Debris flows can grow greatly in size and hazardous potential by eroding bed and bank materials. However, erosion mechanisms are poorly understood because debris flows are complex hybrids between a ...fluid flow and a moving mass of colliding particles, bed erodibility varies between events, and field measurements are hard to obtain. Here, we identify the key controls on debris‐flow erosion based on a field data set that combines information on flow properties, bed conditions, and bed and bank erosion. We show that flow conditions and bed wetness jointly control debris‐flow erosion. Flow conditions describing the cumulative forces exerted at the bed during an event best explain erosion. Shear forces and particle‐impact forces are strongly correlated and act in conjunction in the erosion process. A shear‐stress approach accounting for bed erodibility may therefore be applicable for modeling and predicting debris‐flow erosion. This work provides a foundation for developing effective debris‐flow erosion models.
Plain Language Summary
Debris flows are water‐laden masses of soil and rock, which are common geological hazards in mountainous regions worldwide. They can grow greatly in size and hazardous potential by eroding bed and bank materials. Limited understanding of these erosion processes, however, hampers effective hazard assessment and mitigation. Improving our understanding of erosion is challenging because debris flows are complex hybrids between a fluid flow and a moving mass of colliding particles, bed erodibility varies between events, and field measurements are hard to obtain. Here, we identify the key controls on debris‐flow erosion based on a field data set that combines information on flow properties, bed conditions, and bed and bank erosion. We show that flow properties and bed wetness jointly control debris‐flow erosion. Flow conditions that describe the cumulative forces exerted at the bed during an event best explain erosion. Shear forces and particle‐impact forces are strongly correlated and act in conjunction in the erosion process. A shear‐stress approach accounting for bed erodibility may therefore be applicable for modeling and predicting debris‐flow erosion. This work provides a foundation for developing effective debris‐flow erosion models.
Key Points
Flow conditions and bed wetness jointly control debris‐flow erosion and deposition
Shear forces and particle‐impact forces are strongly correlated and together determine erosion
A shear‐stress approach accounting for bed erodibility may be applicable for modeling debris‐flow erosion
Abstract
Debris flows can grow greatly in size and hazardous potential by eroding bed and bank material, but effective hazard assessment and mitigation is currently hampered by limited understanding ...of erosion and deposition dynamics. We have collected high-resolution pre- and post-flow topography for 6 debris flows over a 3 km long unconsolidated reach of the Illgraben channel in the Swiss Alps with drone-based photogrammetry. We show that the spatio-temporal patterns of erosion and deposition in debris-flow torrents are highly variable and dynamic. Check dams strongly control the spatial patterns of erosion and deposition. We identify a memory effect where erosion is strong at locations of strong deposition during previous flows and vice versa. Large sediment inputs from subcatchments initially result in new channel erosion through the subcatchment deposits and simultaneous upstream deposition, likely as a result of backwater effects. It is generally believed that erosion increases with debris-flow magnitude, but we show that there is a limit to debris-flow bulking set by channel geometry. These findings provide key guidelines for flow volume forecasting, emphasizing the importance of memory effects and the need to resolve both erosion and deposition in predictive models.
Information on the spatial and temporal patterns of plant phenology is important to develop a more comprehensive understanding of food availability and habitat for many animal species. The ...combination of broad scale, regional climatic, and more localized, site-level drivers presents a challenge when upscaling phenology from the plot to the region. Likewise, developing relationships between ground- or camera-based estimates and satellite imagery remains difficult due to the trade-off between temporal and spatial resolution. Landsat imagery, with its 16day temporal resolution, is often thought of as being insufficient for timely observation of changes in vegetation throughout the year. However the free availability of the Landsat archive has enabled a major shift in the way Landsat imagery is processed moving towards pixel, rather than scene, based analyses. In this paper we build on previous research by examining the applicability and accuracy of Landsat derived phenology curves beyond deciduous stands into more mixed stands and conifer dominated forest types in the Rocky Mountains and foothills in Alberta, Canada. In addition, we discuss the application of these Landsat phenology curves to phenology of understorey species which are linked to habitat selection for free roaming wildlife, in particular grizzly bears. The agreement between Landsat- and camera-derived estimates of key phenological events was stronger for green-up (RMSE=7days) than for senescence (RMSE=14days). Our results show that yearly adjustment of green-up and senescence dates using available Landsat observations improved the agreement with camera-derived estimates when compared to average annual curves. Seasonal phenology transition dates accepted as valid ranged from 25% for alpine herbaceous pixels to 75% for closed deciduous, demonstrating the variable success of this approach across land cover types. Season transition dates were rejected if pixels lacked a strong enough green-up signal in Landsat spectral indices or if the estimated dates fell outside of the valid range. We conclude by investigating the spatial patterns of seasonal phenology at the Landsat scale, and assess the relative importance of regional vs. microsite conditions as well as the utility of these data for resource and wildlife management.
