Phosphorus fluxes in two contrasting forest soils along preferential pathways after experimental N and P additions

The assessment of impacts of an altered nutrient availability, e.g. as caused by consistently high atmospheric nitrogen (N) deposition, on ecosystem phosphorus (P) nutrition requires understanding of P fluxes. However, the P translocation in forest soils is not well understood and soil P fluxes based on actual measurements are rarely available. Therefore, the aims of this study were to (1) examine the effects of experimental N, P, and P+N additions on P fluxes via preferential flow as dominant transport pathway (PFPs) for P transport in forest soils; and (2) determine whether these effects varied with sites of contrasting P status (loamy high P/sandy low P). During artificial rainfall experiments, we quantified the P fluxes in three soil depths and statistically analyzed effects by application of linear mixed effects modeling. Our results show that the magnitude of P fluxes is highly variable: In some cases, water and consequently P has not reached the collection depth. By contrast, in soils with a well-developed connection of PFPs throughout the profile fluxes up to 4.5 mg P m−2 per experiment (within 8 h, no P addition) were observed. The results furthermore support the assumption that the contrasting P nutrition strategies strongly affected P fluxes, while also the response to N and P addition markedly differed between the sites. As a consequence, the main factors determining P translocation in forest soils under altered nutrient availability are the spatio-temporal patterns of PFPs through soil columns in combination with the P nutrition strategy of the ecosystem.

Development and Assessment of Methods for Predicting Rainfall in Unmeasured Watersheds Using the Relation Between Observed and Sensor-Measured Rainfall

Recently, with the development of information and communication technology and the Internet of Things (IoT), observation technology using sensors is being applied in a variety of ways, such as using a sensor to observe rainfall in an unmeasured area. In this study, the relationship between the rainfall sensor signal (S) and the amount of rainfall (R) was developed through an experiment in an artificial rainfall generator, and the applicability was evaluated through outdoor observation. The coefficient of determination of the relational expression developed through the indoor experiment was 0.95, the mean absolute error was 2.66 mm/hr, the root mean square error was 3.87 mm/hr, the efficiency coefficient was 0.89, and the concordance index was 0.97, showing very high reliability. In the outdoor test results, the error rate was 7.96% when comparing the data from the rainfall sensors in vehicles and the precipitation station, which were not observed at the same location. Despite such errors, it is judged that accurate rainfall observation using a rainfall sensor is possible in an area where a precipitation station is not installed.

Runoff Characteristics and Soil Loss Mechanism in the Weathered Granite Area under Simulated Rainfall

Soils developed from the parent materials of highly weathered granite are particularly susceptible to soil erosion. Therefore, it is of great significance to conduct in-depth research on runoff characteristics and soil loss mechanisms in weathered granite areas. Using the weathered granite area in the hilly region of southeastern China as the research object, we conducted indoor artificial rainfall simulation experiments involving three slope steepnesses (SSs), 8°, 15°, and 25°, and five rainfall intensities (RIs), 0.5, 1.0, 1.5, 2.0, and 2.5 mm/min. The results showed that sediment load (SL) has positively linear relationships with mean runoff velocity (V), Reynolds number (Re), Froude number (Fr), shear stress (τ), and stream power (w). The eroded sediment was principally composed of silt and clay that accounted for 65.41–73.41% of the total SL. There was a boundary point at 0.02 mm for the particle size distribution (PSD) of the eroded sediment. The enrichment ratio (Er) of sand-grained particles (0.02–2 mm) ranged from approximately 0.45 to 0.65, while the Er of fine-grained particles (<0.02 mm) ranged from approximately 1.37 to 1.80. These results increase our understanding of the relationships among RI, SS, runoff, and soil losses from weathered granite hillslopes, particularly the relationships between different hydraulic parameters and sediment size characteristics.

Distributed Optical Fiber Sensor Applications in Geotechnical Monitoring

We report the experimental application of distributed optical fiber sensors, based on stimulated Brillouin scattering (SBS), to the monitoring of a small-scale granular slope reconstituted in an instrumented flume and subjected to artificial rainfall until failure, and to the monitoring of a volcanic rock slope. The experiments demonstrate the sensors’ ability to reveal the sudden increase in soil strain that foreruns the failure in a debris flow phenomenon, as well as to monitor the fractures in the tuff rocks. This study offers an important perspective on the use of distributed optical fiber sensors in the setting up of early warning systems for landslides in both rock and unconsolidated materials.

