that where ice-free within glacial periods. Paranemastoma silli monticola Babalean, 2011 from Romania is upgraded to species rank, Paranemastoma monticola Babalean, 2011 stat. nov. Recently, molecular genetics (Ischyropsalis, Trogulus, Megabunus) and partly chemical and ecological methods (Megabunus, Nemastoma) helped to understand species delimitations more accurately, resulting in considerably higher number of species in the relevant genera than formerly believed. Due to recent man-made introductions eight species reached our area of investigation after 1978, but considerably more species in partial areas like Great Britain or the Netherlands. Successive range expansions of these species differ considerably from nearly zero to complete coverage of central Europe. Dasylobus graniferus is recorded for the first time in Germany. Following climate warming favourable conditions accelerate northward extension of native species, namely to the British Isles, northern parts of Central Europe and southern Scandinavia. By contrast, rainless dry summer periods influence the Central European opilionid fauna negatively causing regional extinctions.

Experimental investigation of dust accumulation effect on the performance of tubular daylight guidance systems

Tubular daylight guidance systems were developed to introduce daylight into the building’s core. Operating the system in desert climate regions, where both solar irradiance and dust resources are abundant, exposes them to dust accumulation that significantly reduces the system’s efficiency. An experimental investigation was conducted in Cairo to understanding dirt accumulation patterns and impact, and to recommend suitable cleaning procedures. It was found that dust accumulation during three rainless periods, of 44 days each, could reduce the illuminance transmittance by up to 38%. The dust accumulation was found to decrease the system efficiency in a near-linear fashion with a 0.5% daily reduction. The highest illuminance transmittance magnitude and ratio were observed at midday, followed by the morning period and then the afternoon period. Similarly, the transmittance loss by the end of the experiment was found to be around 31%, 26% and 13% at noon, morning and afternoon respectively. It was found that the transmittance loss under a clear sky is up to 25% more than that under a cloudy sky. Further work needs to be done to examine other meteorological factors. Based on the study findings, it is recommended to clean the solar devices bimonthly to restore the system’s efficiency.

Estimating immediate post-fire carbon fluxes using the eddy-covariance technique

Abstract. Wildfires typically affect multiple forest ecosystem services, with carbon sequestration being affected both directly, through the combustion of vegetation, litter and soil organic matter, and indirectly, through perturbation of the energy and matter balances. Post-fire carbon fluxes continue to be poorly studied at the ecosystem scale, especially during the initial window of disturbance when changes in environmental conditions can be very pronounced due to the deposition and subsequent mobilization of a wildfire ash layer and the recovery of the vegetation. Therefore, an eddy-covariance system was installed in a burnt area as soon as possible after a wildfire that had occurred on 13 August 2017 and has been operating from the 43rd post-fire day onwards. The study site was specifically selected in a Mediterranean woodland area dominated by maritime pine stands with a low stature that had burned at high severity. The carbon fluxes recorded during the first post-fire hydrological year tended to be very low so that a specific procedure for the analysis and, in particular, gap filling of the eddy-covariance data had to be developed. Still, the carbon fluxes varied noticeably during the first post-fire year, broadly revealing five consecutive periods. During the rainless period after the wildfire, fluxes were reduced but, somewhat surprisingly, indicated a net assimilation. With the onset of the autumn rainfall, fluxes increased and corresponded to a net emission, while they became insignificant with the start of the winter. From the midwinter onwards, net fluxes became negative, indicating a weak carbon update during spring followed by a strong uptake during summer. Over the first post-fire year as a whole, the cumulative net ecosystem exchange was −347 g C m−2, revealing a relatively fast recovery of the carbon sink function of the ecosystem. This recovery was mainly due to understory species, both resprouter and seeder species, since pine recruitment was reduced. Specific periods during the first post-fire year were analyzed in detail to improve process understanding. Perhaps most surprisingly, dew formation and, more specifically, its subsequent evaporation were found to play a role in carbon emissions during the rainless period immediately after fire, involving a mechanism distinct from degassing the ash–soil pores by infiltrating water. The use of a special wavelet technique was fundamental for this inference.