•Spatial and temporal patterns of plant phenology are critical habitat descriptors.•We fit long term phenological curves to Landsat imagery and adjust annually.•Broadleaf and mixed stands had higher percentages of acceptable fits than conifers.•We compare the timing of Landsat- and camera-derived phenological events.•Agreement was stronger for greenup (RMSE=7days) than senescence (RMSE=14days).
During the COVID-19 pandemic ICU nurses endure high levels of stress. VR relaxation (VRelax, containing 360° immersive environments) provides an easy-to-use and effective means to induce positive ...affect and reduce perceived stress. We investigated feasibility and immediate effect on perceived stress of VRelax use by ICU nurses during work shifts. ICU nurses working with COVID-19 patients in an academic hospital could use VRelax as a 10-min break during their shift. Primary outcome was the difference between perceived stress immediately before and after VRelax use measured by a single-question VAS-stress scale. Statistically significant difference of the mean VAS-stress before and after use was determined using the paired
t
student test. A socio-demographic questionnaire, a questionnaire on perceived stress and stress resilience and VRelax user experiences were sent by email. Eighty-six (26%) nurses used VRelax at least once; 77% (
N
=66) of these filled out the VAS-stress scale before and after use of VRelax. Mean perceived stress lowered with 39.9% after use of VRelax (mean difference=14.0, SD=13.3,
p
<0.005). Mean score on the perceived stress scale-10 was 11.4 (SD=6.50), mean score on the Connor-Davidson Resilience Scale-10 was 29.0 (SD=5.51). Sixty-two percentage of the ICU nurses thought VRelax was helpful to reduce stress. Main barrier for use was a high workload. It is feasible for nurses to use VRelax in an ICU context. VRelax is an effective intervention to reduce immediate perceived stress and is of added value in stressful situations as during the COVID-19 pandemic, inducing a positive affective state and lowering perceived stress.
•Absolute and relative accuracy of 24 UAV-SfM photogrammetry workflows are assessed.•Co-alignment reduces relative errors to below 2 cm regardless of positioning quality.•Co-aligning RTK and generic ...GNSS surveys results in RTK class accuracy.•Absolute z errors are minimized by adding GCPs in least one survey.•We recommend to apply co-alignment in all change detection studies.
Unmanned Aerial Vehicle Structure from Motion (UAV-SfM) photogrammetry is increasingly applied to topographic change detection, which requires multitemporal Digital Surface Models (DSMs) with high relative accuracy. Of these tools, Ground Control Points (GCPs) and an image processing method called co-alignment have so far shown promising results for change detection studies. However, there is still insufficient research on the extent of improving 3D model accuracy by combining these tools. In our study we assess absolute and relative accuracy of 120 DSMs generated through 24 workflows of UAV-SfM photogrammetry. Surveys were acquired with two different UAVs with Real Time Kinematic (RTK) or generic Global Navigation Satellite System (GNSS) positioning, and processed with varying combinations of survey co-alignment and GCPs. We show that co-alignment reduces relative errors to below 2 cm regardless of positioning quality. A single RTK survey in a co-aligned project is sufficient to obtain high absolute xy accuracy, but GCPs for at least one survey are still required to reduce absolute z error. We demonstrate that co-aligning RTK surveys with generic GNSS surveys results in RTK class accuracy for all surveys, even when mixed sensor grades are used. Our findings enable high-accuracy change detection with lower accuracy archived images when combined with RTK surveys. For future UAV-SfM change detection studies, we recommend to apply co-alignment for all studies, and where possible to include GCPs and RTK image coordinates in one survey to optimize absolute accuracy. Collecting and digitizing GCPs in multiple surveys has shown little additional benefit when co-alignment is applied and therefore may be omitted to save time, especially in challenging field conditions.
