Tree-ring reconstruction of past debris flows based on a small number of samples—possibilities and limitations

Tree-ring analyses have often been used in the past for the reconstruction of spatiotemporal patterns of previous debris-flow activity, often yielding very precise and extensive data for torrents where information on former activity was largely missing. Unless dendrogeomorphology is slated for multimillion Euro developments, the large sets of tree-ring series that are usually used in these studies render analysis time-consuming and not necessarily very cost-effective. In this study, we present results on past debris flows obtained with 35 Larix decidua Mill. trees growing on the cone of the Torrent de Pétérey (Zinal, Valais, Swiss Alps). It is concluded that studies based on a limited number of samples may yield valuable data on past events, but that the reconstructed frequency remains widely incomplete and indications on the spatial aspects of past events are only fragmentar

Rainfall characteristics for periglacial debris flows in the Swiss Alps: past incidences-potential future evolutions

Based on observational meteorological data since A.D. 1864 and tree-ring records of debris-flow activity, this paper assesses changes in rainfall characteristics and their impact on the triggering of geomorphic events in a high-elevation watershed of the Swiss Alps since the end of the Little Ice Age. No trends are visible in the frequency of heavy rainfall events, but we observe a reduced number of heavy, short-lived rainfalls in summer and a concentration of advective storms is recorded in late summer and early fall since the late 1980s. These changes in triggering meteorological conditions resulted in a cluster of debris flows in the early decades of the twentieth century and a lowering of debris-flow activity since the mid 1990s, and may be mirroring the observed changes in persistent high-pressure systems over the Alps. We also observe intra-seasonal differences in debris-flow system response reflecting the state of the permafrost body in the source area of debris flows, allowing for very small debris flows to be released by limited rainfall inputs (<20mm) in June and July. The same quantities of rain will not trigger debris flows in August or September, when a thick active layer of the permafrost body is capable of absorbing water. With the projected amplitude of climatic change, seasonality, return intervals and volumes of debris flows are likely to be altered. RCM projections based on the IPCC A2 scenario suggest a decrease in heavy summer rainfalls which will most likely result in a (further) reduction of the overall frequency of debris flows, leaving more time for sediment to accumulate in the channel. Such an increase of channel accumulation rates along with the projected destabilization of the steep rock-glacier body is likely, in turn, to exert control ultimately on sediment volumes released from the source areas during future events. Observations from adjacent catchments suggest that extremely large debris flows, beyond historical experience, could occur at the study site and in similar debris-flow systems of the Valais Alps originating from periglacial environment

Assessing parent-child agreement in health-related quality of life among three health status groups

Purpose: To examine parent-child agreement regarding a child's health-related quality of life (HRQOL) among three health status groups. Methods: Parent-child agreement was evaluated for three health status groups of a population-based sample: (1) children with mental health problems (N=461), (2) children with physical health problems (N=281), and (3) healthy controls (N=699). The KIDSCREEN-27 was used to assess HRQOL. The children were 9-14years of age. Results: Intraclass correlation coefficients were mostly good across all HRQOL scores and health status groups. This relatively high level of agreement was also reflected by the following findings: first, the AGREE group was the largest in three out of five HRQOL subscales in all health status groups; second, when disagreement occurred, it was often minor in magnitude. Despite this relatively high level of agreement, the means of self-ratings were significantly higher for all HRQOL scores and health status groups than the means of proxy ratings. These higher self-ratings were especially pronounced among children with mental health problems in certain HRQOL domains. Conclusions: Even though the level of parent-child agreement regarding a child's HRQOL is relatively high, it should be considered that children (especially those with mental health problems) often report better HRQOL than their parents. It is, therefore, highly recommended that both proxy- and self-ratings are used to evaluate a child's HRQOL comprehensivel

Health-related quality of life among children with mental disorders: a systematic review