Unprecedented Retention Capabilities of Extensive Green Roofs—New Design Approaches and an Open-Source Model

Green roofs are a proven measure to increase evapotranspiration at the expense of runoff, thus complementing contemporary stormwater management efforts to minimize pluvial flooding in cities. This effect has been quantified by numerous studies, ranging from experimental field campaigns to modeling experiments and even combinations of both. However, up until now, most green roof studies consider standard types of green roof dimensions, thus neglecting varying flow length in the substrate. For the first time, we present a comprehensive investigation of green roofs that involves artificial rainfall experiments under laboratory conditions (42 experiments in total). We consider varying flow length and slope. The novelty lies especially in the consideration of flow lengths beyond 5 m and non-declined roofs. This experimental part is complemented by numerical modeling, employing the open-source Catchment Modeling Framework (CMF). This is set-up for Darcy and Richards flow in the green roof and calibrated utilizing a multi-objective approach, considering both runoff and hydraulic head. The results demonstrate that through maximizing flow length and minimizing slope, the runoff coefficient (i.e., percentage of rainfall that becomes runoff) for a 100 years design rainfall is significantly decreased: from ~30% to values below 10%. These findings are confirmed through numerical modeling, which proves its value in terms of achieved model skill (Kling-Gupta Efficiency ranging from 0.5 to 0.95 with a median of 0.78). Both the experimental data and the numerical model are published as open data and open-source software, respectively. Thus, this study provides new insights into green roof design with high practical relevance, whilst being reproducible.

Performance evaluation of water-repellent combat uniforms using a static manikin and human subjects under a rainfall tower system

The purpose of the present study was to evaluate the water-repellent properties of newly-developed combat uniforms using a rainfall tower system. Two types of water-repellent- combat uniforms with an identical level of water repellency through textile tests (WR_M and WR_T) were compared with an untreated-combat uniform (Control). A static manikin was used to evaluate water-repellent properties in a standing position and eight male subjects participated to test walking effects under artificial rainfall. The results showed that it took to saturate the upper body was longer for WR_T than WR_M and Control in the standing position for both normal and heavy rain conditions (P < 0.05). The lower body in WR_T was rarely wet in the standing position after 60 min, whereas the lower body was partially wet while walking within 30 min. Changes in clothing weight after the rainfall test were 729 ± 21, 256 ± 36 and 137 ± 25 g per trial for Control, WR_M, and WR_T, respectively (P < 0.001). Subjects expressed better tactile, less colder, less heavier, and less humid sensations and less uncomfortable feeling for WR_T than Control or WR_M (P < 0.05), while WR_M was better only for tactile sensation and heaviness than Control (P < 0.05). Ten-time-washes had not impaired the water-repellent properties of WR_M or WR_T. These results indicated that the rainfall tower test is valid to verify water-repellent property of clothing ensemble and suggest a possibility of classifying the water repellency of clothing ensemble into sub-levels of an excellent and a fair class. Further studies on wider range of experimental conditions to validate the current results are required.

Monitoring and Data Analysis in Small-Scale Landslide Physical Model

Physical modeling of landslides using scaled landslide models began in the 1970s in Japan at scaled natural slope physical models. Laboratory experiments of landslide behavior in scaled physical models (also known as flume or flume test) started in the 1980s and 1990s in Canada, Japan, and Australia under 1 g conditions. The main purpose of the landslide physical modeling in the last 25 years was research of initiation, motion, and accumulation of fast flow-like landslides caused by infiltration of water in a slope. In October 2018, at the Faculty of Civil Engineering University of Rijeka, started a four-year research project “Physical modeling of landslide remediation constructions’ behavior under static and seismic actions” funded by the Croatian Science Foundation. This paper presents an overview of the methods and monitoring equipment used in the physical models of a sandy slope exposed to artificial rainfall. Landslide development was monitored by observation of volumetric water content and acceleration as well as by observations of surface displacement by means of high-speed stereo cameras, terrestrial laser scanning, and structure-from-motion photogrammetry. Some of the preliminary results of the initial series of experiments are presented, and advantages and disadvantages of the used equipment are discussed.

Hillslope Erosion Mitigation: An Experimental Proof of a Nature-Based Solution

Soil erosion during rainfall events is affected by several factors, such as topography, soil type, land management, and vegetation cover. In this study, a series of tests investigates the influence of selected perennial herbaceous plants with a deep and strong rooting system, called MC1, on runoff generation and soil erosion. The tests on the investigated nature-based solution have been performed in the Cape Fear experimental hillslope with natural and artificial rainfall and for different vegetation heights. For all the experiments, runoff, soil moisture, and erosion data were observed and collected. The results obtained in this study suggest the following conclusions: (1) MC1 is effective in terms of soil erosion reduction already with a minimum vegetation height equal to 30 cm; (2) MC1 maximum efficiency, in terms of soil loss reduction, has been reached for a vegetation height equal to 70 cm; (3) In terms of the eroded material, the use of MC1 allows for a reduction of soil loss up to 300 times higher than the bare soil condition; (4) The use of MC1 allows for a reduction in the runoff coefficient up to 1/3 of the corresponding value in the bare soil condition.