High spatial resolution images allow us to assess the spatial structure and variability of natural vegetation characteristics. In order to optimize quantitative image analysis, we looked for the ...optimal spatial resolution to map natural vegetation in a Mediterranean environment. The optimal spatial resolution was then related to the spatial characteristics of the scene and the mapped parameters. Based on the relation between airborne hyperspectral imagery and field dataset consisting of 227 measured plots of Leaf Area Index (LAI) and aboveground biomass, we found an optimal pixel size of 55 and 95 m for the mapping of LAI and aboveground biomass, respectively. The optimal spatial resolution we found is determined by the spatial structure of the mapped parameters on the one hand, and by the effects of shading patterns and gaps in the canopy on the other. The spatial properties of scene elements influencing the optimal spatial resolution can be detected effectively using average local variance functions and variograms, provided that these are studied at a wide spatial range. The use of an optimally sized mapping unit instead of the original 5 m pixels resulted in an improvement of mapping accuracy of 7 to 17%. It is therefore recommended that the image support used is considered carefully in all quantitative mapping projects based on remotely sensed imagery.
Plant growth in Mediterranean landscapes is limited by the typical summer-dry climate. Forests in these areas are only marginally productive and may be quite susceptible to modern climate change. To ...improve our understanding of forest sensitivity to annual and seasonal climatic variability, we use tree-ring measurements of two Mediterranean evergreen tree species: Quercus ilex L. and Arbutus unedo L. We sampled 34 stems of these species on three different types of substrates in the Peyne study area in southern France. The resulting chronologies were analysed in combination with 38 yr of monthly precipitation and temperature data to reconstruct the response of stem growth to climatic variability. Results indicate a strong positive response to May and June precipitation, as well as a significant positive influence of early-spring temperatures and a negative growth response to summer heat. Comparison of the data with more detailed productivity measurements in two contrasting years confirms these observations and shows a strong productivity limiting effect of low early-summer precipitation. The results show that tree-ring data from Q.ilex and A.unedo can provide valuable information about the response of these tree species to climate variability, improving our ability to predict the effects of climate change in Mediterranean ecosystems.
Question: Can repeat (time-lapse) photography be used to detect the phenological development of a forest stand, and linked to temporal patterns in root nutrition for Hedysarum alpinum (alpine ...sweetvetch) an important grizzly bear food species? Location: Eastern foothills and front ranges of the Rocky Mountains in Alberta, Canada. The area contains a diverse mix of mature and young forest, wetlands and alpine habitats. Methods: We deployed six automated cameras at three locations to acquire daily photographs at the plant and forest stand scales. Plot locations were also visited on a bi-weekly basis to record the phenological stage of H. alpinum and other target plant species, as well as to collect a root sample for determination of crude protein content. Results: Repeat photography and image analysis successfully detected all key phenological events (i.e. green-up, flowering, senescence). Given the relation between phenology and root nutrition, we illustrate how camera data can be used to predict the spatial and temporal distribution and quality of a key wildlife resource. Conclusions: Repeat photography provides a cost-effective method for monitoring vegetation development, food availability, and nutritional quality at a forest stand scale. Since wildlife responds to the availability and quality of their food resources, detailed information on changes in resource availability helps with land-use management decisions and furthers our understanding of grizzly bear feeding ecology and habitat selection.
Phenological patterns of the components within forest ecosystems, such as understory vegetation, are important indicators of climate variability, productivity, and additional ecosystem services such ...as food and habitat availability for wildlife. Proximal sensing systems can provide detailed phenological records at a relatively low cost. As interest in these datasets increases, we need additional information regarding the effect of different approaches on the scale of observations and camera field of view. In this research, we examine the impact of field of view on the capacity of cameras to detect changes in phenology of individual species in an image time series. We examine two co-located series of oblique images acquired using a fine and broad field of view and compare a number of phenological indicators, including the start and end of season derived for individual plant species. Our results indicate both fine and broad field of view camera systems are highly effective at detecting key markers of plant phenology with no significant differences between the two. This result supports environmental monitoring using cost-effective broad field of view cameras, or even-subject to some constraints-readily available camera stations installed for tourism or traffic monitoring.