Purpose: To systematically review studies about the quality of life (QOL) of children with various mental disorders relative to healthy controls and to describe limitations in these studies. Methods: Relevant articles were searched using different databases, by checking reference lists and contacting experts. We included articles that either compared children with mental disorders to healthy controls/norm values or made such a comparison possible. Results: Sixteen out of 4,560 articles met the pre-defined inclusion criteria. These studies revealed that the QOL of children with various mental disorders is compromised across multiple domains. The largest effect sizes were found for psychosocial and family-related domains and for the total QOL score, whereas physical domains generally were less affected. The most important limitations in the existing literature include the lack of study samples drawn from the general population, the failure to use self-ratings, not considering item overlap between measuring QOL and assessing for the presence of a particular mental disorder, and not determining whether the children were receiving medication for their mental disorder. Conclusions: Children with mental disorders experience a considerable reduction in QOL across various domains. Research studies that avoid previous limitations are crucial to fill existing knowledge gap

Spatio-temporal variability in debris-flow activity: a tree-ring study at Geisstriftbach (Swiss Alps) extending back to AD 1736

Past debris-flow activity on the forested cone of the Geisstriftbach torrent (St. Niklaus, Valais, Swiss Alps) was assessed from growth disturbances in old conifer trees, providing a much improved record of past events. The study of 633 tree-ring sequences sampled from 252 European larch (Larix decidua Mill.), Norway spruce (Picea abies (L.) Karst.) and Silver birch (Betula pendula Roth.) trees allowed reconstruction of 53 debris-flow events since AD 1736. The spatial analysis of trees affected during particular events on the geomorphic map allowed for a spatial representation of individual events and a reconstruction of four flow patterns. Based on our results and Siegfried maps, we believe that before the formation of a dogleg near the cone apex in the late 1890s, debris flows preferentially used the channels located in the west-southwestern part of the Geisstriftbach cone. This study contributes to our understanding of debris-flow processes on cones and provides an example of how dendrogeomorphic techniques may help in the reconstruction and understanding of debris flows in Alpine area

Systematic visual analysis of groundwater hydrographs: potential benefits and challenges

Visual analysis of time series in hydrology is frequently seen as a crucial step to becoming acquainted with the nature of the data, as well as detecting unexpected errors, biases, etc. Human eyes, in particular those of a trained expert, are well suited to recognize irregularities and distinct patterns. However, there are limits as to what the eye can resolve and process; moreover, visual analysis is by definition subjective and has low reproducibility. Visual inspection is frequently mentioned in publications, but rarely described in detail, even though it may have significantly affected decisions made in the process of performing the underlying study. This paper presents a visual analysis of groundwater hydrographs that has been performed in relation to attempts to classify groundwater time series as part of developing a new concept for prediction in data-scarce groundwater systems. Within this concept, determining the similarity of groundwater hydrographs is essential. As standard approaches for similarity analysis of groundwater hydrographs do not yet exist, different approaches were developed and tested. This provided the opportunity to carry out a comparison between visual analysis and formal, automated classification approaches. The presented visual classification was carried out on two sets of time series from central Europe and Fennoscandia. It is explained why and where visual classification can be beneficial but also where the limitations and challenges associated with the approach lie. It is concluded that systematic visual analysis of time series in hydrology, despite its subjectivity and low reproducibility, should receive much more attention

Similarity-based approaches in hydrogeology: proposal of a new concept for data-scarce groundwater resource characterization and prediction

A new concept is proposed for describing, analysing and predicting the dynamic behaviour of groundwater resources based on classification and similarity. The concept makes use of the ideas put forward by the “PUB” (predictions in ungauged basins) initiative in surface-water hydrology. One of the approaches developed in PUB uses the principle that similar catchments, exposed to similar weather conditions, will generate a similar discharge response at the catchment outlet. This way, models developed for well-observed catchments can be used to make predictions for ungauged catchments with similar properties (topography, land use, etc.). The concept proposed here applies the same idea to groundwater systems, with the goal to make predictions of the dynamic behaviour of groundwater in poorly observed systems using similarities to well-observed and understood systems. This paper gives an overview of the main ideas, the methodological background, the progress so far, and the challenges that the authors regard as most crucial for further development. One of the main goals of this article is thus to raise interest for this new concept within the groundwater community. There are a multitude of highly interesting aspects to investigate, and a community effort, as with PUB, is required. A second goal is to foster and exchange ideas between the groundwater and surface water research communities who, while often working on similar problems, have often missed the opportunity to learn from each other