Under what conditions do climatic variations lead to incision of alluvial fans? Insights from coupled catchment-fan system in the lab

&lt;p&gt;Although a transition from aggradation to incision is observed in many natural alluvial fans and is usually related to variations in climate, the condition driving such change remain unclear. We address this problem here by considering laboratory experiments of coupled catchment-fans systems forced by oscillatory precipitation. In the 8 experiments considered here, eroded materials from an uplifting mountain may deposit on a plateau, erosion being driven by the surface runoff of water from an artificial rainfall device. These experiments, 700 to 900 minutes-long, were performed with the same uplift rate but with different sequences of variations of the rainfall rate (10 to 40 minutes-long) between two extreme values. The topography was digitized every 10 minutes thanks to a high-resolution laser sheet.&lt;/p&gt;&lt;p&gt;We observe that the sediment (Qs) and water (Qw) fluxes at the outlet of mountain catchments continuously vary with time, not only because of precipitation oscillations but also because of the dynamic state of the landscape. For a given precipitation rate, variations of Qs and Qw depend on whether the catchments enlarge or shrink, with additional variations of Qs depending on the equilibrium degree (steady-state or not). Depending on these conditions, we document a large variety of trends of Qs vs Qw in rivers at catchment outlets, Qs increasing or decreasing with Qw, or being independent of Qw. For a given catchment, oscillations in precipitation rate then drive alternations between two individual Qs vs Qw trends, the slope of these trends being indicative of the sediment concentration in the mini-rivers at the outlet of catchments that feed alluvial fans.&lt;/p&gt;&lt;p&gt;Our experiments indicate that incision of alluvial fans is controlled by two necessary conditions. First, it occurs when rainfall increases and goes with a decrease of the Qs/Qw ratio, i.e. with a decrease of concentration at the outlet of the catchment. Second, this control is modulated by the slope of the fan, incision only occurring for fans above a threshold slope. Then, the decrease in sediment concentration required to initiate the incision is weak for steeper fans, those that developed under a mean dry climate. A larger drop in concentration is necessary for gentle fans, those that develop under a mean wetter climate.&lt;/p&gt;&lt;p&gt;Several studies already demonstrated how a decrease of Qs or an increase of Qw drives incision. We show here that these two parameters are also coupled and covariate following the dynamical state of catchments. We also demonstrate that the decrease of the Qs/Qw ratio required for initiating the incision of a fan is lower for steeper fans, that is for fans that develop under more arid condition.&lt;/p&gt;&lt;p&gt;We conclude that a given amplitude of climate change won&amp;#8217;t have the same imprint on landscapes, erosion and transport depending on the mean prevailing climate.&lt;/p&gt;

Moving towards harmonisation in rainfall simulation

&lt;p&gt;Rainfall simulation experiments are widely used in soil science, geomorphology and hydrology research and teaching. Such experimental setups are particularly important in the study of rainfall-runoff, erosion and pollutant transport processes. Rainfall simulators have been applied within laboratory- and field-based studies and have the advantage of enabling controlled and reproducible rainfall events of varying intensity, duration and drop spectra. The flexibility and adaptability of rainfall simulators to examine diverse research applications of varying temporal and spatial scales means that hundreds of tailor-made rainfall simulator setups can be identified across the literature. Although it is beneficial for researchers to adapt their experimental designs to suit their specific research objectives, the diversity in the type, sizing, form, operation and methodologies of rainfall simulators ultimately results in complications when comparing results and outputs obtained between studies.&lt;/p&gt;&lt;p&gt;Currently, comparisons between studies can be very difficult, if not impossible, as the different measurement methods, artificial rainfall event characteristics and test conditions result in considerable difficulties when benchmarking results and findings obtained from rainfall simulation experiments. We recommend that the scientific community should establish a set of methodological procedures aimed at harmonising basic procedures in rainfall simulator-based studies in the fields of hydrological and geomorphological sciences. This would ensure that results obtained from different rainfall simulator studies and setups are harmonised, regulated and comparable. On the one hand, this process involves harmonising rainfall simulators design characteristics, whereas further steps should focus on measurement methods and metrics so results can be more readily compared.&lt;/p&gt;&lt;p&gt;This presentation highlights the inherit problems in benchmarking and comparing studies at present due to large variations in the way that researchers and institutions assess and quantify rainfall simulator performance and present results. Some degree of &amp;#8216;standardisation&amp;#8217; of rainfall simulator approaches is needed. However, standardising approaches used within rainfall simulation does not allow researchers to adapt their experimental setups to suit their specific research needs, which is one of the key benefits of using rainfall simulators. Instead, &amp;#8216;harmonisation&amp;#8217; (i.e. ensuring that the scientific community develop a set of regulated and comparable methodological procedures and best practices for use in rainfall simulator studies whilst still allowing some degree of adaptability for specific research practices) is required. Here we present a series of harmonisation procedures, which should be developed to ensure that rainfall simulators are designed and constructed to allow for harmonisation, as well as suggesting a series of steps towards harmonising the methods and metrics used to quantify and compare experimental results.&lt;/p&gt;&lt;p&gt;With these objectives in mind, we aim to stimulate the discussion and enhance understanding of the difficulties and requirements of rainfall simulator based experimental research, namely by creating a platform that embraces and consults the International research community across multiple research facilities and institutes. This presentation will kick-start discussions (via web seminar sessions beginning in Summer 2021) leading up to a future international symposium addressing and acting upon these issues and disseminating the findings of this consultation period (Spring/Summer 2022 in Coimbra, Portugal). Everyone is invited to join this step towards harmonisation in rainfall simulation.&lt;/p&gt;