Les patrons phénologiques des composantes au sein des écosystèmes forestiers, comme la végétation de sous-bois, sont des indicateurs importants de la variabilité du climat, de la productivité et des services écosystémiques supplémentaires tels que la disponibilité de nourriture et d'habitats pour la faune. Les systèmes de détection par caméra dans l'environnement peuvent fournir des observations phénologiques détaillées à un coût relativement faible. Comme l'intérêt pour ces ensembles de données s'accroît, nous avons besoin d'informations supplémentaires concernant l'effet des différentes approches sur l'échelle des observations et sur le champ de vision de la caméra. Dans cette recherche, nous examinons l'impact du champ de vision sur la capacité des caméras à détecter des changements dans la phénologie des espèces individuelles dans une série temporelle d'images. Nous examinons deux séries colocalisées d'images obliques acquises en utilisant des champs de vision étroit et large et nous comparons quelques indicateurs phénologiques, y compris le début et la fin de la saison, dérivés pour des espèces de plante individuelle. Nos résultats indiquent que les systèmes de caméras avec des champs de vision large et étroit sont très efficaces pour la détection de marqueurs clés de la phénologie des plantes sans différence significative entre les deux. Ce résultat supporte le concept de la surveillance de l'environnement en utilisant des caméras économiques avec de larges champs de vision, ou même-avec certaines contraintes-des stations de caméras facilement accessibles installées pour le tourisme ou la surveillance du trafic.
Summary
Background
Although they are considered relevant, little is known about satisfaction with treatment and health‐related quality of life (HRQoL) among patients with lichen sclerosus (LS).
...Objectives
In a cross‐sectional study, we aimed to examine (i) satisfaction with treatment, (ii) patient characteristics associated with satisfaction and (iii) HRQoL in Dutch patients with LS.
Methods
Members of the Dutch LS Patient Association (n = 750) were invited to complete a web‐based survey. We measured satisfaction with treatment with a study‐specific questionnaire, and HRQoL with the Skindex‐29. We calculated domain scores for symptoms, emotions and functioning, and categorized scores into little, mildly, moderately or severely impaired HRQoL. We used a multiple linear regression analysis to examine whether patient characteristics were associated with treatment satisfaction.
Results
In total 303 patients (40·4%) were included. Patients under current treatment (n = 265, 87·5%) were moderately satisfied with their treatment. Patients rated ‘treatment effectiveness’ as most important, although 58 (22%) were dissatisfied with the effectiveness of their current treatment. More impairment on the HRQoL emotions domain and a higher degree of disease severity were both associated with lower satisfaction with treatment and explained in total 13·5% of the variance in treatment satisfaction. On all HRQoL domains, one‐third of the patients (range 34·7–38·9%) reported severe impairment.
Conclusions
Patients with LS are moderately satisfied with their treatment, and one‐third of patients experience severe impairment of HRQoL. To improve dermatological care, we recommend enhancement of doctor–patient communication, information provision and organization, which may be more amenable to change than treatment effectiveness or safety.
What's already known about this topic?
Patients' satisfaction with treatment is an important indicator of quality of care.
Little is known about patients' satisfaction with treatment of lichen sclerosus (LS).
LS appears to have a negative impact on health‐related quality of life (HRQoL).
What does this study add?
Patients with LS are moderately satisfied with their current treatment.
Patients with LS are least satisfied with the effectiveness of their treatment, but do rate it as most important.
One‐third of patients with LS experience severe impairment of HRQoL (symptoms, emotions and functioning domains of Skindex‐29).
More impairment on the emotions domain and a higher degree of disease severity are both associated with lower satisfaction with treatment.
What are the clinical implications of this work?
To improve dermatological care, we recommend enhancement of doctor–patient communication, information provision and organization.
In daily clinical practice, we recommend recurrently to assess satisfaction and HRQoL in patients with LS, in addition to clinical measures.
Routine measurement of patient‐reported outcomes in daily practice may be facilitated by a web‐based application, but implementation of such an intervention is not self‐evident.
Respond to this article
Linked Comment: Dizon and Chren. Br J Dermatol 2017; 176:1431–1432
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